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Title: Hawkins Electrical Guide, Vol 4 - Questions, Answers, & Illustrations.
Author: Hawkins, Walter
Language: English
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*** Start of this LibraryBlog Digital Book "Hawkins Electrical Guide, Vol 4 - Questions, Answers, & Illustrations." ***
[Illustration: THE THOUGHT IS IN THE QUESTION THE INFORMATION IS IN THE
ANSWER
HAWKINS
ELECTRICAL GUIDE
NUMBER
FOUR
QUESTIONS
ANSWERS
&
ILLUSTRATIONS
A PROGRESSIVE COURSE OF STUDY
FOR ENGINEERS, ELECTRICIANS, STUDENTS
AND THOSE DESIRING TO ACQUIRE A
WORKING KNOWLEDGE OF
ELECTRICITY AND ITS APPLICATIONS
A PRACTICAL TREATISE
by
HAWKINS AND STAFF
THEO. AUDEL & CO. 72 FIFTH AVE. NEW YORK]
COPYRIGHTED, 1914,
BY
THEO. AUDEL & CO.,
NEW YORK.
Printed in the United States.
TABLE OF CONTENTS GUIDE NO. 4
DISTRIBUTION SYSTEMS 697 to 720
=Classification=—series system—danger in series arc light
system—constant current system—parallel system—arrangement
of feeder and mains in parallel system—series-parallel
system—center of distribution—=Edison three wire
system=—evolution of the three wire system—balanced
three wire system—balancing of three wire system—=copper
economy in three wire systems=—Dobrowolsky three wire
system—modifications of three wire system—three
wire storage battery system—three wire double dynamo
system—three wire bridge system—three wire three brush
dynamo system—Dobrowolsky three wire system—three
wire auxiliary dynamo system—three wire compensator
system—=extension of the three wire principle=—five wire
system—=dynamotor=—connections of balancing set—=balancing
coils=—distribution by dynamo motor sets—=boosters and their
uses=—=auxiliary bus bar.=
WIRES AND WIRE CALCULATION 721 to 764
Preliminary considerations—=various wires=—copper
wire—iron wire—German silver wire—=standard of copper wire
resistance=—relative conductivity of different metals and
alloys—conductors—cable for elevator annunciators—covered
conductors—rubber covered conductors—rubber
insulated telephone and telegraph wires—weather proof
conductors—twisted weather proof wires—precautions in
using weather proof conductors—slow burning wire; where
used—slow burning weather proof wire; where used; how
installed—miscellaneous insulated conductors—=safe
carrying capacity of wire=—pothead wires—=circular
mils=—square mils—mil foot—lamp foot—ampere foot—=center
of distribution—wire gauges—=B. & S. standard wire
gauge—micrometer screw gauge—calculating gauge—=table of
various wire gauges=—table of lamp feet for rubber covered
wires—lamp table for weather proof wires—symmetrical
and unsymmetrical distribution—=wiring table for light
and power circuits=—table of wire equivalents; how to
use—table of cable capacities—=incandescent lamps on
660 watt circuits=—"tree" and "modified tree" system of
wiring—distribution with sub-feeders—wrong and right methods
of loop wiring—table, of amperes per motor; of amperes per
dynamo—calculations for three wire circuit—=three wire
circuit panel board=—size of the neutral wire.
INSIDE WIRING 765 to 798
The term "wiring"—=open or exposed wiring=—selection
of wires—=installation=—disadvantages of open
wiring—=splicing=—pitch of wires—crossing of wires—wiring
across pipes—=practical points relating to exposed
wiring=—methods of carrying wires, through floors; on
walls—protecting exposed wiring on low ceilings—=various
porcelain knobs and cleats=—wires used in mouldings—standard
wooden moulding—=kick box=—usual character of moulding
work—practical points relating to wiring in mouldings—tapping
outlets—=arc light wiring=—arc lamps on low pressure
service—circular fixture block—=concealed knob and tube
wiring=; objections; method of installation—arrangement of
switch and receptacle outlet in knob and tube wiring—switch
boxes—=rigid conduit wiring=; advantage—types of rigid
conduit; requirements—-conduit box—disadvantages of unlined
conduit—=flexible conduit wiring=—Greenfield flexible steel
conduit—"fishing"—insulating point—canopy insulator—fish
plug and method of insertion—=method of installing conduits
in fireproof buildings=—service entrance to rubber conduit
system—condulet outlet to arc lamp—=hickey=—methods of
bending large conduits—=armoured cable wiring=; features;
installation.
OUTSIDE WIRING 799 to 824
=Materials for outside conductors=—tensile strength of
copper wire—=pole lines=—pole constructing tools—wooden
poles—preservation of wooden poles—preservation
processes—methods of setting wooden poles in unsuitable
soil—reinforced concrete poles—cross arms—lineman's
portable platform—poles for light and power wires—spacing
of poles—=erecting the poles=—guy anchors—method of
raising a pole—method of pulling anchor into place—=guys
for poles=—head and foot guying—guying corner poles—guy
stubs and anchor logs—climbers—=wiring the line=—pay out
reels—method of stringing wires—"come alongs"—tension
on wires—=sag table=—lineman's block and fall with
"come alongs"—attaching wire to insulator—=splicing;
American wire joint=; McIntire sleeve and sleeve
joint—=transpositions—insulators—overhead cable
construction=—petticoat insulator—Clark's "antihum"—service
connections and loops—method of making series, and parallel
service connections—=joint pole crossing=—service wires.
UNDERGROUND WIRING 825 to 844
=City conditions=—underground systems—=various
conduits=—vitrified clay pipe conduit—vitrified clay
or earthenware trough conduit—joints in multiple-duct
vitrified clay conduit—concrete duct conduits—=methods of
laying conduit=—method of laying single duct vitrified clay
conduit—method of laying multiple duct clay conduit—wooden
duct conduits—=objection to use of wood;= remedy; adaptation
wooden built-in conduits; method of installation—wrought iron
or steel pipe conduits; method of installation—porcelain
bridgework or carriers—cast iron pipe and trough
conduit; advantages—fibre conduits; joints—=Edison tube
system=—underground cables—metal sheaths on underground
cables—=pot heads=—General Electric manhole junction
box—=pot head connections.=
WIRING OF BUILDINGS 845 to 864
=Preliminary considerations=—electrician's
instructions—=location of receptacles=—ceiling
buttons—hallway wiring—=selection of wiring system=—three
wire convertible system—method of wiring—=location
of panel boards=—current required on each floor of
building—=arrangement of feeders=—installation of
motors—largest size of feeder permissible—=method of cutting
pocket in floor=—outlet baseboard—completed pocket—how
to examine partition interiors—house plan of conduit
wiring—attachment of mains to knobs—=precautions in making
joints=—wiring for heating appliances—wiring with combination
of moulding, flexible tubing or conduit in non-fire proof
building—feeder system for large hotel.
SIGN FLASHERS 865 to 884
=Classification=—Carbon flashers—wiring diagram for Dull's
carbon flashers—brush flashers—knife flashers—flasher
transmission gearing—simple on and off flashers—=flash
system of gas lighting=—high speed flashers—lighting
flashers—wiring diagram for flags—diagram showing method
of wiring for high speed effects on single lines—method of
wiring for a torch—=wiring diagram for high speeds=—Dull's
lightning—=script breakers=—chaser flashers—thermo
flashers—=carriage calls=—monogram for carriage calls—wiring
diagrams for sign illumination—-National carriage call
operating keyboard—clock monogram—Bett's clock mechanism for
operating electric monogram time flasher—=talking signs=—two
way thermal flasher.
LIGHTNING PROTECTION 885 to 892
Lightning rods; =why sharp points are used=; erection—diagram
showing principle of air gap arrestor—=variable gap arc
breaker=—location of lightning arrestor—carbon arresters with
fuses for telephone lines—=ground connection.=
STORAGE BATTERY 893 to 968
Early experiments—=theory=—description of storage
cell—electrolyte—effect of current passing through
electrolyte—types of storage batteries—=Plant
cells=—Willard plates; wood separator—parts of "Autex"
automobile cells—=Faure or pasted type=—comparison
of Plant and Faure plates—=the electrolyte;= kind
generally used; preparation; test; mixing acid and water;
kind of vessel used;—=specific gravity table=—effect
of deep vessel—density of electrolyte—=hydrometer
syringe=—impurities in electrolyte—=tests for impurities=;
chlorine, nitrates, acetic acid, iron, copper, mercury,
platinum—=old electrolyte=—voltage of a secondary
cell—=charging=—connections for charging—charging;
first time; period; regulation of voltage—Edison cell
data—=frequency of charging=—cadmium test—emergency
connections for weak ignition battery—portable testing
instruments—=charge indications=—two methods of charging from
a direct current lighting system—colors of the plates—how
best results are obtained in charging—=charge voltage=—two
ways of charging—diagram of charging connections—how
to keep charging current constant—=tests while charging;
after charging=—charge indications—behavior of electrolyte
during discharge—lead burning outfit—"=boiling=";
causes—hydrogen gas generator for lead burning—=quick
charging=—charging through the night—charging period for new
battery—Willard underhung battery box for automobiles—=high
charging rates=—"National" instructions for taking voltage
readings—=mercury arc rectifier=—capacity—table of capacity
variation for different discharge rates—how to increase
the capacity—=discharging=; too rapidly rating; maximum
rate—=Edison alternating current rectifier=—attention
after discharging—=the battery room=—battery
attendants—points on care and management—=placement of
cells=—how to avoid leakage—precautions when unpacking
cells—=assembling cells=—connections—precaution in joining
terminals—=battery troubles=—short circuiting; indication;
location—overdischarge; buckling—sulphation of plates—data
on National cells; American cells; Autex cells—action in idle
cell—lack of capacity—=how to prevent lead poisoning=—low
specific gravity without short circuits; causes—=treatment
of weak cells=—pole testing paper—disconnecting
cells—=sulphuric acid specific gravity table=—how to take
a battery out of commission—Witham charging board—putting
batteries into commission—cleaning jars—table of voltage
charge as affected by discharge rate—=condensed rules for the
proper care of batteries=.
STORAGE BATTERY SYSTEMS 969 to 996
=Uses of storage batteries=; their importance in power
plants—load curve showing use of storage battery as aid to
the generating machinery—parallel connection of battery and
dynamo—"=floating the battery on the line="—diagram showing
effect of battery in regulating dynamo load—=connections and
circuit control apparatus=—diagram showing action of battery
as a reservoir of reserve power—three wire system with battery
and dynamo—methods of control for storage batteries—diagram
of connections for ignition outfit—variable resistance—end
cell switches—diagram of connection of battery equipment for
residential lighting plant—end cell switch diagram—features
of end cell switch construction—=end cell switch
control=—circuit diagram for charging battery in two parallel
groups and discharging in series—reverse pressure cells;
regulation—Holzer-Cabot dynamotor—=boosters=—application
of series booster system—Bijur's battery system—load
diagram—characteristics of series booster—shunt boosters;
with battery—Entz' carbon pile booster system—=application
of shunt booster=—circuit diagram for non-reversible shunt
booster and battery system—=compound boosters=; their
connections—method of charging battery at one voltage and
supplying lights at a different voltage—connections of one
form of differential booster—=differential boosters=; with
compensating coil; adaptation.
CHAPTER XXXVI
DISTRIBUTION SYSTEMS
The selection of the system of transmission and distribution of
electric energy from the generating plant to lamps, motors, and other
devices, is governed mainly by the cost of the metallic conductors,
which in many electrical installations, is a larger item than the cost
of the generating plant itself. This is especially true in case of long
distance transmission, while in those of the lighting plants, the cost
of wiring is usually more expensive than that of the boilers, engines,
and generators combined.
The principal distribution systems, are classed as:
1. Series;
2. Parallel;
3. Series-parallel;
4. Parallel-series.
=Ques. What is the characteristic feature of each class?=
Ans. In the series systems the current is constant, but the voltage
varies. In the parallel systems, the voltage is constant, but the
current varies.
=Series System of Distribution.=—A series system affords the simplest
arrangement of lamps, motors, or other devices supplied with electric
energy. The connections of such a system are shown in fig. 783. The
current from the terminal of the dynamo passes through the lamps, L,
L, L, L, one after the other and finally returns to the terminal. The
current remains practically constant, but the voltage falls throughout
the circuit in direct proportion to the resistance, and the difference
in pressure between any two points in the circuit is equal to the
current in amperes multiplied by the resistance in ohms included
between them.
For example. Each open arc lamp requires about 50 volts. In
the system shown in fig. 783, the pressure measured across
the brushes of the dynamo is assumed to be 1,000 volts. As
this current flows through the circuit 45 volts will be
actually lost in each lamp, and as the drop on the line wire
is usually about 10 per cent. of the total voltage, there will
be a drop of 5 volts on the conductor between any two lamps.
In the circuit shown, there are twenty lamps, therefore, the
difference in pressure between either terminal of the dynamo
and middle point A of the circuit will be 10 lamps × 50 volts =
500 volts. Likewise, the difference in pressure between any two
points on the circuit will be equal to 50 volts multiplied by
the number of lamps included between them.
[Illustration: FIG. 783.—Series system of distribution. This is
a constant current system, so called because the current remains
practically constant. It is used chiefly for arc lighting.]
=Ques. Describe the danger in a series arc light system?=
Ans. Since the total voltage of the system is equal to the sum of the
volts consumed in all of the lamps, it is high enough to be dangerous
to personal safety.
This is illustrated in fig. 783. If the line be grounded at B
owing to defective insulation, the pressure of the circuit at
that point will be zero, and therefore, a man standing on the
ground could touch that point without receiving a shock, but
if he should touch the line at the point C, he will receive a
slight shock of 150 volts, as there are three lamps between the
point C, and the ground connection B. Therefore, the danger of
touching the circuit increases directly with the resistance
between the point touched and the ground connection, so that
if a man touch the circuit at the point D, he will receive a
dangerous shock of 16 × 50 = 800 volts. In practice, sixty
lamps are often placed on a single arc lighting circuit, so
that its total pressure is about 3,000 volts, thus greatly
increasing the danger of the system.
=Ques. What is a constant current system?=
Ans. The series system is a constant current system, and is so called
because the current remains practically constant, while the voltage
falls throughout the circuit in direct proportion to the resistance.
=Ques. What are the principal applications of the series system?=
Ans. For arc lighting, and telegraphic circuits.
=Ques. What are the advantages of the series system?=
Ans. In the case of telegraphic circuits only one wire is required, and
for lighting and power transmission and distribution, only two wires;
therefore, it is simpler and cheaper than any other system.
=Ques. What is the disadvantage of the series system?=
Ans. The danger due to the high voltage in installations such as arc
lighting circuits.
=Parallel System.=—Parallel or multiple systems are usually more
complicated than series systems, but since the voltage can be
maintained nearly constant by various methods, practically all
incandescent lamps, electric motors, and a large proportion of arc
lamps are supplied by parallel systems.
The general principle of the parallel system is shown in fig.
784. With six lamps on the circuit, each requiring one-half
ampere of current, at 110 volts, the dynamo will have to
supply a current of 3 amperes at a pressure of 112 volts, and
this current will flow through the circuit and distribute
itself as shown on account of the lesser resistance of the
wire relatively to that of the lamps. At the first lamp, the 3
amperes will divide, ½ ampere flowing through the lamp and
the remaining 2½ amperes passing on to the next lamp and so
on through the entire circuit. The reduction of pressure from
112 volts across the brushes to 110 volts at the last lamp is
due to the resistance of the conducting wires.
=Ques. What three effects are due to this drop in pressure?=
Ans. 1, All the lamps or motors in the circuit receive a lower voltage
than that at the dynamo, 2, some lamps or motors may receive a lower
voltage than the others, and 3, the voltage at some lamps or motors may
vary when the others are turned on or off.
[Illustration: FIG. 784.—Parallel system of distribution. This is
a constant voltage system and is used principally for incandescent
lighting and electric motor circuits.]
The first is the least harmful and may be counteracted by
running the dynamo at a little higher voltage; but the second
and third are very objectionable and difficult to overcome.
They are counteracted successfully in practice, however, by
various methods of regulation, the use of _boosters_, and the
operation of dynamos in parallel.
=Ques. What are the principal applications of parallel or constant
pressure systems?=
Ans. They are used on practically all incandescent lamp and electric
motor circuits, and on some arc lamp circuits.
=Ques. Why is it specially applicable to incandescent lamp circuits?=
Ans. Incandescent lamps cannot be made to stand a pressure much over
220 volts, and therefore have to be operated on low voltage systems.
=Ques. What is the principal disadvantage of a parallel system as
compared with a series system?=
Ans. The greater cost of the copper conductors.
[Illustration: FIG. 785.—Arrangement of feeder and mains in parallel
system. By locating the feeder at the electrical center, less copper
is required for the mains. The cut does not show the fuses which in
practice are placed at the junction of feeder and main.]
=Ques. What is the usual arrangement of parallel systems?=
Ans. Conductors known as _a feeder_ run out from the station, and
connected to these are other conductors known as _a main_ to which in
turn the lamps or other devices are connected as shown in fig. 785.
=Ques. In what two ways may feeders be connected?=
Ans. They may be connected at the same end of the mains, known as
_parallel feeding_, or they may be connected at the opposite end of the
main, called _anti-parallel feeding_.
The main may be of uniform cross section throughout, or it may
change in size so as to keep the current density approximately
constant. The above condition gives rise to four possible
combinations:
1. Cylindrical conductors parallel feeding, fig. 786;
2. Tapering conductors, parallel feeding, fig. 787;
3. Cylindrical conductors, anti-parallel feeding, fig. 788;
4. Tapering conductors, anti-parallel feeding, fig. 789.
[Illustration: FIGS. 786 to 789.—Various parallel systems. Fig. 786,
cylindrical conductors parallel feeding; fig. 787, tapering conductors
parallel feeding; fig. 788, cylindrical conductors anti-parallel
feeding; fig. 789, tapering conductors anti-parallel feeding. The term
"tapering" is here used to denote a conductor made up of lengths of
wire, each length smaller than the preceding length, the object of
such arrangement being to avoid a waste of copper by progressively
diminishing the size of wire so that the relation between circular
rails and amperes is kept approximately constant. In an anti-parallel
system, the current is fed to the lamp from opposite ends of the
system.]
=Series-Parallel System.=—This is a combination of the series and
parallel systems, and is arranged as indicated in fig. 790. Several
lamps are arranged in parallel to form a group, and a number of such
sets are connected in series, as shown. It is not necessary for the
groups to be identical, provided they are all adapted to take the
same current in amperes, which should be kept constant, and provided
the lamps of each set agree in voltage. For example, on the ordinary
10-ampere arc circuit, one group might consist of 5 lamps, each
requiring 2 amperes at 50 volts; the next might be composed of 10
lamps, each taking 1 ampere at 100 volts, and so on.
[Illustration: FIG. 790.—Series-parallel system of distribution. It
consists of groups of parallel connected receptive devices, the groups
being arranged in the circuit in series.]
=Parallel-Series System.=—In this method of connection, one or more
groups of lamp are connected in series and the groups in parallel as
shown in fig. 791.
[Illustration: Fig. 791.—Parallel-series system of distribution. It
consists of groups of series connected receptive devices, the groups
being arranged in the circuit in parallel.]
=Ques. When is a parallel-series system used?=
Ans. When it is desired to operate a number of lamps or motors on a
line where voltage is several times that required to operate a single
lamp or motor.
The parallel-series system is employed chiefly in the lighting
circuit on electric traction lines; here, usually five 110
volt lamps are connected to the source of supply which has a
pressure of 550 volts.
=Center of Distribution.=—It is important to determine the point at
which the feeders should be attached to the mains in order to minimize
the amount of copper required. The method employed is similar to that
used in determining the best location of a power plant as regards
amount of copper required. The center of distribution may be called
the electrical center of gravity of the system, and is found by
separately obtaining the center of gravity of straight sections and
then determining the total resultant and point of application of this
resultant of the straight sections.
Feeders (feeding cables or conductors) are run from the source
of supply to the distributing centers, and, as these feeders
are in many cases of considerable length, a substantial loss of
pressure generally occurs in them. The pressure at the source
of supply, however, is so regulated as to compensate for the
drop in the feeders, and the pressure at the distributing
centers is thus kept constant; or the same result is obtained
by the use of regulating devices in the feeders. The
essential condition in most systems is that the pressure at
the distributing centers shall be kept practically constant,
irrespective of the load.
=Edison Three Wire System.=—In electric lighting systems used up to
about 1897, it was not considered practicable to use incandescent lamps
requiring a pressure exceeding 120 volts. This limited the operating
voltage of parallel systems, and necessitated the use of conductors
of large size and weight, especially where the current had to be
transmitted a considerable distance.
The effect of this limiting voltage is more apparent when it is clearly
understood that the size of wire required to carry a current depends
upon the amperes and not upon the volts.
A wire capable of carrying a current of 10 amperes at 20
volts, can carry 10 amperes at 20,000 volts or any other
voltage. Therefore, since the amount of electric energy or
power transmitted through a conductor is equal to the amperes
multiplied by the volts, it is clear that by increasing the
voltage, the power transmitting capacity of a current can be
almost indefinitely increased without increasing the size of
the conducting wire. This is the reason why considerations of
economy dictate the use of the highest voltages possible in
long distance transmissions. The voltage of the current is
determined, however, by the requirements of the apparatus to be
operated.
Incandescent lamps usually require a pressure of 110 volts, and
the current required by a 16 candle power lamp at that voltage
is about ½ ampere. Therefore if the lamp be designed for
a pressure of 220 volts, the current will be reduced to ¼
ampere, and the same size of wire could be used to feed twice
as many lamps.
[Illustration: FIGS. 792 and 793.—Evolution of the three wire system.
Fig. 792 shows two dynamos supplying two independent circuits. These
may be connected in series as in fig. 793, thus operating the two
circuits of fig. 792 with two wires instead of four. To balance the
system in case of unequal loading, a third or _neutral wire_ is used as
shown in fig. 794.]
The saving of copper is the sole merit of the three wire system, and
the object which led to its invention was to effect this economy with
the use of 110 volt lamps.
=Principle of the Three Wire System.=—In fig. 792, two dynamos A and
B are shown supplying two independent incandescent lighting circuits,
each circuit receiving 3 amperes of current at a pressure of 110 volts.
It is evident that the dynamos could be connected with each other in
series, and the lamps connected in series with two each, as shown in
fig. 793, thus making the two wires K and L of the two independent
circuits unnecessary, as the pressure will be increased to 220 volts
while the current will remain at 3 amperes, and each lamp will require
¼ ampere.
[Illustration: FIG. 794.—Balanced three wire system. The middle
conductor, known as the _neutral wire_, keeps the system balanced in
case of unequal loading, that is, a current will flow through it, to or
from the dynamos, according to the preponderance of lamps on the one
side or the other. These current conditions are shown in fig. 797.]
The amount of copper saved will be 100 per cent., but this arrangement
is open to the objection, that when one of the lamps is turned off, or
burned out, its companion will also go out. This difficulty is avoided
in the three wire system by running a third wire N, from the junction
O, between the two dynamos, as shown in fig. 794, thus providing a
supply or return conductor to any one of the lamps, and permitting
any number of lamps to be disconnected without affecting those which
remain. If the system be exactly balanced, no current will flow through
the wire N, because the pressure _toward_ the - terminal of the dynamo
A, will be equal to the pressure _from the_ + terminal of dynamo B,
thus neutralizing the pressure in the wire. For this reason the middle
wire of a three wire system is called the _neutral wire_, and is
usually indicated by the symbol O or ± the latter meaning that it is
positive to the first wire and negative to the second. If the system
be unbalanced, a current will flow through the neutral wire, to or
from the dynamos, according to the preponderance of lamps in the upper
or lower sets. When the number in the lower set is the greater, the
current in the neutral wire will flow _from_ the dynamos as shown in
fig. 797, and _toward_ the dynamos under the reverse condition.
In the case represented in fig. 797, there are five lamps in
circuit, requiring 2½ amperes of current at a pressure
of 110 volts. The two lamps in the upper set will require 1
ampere, and the three lamps in the lower set, 1½ amperes.
Since a pressure of 110 volts can force only a current of one
ampere through resistance of the two lamps in the upper set,
it is evident, that the additional ½ ampere required by the
three lamps in the lower set will have to be supplied through
the neutral wire, as shown.
=Balancing of Three Wire System.=—In practice it is impossible to
obtain an exactly balanced system, as the turning on and off of lamps
as required results in a preponderance of lamps in the upper or lower
sets, and furthermore, even when the number of lamps in the two sets
are equal, they may be located irregularly, thereby causing the
currents to flow for short distances in the neutral line. Therefore,
the larger the number of lamps in the circuit, the easier it will be to
keep the system in a balanced condition.
=Copper Economy in Three Wire Systems.=—Theoretically, the size
of the neutral wire has to be only sufficient to carry the largest
current that will pass through it. A large margin of safety, however,
is allowed in practice so that its cross section ranges from about
one-third that of the outside line, in large central station systems,
to the same as that of each outside line in small isolated systems.
If the neutral wire be made one-half the size of the outside
conductor, as is usually the case in feeders, the amount of
copper required is 5/16 of that necessary for the two wire
system. For mains it is customary to make all three conductors
the same size increasing the amount of copper to ⅜ of that
required for the two wire system.
[Illustration: FIG. 795.—Dobrowolsky three wire system with
self-induction coil. It consists of an ordinary direct current
dynamo, the armature A and pole pieces N and S of which are shown.
A self-induction coil D, is connected to two diametrically opposite
points of the winding of the armature A. The coil D may be carried by
and revolve with the armature; but in the construction represented,
it is stationary, being connected to the armature winding through the
brushes CC, rings and wires JJ. The middle point of the self-induction
coil D, is connected to the neutral conductor O of the three wire
system, the outside conductors + and - being supplied from the brushes
BB in the usual manner. The pressure at the terminals of the coil D
is alternating; hence the latter, on account of its self-induction,
does not act as a short circuit to the armature. Furthermore, the
inductances of the two halves of the coil D being equal, the pressure
of the neutral wire O is kept midway between the pressures of the
outside wires + and -. When the two sides of the system are unbalanced
in load, the difference in current carried in one direction or the
other by the neutral wire passes freely through the coil D, since the
current is steady, or varies slowly, and is therefore unimpeded by the
self-induction. It is evident that the ohmic resistance of D should be
as low and its self-induction as high as possible, in order that the
loss of energy and the difference in voltage on the two sides of the
system shall be as small as possible under all conditions.]
=Modifications of the Three Wire System.=—By the employment of
suitable arrangements, it is possible to operate a three wire system
with only one dynamo. Some of the various arrangements which have
been used or proposed in this connection may be briefly mentioned as
follows:
=Three Wire Storage Battery System=, in which a storage battery
is connected between the two outside wires, and the pressure of
the neutral wire varied to balance the system by shifting the
point at which it is connected to the battery.
=Three Wire Double Dynamo System=, in which a double dynamo
having two armature windings upon the same core, connected to
two separate commutators, is used in the same manner as two
separate dynamos connected in series.
=Three Wire Bridge System=, in which a resistance is connected
across the two outside wires, and the neutral wire is brought
to a point on the resistance through a movable switch. The
pressures on the two sides of the circuit are equalized by
adjusting the arm of the switch for any change of load.
[Illustration: FIG. 796.—Three wire compensator system. A and
B are the compensators or equalizers. They consist of auxiliary
dynamos coupled together and connected to the system as shown.
D is the main dynamo, and E, a booster.]
=Three Wire Three Brush Dynamo System=, in which the neutral
wire is connected to a third brush on the dynamo.
=Dobrowolsky Three Wire System=, in which a self-induction
coil is connected to two diametrically opposite points of the
armature of an ordinary direct current dynamo. The principle of
this system is illustrated in fig. 795.
=Three Wire Auxiliary Dynamo System=, in which the neutral wire
is connected to an auxiliary dynamo which supplies a pressure
one-half as great as that of the main dynamo. The auxiliary
dynamo is usually belt driven by the main dynamo, and acts
as a dynamo when the load is greater on the negative side of
the circuit, and as a motor when the excess of load is on the
positive side.
=Three Wire Compensator System=, in which two auxiliary dynamos
A and B called _compensators or equalizers_, are coupled
together and connected to the system as shown in fig. 796. Each
compensator generates one-half as much pressure as the main
dynamo D, and serves to equalize the pressure and the load, the
compensator on the lightly loaded side operating as a motor
and driving the other as a dynamo. When the system is exactly
balanced, both compensators run as motors under no load,
therefore, consume very little energy. In this arrangement only
one booster E, is required for both sides of the system, as
the compensators are connected to the outside wires at a point
beyond the boosters, and therefore, sub-divide the increased
difference of pressure equally between the two sides of the
system.
[Illustration: FIG. 797.—Three wire double dynamo system having two
separate windings on the same core and separate commutators A and B as
shown.]
=Extension of the Three Wire Principle.=—In order to attain still
greater economy in copper, the principles of the three wire system may
be extended to include four, five, six, and seven wire systems. The
comparative weights of copper required by such systems are as follows:
Two wire system 1.000
Three " " all wires of equal size .370
Three " " neutral wire one-half size .313
Four " " all wires of equal size .222
Five " " " " " " " .156
Seven " " " " " " " .096
The four wire system requires about two-ninths as much copper, and the
seven wire system about one-tenth as much copper, as an equivalent two
wire system; but neither is desirable, as their operation involves too
much inconvenience, too many unavoidable complications, and create a
possibility of accident, which more than offsets the saving in copper.
[Illustration: FIG. 798.—Diagram showing dynamotor connections when
used as an equalizer in the three wire system. DM, dynamotor; G,
generator side; M, motor side.]
=The Five Wire System.=—This system is employed advantageously in many
places in England and Europe, but has not as yet been introduced to any
extent in America. It is very probable that in the future the three
wire 440 volt system will be selected in preference to the five wire
system.
=Dynamotor.=—This is a combination of dynamo and motor on the same
shaft, one receiving current and the other delivering current, usually
of different voltage, the motor being employed to drive the dynamo
with a pressure either higher or lower than that received at the motor
terminals.
The dynamotor in the direct current circuit corresponds to the
transformer in the alternating current circuit.
[Illustration: FIG. 799.—Diagram showing connections of balancing set
in three wire one dynamo system. The set consists of a motor and dynamo
connected, and its operation is practically the same as a dynamotor.]
=Ques. How is the dynamotor used as an equalizer in the three wire
system?=
Ans. When thus used, the machine is connected as in fig. 798. When
both sides of the system are balanced, there will be no current in the
neutral lead N, and a small current will pass through the two armature
windings of the dynamotor in series, both armatures acting as motors.
If the load on one side of the system become larger than the load on
the other side, there will be a greater drop in the leads connected to
the overloaded side and consequently a lower voltage will exist over
the larger load than exists over the smaller load. The armature winding
of the dynamotor connected to the higher voltage will act as a dynamo,
whose pressure will tend to raise the voltage of the more heavily
loaded side.
The direction of the currents in an unbalanced three wire
system that is being supplied with energy from a main dynamo is
shown in the figure. The commutator at G is connected to the
dynamo winding of the dynamotor and is supplying current to the
upper or larger load, and the lower commutator is connected to
the motor winding of the dynamotor and is taking current from
the lightly loaded side.
=Motor-Dynamo or Balancing Set.=—A balancing set or balancer consists
of a motor mechanically connected to a dynamo used to balance a three
wire system. The operation of such a combination is practically the
same as the dynamotor just described. The balancer is connected as
shown in fig. 799.
[Illustration: FIG. 800.—Holzer-Cabot type M motor-dynamo set. This
combination is known as a booster, and is used to raise or lower the
voltage on feeders. The motor is series wound and connected in series
with one leg of the feeder. Thus, the voltage which the booster will
add to the line will be directly in proportion to the current flowing
in the feeder. The regulation is therefore automatic.]
When an unbalanced load comes on, the voltage on the lightly loaded
side rises and on the heavily loaded side drops. The machine on the
light side then takes power from the line and runs as a motor driving
the machine on the heavy side as a dynamo, supplying the extra current
for that side. This action tends to bring the voltage back to normal
and gives good regulation.
In some cases the field of each machine is connected to the
opposite side of the system which gives a quicker action. This
regulation is automatic and the set takes care of unbalanced
loads in either direction without adjustment.
=Balancing Coils.=—Another method of balancing a three wire system
which does away with any additional rotating machines makes use of
balance coils.
=Ques. Describe the type of dynamo used with balancing coils?=
[Illustration: FIG. 801.—Diagram showing connections of balancing coil
system. The dynamo used in this system is provided with both commutator
and collector rings.]
Ans. The regular two wire dynamo is used supplying power to the outside
wires, but there are collector rings connected to the armature. These
rings are much lighter than they would be for a converter as they carry
only about ⅛ of the dynamo load. These rings being light are usually
placed at the end of the commutator and are connected directly to the
commutator bars.
=Ques. How are the balancing coils constructed?=
Ans. They are built of standard transformer parts, and are placed in
cases similar to those of ordinary small transformers.
[Illustration: FIGS 802 and 803.—Distribution by dynamo-motor sets.
Fig. 802, sets in parallel; fig. 803, sets in series. In fig. 802,
current produced by the main dynamo G, is carried to the machines by
the conductors A and B to which the motor portions M are connected
in parallel. These motors are provided with shunt wound field coils
which may be connected to the primary or to the secondary circuit,
consequently the machines run at a practically constant speed. The
dynamo portions D of the transformers are connected to the secondary
circuits which supply the lamps, etc., L, as indicated. The field
magnets of these dynamos may also be fed by the main circuit AB, or
they may be self-excited by shunt or compound winding. In fig. 803, the
motors M are all connected in series with the main dynamo G, and the
dynamo elements D of the transformers, connected to the lamps, etc.,
L. If the current be kept constant (the dynamo G having a regulator
like a series arc dynamo), and the motors M are simple series wound
machines, they will exert a certain torque, or turning effort, which
will be constant. It follows, therefore, that if the dynamos D be
also series wound, each will generate a certain current which will
be constant. If lamps or other devices, designed for that particular
current, be connected in series on the secondary circuits, the dynamos
D will always maintain that current, no matter how many lamps there
may be. When lamps are added, the resistance of the local circuit is
raised, and the current in it decreases, so that the dynamo increases
its speed until it generates sufficient pressure to produce practically
the same current as before. Hence this constitutes a system which is
self-regulating, when lamps, etc., are cut in or out of the secondary
circuits. No harm results even if the secondary be short circuited,
since only the normal current can be generated. But if the secondary
circuit be opened, then the machine will race, and probably injure
itself by centrifugal force, because the torque of the motor M has its
full value, and there is no load upon the dynamos D. To guard against
this danger, some automatic device should be provided to short circuit
the field or armature of the motor when its speed or reverse voltage
rises above a certain point.] The coil has a straight continuous
winding, both ends and a connection from the middle point of the
winding being brought out of the case.
=Ques. How are the coils connected to the dynamo?=
Ans. Two coils are used and are connected to the collector rings as
shown in fig. 801, one coil across each phase. The connections from the
middle points of the coils are connected together and to the neutral
wire of the system.
[Illustration: FIG. 804.—Diagram to show correctness of balancing coil
connection. In the figure, AE, BF, CG, and DH represent the balance
coil and its connection for different positions of the armature of a
bipolar machine.]
=Ques. What is the action of the coils in equalizing the load?=
Ans. On balanced load, the coils take a small alternating exciting
current from the collector rings as any transformer does when connected
to an alternating current line with its secondary open. When an
unbalanced load comes on, the current in the neutral divides, half
going to each coil. This enters the coil at the middle point and half
flows each way through the coil and the slip rings into the armature
winding. The unbalanced current is thus fed back directly into the
dynamo armature continuously.
The coils are small and can be placed back of the switchboard
or below the floor, as they require no attention. The current
flowing to each slip ring is 25% of the direct current in the
neutral wire with the small exciting current taken by the coil
added.
The coils are usually built to take care of current in the
neutral equal to 25% of full load current of the dynamo with a
voltage regulation not to exceed 2 per cent.
=Ques. Upon what does the operation of the balancing coil system
depend?=
Ans. It depends on the following points: First, the _impedance_[1] of
the coils keeps the exciting current which they take from the collector
rings down to a small value as it is alternating current. At the same
time the current from the neutral wire flows through the four half
coils in parallel, and being direct current is impeded only by the
ohmic resistance of the coils, which is low, giving only a slight loss
in the coils. The common point to which the neutral wire is connected
must at all times be neutral to the - and + direct current brushes.
[1] NOTE.—The term _impedance_ means the total opposition in an
electric circuit to the flow of an alternating current, being made up
of the actual or ohmic resistance and the apparent resistance due to
self-induction, or if the circuit contain also capacity, the resultant
apparent resistance due to self-induction and capacity.
That this common point is at all times neutral is readily
shown. Referring to fig. 804, let AE, BF, CG and DH represent
the balance coil and its connection for different positions
of the armature of a bipolar machine. Let O be the tap to the
middle point of the winding.
Take the instant when the balance coil taps are directly
under the direct current brushes as shown at position AE. It
is evident that since the point O is the middle point of the
coil, it is neutral between A and E. When the armature turns so
that the balance coils take the position BF, the voltage drop
between A and E may be divided into 4 parts, AB, BO, OF and FE.
As in the first instance, O is neutral between the ends of the
coil, and the voltage drop over OF equals that over OB.
Since the space AB includes the same number of armature coils
as space FE and they are in fields of equal strength, the
voltages across the two spaces will be equal, and the voltage
over AB equals that over FE. Then adding equals: AB + BO = FE +
FO and O is neutral between A and E as in the first case.
In the same way it can be shown that O is neutral between the
direct current brushes for any position of the balance coil
taps. One coil will operate the system, but two coils, giving
four points spaced 90 electrical degrees apart, give better
distribution of the current to the armature winding and better
regulation of the voltage.
=Boosters.=—A booster may be defined as, _a dynamo inserted in a
circuit at a point when it is necessary to change the voltage_. A
booster is generally driven by a motor, the two armatures being
directly coupled, although boosters are sometimes driven from the
engine or line shaft.
[Illustration: FIG. 805.—Crocker Wheeler motor-dynamo set. There are
numerous cases where such a combination is useful for furnishing a
circuit with a voltage different from that of the main plant or with a
voltage that can be varied independently. For storage battery charging
and electrolytic work, where constant current is desirable, it forms a
simple means of voltage regulation. Where a circuit of special voltage
is required, the set not only supplies current at the desired pressure,
but insulates the special circuit, which may be subject to more severe
requirements than the main system. The advantage of the three wire
distribution can be obtained from any two wire dynamo by means of a
small rotary balancer or balancing transformer, which consists of two
direct current machines of the same voltage, mechanically connected
together with their armatures in series. Multiple voltage systems for
speed regulation can also be obtained by a similar arrangement.]
=Ques. Explain the use of a booster?=
Ans. When a number of feeders run out from a station, the longest
and those carrying the heaviest loads will have so much drop on the
line that the pressure at distant points is too low. It is therefore
necessary to raise the pressure to compensate for the drop and this is
done by inserting a booster in the circuit.
It would not be economical to raise the voltage on all the
lines by supplying current from the main dynamo at higher
pressure, hence the voltage is raised only on the lines which
need it by means of the booster working in series with the main
dynamo.
[Illustration: FIG. 806.—Diagram showing use of auxiliary bus bar. In
order to avoid the necessity for boosters, some stations have an extra
bus bar, which is kept at a higher pressure than the main bus, and to
this are connected the feeders that have an extra large drop.]
=Ques. For what other service are boosters employed?=
Ans. They are used in connection with storage battery plants for
the purpose of raising the voltage of the bus bars to the pressure
necessary for charging storage batteries.
=Ques. What is an auxiliary bus bar?=
Ans. An extra bus bar which is kept at higher pressure than the main
bar.
=Ques. What is the object of an auxiliary bus bar?=
Ans. It is used in place of a booster as shown in fig. 806. One or more
dynamos maintain the pressure between the auxiliary bar and the common
negative bar. The feeders which need boosting are connected to the
common negative bar and the auxiliary bar as shown.
CHAPTER XXXVII
WIRES AND WIRE CALCULATIONS
The wireman who is called upon to plan and install a system of wiring
will find it necessary first to have a knowledge of the various kinds
of wire so as to select the one best suited for the work, and to be
able to make simple calculations in order to determine the proper sizes
of wire for the various circuits.
Wires are generally made of circular cross section. The process
of manufacture consists in drawing the material through steel
dies, when its properties permit this treatment. In the case of
some substances, as for instance, tin and lead, difficulties
arise in the drawing process, and these are therefore
"squirted."
The metals most extensively used for wires are copper and
iron; German silver, tin and lead are also employed, but only
at points where it is desirable to have a comparatively high
resistance in the circuit.
=Copper Wire.=—Copper is used in nearly all cases of wiring because it
combines high electrical conductivity with good mechanical qualities
and reasonable price. In conductivity it is only surpassed by silver,
but the cost of the latter of course prohibits its use for wiring
purposes.
Copper wire is used for electric light and power lines, for most
telephone and some telegraph lines, and for all cases where low
resistance is required at moderate cost.
Hard drawn copper wire is ductile, and has a high tensile
strength; these properties allow it to be bent around corners
and drawn through tubes without injury.
Pure annealed copper has a specific gravity of 8.89 at 60°
Fahr. One cubic inch weighs .32 pound; its melting point is
about 2,100° Fahr.
Good hard drawn copper has a tensile strength of about three
times its own weight per mile length. Thus, a number 10 B. &
S. gauge copper wire, weighing 166 lbs. per mile, will have a
breaking strength equal to approximately 3 × 166 = 498 lbs.
=Iron Wire.=—This kind of wire is largely used for telegraph and
telephone lines, although it is rapidly being replaced by copper in
long lines.
There are three grades of iron wire:
1. =Extra best best (E. B. B.)= which has the highest
conductivity and is the nearest to being uniform, in quality,
being both tough and pliable;
2. =Best best (B. B.)=, which varies more in quality, is not so
tough, and is lower in conductivity. _It is frequently sold as_
=E. B. B.=;
3. =Best (B.)=, which is the poorest grade made, being more
brittle, and lowest in conductivity. Iron wire should be well
galvanized.
=German Silver Wire.=—German silver is an alloy consisting of 18 to
30% nickel, and the balance about four parts copper to one part zinc.
It is very largely used as a resistance material in making resistance
coils, and is sold in the form of wire, and strip. The resistance of
this wire varies with its composition.
The resistance of the 18% alloy at 25° C. is 18 times that of
copper, and of the 30% alloy about 28 times that of copper.
The safe carrying capacity of the wire in spirals in open air
for continuous duty is such that the circular mils per ampere
varies from about 1,500 in No. 10 wire to about 475 in No. 30.
For intermittent duty the capacity is twice as great.
=Standard of Copper Wire Resistance.=—Matthiessen's standard for
resistance of copper wire is as follows: _A hard drawn copper wire
one meter long, weighing one gramme, has a resistance of .1469 B. A.
unit at 32° Fahr._ Relative conducting power: silver, 100; hard or
un-annealed copper, 99.95; soft or annealed copper, 102.21.
A committee of the Am. Inst. Electrical Engineers recommends the
following form of Matthiessen's standard, taking 8.89 as the specific
gravity of pure copper: _A soft copper wire one meter long and one
millimeter in diameter has an electrical resistance of .02057 B. A.
unit at 0°C._[2] From this the resistance of a soft copper wire one
foot long and .001 in. in diameter (mil-foot) is 9.72 B. A. units at
0°C.
[2] NOTE.—The international ohm ÷ B. A. ohm = 1 ÷ .9866. The B. A. ohm
÷ International ohm = 1 ÷ 1.0136. Hence, to reduce British Association
ohms to International ohms, divide by 1.0136. or multiply by .9866.
For every degree Fahr., the resistance of copper wire increases
.2222%. Thus a piece of copper wire having a resistance of 10
ohms at 32°, would have a resistance of 11.11 ohms at 82°.
Relative Conductivity of Different Metals and Alloys.
(According to Lazare Weiler.)
Pure silver 100
Pure copper 100
Alloy, ½ copper, ½ silver 86.65
Telephonic siliceous bronze 35
Pure zinc 29.9
Brass with 35% zinc 21.5
Swedish iron 16
Pure platinum 10.6
Copper with 10% nickel 10.6
Pure lead 8.88
Pure nickel 7.89
Phosphor-bronze, 10% tin 3.88
=Conductors.=—Copper is used more than any other metal for
transmitting electrical energy, and for interior wiring it is used
exclusively. Copper conductors should be of the highest commercial
conductivity, not less than 97%.
For conductors up to sizes as large as No. 8 B. & S. gauge, single
conductors may be used, but for larger sizes the necessary conductivity
should be obtained by conductors made up of strands of smaller wires.
The size of these strands depend upon the size of the conductors and
the conditions under which they are to be used.
Where conductors are very large (as for instance dynamo leads),
and where it is essential that they should be as flexible as
possible, strands as small as No. 20 or 22 B. & S. gauge may be
used.
Conductors for flexible cords, pendants, fixtures, etc.,
should also consist of very fine strands, so that they may be
perfectly pliable and flexible.
The individual strands for instance, for a No. 16 B. & S. gauge
flexible cord should be as fine as No. 30.
[Illustration: FIG. 807.—Elevator cable for annunciators. This type
of cable is designed for connecting the movable elevator car with the
signal buttons upon the different floors, and is constructed so as to
secure strength and flexibility.]
=Covered Conductors.=—For most conditions of service, wires are
protected with an insulating covering. Wires used in interior circuits
should have a covering which shall act both as an electrical insulator
and as a mechanical protection. In some instances, however, the
insulating qualities are of secondary importance.
The various forms of covering now in use commercially for wires are:
1. Rubber;
2. Weather proof;
3. Slow burning;
4. Slow burning weather proof;
5. Armoured.
=Rubber Covered Conductors.=—This class of conductor consists of a
tinned copper wire with a rubber covering, protected by an outside
braiding of cotton saturated with a preservative compound.
=Ques. What are the advantages of rubber insulation for conductors?=
Ans. It is waterproof, flexible, fairly strong, and has high insulating
qualities.
[Illustration: FIG. 808.—Rubber insulated telephone and telegraph
wires. The inner coat of rubber should be free from sulphur or other
substances liable to corrode the copper.]
=Ques. What are the disadvantages of rubber insulation?=
Ans. It deteriorates more or less rapidly and is quickly injured by
temperatures above 140° Fahr.
=Ques. For what service are rubber covered conductors adapted?=
Ans. For interior wiring.
=Ques. Is pure rubber used?=
Ans. No. The covering should be made from a compound containing from 20
to 35 per cent. of pure rubber.
It would be difficult to place pure rubber on a wire,
and moreover a covering made of pure rubber would not be
durable and would deteriorate very rapidly, particularly at
temperatures above 120° Fahr. Accordingly, it is mixed with
other materials, such as French chalk, silicate of magnesia,
sulphur, red lead, etc.
=Weather Proof Conductors.=—In this class of conductor, the wire is
protected from the weather by a waterproof covering, consisting usually
of braided cotton of two or three thicknesses saturated with a moisture
resisting insulating compound.
=Ques. Where are weather proof conductors used?=
Ans. In places subject to dampness, such as cellars, tunnels, open
sheds, breweries, etc.
[Illustration: FIG. 809.—Twisted weather proof wires. The insulation
consists of two or three thicknesses of braided cotton saturated with a
moisture resisting insulating compound.]
=Ques. What are the advantages of weather proof conductors?=
Ans. The insulation is cheap, very durable, and does not deteriorate
unless exposed to high temperatures such as will melt the compound.
=Ques. State the disadvantages.=
Ans. The covering is more or less inflammable and is not very efficient
as an insulator.
=Ques. What precaution should be taken in using weather proof
conductors?=
Ans. On account of the inflammable character of the covering, care
should be taken in wiring at points where any considerable number of
conductors are brought together, or where there is much woodwork or
other combustible material.
=Ques. For what use are weather proof conductors especially adapted?=
Ans. For outside wiring where moisture is certain and where fireproof
quality is not necessary.
Obviously conductors of this class should not be used in
conduits, nor in fact, in any way except exposed on glass or
porcelain insulators.
=Slow Burning Wire.=—This class of conductor is defined as: _one
that will not carry fire_. The covering consists of layers of cotton
or other thread, all the interstices of which are filled with the
fireproofing compound, or of material having equivalent fire resisting
and insulating properties. The outer layer is braided and specially
designed to withstand abrasion. The thickness of insulation must not
be less than that required for slow burning weather proof wire and
the outer surface must be finished smooth and hard.—_Underwriters'
requirements._
[Illustration: FIG. 810.—Slow burning wire, formerly known as
Underwriter's Wire. The insulation is triple braided, saturated with a
white fireproof compound. Solid conductor.]
=Ques. Where should slow burning wires be used?=
Ans. In hot dry places, where ordinary insulations would be injured,
and where wires are bunched, as on the back of a large switchboard or
in a wire tower.
A slow burning covering is considered good enough when the
wires are entirely on insulating supports. Its main object is
to prevent the copper conductors coming into contact with each
other or anything else.
=Ques. What must be done before using weather proof wire?=
Ans. Permission to use the wire must first be obtained from the local
Inspection Department.
=Slow Burning Weather Proof Wire.=—The covering of this type wire
is a combination of the underwriters and weather proof insulations.
The fireproof coating comprises a little more than half of the total
covering. When the fireproof coating is placed on the outside, the wire
is called "slow burning weather proof."
[Illustration: FIG. 811.—Slow burning weather proof wire. The
insulation is composed of two braids thoroughly saturated with a fire
proof composition, over which is a highly polished weather proof third
braid. This wire was formerly known as "fire and weather proof" wire.]
=Ques. How does slow burning weather proof wire compare with weather
proof wire?=
Ans. It is less inflammable and less subject to softening under heat.
=Ques. Where should slow burning weather proof wire be used?=
Ans. In places where the wires are to be run exposed and where moisture
resisting quality is desired, also where at the same time it is
desirable to avoid an excess of inflammable covering.
=Ques. How should it be installed?=
Ans. It should be set on glass or porcelain insulators.
=Miscellaneous Insulated Conductors=
[Illustration: FIG. 812.—Armoured submarine cable. This type of cable
is insulated with a rubber compound containing not less than 30% of
pure Para rubber. The following specifications have been adapted by
various telegraph companies and the United States Government for
general use.]
+————————————-+————————————+————————-+——————————————+——————————+——————————-+
| No. of | Gauge of | No. of | Gauge of | Outside | Weight |
| Conductors | Conductors | Armour | Armour Wires | Diameter | per 1,000 |
| | (B. & S.) | Wires | B. W. G. | (inch) | Feet |
+————————————-+————————————+————————-+——————————————+——————————+——————————-+
| | | | | | |
| 1 | 14 | 12 | 8 | ⅞ | 1,150 |
| 2 | 14 | 16 | 8 | 1-31/32 | 1,675 |
| 3 | 14 | 14 | 6 | 1¼ | 2,400 |
| 4 | 14 | 16 | 6 | 1-5/16 | 2,750 |
| 5 | 14 | 19 | 6 | 1⅜ | 3,100 |
| 6 | 14 | 21 | 6 | 1½ | 3,500 |
| 7 | 14 | 21 | 6 | 1½ | 3,600 |
| 10 | 14 | 22 | 4 | 1⅞ | 4,600 |
| | | | | | |
+————————————-+————————————+————————-+——————————————+——————————+——————————-+
NOTE.—The above specifications refer only to river and harbor
cables. Ocean cables are of an entirely different character,
and consist of "shore end," "intermediate" and "deep sea" types.
[Illustration: FIG. 813.—Gas engine ignition cable. This is a special
cable made to stand the hard service necessary on automobiles. The
conductor is composed of 36 strands of No. 27 tinned copper wire, equal
to No. 14 in capacity, which gives it necessary flexibility. About this
conductor are woven two layers of cotton thread. Over this are woven,
in opposite directions, several layers of specially prepared tape which
has been given two coatings of fine insulating varnish. Two strong
braids of cotton form the outside covering, and each of these different
braids is passed through a bath of insulating liquid and baked in a
steam heated oven. With three layers of tape the cable will stand a
test of 18,000 to 20,000 volts, and with five layers, 30,000 volts.]
[Illustration: FIG. 814.—Paper insulated lead encased telephone
cable.]
=Ques. For what service is slow burning weather proof wire not suited?=
Ans. It is not adapted to outside work.
=Safe Carrying Capacity of Wire.=—All wires will heat when a current
of electricity passes through them. The greater the current or the
smaller the wire, the greater will be the heating effect. Large wires
are heated comparatively more than small wires because the latter have
a relatively greater radiating surface.
[Illustration: FIG. 815.—Pothead wires. The standard wire for pothead
work is either No. 19, 20 or 22 B. & S. gauge, either single conductor
or twisted pair, insulated to a diameter of 3/32 inch over rubber,
without any outer braid or protection. In the case of twisted pairs
one conductor is usually made of a differently colored rubber than the
other, so as to distinguish between them.]
The temperature of a wire increases approximately as the square of the
current, and inversely as the cube of the diameter of the wire.
The elevation in temperature of a wire carrying a current represents so
much lost energy.
From these considerations it must be clear that it is important not to
overload conductors in order to secure efficient working, and to avoid
risk of fire on inside installations.
The Board of Underwriters specifies that the carrying capacity
of a conductor is safe when the wire will conduct a certain
current without becoming painfully hot.
In the following table of carrying capacity, prepared by
the underwriters, a wire is assumed to have a safe carrying
capacity when its temperature is not increased by the given
current over 30° Fahr. above that of the surrounding air.
SAFE CARRYING CAPACITIES OF WIRES
(Maximum amperes allowed by the Underwriters.)
+————————+——————————————-+————————————+————————————+
| Brown | | Rubber | Other |
| and | | insulation | insulations|
| Sharpe | Circular mils | —————— | —————— |
| Gauge | | Amperes | Amperes |
| | | | |
+————————+——————————————-+————————————+————————————+
| | | | |
| 18 | 1,624 | 3 | 5 |
| 16 | 2,583 | 6 | 8 |
| 14 | 4,107 | 12 | 16 |
| 12 | 6,530 | 17 | 23 |
| 10 | 10,380 | 24 | 32 |
| 8 | 16,510 | 33 | 46 |
| 6 | 26,250 | 46 | 65 |
| 5 | 33,100 | 54 | 77 |
| 4 | 41,740 | 65 | 92 |
| 3 | 52,630 | 76 | 110 |
| 2 | 66,370 | 90 | 131 |
| 1 | 83,690 | 107 | 156 |
| 0 | 105,500 | 127 | 185 |
| 00 | 133,100 | 150 | 220 |
| 000 | 167,800 | 177 | 262 |
| 0000 | 211,600 | 210 | 312 |
| | 200,000 | 200 | 300 |
| | 300,000 | 270 | 400 |
| | 400,000 | 330 | 500 |
| | 500,000 | 390 | 590 |
| | 600,000 | 450 | 680 |
| | 700,000 | 500 | 760 |
| | 800,000 | 550 | 840 |
| | 900,000 | 600 | 920 |
| | 1,000,000 | 650 | 1,000 |
| | 1,100,000 | 690 | 1,080 |
| | 1,200,000 | 730 | 1,150 |
| | 1,300,000 | 770 | 1,220 |
| | 1,400,000 | 810 | 1,290 |
| | 1,500,000 | 850 | 1,360 |
| | 1,600,000 | 890 | 1,430 |
| | 1,700,000 | 930 | 1,490 |
| | 1,800,000 | 970 | 1,550 |
| | 1,900,000 | 1,010 | 1,610 |
| | 2,000,000 | 1,050 | 1,670 |
| | | | |
+————————+——————————————-+————————————+————————————+
The lower limit is specified for rubber covered wires to
prevent gradual deterioration of the high insulations
by the heat of the wires, but not from fear of igniting
the insulation. The question of drop is not taken into
consideration in the table on page 731.
The carrying capacity of Nos. 16 and 18 B. & S. gauge wire is
given, but no smaller than No. 14 is to be used, except as
allowed under rules for fixture wiring.—_Underwriters' Rules._
=Circular Mils.=—The unit of measurement in measuring the cross
sectional area of wires is the _circular mil_; it is the area of a
circle one mil (.001 in.) in diameter.
_The area of a wire in circular mils is equal to the square of the
diameter in mils._
[Illustration: FIG. 816.—Diagram illustrating circular mils. The
circular mil is used as a unit of cross sectional area in measuring
wires. It is equal to the area of a circle .001 in. diameter; its value
is .0000007854 square inch. In the figure the sum of the areas of the
nine small circles equals the area of the large circle. This is evident
from the following: Take the diameter of the small circles as unity,
then the diameter of the large circle is three. Hence, the sum of the
area of the small circles × (¼ π × 1²) × 9 = .7854 × 9 =
7.0686; area of the large circle = ¼ π × 3² = .7854 × 9 =
7.0686. Therefore since the area of the large circle equals the sum of
the areas of the small circles, the area of a wire in circular mils is
equal to _the square of its diameter expressed in mils_.]
Thus a wire 2 mils in diameter (.002 in.) has a cross sectional
area of 2 × 2 = circular mils. Accordingly to obtain the area
of a wire in circular mils, _measure its diameter with a
micrometer which reads directly in mils or thousandths of an
inch, and square the reading_.
The circular mil (abbreviated C.M.) applies to all _round_
conductors, and has a value of .7854 times that of the square
mil, that is, 1 circular mil = .7854 square mil. If the
diameter be expressed as a fraction of an inch, as for instance
⅓ in., the circular mil area may be found as follows: Reduce
the fraction ⅓ to the decimal of an inch, multiply the result
by 1,000 to express the diameter in mils, and square the
diameter so expressed, thus: ⅓ = 1,000 ÷ 3 = .333. .333 ×
1,000 = 333 mils; 333 × 333 = 110,889 circular mils.
The diameter of any wire may be found when its circular mil
area is known by extracting the square root of the circular mil
area.
=Square Mils.=—For measuring conductors of square or rectangular cross
section, such as bus bars, copper ribbon, etc., the square mil is used.
A square mil is the area of a square whose sides are one mil (.001 in.
long) and is equal to .001 × .001 = .000001 square inch.
[Illustration: FIG. 817.—Diagram illustrating square mils. A square
mil is a unit of area employed in measuring the areas of cross sections
of square or rectangular conductors. It is equal to .000001 square
inch. One square mil equals 1.2732 circular mils. The figure shows
an area of nine square mils; this is equal to 9 × 1.2732 = 11.4588
circular mils.]
EXAMPLE.—A copper ribbon for a field coil measures ⅝ inch by
⅛ inch. What is its area in square mils? What is its area in
circular mils?
⅝ = .625 in., or 625 mils; ⅛ = .125 in., or 125 mils.
Area in square mils = 625 × 125 = 78,125.
Area in circular mils= { 78,125 ÷ .7854 }
{or 78.125 × 1.2732} = 99,469.
=Mil Foot.=—This unit is used as a basis for computing the resistance
of any given wire. A mil foot means _a volume one mil in diameter and
one foot long_.
_The resistance of a wire of commercially pure copper one mil in
diameter and one foot long is taken as a standard in calculating the
resistance of wires, and has been found to be equal to 10.79 ohms at
75° Fahr._
The calculation is made according to the following rule:
_The resistance of a copper wire is equal to its length in feet,
multiplied by the resistance of one mil foot (10.79 ohms) and divided
by the number of circular mils, or the square of its diameter._
Expressed as a formula:
length of wire in ft. × 10.79
resistance in ohms = —————————————————————————————— (1)
circular mils
EXAMPLE. What is the resistance of a copper wire 1,500 feet
long and having a transverse area of 10,381 circular mils?
Substituting these values in formula (1)
1,500 × 10.79
resistance = ———————————————————— = 1.559 ohms.
10,381
_The transverse area of a copper wire is found by multiplying the
resistance of a mil foot (10.79) by its length in feet and dividing the
result by its resistance in ohms._
This is obtained directly from the formula (1) by solving the equation
for circular mils, thus:
length of wire in ft. × 10.79
circular mils = ——————————————————————————————- (2)
resistance in ohms
EXAMPLE. What is the circular mil area of a wire 1,500 feet
long and having a resistance of 1.559 ohms?
Substituting the values in equation (2)
1,500 × 10.79
circular mils = ————————————- = 10,381
1.559
[Illustration: FIGS. 818 and 819.—Diagrams illustrating the meaning
of the term lamp foot, and how to apply it in calculating a circuit.
As defined, _one 16 candle power lamp at a distance of one foot from
the fuse block or point of supply is called a lamp foot_; this is
equivalent to one 8 candle power lamp at a distance of 2 feet, or one
32 candle power lamp one-half foot from the fuse block. In fig. 819,
there are four 8 candle power lamps, and the distance to center of
distribution is 10 feet. The circuit then contains 4 ÷ 2 × 10 = 20 lamp
feet.]
=Lamp Foot.=—This unit facilitates laying out wiring and calculating
the drop. A lamp foot is defined as _one 16 candle power lamp at a
distance of one foot from the point of supply_. Accordingly the number
of lamp feet in any circuit is equal to the number of 16 candle power
lamps (or equivalent in other sizes) in the circuit multiplied by the
distance in feet from the fuse block to the center of distribution.
When no point is specified, the feet are always measured from
the supply point to the center of distribution. When other than
16 c.p. lamps are in the circuit they must be reduced to 16
c.p. lamps. Thus two 8 c.p. lamps would be counted one 16 c.p.
lamp, one 32 c.p. lamp would be counted two 16 c.p. lamps, etc.
=Ampere Foot.=—From the foregoing explanation of _lamp foot_, the
significance of _ampere foot_ is easily understood—the two terms are
in fact self-defining.
An ampere foot may be defined as _the product of one ampere multiplied
by one foot_.
The unit ampere foot is used in figuring motor circuits or currents
designed to carry a mixed load.
[Illustration: FIG. 820.—The center of distribution of a circuit
coincides with the geometrical center of the group of lamps when the
lamps are of uniform size and spaced equal distances apart. The center
of distribution is here indicated by the dotted line A B.]
The ampere feet of a main are found by _multiplying the maximum load in
amperes by the distance from the fuse block to the electrical center of
the load_.
Thus if the center of distribution be 50 feet from the fuse
block and the maximum load is 9 amperes, the number of ampere
feet is equal to 9 × 50 = 450.
=Electrical Center of Distribution.=—The electrical center of a
circuit depends upon the distances between the lamps and the fuse
block; also the relative sizes of the lamps.
It may be defined as _the sum of the lamp feet for each section divided
by the number of 16 candle power lamps in the circuit_.
If the lamps be of uniform capacity, and placed at equal distances
apart, the center of distribution will coincide with the geometrical
center of the group of lamps. However, if the lamps vary in size, and
be irregularly spaced, the electrical center will not coincide with the
geometrical center unless the lamps be symmetrically arranged so as to
compensate for the difference in sizes and spacing.
[Illustration: FIG. 821.—Diagram of an irregular circuit illustrating
method of finding the center of distribution. Rule: _Divide the sum of
the lamp feet for each section by the number of 16 candle power lamps
or equivalent in the circuit_; the quotient gives the distance in feet
from the fuse block to the center of distribution.]
In such cases, as shown in fig. 821, the electrical center can
be determined by adding together the lamp feet of the several
sections A, B, C, etc., of the main and dividing the result by
the 16 c.p. units. Thus the lamp feet of
Section A = 10 lamps × 10 feet= 100
" B = 9 " × 5 " = 45
" C = 7 " × 6 " = 42
" D = 6 " × 4 " = 24
" E = 5 " × 5 " = 25
" F = 4 " × 10 " = 40
" G = 2 " × 5 " = 10
——-
which added together gives a total of 286 lamp feet.
This when divided by the ten 16 c.p. units comprising four 16
c.p. lamps and three 32 c.p. lamps, gives a little over 28½
feet as the distance from the fuse block to the center of
distribution, the position of which is shown by the line M N in
fig. 821, while that of the geometrical center is shown by the
line K L.
When the center of distribution is at a considerable distance
from the supply circuit, and it becomes advisable to divide
the wiring into two distinct elements—a feeder and one or
more mains, the junction of the feeder and the mains should
be located at the electrical center of the mains whenever
possible. When this is done, it is obvious that the wire size
of only one half the main needs to be calculated, as both
halves of the main are identical.
[Illustration: FIG. 822.—Brown and Sharpe (B. & S.), or American
Standard wire gauge. This gauge was adopted by the brass manufacturers
Jan., 1858. The cut is full size, and therefore, shows the actual sizes
corresponding to the gauge numbers.]
=Wire Gauges.=—For the purpose of facilitating the measurement
of wire, a number of gauges have been designed by various wire
manufacturing concerns. The principal gauges used in the United States
are the American or Brown & Sharp's gauge; the English standard or
Birmingham gauge; Washburn & Moen's standard gauge; Imperial wire
gauge; Stubs' steel wire gauge, and the U. S. Standard wire gauge.
The several gauges are here given with explanation of their use.
=The American Standard or Brown and Sharp's Gauge.=—This gauge
is commonly designated as A. W. G. or B. & S., and has been
adopted by brass manufacturers and is used mostly in measuring
brass, copper, silver, German silver, and gold in both wire and
plate.
=Birmingham or Stub's Wire Gauge (B. W. G.).=—Old English
Standard and Iron Wire Gauge. _Birmingham or Stubs' Iron Wire
Gauge is not the same as Stubs' Steel Wire Gauge_. A table of
Stub's Steel Wire Gauge is given on page 741.
[Illustration: FIG. 823.—Micrometer screw gauge. It consists
essentially of a screw whose thread is accurately turned to a pitch
of some convenient fraction of an inch or centimetre. When the screw
is screwed home, the surfaces of A and B meet, and the instrument
should then read zero on both the straight and the circular scale. If
this be not so, there is a zero error which must be either allowed
for, or corrected by means of the screw provided for that purpose. If
the former course be adopted, the reading of the instrument is taken
when the faces A and B are in contact, and this number added to or
subtracted from the final reading according to whether the error makes
the wire apparently smaller or greater than its real size. The surfaces
A and B are now screwed apart and then, after the wire to be measured
(which should be clean and straight) has been introduced between them,
they are screwed together to lightly grip the wire. If the gauge be
screwed up too tightly the value of the measurement is destroyed, since
a copper wire can easily be crushed, and in addition the accurate
screw may be permanently damaged. To avoid the possibility of this
happening, screw gauges are provided with a ratchet which prevents an
excessive force being applied to the screw. If the pitch of the screw
in the gauge be ½0th of an inch, and the circular scale consist of
50 divisions, then for each revolution of the screw, the surface B
will travel a distance equal to the pitch, that is ½0th of an inch.
The graduations on an instrument of this kind are generally ⅒th of
an inch on the straight scale, with shorter lines to mark the half
divisions. The thickness of a wire on the straight scale can therefore
be read to the nearest ½0th inch. Each division of the circular scale
represents 1/50th of a revolution of the screw, which corresponds to a
change in distance between A and B, of 1/50 of 1/20 = 1/1,000 in. If
then the reading on the straight scale be 1 and on the circular scale
35, the distance between A and B is .1 + .035 = .135 inch.]
=Washburn and Moen's Standard Wire Gauge.=—Commonly designated
as W. & M. G. has been adopted by the U. S. Steel Corporation
in making their wire.
=New British Standard (N. B. S.).=—British Imperial English
Legal Standard and Standard Wire Gauge, and is variously
abbreviated by S. W. G. and I. W. G.
=Roebling Gauge.=—Washburn Moen, American Steel & Wire Co.'s
Iron Wire Gauge.
[Illustration: FIGS. 824 and 825.—U. S. wireman's calculating gauge;
views showing both sides. On the side shown in fig. 824, set the
required number of feet on the small circle opposite the required
number of amperes on the large circle, then set the small pointer at
the required voltage and loss. Then on the other side (fig. 825) the
large pointer will indicate the required size of wire in B. & S. gauge,
and will also indicate the safe carrying capacity, while the wire may
be gauged by slot A (fig. 824).]
=U. S. Standard Wire Gauge.=—This gauge is used for measuring
sheet and plate iron, and steel, by the U. S. Government in
assessing duties, and in making requisitions for supplies.
=Old English Standard Wire Gauge.=—The old English gauge is
the same as the Birmingham or Stubs' standard gauge, commonly
designated as B. W. G. It is used chiefly for measuring sheet
iron and steel, also soft steel and iron wire.
=London Gauge.=—Old English (_not Old English Standard_).
From the foregoing it is seen that great confusion exists with
such a multiplicity of gauges and emphasizes the importance of
specifying the gauge and of knowing what gauge to use.
In using the gauges known as Stubs' Gauges, there should be
constantly borne in mind the difference between the Stubs' Iron
Wire Gauge and the Stubs' Steel Wire Gauge. The Stubs' Iron
Wire Gauge is the one commonly known as the English Standard
Wire, or Birmingham Gauge and designates the Stubs' _soft_ wire
sizes. The Stubs' Steel Wire Gauge is the one that is used in
measuring drawn steel wire or drill rods of Stubs' make and is
also used by many makers of American drill rods.
=STUBS' STEEL WIRE GAUGE=
——————-+————————-++——————+————————-++——————+————————-++——————+———————-
| Size of || | Size of || | Size of || | Size of
Letter.| Letter ||No. of| Number ||No. of| Number ||No. of| Number
| in || Wire | in || Wire | in || Wire | in
|Decimals.||Gauge.|Decimals.||Gauge.|Decimals.||Gauge.|Decimals.
——————-+————————-++——————+————————-++——————+————————-++——————+———————-
Z | .413 || 1 | .227 || 28 | .139 || 55 | .050
Y | .404 || 2 | .219 || 29 | .134 || 56 | .045
X | .397 || 3 | .212 || 30 | .127 || 57 | .042
W | .386 || 4 | .207 || 31 | .120 || 58 | .041
V | .377 || 5 | .204 || 32 | .115 || 59 | .040
U | .368 || 6 | .201 || 33 | .112 || 60 | .039
T | .358 || 7 | .199 || 34 | .110 || 61 | .038
S | .348 || 8 | .197 || 35 | .108 || 62 | .037
R | .339 || 9 | .194 || 36 | .106 || 63 | .036
Q | .332 || 10 | .191 || 37 | .103 || 64 | .035
P | .323 || 11 | .188 || 38 | .101 || 65 | .033
O | .316 || 12 | .185 || 39 | .099 || 66 | .032
N | .302 || 13 | .182 || 40 | .097 || 67 | .031
M | .295 || 14 | .180 || 41 | .095 || 68 | .030
L | .290 || 15 | .178 || 42 | .092 || 69 | .029
K | .281 || 16 | .175 || 43 | .088 || 70 | .027
J | .277 || 17 | .172 || 44 | .085 || 71 | .026
I | .272 || 18 | .168 || 45 | .081 || 72 | .024
H | .266 || 19 | .164 || 46 | .079 || 73 | .023
G | .261 || 20 | .161 || 47 | .077 || 74 | .022
F | .257 || 21 | .157 || 48 | .075 || 75 | .020
E | .250 || 22 | .155 || 49 | .072 || 76 | .018
D | .246 || 23 | .153 || 50 | .069 || 77 | .016
C | .242 || 24 | .151 || 51 | .066 || 78 | .015
B | .238 || 25 | .148 || 52 | .063 || 79 | .014
A | .234 || 26 | .146 || 53 | .058 || 80 | .013
| || 27 | .143 || 54 | .055 || |
——————-+————————-++——————+————————-++——————+————————-++——————+———————-
The following table gives the diameters, in decimal parts of an inch,
of the various sizes of wire corresponding to the number of gauge
numbers of the different standard wire gauges used in the United
States.
=TABLE OF VARIOUS WIRE GAUGES=
=In decimal parts of an inch=
————————+————————-+————————-+——————————+——————-+——————-+——————-+——————-
Number | Ameri- | Birming-| Wash- | Tren- |G.W. | Old | Brit-
of | can, or | ham, or | burn & | ton | Pren- | Eng- | ish
Wire | Brown & | Stubs | Moen | Iron | tiss, | lish, | Stan-
Gauge | Sharpe | (B.W.G.)| Mfg. Co.,| Co., | Holy- | From | dard
| (B.&S.) | | Worces- | Tren- | oke, | Brass | (S.W.-
| | | ter, | ton, | Mass. | Mfrs' | G.)
| | | Mass. | N.J. | | List |
————————+————————-+————————-+——————————+——————-+——————-+——————-+——————-
0000000 | | | | | | | .500
000000 | | | .460 | | | | .464
00000 | | | .430 | .450 | | | .432
0000 | .46000 | .454 | .393 | .400 | | | .400
000 | .40964 | .425 | .362 | .360 | .3586 | | .372
00 | .36480 | .380 | .331 | .330 | .3282 | | .348
0 | .32486 | .340 | .307 | .305 | .2994 | | .324
1 | .28930 | .300 | .283 | .285 | .2777 | | .300
2 | .25763 | .284 | .263 | .265 | .2591 | | .276
3 | .22942 | .259 | .244 | .245 | .2401 | | .252
4 | .20431 | .238 | .225 | .225 | .2230 | | .232
5 | .18194 | .220 | .207 | .205 | .2047 | | .212
6 | .16202 | .203 | .192 | .190 | .1885 | | .192
7 | .14428 | .180 | .177 | .175 | .1758 | | .176
8 | .12849 | .165 | .162 | .160 | .1605 | | .160
9 | .11443 | .148 | .148 | .145 | .1471 | | .144
10 | .10189 | .134 | .135 | .130 | .1351 | | .128
11 | .090742 | .120 | .120 | .1175 | .1205 | | .116
12 | .080808 | .109 | .105 | .1050 | .1065 | | .104
13 | .071961 | .095 | .0920 | .0925 | .0928 | | .0920
14 | .064084 | .083 | .0800 | .0800 | .0816 | .08300| .0800
15 | .057068 | .072 | .0720 | .0700 | .0726 | .07200| .0720
16 | .050820 | .065 | .0630 | .0610 | .0627 | .06500| .0640
17 | .045257 | .058 | .0540 | .0525 | .0546 | .05800| .0560
18 | .040303 | .049 | .0470 | .0450 | .0478 | .04900| .0480
19 | .035890 | .042 | .0410 | .0400 | .0411 | .04000| .0400
20 | .031961 | .035 | .0350 | .0350 | .0351 | .03500| .0360
21 | .028462 | .032 | .0320 | .0310 | .0321 | .03150| .0320
22 | .025347 | .028 | .0280 | .0280 | .0290 | .02950| .0280
23 | .022571 | .025 | .0250 | .0250 | .0261 | .02700| .0240
24 | .020100 | .022 | .0230 | .0225 | .0231 | .02500| .0220
25 | .017900 | .020 | .0200 | .0200 | .0212 | .02300| .0200
26 | .015940 | .018 | .0180 | .0180 | .0194 | .02050| .0180
27 | .014195 | .016 | .0170 | .0170 | .0182 | .01875| .0164
28 | .012641 | .014 | .0160 | .0160 | .0170 | .01650| .0148
29 | .011257 | .013 | .0150 | .0150 | .0163 | .01550| .0136
30 | .010025 | .012 | .0140 | .0140 | .0156 | .01375| .0124
31 | .008928 | .010 | .0130 | .0130 | .0146 | .01225| .0116
32 | .007950 | .009 | .0120 | .0120 | .0136 | .01125| .0108
33 | .007080 | .008 | .0110 | .0110 | .0130 | .01025| .0100
34 | .006305 | .007 | .0100 | .0100 | .0118 | .00950| .0092
35 | .005615 | .005 | .0095 | .0095 | .0109 | .00900| .0084
36 | .005000 | .004 | .0090 | .0090 | .0100 | .00750| .0076
37 | .004453 | | .0085 | .0085 | .0095 | .00650| .0068
38 | .003965 | | .0080 | .0080 | .0090 | .00575| .0066
39 | .003531 | | .0075 | .0075 | .0083 | .00500| .0052
40 | .003145 | | .0070 | .0070 | .0078 | .00450| .0048
41 | | | | | | | .0044
42 | | | | | | | .0040
————————+————————-+————————-+——————————+——————-+——————-+——————-+——————-
NOTE.—The sizes of wire are ordinarily expressed by an
arbitrary series of numbers. Unfortunately there are several
independent numbering methods, so that it is always necessary
to specify the method or wire gauge used. The above table gives
the numbers and diameters in decimal parts of an inch for the
various wire gauges in general use.
=Wiring Terms.=—The various members of a complex wiring installation
are designated feeders, sub-feeders, mains, branches, and taps.
A _feeder_ is a stretch of wiring to which no connection is made except
at its two ends.
A _sub-feeder_ is of the same class as a feeder, but is distinguished
either by being one of two or more connecting links between the end of
a single feeder and several distributing mains, or by constituting an
extension of a feeder.
[Illustration: FIG. 826. Circuit diagram illustrating names of the
various parts. A circuit may consist of the following parts as defined
in the accompanying text: 1, feeder, 2, sub-feeders, 3, mains, 4,
branches, 5, taps. It is well to clearly distinguish between these
divisions because the terms are constantly used in wiring.]
A _main_ is a stretch of wiring supplied from one or more feeders or
sub-feeders and distributing current to a number of taps, or else to a
number of branches.
A _branch_ distributes current among a number of lamps, etc.
A _tap_ almost invariably delivers current to a single lamp or other
device.
Reference to fig. 826 will make these definitions clearer. This
diagram is intended merely to illustrate the above definitions
and does not represent any special plan of wiring.
[Illustration: FIGS. 827 and 828. Simplest forms of circuit, consisting
of a main with one or more lamps at the end. The smallest size wire
allowed (No. 14 B.&S. gauge) will generally be found amply large for
such circuits. Note carefully the difference between a main and a
branch by comparison with fig. 826. A main begins from a fuse block,
while a branch is an offset from a main without any fuse block.]
The simplest possible wiring installation is one in which a
single lamp or compact cluster of lamps is located at the
end of a main, as shown in figs. 827 and 828. In such cases
calculations are almost always unnecessary, for the reason that
No. 14 wire, the smallest size allowed by the underwriters,
will supply several lamps at a long distance (as interior
wiring goes) with a very moderate drop. For example, if the
three lamps shown at the end of the main in fig. 828, be of 16
candle power each, and the voltage of the supply circuit be
110 volts, a main of No. 14 wire would supply the lamps at a
distance of 135 feet from the fuse block with a drop of only 1
per cent.
When the lamps are strung along the main, however, as in fig.
826, it is sometimes necessary to choose the size of wire with
regard to the drop, and in order to do this the main must be
measured for either "ampere feet" or "lamp feet."
=Wire Calculations.=—The problem of calculating the size of wire will
be presented here in as simple a form as possible, with explanation of
the various steps so that any one can understand how the formula is
derived.
In determining the size of wire, there are four known factors which
enter into the calculation, viz.:
1. Length of circuit in feet;
2. Maximum current in amperes;
3. Drop or volts lost in the circuit, _in % of the impressed voltage_;
4. Heating effect of the current.
The calculation is based on the _mil foot_, which as previously
explained, is a foot of copper wire one mil in diameter and whose
resistance is equal to 10.79 ohms at 75° Fahr.
[Illustration: FIG. 829.—Wiring for lights requiring unusually long
feeders.]
The first step is to find an expression for the resistance of the wire
which may be later substituted in Ohm's law formula. Accordingly, the
resistance of any conductor is equal to _its length in feet multiplied
by its resistance per mil foot and the product divided by its area in
circular mils_, thus:
length in feet × resistance per mil foot
resistance in ohms = —————————————————————————————————————————
circular mils
feet × 10.8
or ohms = ————————————- (1)
circular mils
(calling the resistance per mil foot 10.8 instead of 10.79 to
facilitate calculation).
LAMP TABLE FOR RUBBER COVERED WIRES
Showing the maximum number of 16 candle power 110 to 240 volt
lamps in parallel that may be carried by the various sizes of
wire without violating the underwriters' rules.
+——————————+———————+——————————————+————————————————+————————————-+
|Wire size |Amperes|3.1-watt lamps|3.5-watt lamps. |4-watt lamps.|
|B. & S. | +——————————————+————————————————+————————————-+
| gauge | | At 110 220 | At 110 220 | 220 230 240 |
| | | volts V. | volts V. | V. V. V. |
+——————————+———————+——————————————+————————————————+—————————————+
|0000 | 210 | 462 924 | 412 825 | 722 754 787 |
| 000 | 177 | 389 778 | 347 695 | 608 636 663 |
| 00 | 150 | 330 660 | 294 589 | 515 539 562 |
| | | | | |
| 0 | 127 | 279 558 | 249 499 | 436 456 476 |
| 1 | 107 | 235 470 | 210 420 | 367 384 401 |
| 2 | 90 | 197 396 | 176 353 | 309 323 337 |
| | | | | |
| 3 | 76 | 167 334 | 149 298 | 261 273 285 |
| 4 | 65 | 143 286 | 127 255 | 223 233 243 |
| 5 | 54 | 118 237 | 106 212 | 185 194 202 |
| | | | | |
| 6 | 46 | 101 202 | 90 180 | 158 165 172 |
| 8 | 33 | 72 145 | 64 129 | 113 118 123 |
| 10 | 24 | 52 105 | 47 94 | 82 86 90 |
| | | | | |
| 12 | 17 | 37 74 | 33 66 | 58 61 63 |
| 14 | 12 | 26 52 | 23½ 47 | 41 43 45 |
| 16[3] | 6 | 13 .. | 11 .. | 20 21 22 |
+——————————+———————+——————————————+————————————————+—————————————+
[3] This size can be used only in the shape of flexible cord.
Now, according to Ohm's law,
volts = amperes × ohms (2)
hence, substituting in (2) the value for the resistance in ohms, as
obtained in (1):
feet × 10.8
volts = amperes × ————————————-
circular mils
or using the usual symbols
feet × 10.8
E = I × ————————————- (3)
circular mils
or expressed in words, formula (3) means that the volts lost or
_drop_ between the beginning and end of a circuit is equal to the
current flowing through the circuit multiplied by the product of the
conductors' length in feet multiplied by the resistance of one mil foot
of wire, divided by the area of the conductor in circular mils.
LAMP TABLE FOR WEATHER PROOF WIRES
Showing the maximum number of 16 candle power 120 to 240 volt
lamps in parallel that may be carried by various sizes of
weather proof wire without violating the underwriters' rules.
+———————+————————+———————————————+———————————————+———————————————-+
|Wire |Amperes |3.1-watt lamps.|3·5-watt lamps.| 4-watt lamps. |
|size | +——————————————-+——————————————-+————————————————|
|B. & S.| | 110 220 | 110 220 | 220 230 240 |
|gauge | | V. V. | V. V. | V. V. V. |
+———————+————————+———————+———————+————————+——————+———————————————-+
| 0000 | 312 | 686 | 1372 | 612 | 1225 | 1072 1121 1170 |
| 000 | 262 | 576 | 1152 | 514 | 1029 | 900 941 982 |
| 00 | 220 | 484 | 968 | 432 | 864 | 756 790 825 |
| | | | | | | |
| 0 | 185 | 407 | 814 | 363 | 726 | 636 665 693 |
| 1 | 156 | 343 | 686 | 306 | 612 | 536 560 585 |
| 2 | 131 | 288 | 576 | 257 | 514 | 450 470 491 |
| | | | | | | |
| 3 | 110 | 242 | 484 | 216 | 432 | 378 395 412 |
| 4 | 92 | 202 | 404 | 180 | 361 | 316 330 345 |
| 5 | 77 | 169 | 338 | 151 | 302 | 264 276 288 |
| | | | | | | |
| 6 | 65 | 143 | 286 | 127 | 255 | 223 233 243 |
| 8 | 46 | 101 | 202 | 90 | 180 | 158 165 172 |
| 10 | 32 | 70 | 140 | 62 | 125 | 110 115 120 |
| | | | | | | |
| 12 | 23 | 50 | 101 | 45 | 90 | 79 82 86 |
| 14 | 16 | 35 | 70 | 31 | 62 | 55 57 60 |
+———————+————————+———————+———————+————————+——————+———————————————-+
Now, since the length of the circuit is given as the "run" or distance
one way, that is, one half the total length of wire in the circuit,
formula (3) must be multiplied by 2 to get the total drop, that is:
feet × 10.8 X 2 I × feet × 21.6
E = I × ——————————————- = ———————————————- (4)
circular mils circular mills
Solving the last equation for the unknown quantity, the following
equation is obtained for size of wire:
[Illustration: FIGS. 830 and 831.—Symmetrical and unsymmetrical
distribution. When a main is supplied by a feeder, the junction of the
two, if practicable, is located at the electrical center of the main,
as indicated in fig. 830, so that the distribution is symmetrical, that
is, the ampere feet each way from the junction are the same. This is
nearly always practicable in surface wiring, and when it is practiced
it is only necessary to calculate the wire size for one-half of the
main, as the other half is identical. In fig. 830 there are four lamps
on each side of the junction, J; the center of each group is at a
distance, M, so that the lamp feet in each half of the main are 5 × M.
The lamp feet of the feeder would be 10 × N, N being the distance from
the feeder fuse block to the junction, J. In concealed work, however,
it does not always happen that a feeder can be made to join a main at
its electrical center; when this is not practicable, each end of the
main should be figured separately. In fig. 831, for instance, the main
has five lamps on one side and two on the other, and the distances from
the junction to the centers of the two groups are at unequal distances
S and S'. If the distance S be 14 feet, and the lamps, 16 c. p., the
lamp feet in the left hand main equals 5 × 14 = 70, while in the main
to the right, taking S' at 10 feet, there are only 2 × 10 = 20 lamp
feet. Hence what appears to be one continuous main in this case would
have to be treated as two mains, and each part figured separately.]
I × feet × 21.6 amperes × feet × 21.6
circular mils = ———————————————- = ————————————————————— (5)
E "drop"
The following practical example is given to illustrate the application
of the formula just obtained:
EXAMPLE.—What size wire should be used on a 250 volt circuit
to transmit a current of 200 amperes a distance of 350 feet to
a center of distribution with a loss of three per cent. under
full load?
The volts lost or drop is equal to 250 × .03 = 7.5 volts.
=PROPERTIES OF COPPER WIRE=
+————————+————————+——————————+—————————————————————————————+———————————————————————-+
| Number |Diameter| Area in | Weight in pounds | Resistance at 68° Fahr.|
|of gauge| in | circular |——————————————————————————————————————————————————————|
|B. & S. | mils | mils | 1,000 feet| mile |feet per| 1,000 feet | mile |
| | | | | | pound | | |
+————————+————————+——————————+———————————+—————————————————+———————————————————————-+
| 0000 | 460 | 211,600 | 640.5 |3,381 | 1.561 | .04893 | .2583 |
| 000 | 409.6 | 167,800 | 508 |2,682 | 1.969 | .06170 | .3258 |
| 00 | 364.8 | 133,100 | 402.8 |2,127 | 2.482 | .07780 | .4108 |
| 0 | 324.9 | 105,500 | 319.5 |1,687 | 3.130 | .09811 | .5180 |
| | | | | | | | |
| 1 | 289.3 | 83,690 | 253.3 |1,337 | 3.947 | .12370 | .6531 |
| 2 | 257.6 | 66,370 | 200.9 |1,062 | 4.977 | .1560 | .8237 |
| 3 | 229.4 | 52,630 | 159.3 | 841.1 | 6.276 | .1967 | 1.0386 |
| 4 | 204.3 | 41,740 | 126.4 | 667.4 | 7.914 | .2480 | 1.3094 |
| | | | | | | | |
| 5 | 181.9 | 33,100 | 100.2 | 529.0 | 9.980 | .3128 | 1.6516 |
| 6 | 162.0 | 26,250 | 79.46 | 419.5 | 12.580 | .3944 | 2.0824 |
| 7 | 144.3 | 20,820 | 63.02 | 332.7 | 15.87 | .4973 | 2.6257 |
| 8 | 128.5 | 16,510 | 49.98 | 263.9 | 20.01 | .6271 | 3.3111 |
| | | | | | | | |
| 9 | 114.4 | 13,090 | 39.63 | 209.2 | 25.23 | .7908 | 4.1754 |
| 10 | 101.9 | 10,380 | 31.13 | 166.0 | 31.82 | .9972 | 5.2652 |
| 11 | 90.74| 8,234 | 24.93 | 131.6 | 40.12 |1.257 | 6.6370 |
| 12 | 80.81| 6,530 | 19.77 | 104.4 | 50.59 |1.586 | 8.374 |
| | | | | | | | |
| 13 | 71.96| 5,178 | 15.68 | 82.79| 63.79 |2.000 | 10.560 |
| 14 | 64.08| 4,107 | 12.43 | 65.63| 80.44 |2.521 | 13.311 |
| 15 | 57.07| 3,257 | 9.858 | 52.05|101.4 |3.179 | 16.785 |
| 16 | 50.82| 2,583 | 7.818 | 41.28|127.9 |4.009 | 21.168 |
| | | | | | | | |
| 17 | 45.26| 2,048 | 6.200 | 32.74|161.3 |5.055 | 26.690 |
| 18 | 40.30| 1,624 | 4.917 | 25.96|203.4 |6.374 | 33.655 |
| 19 | 35.89| 1,288 | 3.899 | 20.59|256.5 |8.038 | 42.440 |
| 20 | 31.96| 1,022 | 3.092 | 16.33|323.4 |10.14 | 53.540 |
+————————+————————+——————————+———————————+—————————————————+———————————————————————-+
Substituting the given value in formula (5)
350 × 200 × 21.6
circular mils = —————————————————— = 201,600.
7.5
Diameter = 2 √201,600 = 449 circular mils or .449 in.
From the table (on page 731 or on page 742) the nearest
(=larger=) size of wire is 0000 B. & S. gauge.[4]
[4] =CAUTION.=—The size thus obtained should be compared with the table
of carrying capacity of wires as given on page 731 to see if the wires
would have to carry more than the allowable current.
WIRING TABLE FOR LIGHT AND POWER CIRCUITS
===================+=======================================================
VOLTS | PERCENTAGE OF LOSS
===================+=======================================================
2000 | 1.7 1.5 1.4 1.2 1.1 1.0 0.75 0.5
1000 | 3.4 2.9 2.7 2.4 2.2 2.0 1.5 1.0
500 | 6.5 5.7 6.2 4.8 4.3 3.9 2.9 2.0
220 | 13.7 12.0 11.0 10.3 9.3 8.3 6.5 4.4
110 | — — 20.0 18.5 17.0 15.4 12.0 8.4
52 | — — — — — — 22.4 16.1
===================+=======================================================
ACTUAL VOLTS LOST
=========+=========+=======================================================
Carrying | |
Capacity | Size | 35 30 27.5 25 22.5 20 15 10
Amperes. | B. & S. |
=========+=========+=======================================================
300 | 0000 | 345800 296400 271700 247000 222300 197600 148200 98800
245 | 000 | 274400 235200 215600 196000 176400 156800 117600 78400
215 | 00 | 217525 186450 170912 155375 139837 124300 93225 62150
190 | 0 | 172550 147900 135575 123250 110925 98600 73950 49300
160 | 1 | 136850 117300 107525 97750 87975 78200 58650 39100
135 | 2 | 108500 93000 85250 77500 69750 62000 46500 31000
115 | 3 | 86100 73800 67650 61500 55350 49200 36900 24600
100 | 4 | 68250 58500 53625 48750 43875 39000 29250 19500
90 | 5 | 54250 46500 42625 38750 34875 31000 23250 15500
80 | 6 | 43050 36900 33825 30750 27675 24600 18450 12300
60 | 8 | 26965 23130 21202 19275 17347 15420 11565 7710
40 | 10 | 16975 14550 13337 12125 10912 9700 7275 4850
30 | 12 | 10675 9150 8388 7625 6862 6100 4575 3050
22 | 14 | 6720 5760 5280 4800 4320 3840 2880 1920
5[5] | 16 | 4235 3630 3328 3025 2723 2420 1815 1210
————————-+————————-+——————————————————————————————————————————————————————-
===================+=====================================================
VOLTS | PERCENTAGE OF LOSS
===================+=====================================================
2000 | 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05
1000 | 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
500 | 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
220 | 3.9 3.5 3.1 2.7 2.2 1.8 1.4 0.9 0.45
110 | 7.6 6.8 6.0 5.2 4.4 3.5 2.7 1.8 0.9
52 | 14.7 13.3 11.8 10.3 8.8 7.1 5.5 3.7 1.9
===================+=====================================================
ACTUAL VOLTS LOST
=========+=========+=====================================================
Carrying | |
Capacity | Size | 9 8 7 6 5 4 3 2 1
Amperes. | B. & S. |
=========+=========+=====================================================
300 | 0000 | 88920 79040 69160 59280 49400 39520 29640 19760 9880
245 | 000 | 70560 62720 54880 47040 39200 31360 23520 15680 7840
215 | 00 | 55935 49720 43505 37290 31075 24860 18645 12430 6215
190 | 0 | 44370 39440 34510 29580 24650 19720 14790 9860 4930
160 | 1 | 35190 31280 27370 23460 19550 15640 11730 7820 3910
135 | 2 | 27900 24800 21700 18600 15500 12400 9300 6200 3100
115 | 3 | 22140 19680 17220 14760 12300 9840 7380 4920 2460
100 | 4 | 17550 15600 13650 11700 9750 7800 5850 3900 1950
90 | 5 | 13950 12400 10850 9300 7750 6200 4650 3100 1550
80 | 6 | 11070 9840 8610 7380 6150 4920 3690 2460 1230
60 | 8 | 6939 6168 5397 4626 3855 3084 2313 1542 771
40 | 10 | 4365 3880 3395 2910 2425 1940 1455 970 486
30 | 12 | 2745 2440 2135 1830 1525 1220 915 610 305
22 | 14 | 1728 1536 1344 1152 960 768 576 384 192
5[5] | 16 | 1089 968 847 726 605 484 363 242 121
————————-+————————-+————————————————————————————————————————————————————-
[5] NOTE.—In case a larger loss than any given in the table is
required, proceed as follows:—Divide the ampere feet by 10 and then
refer to column of Actual Volts Lost divided by 10, from which the size
of wire is found as before.
RULE.—_Multiply current in amperes by single distance and refer to the
nearest corresponding number under column of actual volts lost, to find
size of wire._ It should also be noted that the underwriters prohibit
the use of wire smaller than No. 14 B. & S. gauge, except as allowed
for fixture work and pendant cord.
TABLE OF WIRE EQUIVALENTS
GAUGE NUMBER OF WIRES
B. & S. 2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384
0000 0 3 6 9 12 15 18 21 24 27 30 33 36 39
000 1 4 7 10 13 16 19 22 25 28 31 34 37 40
_____
00 2 5 8 11 14 17 20 23 26 29 32 35 38| 0+6
0 3 6 9 12 15 18 21 24 27 30 33 36 39| 1+7
1 4 7 10 13 16 19 22 25 28 31 34 37 40| 2+8
_____|
2 5 8 11 14 17 20 23 26 29 32 35 38|3+9 4+6
3 6 9 12 15 18 21 24 27 30 33 36 39|4+10 5+7
4 7 10 13 16 19 22 25 28 31 34 37 40|5+11 6+8
_____|
5 8 11 14 17 20 23 26 29 32 35 38|6+12 7+9
6 9 12 15 18 21 24 27 30 33 36 39|7+13 8+10
7 10 13 16 19 22 25 28 31 34 37 40|8+14 9+11
_____|
8 11 14 17 20 23 26 29 32 35 38|9+15 10+12
9 12 15 18 21 24 27 30 33 36 39|10+16 11+13
10 13 16 19 22 25 28 31 34 37 40|11+17 12+14
_____|
11 14 17 20 23 26 29 32 35 38|12+18 13+15
12 15 18 21 24 27 30 33 36 39|13+19 14+16
13 16 19 22 25 28 31 34 37 40|14+20 15+17
____|
14 17 20 23 26 29 32 35 38|15+21 16+18
15 18 21 24 27 30 33 36 39|16+22 17+19
16 19 22 25 28 31 34 37 40|17+23 18+20
____|
17 20 23 26 29 32 35 38|18+24 19+21
18 21 24 27 30 33 36 39|19+25 20+22
19 22 25 28 31 34 37 40|20+26 21+23
____|
20 23 26 29 32 35 38|21+27 22+24
21 24 27 30 33 36 39|22+28 23+25
22 25 28 31 34 37 40|23+29 24+26
____|
23 26 29 32 35 38|24+30 25+27
24 27 30 33 36 39|25+31 26+28
25 28 31 34 37 40|26+32 27+29
____|
26 29 32 35 38|27+33 28+30
27 30 33 36 39|28+34 29+31
28 31 34 37 40|29+35 30+32
____|
29 32 35 38|30+36 31+33
30 33 36 39|31+37 32+34
31 34 37 40|32+38 33+35
____|
32 35 38|33+39 34+36
33 36 39|34+40 35+37
34 37 40|36+39
___|
35 38|37+39
36 39|38+40
37 40|
=Ques. If the calculated size of wire be larger than any in the table
how is the required area obtained?=
Ans. By using two or more smaller wires in parallel, whose combined
area is equal to the required area.
To facilitate finding the equivalent sizes the above table of
wire equivalents has been prepared.
=Ques. How is the table of wire equivalents used?=
Ans. To use the table, find in the vertical column at left the size
of conductor desired; then follow along horizontally until the size
of wire that is desired to use for the strands, and the corresponding
number at top of column will give the number of strands of that size
wire required.
[Illustration: FIG. 832.—Break down switch for use on three wire
circuit, enabling it to be operated break down fashion with the two
outers connected together and the neutral wire serving as one side
of the resultant two wire circuit. Such circuits must be figured as
two wire installations of one half the three wire voltage. The size
of the neutral wire of a three wire circuit depends on conditions of
operation. Three wire circuits for occasional two wire working, must
have a neutral wire whose cross section is equal to the combined cross
sections of the two outer wires. This plan is useful for buildings
supplied from a central station, as it will be satisfactory for two
wire operation in emergencies, and for three wire, two phase or three
phase distribution should the central station ultimately be changed
over to either of those alternating current systems. The expense for
the extra copper in the beginning will not be nearly so great as that
entailed by a change in the wiring later on should developments require
it. It is permissible, however, to make the cross section of the
neutral wire smaller than that of each outer wire, if one be reasonably
sure that there will never be any changes such as those just mentioned,
and if the drop in the two outer wires do not exceed 1½ per cent.
Under such conditions, it will be found a very good rule to calculate
the neutral wire of a principal feeder for a maximum unbalancing of 25
per cent, that is, a condition under which the current in one outer
wire will be 75 per cent of the current in the other one, the current
in the neutral being 25 per cent of that in the heavier loaded outer
wire.]
=Ques. What is the significance of the zig-zag line?=
Ans. The figures below this line give the gauge numbers of two wires
which will have the same conductivity as the corresponding conductor in
left hand column.
TABLE OF CABLE CAPACITIES
[Illustration: FIG. 833.—Diagram showing capacities of cables for both
open and concealed work as allowed by the underwriters.]
=Incandescent Lamps on 660 Watt Circuits.=—The standard incandescent
lamp is rated as equivalent to the light given by 16 candles, and may
consume, according to type and make, from 50 to 56 watts, or from 3.1
to 3.5 watts per candle power. Therefore, a 660 watt circuit will carry
thirteen 16 candle power 49.6 watt lamps, or eleven 56 watt lamps.
[Illustration: FIG. 834.—Diagram showing symmetrical and unsymmetrical
distribution. The two 5 lamp centers are located at equal distances
from the distributing pocket or cabinet, P, so that the sub-feeders,
A and A', have equal values of lamp feet. The sub-feeders, B, B',
have equal lengths, but as one supplies 10 lamps, and the other 16,
the lamp feet are different, and each sub-feeder must therefore be
figured separately. The main, G, should be considered as a part of
the sub-feeder, B, in order to avoid the necessity for a fuse at the
junction of the two. As it is symmetrically divided, only one-half of
it would be considered. Thus, if the sub-feeder, B, were 50 feet long,
and the main, G, 30 feet long, B would have 16 × 50 = 800 lamp feet and
one-half of the main would have 8 × 15 = 120 lamp feet (assuming all
16 c. p. lamps). Hence 800 + 120 = 920 lamp feet should be taken as
the load length and the proper size wire used for that figure, making
the sub-feeder, B, of the same size as the main, G. The same procedure
applies to the sub-feeder B' and main G'; also to the sub-feeder, E,
and the main, F. The proper sizes of wire for the different circuits is
easily found from the lamp feet table, after having calculated the lamp
feet assigned the drop.]
[Illustration: FIGS. 835 and 836.—The "tree" and "modified tree"
systems of wiring. The tree system consists of a feeder reducing in
size and supplying mains for each floor, the general arrangement
resembling the trunk and branches of a tree. Since fuses must be
inserted on each floor where the size of the feeder is reduced, the
system requires a large number of joints, and in the event of a fuse
blowing it could not be quickly located. The tree system is not to be
recommended, as it results in considerable drop, and at full load the
lamps nearest the point of supply will either burn too brightly or
those more remote will not give the rated candle power. In the modified
tree system, fig. 836, the size of the feeder is not reduced. With
this arrangement the losses are considerably reduced owing to the much
smaller losses on the feeder between those centers farthest away from
the point of supply.]
The proper size of wire for a 660 watt circuit will depend upon
the voltage for which the lamps are made. For example: a 16
candle power lamp which consumes 56 watts on 110 volt circuit
will take, 56 ÷ 110 = .5 or ½ ampere of current, while the
same lamp, if made for 220 volts, will take only 55 ÷ 220 = .25
or ¼ ampere. Therefore, eleven 16 candle power 56 watt lamps
will require a current of 5½ amperes at 110 volts, or 2¾
amperes at 220 volts.
According to the laws of resistance, the resistance of a round
wire is inversely proportional to the square of the diameter,
and if the circuit be taken at 100 feet, and the allowable
percentage of drop at 1 volt, then according to formula, (5)
on page 748, the wire required for a circuit carrying eleven
16 candle power 56 watt 110 volt lamps, will have a cross
sectional area of,
5.5 × 100 × 21.6
———————————————— = 11,880 circular mils.
1
while the same number of lamps on a 220 volt circuit will
require wire having a cross sectional area of,
2.75 × 100 × 21.6
————————————————- = 5,940 circular mils.
1
In order to conform to the underwriters' requirements, No. 8.
B. & S. gauge, wire must be used for the circuit carrying the
110 volt lamps, while No. 12, B. & S. wire, would be sufficient
for the 220 volt circuit.
In the case shown in fig. 829, the branch circuits A and B are
identical, each supplying four 16 candle power lamps requiring
3.5 watts per candle power at 110 volts or carrying a load of 4
× 16 × 3.5 = 224 watts, = 224 ÷ 110 = 2 _amperes_.
[Illustration: FIG. 837.—Distribution with sub-feeders (multi-center
distribution). The feeder connects at a central point, A, with several
sub-feeders which run to distributing centers, as at B, C, D, and E.
With this arrangement, compound wound dynamos may be so designed that
the pressure at A will remain nearly uniform for all loads. If, for
instance, the wiring be proportioned for 2% drop, the dynamos may
be over compounded to that extent, and the even illumination will
compensate for the extra cost in the installation.]
The distance from the feeder junction or cut out to the
electrical center of each branch circuit is 12.5 _feet_. The
compact area of distribution permits the reduction of the
loss of volts to 1 per cent, or 110 × .01 = 1.1 volts "drop."
Then substituting in formula (5) on page 748 the values for
_amperes_, _feet_ and _drop_ as obtained above
2 × 25 × 21.6
————————————- = 981 circular mils,
1.1
or a value far below that of even No. 18 wire, B. & S. gauge
(see table on page 731), but the smallest wire allowed by the
underwriters for the mains A and B is No. 14, B. & S. gauge.
In calculating the size of wire for the feeders the total load
must be considered. This is equal to eight 16 candle power
lamps, requiring 3.5 watts per candle power at 110 volts =
8×16×3.5 = 448 watts = 4 amperes.
The distance from the entrance cut out to the feeder cut out is
200 feet. The drop should not be greater than 1.5 per cent. or
110×1.5 = 1.6 volts. Then,
4×200×21.6
—————————— = 10,800 circular mils
1.6
a value which indicates that No. 8 wire, B. & S. gauge, must be
used for the feeders in order to keep the drop within the limit
of predetermined value.
TABLE FOR TAPS, BRIDGES OR OTHER WIRES AT NEGLIGIBLE DROP
—————————————————————————————————————————————————————————————————————————
Wire Nos. |0 |1 |2 |3 |4 |5 |6 | 7 |8 |10 |12 |14|16|18
—————————————————————————————————————————————————————————————————————————
Lamp Feet|52 v.| 300| 260|200|160|130|100| 80| 65| 50| 38| 24|15| 9| 6
|110v.|1,280|1,085|860|680|560|435|345|280|220|160|100|60|40|25
—————————————————————————————————————————————————————————————————————————
NOTE.—In using this table, it is only necessary to
calculate the lamp feet of the tap and take the size of wire
corresponding to the nearest greater number of lamp feet in
the table. The lamp feet specified by this table should not be
exceeded by more than 10 per cent. Thus, if a tap measure 108
lamp feet, in 110 volt lamps, No. 12 wire would be used. But if
it measure 115 lamp feet, it would be advisable to use No, 10
wire.
=Constant Voltage Arc Lamp Circuits.=—The branch conductor should
have a carrying capacity about fifty per cent. greater than the normal
current required by the lamp, so as to provide for the heavy current
required when the lamp is started. The underwriters prohibit the use of
any size wire under No. 12 for parallel connected arc light circuits.
=Constant Current Series Arc Lamp Circuits.=—The wiring for series
connected arc lamps should never be concealed nor encased unless
requested by the electrical inspector.
For all interior wiring of this class, approved rubber covered wire
should be used, and the wire should always be rigidly supported on
porcelain or glass insulators which will hold the wires at a distance
of at least one inch from the surface wired over. The wires on all
circuits up to 750 volts, should be kept at least 4 inches from each
other, and 8 inches apart on circuits of over 750 volts. No wires
carrying a current having a pressure exceeding 3,500 volts should
be carried into or over any building except central stations and
sub-stations.
[Illustration: FIG. 838.—Diagram showing "bridge wiring." This method
is used in the case of two parallel mains where one feeder is ample for
both. The feeder is run to a central point as shown and connected to
the two mains by a so called "bridge." The arrangement clearly gives
good distribution and effects a saving in copper and labor, for if the
bridge were omitted, two feeders would be necessary.]
=Wire Calculations for Motors.=—The proper size of wire for a motor
may be readily determined by means of the following formula:
H.P. × 746 × D × 21.6
circular mils = ————————————————————- (6)
E × L × K
in which
H.P. = horse power of motor;
746 = watts per H.P.;
D = length of motor circuit from fuse block to motor;
21.6 = ohms per foot run in circuit where wires are one mil in diameter;
E = voltage at the motor;
L = drop in percentage of the voltage at the motor;
K = efficiency of the motor expressed as a decimal.
The average values for K are about as follows: 1 H.P., .75; 3
H.P., .80; 5 H.P., .80; 10 H.P. and over, 90 per cent.
[Illustration: FIGS. 839 and 840.—Wrong and right methods of loop
wiring. In general, when a large percentage of loss is allowed with
lamps at short distances, the size of wire, calculated simply in
accordance with the resistance rules, will be found too small to carry
the current safely. This fact is often overlooked, and even though
wires may have been correctly calculated for a uniform percentage
of loss, they will become painfully hot simply because the table of
carrying capacity was not consulted. The cross connection of mains
wherever possible, for the purpose of equalizing the pressure, will
also often reduce the heating effects of the current. An example of
this is shown in the above figures. A circle of lights was wired as
in fig. 839, and after the current had been turned on, the wires of
the circle became hot, and there was quite a perceptible difference of
candle power between the lights near A and those near B. Investigation
disclosed the fact that the loop, contrary to instructions, had been
left open. A few inches of wire as shown in dotted lines remedied the
fault. A better arrangement, however, is shown in fig. 840.]
EXAMPLE.—What is the proper size of wire for a 10 H.P. motor,
run at 220 volts, allowable drop 2 per cent. on 200 foot
circuit.
Substituting the given values in the formula on page 758:
10 × 746 × 200 × 21.6
Circular mils = ————————————————————- = 36,991.
220 × 4.4 × .9
The nearest larger value to this result, in the table of
carrying capacities of copper wire (page 731), is 41,740,
corresponding to No. 4 wire, B. & S. gauge.
_In all cases the size of the wire thus formed should be
compared with that allowed by the underwriters for full load
current of motor, plus 25 per cent. of that current_, and if
the size calculated happen to be smaller than the allowable
size, it should be increased to the latter, otherwise it will
not pass inspection.
TABLE OF AMPERES PER MOTOR
——————————————————————————————————————————————————————————————————————————————-
H.P. Per Cent. Eff. Watts Input 50 Volts 100 Volts 220 Volts 500 Volts
¾ 70 800 16 7 4 2
1½ 70 1600 32 15 7 3
3 75 2980 60 27 14 6
5 80 4660 93 42 21 9
7½ 85 6580 132 60 30 13
10 85 8780 176 80 40 18
15 85 13200 264 120 60 26
20 85 17600 352 160 80 35
25 85 21900 438 199 100 44
30 90 24900 498 226 113 50
40 90 33200 664 301 151 66
50 90 41400 828 376 188 83
60 90 49700 994 452 226 99
70 90 58000 1160 527 264 116
80 90 66300 1330 608 302 133
90 90 74600 1490 678 339 149
100 90 82900 1660 755 377 166
120 90 99500 1990 905 453 199
150 90 124000 2480 1130 564 248
——————————————————————————————————————————————————————————————————————————————-
TABLE OF AMPERES PER DYNAMO
——————————————————————————————————————————————————————————————————————————————-
Appx. Appx.
K.W. 125 Vs. 250 Vs. 500 Vs. H.P. K.W. 125 Vs. 250 Vs. 500 Vs. H.P.
1. 8 4 2 1.3 30. 240 120 60 40.
2. 16 8 4 2.7 37.5 300 150 75 50.
3. 24 12 6 4.0 40. 320 160 80 53.
5. 40 20 10 6.7 50. 400 200 100 67.
7.5 60 30 15 10. 60. 480 240 120 80.
10. 80 40 20 13. 75. 600 300 150 100.
12.5 100 50 25 17. 100. 800 400 200 134.
15. 120 60 30 20. 125. 1000 500 250 167.
20. 160 80 40 27. 150. 1200 600 300 201.
25. 200 100 50 34. 200. 1600 800 400 268.
——————————————————————————————————————————————————————————————————————————————-
To determine the current required for a motor, as for instance,
the 10 H. P. motor under consideration, _multiply the
horsepower by 746, and divide the product by the voltage of the
motor multiplied by its efficiency as follows_: (10 × 746) ÷
(220 × .90) = 37.6 amperes.
This value increased by 25 per cent. of itself (37.6 × .25 =
9.4 amp.) is equal to 37.6 plus 9.4 = 47 amperes. In the table
of carrying capacities of copper wire (page 731), 46 amperes
is given as the allowable carrying capacity of No. 6, B. & S.
gauge, rubber covered wire; therefore No. 5 wire must be used.
=Calculations for Three Wire Circuit.=—In all cases of interior
conduit work, and in most cases of inside open work, the main feeders
from a three wire source of supply are installed on the three wire
plan, and the sub-feeders and distributing mains, on the two wire plan,
except where the application of the method necessitates the use of
unwieldy sizes.
In laying out sub-feeders and mains, the total load, under normal
operating conditions, should be divided as nearly as possible into two
equal parts, and one part connected on each side of the neutral part
of the entrance cut out, or the neutral bus bar of the switch board or
panel board in an isolated plant, thus making the load on each side of
the neutral wire of the feeder as near equal as possible.
Fig. 841 shows a three wire panel board with connection for
12 mains; those shown in solid lines as A, B, C, etc., being
connected between the neutral wire and the negative wire of the
feeder, and those shown by dotted lines as G, H, I, etc., being
connected between the neutral wire and the positive wire of the
feeder. The total load consists of ninety-one 16 candle power
lamps, which are so distributed that the positive wire of the
feeder carries the current for 46 lamps, and the negative wire,
45 lamps, the neutral wire carrying the difference or current
for 1 lamp.
The proper size of wire for the mains may be calculated as already
explained, but in calculating the outer wires of the three wire feeder,
the neutral wire should be disregarded and the outer wires connected as
a _two wire circuit carrying the total load of 91 lamps at the over all
pressure of 220 volts_.
EXAMPLE.—Ninety-one 16 candle power lamps consuming 3.1 watts
per candle power at a pressure of 110 volts, will require a
current of
16 × 3.1 × 91
————————————- = 41 amperes.
110
The distance from the entrance cut out to the main or feeder
switch is 200 feet, then for a 2 per cent. drop, or a loss of
110×.02=2.2 volts, the cross sectional area of the wire will be,
41 amperes × 200 feet × 21.6
———————————————————————————— = 80,509 circular mils.
2.2 volts
[Illustration: FIG. 841.—Three wire circuit panel board with
connections for 12 mains. The wires shown in solid lines as A, B, C,
etc., are connected between the neutral wire and the negative wire of
the feeder, and those shown by dotted lines, as G, H, I, etc., are
connected between the neutral wire and the positive wire of the feeder.]
The joint resistance of the lamps on a three wire system,
however, would be four times greater than on a two wire system;
consequently the resistance of the outer wires of the feeder in
this case will be four times greater for the same percentage
of loss, and the cross sectional area of each of the outer
wires will be, 80,509÷4=20,127 circular mils. According to the
underwriters' rules, this value compels the use of No. 6 B. &
S. gauge wire.
If the _lamp_ voltage, 110 volts, be used, the two wire formula (5)
given on page 748 must be modified to,
amperes × feet × 21.6
circular mils = ————————————————————-
drop × 4
but if an _over all_ voltage, (that is, the voltage between the outer
wires), of 220 volts be used, the two wire formula does not require any
modification.
The proper size of wire may also be calculated by means of the formula
drop
———————————————————————- = resistance per foot . . . . (1)
2 × distance × amperes
Example.—If in calculating a three wire feeder, the over all
voltage be 220 volts, the drop = 4.4 volts, twice the distance
= 400 feet, and the current = 20.5 amperes, then,
4.4 volts
————————————————————————- = .0005365 ohms per foot.
400 feet × 20.5 amperes
In the table of the properties of copper wire which gives the
resistance of various sizes of wire, it will be noted that
at all of the given temperatures No. 8 wire has a resistance
greater than the value just calculated, therefore, No. 6 B. &
S. gauge wire should be used for the outer wires of the feeder.
In the table the resistance is given per 1,000 feet, hence
it is only necessary to move the decimal point to obtain the
resistance per foot.
If the calculation be based on the lamp voltage, 110 volts, the formula
(1) must be modified to
drop × 4
———————————————————————— = resistance . . . .(2)
2 × distance × amperes
In this case, drop = 2.2 volts, 2 × distance = 400 feet, and current =
41 amperes, then,
2.2 volts × 4 8.8
———————————————————— = ———————— = .005364 ohms.
400 feet × 41 amp. 16,400
=Size of the Neutral Wire.=—In three wire circuits, the size of the
neutral wire will depend to a great extent upon operating conditions.
In the case of installations which occasionally have to be worked as
two wire systems, the cross section of the neutral wire should be equal
to the combined cross section of the two outer wires.
For interior wiring which must pass inspection, the neutral wire must
always be twice the size of one of the outside wires. However, for
general distribution, if it be reasonably sure that the system will
always be worked three wire and that the drop in the two outer wires
does not exceed 1½ per cent., the cross section of the neutral
wire may be made smaller than that of one of the outer wires. In such
a case the size of the neutral wire may be calculated for a maximum
unbalancing of 25 per cent., when the current in one of the outer wires
is 75 per cent. of the current in the other outer wire.
For instance, suppose that in a balanced system, the total load
on each of the outer wires of a feeder be 211 amperes, and that
on account of certain operating conditions, this load has to be
divided unequally so as to put 242 amperes on one of the outer
wires, and 181 amperes on the other outer wire. In this case
the neutral wire will carry 60 amperes, or 25 per cent. of the
current carried by the heavier outer wire.
If the drop in the outer wires exceed 1½ per cent., the
cross section of the neutral wire will have to be equal to or
larger than that of each of the outer wires, otherwise the drop
in the neutral wire will exceed ½ volt with an unbalancing of
25 per cent.
CHAPTER XXXVIII
INSIDE WIRING
The term _wiring_ is commonly understood to mean the methods employed
in laying the conductors used for the transmission and distribution of
electrical energy for lighting, power, and other purposes. Interior
wiring, comprises the various methods of installing the conductors from
the entrance devices in the walls or other parts of the buildings to
the lamps, motors, and other electrical apparatus within the buildings.
The different methods of interior wiring may be conveniently grouped
into the following general classes:
1. Open or exposed wiring;
2. Wires run in mouldings;
3. Concealed knob and tube wiring;
4. Rigid conduit wiring;
5. Flexible conduit wiring;
6. Armoured cable wiring.
=Open or Exposed Wiring.=—This method of wiring possesses the
advantages of being cheap, durable and accessible. It is used a great
deal in factories, mills and buildings where the unsightly appearance
of the wires exposed on the walls or ceilings is of no consequence.
=Ques. What kinds of wires are suitable for this method of wiring?=
Ans. Either rubber covered or slow burning weather proof wire.
Rubber insulation should always be used where the wire is in
a damp place, such as a cellar, and either weather proof or
rubber insulation may be used to protect it against corrosive
vapors.
[Illustration: FIGS. 842 to 844.—Open or exposed wiring. Fig. 842,
wires passing through beams. The holes are bored at an angle and wire
run through in zig-zag course. Porcelain tubes are used where the wire
passes through beams; fig. 843, cleat work across beams, the cleats are
carried by boards attached to the beams; fig. 844, method of carrying
wires on cleats around beams.]
=Ques. How are the wires installed?=
Ans. They are laid on some cornice, wainscoting, beam, or other
architectural feature suitable for the purpose, by means of porcelain
knobs and cleats, as shown in figs. 842 to 844.
Porcelain knobs should preferably be of the two piece type
(fig. 863) in which the wire is carried between the upper and
lower portions rather than being tied to a one piece knob with
a tie wire as in fig. 860. Various porcelain knobs and cleats
are shown in figs. 860 to 866.
=Ques. What are the disadvantages of open wiring?=
Ans. The wiring is not sufficiently protected from moisture, and the
effects of fire which will destroy the insulation of the wires; it is
also liable to mechanical injury.
[Illustration: FIGS. 845 to 847.—Splicing. Figs. 845 and 846, making
a wire splice, and the twist completed; fig. 847, a wrapped joint on
large wire. Splicing of wires or joining a branch to a main wire should
always be made by twisting the wires together or twisting one wire
around the other, so that the joint will be mechanically strong enough
to carry all strain which may come upon it, without any soldering.
The joint should then be carefully tinned and soldered in order to
give good electrical contact and to avoid corrosion along the contact
surface. Where wires are too large to be twisted together, the ends
are given a short bend and the two wires wrapped firmly together with
a smaller bare copper wire, after which the joint is thoroughly tinned
and soldered, preferably by pouring hot solder over the joint. The
joint is then insulated by wrapping it with two layers of pure rubber,
and three layers of tape, sufficient to make the insulation thickness
equal to that of the wire, after which the whole joint should be
painted with water proof paint.]
=Ques. How far apart should the wires be placed?=
Ans. When installed in dry places and for pressures below 300 volts,
the insulators should separate the wires 2½ inches from each other
and ½ inch from the surface along which they pass. For voltages from
300 to 500, the wires should be separated four inches from each other
and one inch from the surface along which they pass.
If the wiring be in a damp place, the wires should be at least
one inch from the surface.
[Illustration: FIGS. 848 to 850.—Crossing of wires. Where wires cross
each other, tubes should be used except in case of large stiff wires
as in fig. 848; here one wire may be bent down and carried under the
other; fig. 849, short bushing strung on the wire—this method is
usually unsatisfactory, especially where a large number of wires cross
each other; fig. 850, wires crossing each other through tubes. Flexible
tubing, such as circular loom may be used in crossing wires in dry
locations. Insulators should always be provided where wires cross to
support the wires, thus preventing the upper wires sagging and touching
those below.]
[Illustration: FIGS. 851 to 853.—Methods of wiring across pipes. The
wires should preferably run over rather than under the pipes. Fig. 851
shows crossing with circular loom, and fig. 852, one in which a tube is
used. Both of these methods are satisfactory in the case of gas pipes,
but for steam pipes or water pipes which are liable to leak or sweat
and drip moisture, the crossing should be above as shown in fig. 853.
On side walls where vertical wires run across horizontal water pipes,
the latter should be enclosed and the moisture deflected to one side.]
=Ques. How should wires be protected when run vertically on walls?=
Ans. They should be boxed in or run in a pipe as shown in fig. 854, the
covering extending 6 feet above the floor.
When placed inside a box there should be a clearance of at
least one inch around the wires; the box should be closed at
the end as shown, and the wires protected where they enter the
top with bushings. When the wires are placed in a pipe they
should be first encased in a piece of flexible tubing that will
extend from the insulator below the end of the pipe to the
first one above it.
[Illustration: Fig. 854.—Methods employed in open wiring when run
vertically on walls. Either a box casing or iron pipe should be used
to protect the wires. The covering need only extend six feet above the
floor.]
=Ques. What kind of incandescent lamp receptacle or wall socket is best
adapted to exposed wiring?=
Ans. One which does not have exposed contact ears, an approved form
being shown in fig. 859.
=Practical Points Relating to Exposed Wiring.=—Some of the principal
points which should be remembered in this connection, together with the
methods which may be applied to special cases, may be briefly stated as
follows:
1. In interior wiring no wires smaller than No. 14 B. & S.
gauge should be used, except as allowed by the underwriters,
and no more than 660 watts should be allowed to a circuit.
2. Tie wires should have an insulation equal to that of the
conductors which they secure.
3. In all cases, whether the wires be run on knobs, split
insulators, or cleats, the wires should be supported at
intervals of at least 4½ feet, and if exposed to mechanical
injury, the supporters should be placed at closer intervals.
4. Wires run on bare ceilings of low basements, especially
where they are liable to injury, should be protected by two
wooden guard strips as shown in fig. 858. The protective strips
should be at least ⅞ inch in thickness and slightly higher
than the knobs, insulators, or cleats. The two circuit wires
should not be run closer than 6 inches apart, and wires run
near water tanks must be rubber covered so as to render them
moisture proof.
5. Cleats should be used for the wiring of stores, offices,
or buildings having flat ceilings, provided the wiring is
installed in dry locations.
6. When the installation is exposed to dampness or acid fumes
such as those developed in stables, bakeries, etc., the wires
should run on knobs or split insulators, and should be rubber
covered.
[Illustration: Figs. 855 to 857.—Methods of carrying wires through
floors. In passing through floors (or walls) the wires often come in
contact with concealed pipes or other grounded material, hence the only
way they can be properly protected is by making the bushing continuous.
This may consist of continuous porcelain tubes as shown in fig. 855,
or short bushings may be arranged in iron pipes as in fig. 856. The
method followed in case of an offset in the wall is shown in fig. 857.
Sometimes the floor can be taken up and an iron conduit, properly
bent, put in place, the wires being reinforced with flexible tubing.
Another method is to attach the wires to insulators; in this case the
floor must not be put down until the wiring has been examined by the
inspector.]
7. When wires are run at right angles to beams which are more
than 4½ feet apart, a running board should be used and the
wires cleated to it as shown in fig. 843. It is desirable,
however, to avoid the use of running boards, whenever possible
by running the wires parallel with the beams, thus reducing the
cost of insulation.
8. In factories or other buildings of open mill construction,
mains of No. 8 B. & S. gauge or larger wire, where they are
not exposed to injury, may be placed about 6 inches apart and
run from timber to timber, not breaking around, and may be
supported at each timber only.
[Illustration: Fig. 858.—Method of protecting exposed wiring on low
ceilings by two guard strips.]
[Illustration: Fig. 859.—Receptacle suitable for use with open wiring,
the requirement being that the contact ears should not be exposed.]
9. The best location for feeders is on the walls. In dry
buildings the fire and weather proof wire can be used with
safety; but covered wire must be used on buildings subject to
any form of dampness. In all cases where feeders are run on
the walls, they should be protected from mechanical injury by
boxings at least 6 feet high on each floor. If floor switches
be used, they may be mounted on the front of the boxing. In
such cases, the holes in the boxing through which the wires
pass to the switches should be provided with porcelain bushings.
10. The rosettes, receptacles, sockets, snap switches, etc.,
used in connection with exposed wiring should conform in all
respects to the standards specified by the underwriters.
[Illustration: FIG. 860 to 866.—Various porcelain knobs and cleats. In
open work various forms of these devices are used.]
[Illustration: FIG. 867.—Porcelain tube for entrance of wire into
a building. There must be a drip loop outside to drain off water,
and the hole through which the conductor passes must be bushed with
a non-combustible, non-absorptive insulating tube slanting downward
toward the outside. The object of the inclination is to allow any water
that might enter the tube to gravitate to the drip loop.]
[Illustration: FIG. 868.—Interior bushing. Wires must be separated
from contact with walls, floors, timbers or partitions through which
they may pass by non-combustible, non-absorptive, insulating tubes,
such as glass or porcelain, except at outlets where approved flexible
tubing is required. Bushings must be long enough to bush the entire
length of the hole in one continuous piece, or else the hole must
first be bushed by a continuous water proof tube. This tube may be a
conductor, such as iron pipe, but in that case an insulating bushing
must be pushed into each end of it, extending far enough to keep the
wire out of contact with the pipe.]
=Wires Run in Mouldings.=—Wooden mouldings are extensively used in
connection with the wiring of stores, factories and buildings. The
advantages of this type of construction are: simplicity, cheapness, and
accessibility, and when the moulding is run straight and accurately
mitred it makes a neat job. Any class of wooden moulding wiring,
however, is not sufficiently impervious to moisture to render it
suitable for use in damp places, and it is liable to be crushed or
punctured. Furthermore, it is naturally very combustible. These
difficulties are overcome to a certain extent by impregnating the
moulding with some kind of moisture repellant, or by coating it both
inside and out with water proof paint. Hardwood moulding should be used
wherever possible, but soft wood moulding usually conforms much better
to the wall line.
[Illustration: FIG. 869.—Standard wooden moulding for encasing wires.
Wooden moulding must not be used in concealed or damp places, nor be
placed directly against a brick wall where sweating may introduce
moisture that may ultimately cause a short circuit. Wooden moulding for
concealing electrical conductors is prohibited by ordinances in some
cities.]
=Ques. For what conditions is wiring in mouldings suitable?=
Ans. It is adapted to installations in which the wires have to be laid
after the completion of the buildings.
=Ques. Describe the moulding usually employed.=
Ans. It is made of hardwood in two pieces, a backing and cap, so
constructed as to thoroughly encase the wire.
It should provide a one-half inch tongue between the conductors
and a solid backing which should not be less than three-eighths
of an inch in thickness under the grooves; it should be able to
give suitable protection from abrasion.
The inside of the moulding and the cap must have at least two
coats of waterproof material, or else the whole moulding must
be impregnated with moisture repellant.
Only one conductor is placed in a groove.
The backing is secured to the walls or ceilings by means of
wire nails. The wires are then laid in the grooves and the
capping put in place and fastened by small brads.
The wires should be continuous, and only rubber covered wire
should be employed.
Wooden moulding is made in a great variety of size and design.
The general appearance of this type of moulding being shown in
fig. 869.
=Ques. What other kind of moulding is used?=
[Illustration: FIGS. 870 to 872.—Metal moulding. An approved form
consists, as shown, of two pieces: base (fig. 870), and cap (fig. 871),
so formed as to snap together, the cap snapping over the base as in
fig. 872. The entire moulding should be galvanized or coated with a
rust preventive. When the base is held in place by screws or bolts from
the inside surface, depressions must be provided so that the heads of
the screws will be flush with the surface of the moulding.]
Ans. Metal moulding, as shown in figs. 870 to 872.
Metal moulding is permitted on circuits requiring not more than
660 watts and where the pressure is not over 300 volts. Special
fittings must be used with this class of moulding so that it
is continuous both mechanically and electrically. The moulding
should be grounded. The installation rules are practically the
same as those governing conduit work.
=Ques. What is a kick box?=
[Illustration: FIG. 873.—"Kick box;" a device used to protect wires
encased in porcelain tubes where they pass through floors.]
Ans. A fitting, as shown in fig. 873, for protecting wires at the
points where they enter or emerge from the floor.
=Ques. How is moulding work installed on brick or plaster walls which
are liable to dampness?=
Ans. A backing board must be put on before the moulding is used.
=Ques. How should moulding be placed on a ceiling with respect to
appearance?=
Ans. The appearance is improved if the moulding be carried through to
the side of the room, even if part of it be not used. This will give a
neat and finished appearance to the ceiling as shown in fig. 874.
Moulding should always be run in as inconspicuous position as
possible, and if it be necessary to run it on the open ceiling,
it should be arranged so as to form regular panels. Often it
can be run so as to take the place of a picture moulding or as
a part of the baseboard so that it becomes merely a part of the
wooden trim of the building; and in certain cases it should be
made of material to match the rest of the trim.
[Illustration: FIG. 874.—Treatment of moulding work on ceilings. All
installations should be planned out so as to conform to symmetrical
designs, as far as practicable with the proper distribution of the
lights, etc., and all runs finished off, whenever necessary, by "dead"
mouldings continued to the walls to improve the appearance. In the
figure the sectioned portions show the location of the dead moulding.
Sometimes, especially in the wiring of private houses the use of
special moulding is necessary. In such cases the shape and kind of
wood should match that of the finish or trim of the room, and the
receptacles should be stained to match the moulding. When the moulding
is run along the walls, the capping may be made to match the trim
or the picture moulding already in place, thus giving an apparently
concealed job. In this kind of work the feeders can be run through
the spaces between the walls, and if flexible tubes such as circular
loom or flexiduct be used, no splice box will be necessary where the
system of wiring changes and single braided rubber wire may be used
throughout.]
=Ques. What is the usual character of moulding work?=
Ans. Usually, a certain part of the work will be run as concealed, that
is, inside the partitions, the wires being "fished" from the moulding
to the outlet.
=Practical Points Relating to Wiring in Mouldings.=—The following
practical points will be found useful in the satisfactory execution of
any class of wiring with wooden moulding:
1. Wooden moulding should never be concealed, and should not be
used in damp places or in buildings subject to acid fumes, such
as ice houses, breweries, or stables, etc.
2. Wooden moulding selected for use should be formed of good
straight stock and free from knots, knot holes and other
imperfections. The saving effected in the lower cost of second
hand moulding does not compensate for the additional cost
increase in its working.
3. When wooden moulding is used in connection with solid pipe
or flexible tube conduit, an iron box or conduitlet must be
installed where the system of wiring changes, as shown in fig.
875. The pipe conduit is secured to the box by means of lock
nuts, with porcelain bushings or flexible tubes protecting the
wires. In all cases the loom should run up to the moulding.
[Illustration: FIG. 875.—Method of tapping outlets for feeder circuits
when wiring with wooden moulding.]
=Arc Light Wiring.=—All wiring for high voltage arc lighting
circuits should be done with rubber covered wire. The wires
should be arranged to enter and leave the building through an
approved double contact service switch which should close the
main circuit and disconnect the wires in the building when
turned "off" and be so constructed that they will be automatic
in their action, not stopping between points when started and
to prevent arcing between points under any circumstances, and
should indicate plainly whether the current is "on" or "off."
Never use snap switches for arc lighting circuits. All arc
light wiring of this class should be in plain sight and never
enclosed, except when required, and should be supported on
porcelain or glass insulators which separate the wires at least
one inch from the surface wired over. The wires should be kept
rigidly at least eight inches apart, except, of course, within
the lamp, hanger board or cut out box or switch. On side walls,
the wiring should be protected from mechanical injury by a
substantial boxing, retaining an air space of one inch around
the conductors, closed at the top (the wires passing through
bushed holes) and extending not less than seven feet from the
floor. When crossing floor timbers in cellars or in rooms,
where they are liable to be injured, wires should be attached
by their insulating supports to the under side of a wooden
strip not less than one-half an inch in thickness.
=Arc Lamps on Low Pressure Service.=—For this service there
should be a cut out for each lamp or series of lamps. The
branch conductors for such lamps should have a carrying
capacity about 50 per cent. in excess of the normal current
required by the lamp or lamps to provide for the extra current
required when the lamps are started or should a carbon become
stuck without over fusing the wires. If any resistance coils be
necessary for adjustment or regulation, they should be enclosed
in non-combustible material and be treated as sources of heat;
it is preferable that such resistance coils be placed within
the metal framework of the lamp itself. Incandescent lamps
should never be used for resistance devices. These lamps should
be provided with globes and spark arresters, as in the case
of arc lamps on high voltage series circuits, except when the
closed arc lamps are used.
4. Wooden moulding should never be run in elevator shafts, or
shafts of any kind, and should never be run on the inner side
of the outside walls of the buildings, as these locations are
usually subject to dampness.
5. In laying out feeders it is usually cheaper to use iron
conduit in a shaft, than to run moulding through the floor
timbers.
6. When tapping outlets for feeder circuits, an iron outlet box
with cover should be used, as shown in fig. 886. The one splice
box is held up to the outlet box already installed by means of
two long screws, and the loom is run right up to the moulding
so as to leave no exposed wire.
[Illustration: FIG. 876.—Circular fixture block for outlet from
moulding work on ceiling.]
7. Wherever fixture outlets are installed, a circular fixture
block as shown in fig. 876 should be used, to give a good
support for the fixture and to make a neat backing for the
fixture canopy. The wires should be brought through the fixture
without cutting and disfiguring the canopy.
=Concealed Knob and Tube Wiring.=—This method of wiring should be
discouraged as far as possible, as it is subject to mechanical injury,
is liable to interference from rats, mice, etc. As the wires run
according to this method are liable to sag against beams, laths, etc.,
or are likely to be covered by shavings or other inflammable building
material, a fire could easily result if the wires become overheated or
short circuited.
[Illustration: FIG. 877.—Concealed knob and tube wiring. The wires are
carried on porcelain knobs attached to the beams. If run perpendicular
to the beams, holes are bored in the latter and porcelain tubes with
a shoulder at one end, inserted in the holes through which the wires
pass. The knobs should support the wires at least one inch from the
surface over which they run, and should not be spaced further than
4½ feet apart. The wires should be attached with tie wires having an
insulation equal to that of the conductor which it secures to the knob.
The use of split knobs does away with the necessity of using tie wires.
The conductors must be at least 5 inches apart and it is better to
support them on separate beams when possible. Each wire must be encased
in a piece of flexible tube at all switches, outlets, etc., and this
piece of tubing should be sufficiently long to extend from the last
insulator and project at least one inch beyond the outlet.]
Concealed knob and tube wiring is still allowed by the
Underwriters, although many vigorous attempts have been made to
have it abolished. Each of these attempts has met with strong
opposition from electric light companies and contractors,
especially in small villages and towns the argument being that
it is the cheapest method of wiring, and if forbidden, many
places which are wired according to this method would not
be wired at all, and the use of electricity would therefore
be much restricted, if not entirely dispensed with in such
communities. This argument, however, is only a temporary
makeshift obstruction against progress, and in the near future,
no doubt, concealed knob and tube wiring will be forbidden by
the underwriters.
[Illustration: FIGS. 878 to 880.—Methods of making fixture outlets in
concealed knob and tube wiring. A cleat consisting of a piece of board
at least ⅞ in. thick, should be nailed between the joists or studs
into which the wood screws supporting the electrolier can be secured.
Holes are then bored through the cleat, through which the flexible
tubing can pass. With a combination gas and electric fixture as shown
in fig. 879, no cleat is necessary, because the gas pipe supports
the fixture. The flexible tubing should be wired to the gas pipe, to
prevent displacement by artisans who have occasion to work around the
outlet.]
=Ques. Describe the method of concealed knob and tube wiring.=
Ans. It consists in running the wires concealed between the floor beams
and studs of a building, knobs being used to support the wires when run
parallel to the beams or studs, and porcelain tubes, when run at right
angles through the beams, or studs as shown in fig. 877.
In this method of wiring, usually nothing need be disturbed on
the first floor as the various outlets can be reached from the
basement and from the second floor.
[Illustration: FIG. 881 and 882.—Arrangement of switch and receptacle
outlets in knob and tube wiring. In wiring for switches, flexible
tubing must be used on the conductor ends from the last porcelain
support, as shown, the same as on conductor ends for other outlets. A
pressed steel switch box should be used to encase each flush switch
mechanism, even though it already be encased in porcelain. A ⅞ in.
wood cleat or cleats are arranged to support the switch box. These
wooden cleats should not be set out flush with the outer edges of the
studs, but should be set about ⅜ in. back, as illustrated, to allow a
space in which the plaster can take a "grip."]
For instance, if it be necessary to make an outlet for the
center fixture in the parlor, a strip of flooring can be
removed from the floor above so as to expose the beams. Then
the wireman can bore two holes through each of the beams,
insert porcelain tubes therein, slip the wires through the
outlet and replace the strip of flooring.
Various simple methods may be employed for carrying the wires
to the outlets on the side walls. For example: a small hole
can be made in the wall, and the wire may be dropped through
the spaces between the walls, or they may be pulled up from
the basement by means of a cord lowered with a weight attached
to its end. Outlets for switches and base receptacles may be
provided for, in a similar manner.
[Illustration: FIGS. 883 and 884.—Elevation and sectional view showing
arrangement of switch outlet in concealed knob and tube wiring.]
[Illustration: FIG. 885.—Arrangement of surface switch in concealed
knob and tube wiring. For a surface snap switch outlet, an iron box is
not necessary, but a ⅞ in. cleat must be installed to hold the tubing
in place and to provide a proper support for the screws that hold
the switch. In wiring old buildings where supporting cleats were not
provided back of the plaster, a ¾ in. wooden block or plate should be
installed on the surface, to which the switch can be attached.]
=Ques. What are the advantages of concealed knob and tube wiring?=
Ans. Its cheapness, especially in wiring completed buildings, and the
absence of any wires or casings on the walls or ceilings.
=Ques. What kind of wire must be used?=
Ans. Wire having an approved rubber insulating covering.
[Illustration: FIGS. 886 to 888.—Switch boxes for concealed knob and
tube wiring. These are for flush switches and are formed from sheet
steel. A single switch box can be expanded for any number of switches,
by using the proper number of spacers. Single and double switch boxes
can be supplied already assembled and are used where feasible, because
it is cheaper to buy them this way than to assemble them. Holes
partially punched, which can be knocked out with a hammer blow, are
provided in the sides and back through which the flexible conduit wire
protection can be extended.]
=Rigid Conduit Wiring.=—The installation of wires in conduits not
only affords protection from mechanical injury, but also reduces the
liability of a short circuit or ground on the wires producing an arc
which would set fire to the surrounding material; the conduit being of
sufficient thickness to blow a fuse before the arc can burn through the
conduit.
=Ques. Describe the unlined type of conduit.=
Ans. It consists of an iron or steel pipe, similar in size, thickness,
and in every other way to gas pipe, except that special precautions
are taken to free it inside from scale or any irregularities; it is
then coated inside with enamel, outside it is sometimes enameled and
sometimes galvanized.
=Ques. Describe the lined type of conduit.=
Ans. It usually consists of a plain iron pipe lined with a tube of
paper which has been treated with an asphaltic or similar compound;
this paper tube is cemented or fastened to the inside of the iron pipe
so that it forms practically an integral part of the same.
=Ques. What are the advantages of unlined conduit?=
Ans. It is cheaper, because having no lining a smaller size of conduit
can be used for any given size of conductor; it is also cheaper to
install, as it can be bent, threaded, and cut more readily than the
lined conduit. Wires may be more easily inserted and withdrawn as the
inside is smoother than that of the lined conduit.
NOTE.—Conduits for inside wiring which are subject to
inspection, must have an inside diameter of not less than
⅝ inch. They must be continuous from outlet to outlet or
to junction bores, and must properly enter and be secured to
all fittings, and the entire system be mechanically secured
in position. In case of service connections and main wires,
this involves running each conduit continuously into a main
cut out cabinet or gutter surrounding the panel board as the
case may be. Conduits must first be installed without the
conductors, and be equipped at every outlet with an approved
outlet box or plate. Outlet plates must not be used where it
is practicable to install outlet bores. The outlet box or
plate must be so installed that it will be flush with the
finished surface, and if this surface be broken, it shall be
repaired so that it will not show any gaps or open spaces
around the edge of the outlet box or plate. In buildings
already constructed where the conditions are such that neither
outlet box nor plate can be installed, these appliances may
be omitted by special permission, providing the conduit ends
are bushed and secured. It is suggested that outlet boxes and
fittings having conductive coatings be used in order to secure
better electrical contact at all points throughout the conduit
system. Metal conduits where they enter junction boxes, and
at all other outlets, etc., must be provided with _approved_
bushings or fastening plates, fitted so as to protect wire from
abrasion, except when such protection is obtained by the use
of _approved_ nipples, properly fitted in boxes or devices.
Conduits must have the metal of the conduit permanently and
effectually grounded. Conduits and gas pipes must be securely
fastened in metal outlet boxes so as to secure good electrical
connections. If conduit, couplings, outlet boxes or fittings
having protective coating of insulating material, such as
enamel, be used, such coating must be thoroughly removed from
threads of both couplings and conduit and from surfaces of
boxes and fittings where the conduit is secured in order to
obtain requisite good connection. Where boxes used for centers
of distribution do not afford good electrical connection, the
conduits must be joined around them by suitable bond wires.
Where sections of metal conduit are installed without being
fastened to the metal structure of buildings or grounded metal
piping, they must be bonded together and joined to a permanent
and efficient ground connection. Junction boxes must always be
installed in such a manner as to be accessible. All elbows or
bends must be so made that the conduit or lining of same will
not be injured. The radius of the curve of the inner edge of
any elbow must not be less than three and one-half inches. Must
have not more than the equivalent of four quarter bends from
outlet to outlet, the bends at the outlets not being counted.
[Illustration: FIG. 889.—Conduit box showing arrangement for
combination side outlet with open cover. Outlet or junction boxes are
of two general types: 1, those which are made for a particular position
and have a given number of outlets, and 2, those which have a variable
number of outlets which are plugged with metal discs in such a manner
that the latter can be knocked out by a slight blow of a hammer. The
illustration shows a universal plugged steel conduit box, which can be
used as a straight electric, or combination gas and electric, ceiling
or side wall outlet, or for flush rotary or push button switches, or
for flush receptacles. When rigid conduits are used, they are screwed
to the outlets by means of lock nuts and washers. In the case of
flexible conduits, the entering ends of the conduits are provided with
clamp bushings which are secured to the outlet by means of lock nuts.
All outlet boxes are fitted with covers of various designs, which
permit their use for various types of construction such as ceiling and
wall work in lath or plaster, fireproofing ceiling work, etc., while
many designs of outlet plates and receptacle plates may be obtained
from the supply houses to satisfy the requirement of any special case.]
=Ques. What are the disadvantages of the unlined conduit?=
Ans. The Underwriters require the use of double braided conductors
instead of single braided which are allowed for lined conduits.
=Ques. Where may unlined conduits be used?=
Ans. In buildings where the conduit is not liable to corrosive action.
=Flexible Conduit Wiring.=—Flexible conduits are used to advantage
in many cases where rigid conduits would not be desirable. It is
especially adapted to completed buildings where it is desired to
install the wiring by "fishing" without greatly disturbing the walls,
floors, or ceilings.
[Illustration: FIGS. 890 and 891.—Greenfield flexible steel conduit;
fig. 890 single strip type; fig. 891 double strip type. The former
(fig. 890) is formed with a single strip of galvanized steel,
interlocked and gasketed in such a manner as to be suitable for
concrete construction. The double strip type (fig. 891) is constructed
of a concave and convex steel strip, spirally wound upon each other
in such a manner as to interlock their concave surfaces. Thus the
convex surfaces of the two strips form respectively the outer and inner
surfaces of the conduit. This construction insures a smooth interior
surface, thus reducing the possibility of friction in the drawing in
of conductors. A gasket is provided between the inner and outer strips
rendering the conduit moisture proof. This form of flexible conduit
is especially adapted to use where the wiring is installed after
completion of building, because it is very flexible.]
=Ques. How is a flexible conduit installed by "fishing"?=
Ans. It is "fished" under floors, in partitions between the floor and
ceiling, by making pockets in the floors, walls or ceilings, say every
15 or 20 feet, and fishing through first a stiff metal wire called a
"snake," and then attaching the conduit to same and pulling the conduit
in place from pocket to pocket.
[Illustration: FIG. 892.—Insulating joint. This fitting is used
in fixture work. The part A screws on to the gas pipe and B to the
fixture. The parts are separated by insulating material E, and
the outside of the joint is covered with moulded insulation D. In
connecting fixtures to the wiring, all wires should be kept away
from the gas pipe above the joint, but they may be bunched in below
the insulating joint after the wires have been spliced, soldered,
and taped. It is important to protect the gas pipe at this point.
Insulating joints should be tested before being used.]
[Illustration: FIG. 893.—Canopy insulator. This fitting should be
installed wherever there are metal ceilings against which the canopies
of fixtures might come. The canopy is the brass cup shaped piece used
at the top of fixtures to cover the joint, and is simply an insulating
ring placed between the canopy and the ceiling. It is in contact with
the fixture; hence, it is important that it be insulated from metal
ceilings, or else all the benefits derived from an insulating joint
will be lost.]
=Ques. How is the conduit fished on vertical runs?=
Ans. A chain or weighted string is used which is dropped from the
outlet to the floor and its lower end located by sound of the chain end
or weight striking the floor.
[Illustration: FIG. 894.—Section of flooring illustrating use of
fishing hook. In fishing wires, punch a hole through the plastering
at the required position, being careful that there is no studding at
that place. Use a brad awl and cut the hole large enough to permit
running of the wires. With a short length of small brass spring wire,
push through the opening a few inches of number 19 double jack chain
such as is used for general fishing purposes, first having connected
the end of the chain with a piece of heavy linen thread. Run out the
thread between the laths and the outside wall until the chain touches
the floor beneath; move the thread and locate the chain by the sound;
bore a hole through the baseboard or floor, as the case may be, toward
the chain. Use a two or three foot German twist gimlet. With a small
brass spring wire bent at the end in the shape of a hook, fish for the
chain and draw it out. At the other end of the thread attach the wire
and draw it through with the thread. Passing under the floor bore a
second hole through the floor as near the other as possible. Run into
this a piece of snake or fishing wire with a hook at the end, until it
comes to an obstruction. Locate the obstruction by sound. In running
wires under the flooring first carefully examine all parts and find
the direction in which the beams and timbers run, and run the wires
parallel with these. After locating the end of the fishing wire see
if the obstruction be a timber; if so, find the center and bore from
the middle diagonally through it in the direction of the fishing wire.
Drop the jack chain and thread through the hole; fish for it and draw
it through hole number 2; attach the insulated wire and draw it back.
Starting hole number 3, bore hole number 4 diagonally through the
timber in the direction in which the wire is to be run, making holes
3 and 4 form an inverted "V" through the timber. Run the fishing wire
through hole number 4 until it meets an obstruction. If at the end of
the room, bore through the floor, drop the chain, fish it out, attach
wire and draw it home. Putty up holes after having finished the work,
in case of hard finish, plug them up with wood. In lightly built houses
it is often found easier to take off the moulding above the baseboard
and run the wire under it. In such cases care should be taken to break
off the old nails, as any attempt to drive them out would cause a bad
break. In closets and around chimneys it is usually found easy to work.
A "mouse" or lead weight attached to a string may often be dropped from
the attic to the cellar ceiling through the space outside the chimney.]
=Ques. What is the difference between flexible conduit and flexible
tubing?=
Ans. Flexible conduits are made of metal while flexible tubing is
non-metallic.
=Ques. Describe a flexible conduit.=
Ans. It is a continuous flexible steel tube composed of convex and
concave metal strips, wound spirally upon each other in such a way as
to interlock their concave surfaces.
=Ques. What are the advantages of this form of flexible conduit?=
Ans. It possesses considerable strength and can be obtained in long
lengths (50 to 200 feet); elbow fittings are not required as the
conduit may be bent to almost any radius. The fissures of the conduit
provide some ventilation; this is an advantage in some places and a
disadvantage in others.
[Illustration: FIGS. 895 to 897.—Greenfield flexible steel conduit
and fish plug, showing method of insertion. Fish plugs are made for
⅜ inch, ½ inch, and ¾ inch conduit and are useful in drawing in
the conduit in finished buildings where it is desired to fish it under
doors or in partitions. After the conduit has been cut off square in
the special vise, the fish plug may be screwed into the tube and the
fish wire or drawing-in line should then be attached to the eyelet on
the end of the plug.]
=Ques. In what places are flexible conduits not desirable?=
Ans. In damp places.
=Ques. Why?=
Ans. Because of the fissures.
=Practical Points Relating to Inside Conduit Wiring.=—The following
instructions apply to the installation of wiring in both rigid and
flexible conduit:
1. All conduits should be made continuous from one junction or
outlet box to another, or to the various fixtures. A conduit
installation is made a complete system by the use of outlets,
outlet boxes, switch or junction boxes, and panel boxes with
doors and locks, which serve to thoroughly protect the circuit
at all points.
[Illustration: FIGS. 898 to 901.—Pull boxes and their use in conduit
work. A pull box is a convenient device used for the purpose of
avoiding the disadvantages of having too many bends in one continuous
line of conduit; too many bends will give trouble when the conductors
are drawn in. Pull boxes are also useful in places where the
arrangement of the conduit is such that trouble would be experienced in
bending it to a fit, and also in the case of conduits which are first
run on a side wall and then have to be carried across the ceiling at
right angles to the wall. Fig. 898 shows an example of objectionable
bends, and fig. 899, the method of overcoming the difficulty by the use
of a pull box. It is evident that it would be impossible to make some
of these bends so as to permit the drawing in of the conductors. This
difficulty is overcome, as shown, by placing a pull box on the wall,
with its top close to the ceiling. A board B, having the proper size
holes for the conduits is fastened to the front of the box and close
to the ceiling. After the conductors have been drawn into the conduits
along the wall as far as the pull box, they can be readily pulled away
from the box through the holes in the board into the corresponding
conduit on the ceiling. Fig. 901, shows the use of a pull box in a case
where it is necessary to run conduit through partitions at right angles
to each other. Pull boxes can be designed to suit any condition liable
to occur in practice, and when properly used will always save much
time and labor. Locknuts should be placed on the ends of all conduits,
both inside and outside the pull box in order to prevent their being
displaced when drawing in the conductors. After all the conductors have
been drawn into the conduit, all the outlets should be plugged up with
wood or fibre plugs made in parts to fit around the wires and cables,
and the outlets given a coating of some compound which will render the
whole system air tight and moisture proof. A final test should then be
made to ascertain that there are no grounds on the different parts of
the wiring, and that the insulation comes up to the requirements of the
underwriters. The metal of all conduits, and the sheathing of steel
armoured cables should be effectually and permanently grounded.]
2. In the installation of interior conduit wiring, the tubes
are usually put in place as soon as the partitions of the
buildings have been constructed. In non-fireproof buildings,
the tubes are usually supported from the underside of the floor
beams, but in fireproof buildings they are placed on top of the
floor beams and under the floor as in fig. 902.
3. When conduit is used in damp places, lead encased wires
should be used, and the wires drawn in very carefully so as to
prevent any injury to the casings.
4. For wiring installations in buildings constructed entirely
of reinforced concrete, the preliminary work should be laid out
during the progress of the building operations so as to avoid,
as much as possible, the necessity of drilling holes in the
finished concrete work.
[Illustration: FIG. 902.—Method of installing conduits in fire proof
buildings. The installation of the conduit includes the placing of
all outlet boxes, and when this has been completed, the lathing or
plastering work is executed, and after that is finished, the wire is
pulled into the tubes, and the receptacles, switches, etc., put in
position. The work of pulling in the wires may be greatly facilitated
by the use of _pull boxes_ as shown in figs. 899 and 901.]
5. For concealed wiring, the location of all the outlets
should be marked by sheet iron tubes large enough to hold the
conduits. These tubes should be properly plugged, and set in
the false work before the concrete is poured in. In a similar
manner, threaded pieces of conduit of the proper size, should
be placed in the false work for risers.
6. For exposed wiring on concrete walls and ceilings, suitable
cast iron supports should be set in the moulds at regular
intervals. When liberally used, these supports will also serve
as good supports for other pipes.
7. Where a conduit line terminates on the outside of a building
some suitable fitting such as a pipe cap should be used, as
shown in fig. 903, to prevent the entrance of moisture into the
conduit system. A variety of devices suitable for this purpose
are available at supply houses; but those having porcelain
covers which spread the wires the proper distance apart are the
most satisfactory.
8. Where it is desirable or necessary to continue open wiring
from conduits, or where the character of the wiring makes it
necessary to bring the wires over from the conduit, as in an
arc lamp, neat and safe work can be done by use of a suitable
form of _condulet_ as shown in fig. 904.
[Illustration: FIG. 903.—Service entrance to interior conduit system;
showing method of preventing moisture reaching the interior of the
conduit system.]
[Illustration: FIG. 904.—Outlet to arc lamp from conduit by use of
condulet. The wires are brought out from the conduit system at a
distance of 2½ inches apart. Conduits are made in a great variety
of design with interchangeable porcelain covers which render them
adaptable to almost all cases requiring the installation of outlet
boxes.]
9. Where a conduit line terminates in a switch or panel box,
the lining or casing of the panels should be of iron, and the
conduit firmly secured to it so as to make good electrical
contact. Vertical lines of conduit should be fastened to the
wall or other supports in such a manner as to prevent the
weight of the conduit coming on the panel box, and each length
of conduit installed should be fastened so as to bear only
its own weight. The best method of fastening conduit to brick
walls is by the use of expansion bolts and screws. In the case
of fire brick ceilings or other plastered walls, toggle bolts
should be used. When conduits are run on wooden or iron beams,
various kinds of pipe hanger may be employed.
10. There are numerous devices on the market for bending
conduit for the making of elbows, offsets, etc., but the
majority possess the disadvantage that the conduit must be
taken to them to be bent. In the case of the smaller sizes,
this difficulty is avoided by the use of some form of conduit
bender such as shown in figs. 910 and 911.
[Illustration: FIGS. 905 to 909.—Sprague multilet covers. Fig. 905,
six wire porcelain cover; 906, P & S. rec. cover; 907, cover for five
ampere snap switch; 908, G. E. and P. & S. rec. cover; 909, cover for
ten ampere snap switch.]
11. In all cases, the interior diameter of the conduit
installed should be amply sufficient to permit of the wires
being drawn in easily, thus providing a substantial raceway for
the conductors. The practice of pulling wires through conduit
by means of a block and tackle is very objectionable. It is
evident that if the wires be pulled in by the application of
much force the insulation is very liable to become damaged;
furthermore, much difficulty will be experienced in pulling
them out again, especially in warm places where the heat tends
to soften the lining of the conduit, and also the rubber
covering of the wire. Powdered soapstone put in the pipe while
the wires are being drawn in will lessen the friction and
permit the wire to go in more readily.
[Illustration: FIG. 910.—Ordinary form of hickey or conduit bender. It
consists of a piece of one inch steam pipe about three feet long with a
one-inch cast iron tee screwed onto one end of the pipe. This device is
used as follows: the conduit to be bent is placed on the floor and the
tee slipped over it. The workman then places one foot on the conduit
close to the tee, and pulls the handle of the bender towards him. As
the bending progresses, the workman should take care to continually
move the bender away from himself, to prevent the buckling of the
conduit.]
[Illustration: FIG. 911.—Commercial form of hickey or conduit bender.]
[Illustration: FIGS. 912 and 913.—Methods of bending large conduits. A
substantial support is necessary which may consist, as in fig. 912, of
two pieces of 2 × 4 studding A and B securely fastened to an upright.
The conduit is placed under the block A and over the block B, and then
bent by a downward pressure exerted at C, the conduit in the meantime
being gradually advanced in the direction D to give a curve of the
required radius. The method shown in fig. 913, may be used wherever
a ring A can be attached to a beam or girder by means of clamps or
otherwise to serve as a support. In this case the conduit is slipped
through the ring and placed on the top of blocking B. The bending is
accomplished by means of a block and tackle rigged to an overhead beam
as shown. Where ring supports cannot be arranged, the application of
frame bending methods give the most satisfactory results.]
=Armoured Cable Wiring.=—Where a conduit system cannot be conveniently
installed, armoured cable is used. Armoured cable is made by winding
steel strips over the insulated conductors, the latter being
permanently retained inside the steel casing. Armoured cable is
manufactured in long lengths, the actual lengths being determined by
convenience in handling.
[Illustration: FIGS. 914 and 915.—Greenfield flexible steel armoured
conductors. The armour is composed of convex and concave galvanized
metal strips, wound spirally upon each other and over the insulated
conductors. A gasket is placed between the inner and outer metal
strips, thus further rendering the conductor moisture proof.
FIG. 916.—Greenfield flexible steel armoured lead covered conductors
for use in wet places, such as breweries, packing houses, cold
storage buildings, coal breakers and the like, and for underground
construction, in which classes of work these materials are being
extensively and satisfactorily used.]
=Ques. What are the features of armoured cable?=
Ans. It is flexible and the conductors are well protected from
mechanical injury. While this form of wiring has not the advantage of
the conduit system—namely, that the wires can be withdrawn and new
wires inserted without disturbing the building in any way whatever—yet
it has many of the advantages of the flexible steel conduit, and it
has some additional advantages of its own. For example, in a building
already erected, this cable can be fished between the floors and in the
partition walls, where it would be impossible to install either rigid
conduit or flexible steel conduit without disturbing the floors or
walls to an extent that would be objectionable.
[Illustration: FIGS. 917 to 920.—Greenfield flexible conduit tools.
Special tools are necessary for installing this type of conduit. Fig.
917, universal reamer; fig. 918, bushing tool; fig. 919, cable armour
cutter; fig. 920, vice for holding conduit. To remove cable armours,
clamp the conductor firmly in the armour cutter and with a pair of
cutting pliers back the armour off, one strip at a time, to the point
of contact with the cutting edge of the tool. The vise for holding
conduit takes all sizes. The conduit can be cut with an ordinary
hacksaw. To protect the insulation against any possible injury while
the wire is being drawn in, a soft metal bushing should be inserted in
the end of the tube and secured permanently thereto by means of the
bushing tool. The bushing provided for this purpose has an outside
thread, which permits its being screwed into the end of the tube and
then expanded by the use of the tool. The tool should always be used
after the bushing has been screwed into the pipe, then the bushing tool
should be inserted.]
=Ques. How should armoured cable be installed?=
Ans. It should be continuous from outlet to outlet, without being
spliced and installed on the loop system. Outlet boxes should be
installed at all outlets, although, where this is impossible, outlet
plates may be used under certain conditions. Clamps should be provided
at all outlets, switch boxes, junction boxes, etc., to hold the cable
in place, and also to serve as a means of grounding the steel sheathing.
=Ques. Is armoured cable wiring expensive?=
Ans. It is less expensive than the rigid conduit or the flexible steel
conduit, but more expensive than cleat wiring or knob and tube wiring,
and is strongly recommended in preference to the latter.
CHAPTER XXXIX
OUTSIDE WIRING
In the equipment of lighting and power plants, the cost of the outside
wiring represents a considerable proportion of the total investment,
sometimes costing more than the engines, boilers and dynamos.
A thorough knowledge of outside wiring is therefore necessary to
properly proportion and install the wires so that the system will prove
economical and safe.
=Materials for Outside Conductors.=—Copper wire is now considered to
be the most suitable material not only for the transmission of current
for electric light and power purposes, but also for telegraph and
telephone lines, in place of the iron wire formerly employed.
Hard drawn copper wire is used in outside construction, because its
tensile strength ranges from 60,000 to 70,000 pounds or about twice
that of soft copper. This is desirable to withstand the stresses to
which the wire is subjected which, in the case of long spans, are
considerable.
The table on the next page gives the tensile strength, in pounds per
square inch of cross section, hard drawn copper wire of various sizes
B. & S. gauge.
The metal _aluminum_ possesses certain advantages as a material
for overhead wires. Its conductivity is about .6 that of
copper. The specific gravity of aluminum is about 2.7, while
that of copper is 8.89, so that a given volume of copper will
weigh 3.3 times more than an equal volume of aluminum, and
copper wire of given length and resistance would be about twice
as heavy as an aluminum wire of equal length and resistance.
There are several disadvantages, such as, low tensile
strength, high electro-positive quality of the metal, higher
electrostatic capacity, etc.
TENSILE STRENGTH OF COPPER WIRE
+——————————————-+————————————————+——————————————-+————————————————+
| Size of wire | Tensile | Size of wire | Tensile |
| B. & S. gauge | strength, lbs. | B. & S. gauge | strength, lbs. |
+——————————————-+————————————————+——————————————-+————————————————+
| 0000 | 9971 | 9 | 617 |
| 000 | 7907 | 10 | 489 |
| 00 | 6271 | 11 | 388 |
| 0 | 4973 | 12 | 307 |
| 1 | 3943 | 13 | 244 |
| 2 | 3127 | 14 | 193 |
| 3 | 2480 | 15 | 153 |
| 4 | 1967 | 16 | 133 |
| 5 | 1559 | 17 | 97 |
| 6 | 1237 | 18 | 77 |
| 7 | 980 | 19 | 61 |
| 8 | 778 | 20 | 48 |
+——————————————-+————————————————+——————————————-+————————————————+
=Pole Lines.=—In the majority of cases overhead conductors are
supported by wooden poles. In tropical countries, however, such as
India, Central America, etc., where wood is rapidly destroyed by
the ravages of white ants and other insects, iron poles are almost
exclusively used for telegraph, telephone, and other electric
transmission lines. The form of iron pole generally adopted consists of
tapering shells of sheet iron of convenient length, riveted together at
their ends and set into cast iron base plates which are buried in the
ground.
[Illustration: FIGS. 921 to 929.—Pole construction tools. Fig. 921,
long handled digging shovel; fig. 922, digging bar; fig. 923, crow and
digging bar; fig. 924, tamping and digging bar; fig. 925, wood handle
tamping bar; fig. 926, slick digging tool; fig. 927, post hole augur;
fig. 928, carrying hook; fig. 929, tamping pick.]
=Wooden Poles.=—On account of their size and straightness, various
species of northern pine, cedar and cypress are especially suitable for
large poles. Chestnut, which can be readily sawed and hewed is a very
good material for smaller poles. Sawed redwood is extensively used in
California.
=Preservation of Wooden Poles.=—The preservation of wooden poles
employed in line work is a matter of importance. Decay of the pole at
or near the soil line is caused primarily by various forms of bacteria
or fungi, and in some cases by insects. Bacteria and fungi attack
either dead or living timber. In the case of dead timber, such as that
of poles, they attack the walls of the cells and cause the familiar rot
or decay which eventually destroys the usefulness of the pole.
It is well known that the rapid multiplication or action of the
bacteria and the growth of the fungi are induced by a certain
per cent. of moisture and the heat of the sun, that is, the
portion of the pole at or near the soil line is alternately
moistened and dried. Therefore, in order to protect it against
this action, it is necessary to sterilize the pole by the
application of an antiseptic which will penetrate the pores of
the wood.
=Preservation Processes.=—There are several processes which may be
successfully employed for the preservation of poles or other exposed
timber. The best known of these are the creosoting, burnettizing,
kyanizing, carbolizing, and vulcanizing processes.
In England, creosoted poles showed no sign of decay at the
end of 35 years of service. In the United States they have an
average life of 22 years. In Europe impregnation with copper
sulphate has been extensively used, but this impregnation must
take place within a few days after cutting down the tree.
Uniformly good results have been obtained by impregnation with
corrosive sublimate, involving simply immersion in the liquid
from ten to fourteen days. German authorities state that the
average life of such poles is about 17 years, compared with 14
years for natural or untreated poles.
The application of pitch and tar oftentimes results in more
harm than good. It is authoritatively stated, however, that
in Europe wooden poles are effectively protected by painting
them with tar up to about 2 feet above, and down to about 1½
feet below the soil line. The painted parts of the pole are
then covered with a cloth which after being nailed to the pole,
is also painted with tar. Finally a zinc plated sheet of iron
painted on both sides with tar, is placed around the cloth and
tightened to the pole.
The saving due to the use of sterilized poles is 40 per cent.
of the cost of unsterilized poles. The comparison is made on
the following basis: Cost of pole, $5 each; sterilizing, $1.25;
renewal of sterilized pole in 24 years, unsterilized pole, in
12 years.
[Illustration: FIGS. 930 to 932.—Pole line construction tools. Fig.
930, split wooden handle post hole auger; fig. 931, cant hook; fig.
932. socket peavey.]
=Methods of Setting Wooden Poles in Unsuitable Soil.=—In places where
salt is plentiful and cheap, such as the Great Salt Lake region in
Utah, it has been found that the liberal use of salt mixed with the
dirt filling tamped in around the foot of the pole is very effectual in
preventing decay below the soil line.
Where poles have to be planted in low, swampy ground, or where the
climatic conditions are such that timber decays rapidly, it has been
found advantageous to place the poles in concrete settings. This method
is extensively employed in various parts of the Southern States, square
poles being placed in settings about 7 feet deep and 3½ feet
square. In very soft ground the employment of a concrete setting is
sometimes impracticable. In such cases piles are driven deep into the
soil, and the pole bolted to the part of the pile extending above the
ground.
=Reinforced Concrete Poles.=—The strongest point in favor of concrete
poles is their durability. Untreated wooden telephone and telegraph
poles have to be replaced by new poles about every six or seven
years, depending on the percentage of moisture in the soil, the drier
the soil, the longer being the life of the pole. Concrete poles are
not affected by soil conditions, and if properly made will last
indefinitely.
[Illustration: FIGS. 933 to 935.—Glass insulator and insulator pin and
bracket. The insulator here shown is of the pony double petticoat type.
Insulator pins are used with cross arms, brackets are attached direct
to the pole.]
One form of reinforced concrete pole consists of a skeleton
frame work of four corrugated iron rods covered with ordinary
concrete. The pole is octagonal in shape, 30 feet long, and
provided with mortises for cross arms, the latter being
fastened in place by means of iron bolts. It is stated that
they are less expensive than pine poles, and that each pole can
be manufactured at the point on the line at which it is to be
installed or planted.
In Canada, reinforced concrete poles are made square on account
of the ease of making, and also on account of the steel economy
permitted thereby. All poles are made at the point of erection.
They are moulded in wooden forms, in a horizontal position,
the top side being left open and finished with a trowel. The
concrete is composed of one part of Portland cement, two parts
clean sharp sand, and four parts broken stone. A 35 foot pole
for ordinary line work weighs about 2½ tons and a 50 foot
pole about 5 tons.
=Cross Arms.=—The familiar cross arms for stringing wires are usually
attached to the poles before they are erected. They are commonly made
from yellow pine wood, generally 3¼ x 4¼ inches, and are freely
coated with good mineral paint as a preservative. Attachment is made to
the pole by cutting a _gain_ one inch deep and of sufficient breadth to
allow the longest side of the cross arm to fit accurately. It is then
secured in place by a lag screw, with a square head, so that it may be
driven into place with a wrench.
[Illustration: FIG. 936.—Cross arm which carries the insulator pins.
The standard cross arm is 3¼ x 4¼ inches, double painted, and
bored for 1½ inch pins and two ½ inch bolt holes. Telephone arms
are 2¾ x 3¾ inch, bored for 1¼ inch pins and two ½ inch
bolts.]
The cross arm is further secured to the pole with braces. These are
flat strips of wrought iron or low carbon steel, 30 inches long, ¼
inch thick and 1¼ inches wide, according to standard specifications.
Holes are bored at points one inch from either end, one for attaching
to the pole, the other for attaching to the cross arm; two braces
forming a triangle with the cross arm for the base and with the apex
at the point of connection to the pole. Like all other iron work used
on pole lines, the braces are carefully "galvanized," so as to stand
three immersions of one minute each in a saturated solution of copper
sulphate without showing copper deposits, the color being black at the
completion of the test.
Before the cross arm is set in place the gain is carefully painted with
white lead. As it is important that cross arms on a line of poles,
particularly when there are several on each pole, should be at equal
distances from the ground as well as being uniformly spaced, it is
necessary that some measuring instrument should be used to accomplish
this. Such an instrument is the ordinary _template_, which is a length
of board carrying a pointed block at one end, to correspond exactly
with the top of the pole, and also cross cleats nailed at precisely the
same intervals below it as it is proposed attaching the cross arms. The
template, laid upon a pole, shows where to cut the gains.
In planting the poles it is customary to so arrange them that the cross
arms on alternate poles shall face in opposite directions, for the
purpose of equalizing the strain on the line. On curves, however, all
cross arms are placed on the side of the pole facing the middle of the
curve.
=Ques. What provision is made for attachment of the wires?=
Ans. The cross arms are bored with holes for the insertion of the
insulator pins, which are made of locust wood and threaded at the upper
end to receive the glass insulator.
The cross arm is made of such a length as to accommodate the
number of pins to be inserted. An arm for two pins is made
three feet long, according to the standard usually followed,
with holes for the pins at center points three inches from
either end and a space of 28 inches between them in the center.
=Ques. How must electric light and power wires be placed when wired on
telephone or telegraph poles?=
Ans. They must not be put on the same cross arm with the telegraph,
telephone, or similar wires, and when placed on the same pole with such
wires the distance between the two inside pins of each cross arm must
not be less than twenty-six inches.
[Illustration: FIG. 937.—Portable platform with rigging as used by
linemen in wiring and making repairs.]
=Poles for Light and Power Wires.=—In selecting the style of
pole necessary for a certain class of work, the conditions and
circumstances should be considered. Poles may be divided into
three classes, the size of wire to be carried being one of the
important considerations.
_First Class._—Main line of poles should range in length of
from 30 to 35 feet with 6 inch tops. The height of trees, of
course will have to be considered in many cases.
_Second Class._—Town lighting by arc lights. All poles should
have at least 6 inch tops. The corner poles should have 6½
inch tops, and wherever the cross arms are placed on a pole at
different angles, the pole should have at least a 6½ inch
top. A 30 foot pole is sufficiently long for the main line, but
it would be advisable to place 35 foot poles on corners.
_Third Class._—Where heavy wire, such as No. 00, is used for
feeder wire, the poles should have at least 7 inch tops. Where
mains are run on the same pole line the strain is somewhat
lessened, and poles of smaller size will answer.
_Cull Poles._—All poles that are smaller at the top than the
sizes agreed upon, are troubled with dry rot, large knots
and bumps, have more than one bend, or have a sweep of over
twelve inches, should certainly be classed as cull poles.
Specifications for electric light and power work should be,
and in many cases are, much more severe than those required by
telegraph lines. A cull pole, one of good material, is the best
thing for a guy stub, and is frequently used for this purpose.
A cedar pole is always preferable to any other, owing to the
fact that it is very light in comparison to other timber, and
is strong, durable, and very long lived.
_Pole Setting._—In erecting poles, it seems to be the
universal opinion of the best posted construction men that a
pole should be set at least five feet in the ground, and six
inches additional for every five feet additional length above
thirty-five feet; also additional depths on corners. Wherever
there is much moisture in the ground, it is of much value to
paint or smear the butt ends of the pole with pitch or tar,
allowing this to extend about two feet above the level of
the ground. This protects the pole from rot at the base. The
weakest part of the pole is just where it enters the ground.
Never set poles further than 125 feet apart; 110 feet is good
practice.
_Painting._—When poles are to be painted, a dark olive
green color should be chosen, in order that they may be as
inconspicuous as possible. One coat of paint should be applied
before pole is set, and one after pole is set. Tops should be
pointed to shed water.
=Spacing the Poles.=—In general, the spacing of poles, like their
dimensions, is regulated by the weight of the lines they are designed
to carry—the heavier the lines the greater the number of poles. The
spacing of poles also depends on their liability to injury from storms
and wind in any given locality, and the nature of the service. Poles
for a telephone line may be spaced twenty to fifty to the mile—that
is, from about 260 to 100 feet apart.
[Illustration: FIGS. 938 to 941.—Pole line construction tools. Fig.
938, pike pole; fig. 939, raising fork; fig. 940, mule pole support;
fig. 941, jenny pole support.]
=Erecting the Poles.=—Since each pole on a properly constructed line
is sawed to the right length and carefully shaped before it is finally
inserted in the ground, it is necessary that the holes be dug to as
nearly the required depth as possible. Holes for poles are dug very
little wider than their diameter at the butt, and the depth is usually
computed according to the nature of the soil and the weight of the
proposed line. Excavation, while sometimes accomplished with patent
post hole augers, or even dynamite, is usually done with a long handled
digging shovel, and the earth removed with a spoon shovel, such as is
shown in fig. 921.
[Illustration: FIG. 942.—Guy anchor log in position.]
[Illustration: FIG. 943.—Stombaugh guy anchor. It is made of cast iron
and can be screwed into the ground like an auger.]
Wherever required by the nature of the soil, a "grouting" or foundation
of loose stones is formed in the bottom of the hole, and, in marshy or
springy ground, a base of concrete and cement is laid, with filling of
the same material around the pole, when raised.
=Ques. How are the poles transported to the holes?=
Ans. They are rolled or carried on hooks similar to those used for
carrying blocks of ice, except for a long handle for lifting the load
at either side.
[Illustration: FIG. 944.—Method of raising a pole. When the pole has
been properly placed, it is seized by several linemen. As soon as the
top of the pole is raised high enough to permit the pikes to be thrust
into the pole, it is then raised to a vertical position. At about 50°
the butt end slides into the hole. The earth is then filled in around
the pole and firmly tamped down. Eight or ten poles are about as many
as can be set by the average gang in a day.]
=Ques. How are the poles raised and placed in the holes?=
Ans. A piece of timber is inserted in the hole as a slide to prevent
crumbling of the earth as the pole is slid into place. The end is
raised by hand sufficiently to allow the "dead man," or pole hoist, to
be placed beneath, and this is moved along regularly as the pole is
lifted with pike poles, until it slides into place through the force of
gravity.
[Illustration: FIG. 945.—Method of pulling an anchor into place before
the guy wire is fastened to the top of the pole, thus obviating the
liability of pulling the pole out of plumb.]
This accomplished, the pole is held in a perpendicular position
by pikes in the hands of assistants, or planted in the ground
around it, while the earth is carefully shoveled into the hole
and thoroughly packed down with a tamper.
=Guys for Poles.=—Where poles are subject to severe strains which
might throw them down and break the wires, guy cables are largely
employed, these being attached near the top and secured either to the
base of the next pole, to a suitable guy stub or post, or to a guy
anchor, which is buried about eight feet in the earth and held down by
stones and concrete.
=Ques. Under what conditions is it necessary to guy poles?=
Ans. They are guyed at corners in order to thoroughly secure the poles
so that no strain may come on the cornerwise span. It is also necessary
to guy a line where it is to be deflected from a straight path, as when
rounding a hill, water course or railway curve, in order to neutralize
the pull of the wires, tending to incline the poles toward the center
on which the arc is described; also when descending a hill.
[Illustration: FIGS. 946 to 948.—Methods of guying corner poles. The
proper guying of corner and terminal poles is especially important; on
corners and curves, the guys should be stronger and more frequent and
should be placed on the outer side as shown in the diagrams.]
[Illustration: FIG. 949.—Head and foot guying of a pole line in
descending a hill.]
=Guy Stubs and Anchor Logs.=—In guying a line under such conditions,
each pole is connected by a suitable cable to a guy post or "stub," or
to an anchor log. Standard rules specify stubs between 18 and 25 feet,
with exact limits as to circumference measures at the top and at a
point 6 feet from the butt, according to the kind of wood used.
[Illustration: FIGS. 950 to 952.—Lineman's tools. Figs. 950 and
951, Eastern pole climbers, with and without strap for attaching to
legs; fig. 952, portable vise with strap for pulling up the slack in
splicing.]
Thus, guy stubs of cedar or juniper, either 18 or 25 feet in
length, must have a circumference of 22 inches at the top and
of 32 inches 6 feet from the butt; stubs of chestnut must
measure 24 inches in the first, and 34 in the second, while
those of cypress require 28 in the first, and in the second,
39 inches for an 18 foot length, and at least 41 for a 25 foot
length. In planting guy stubs the same rules are followed as
hold for poles, every means being adopted to promote security
of construction except that the stub is raked or tilted against
the strain on the guy cable.
=Wiring the Line.=—The erection and guying of the poles of a line as
well as the attachment of the cross arms and the screwing on of the
insulators are completed before the stringing of the line is begun. It
is particularly essential that the pull on poles of a given line be
accurately calculated, and that each one be guyed accordingly before
the line is strung, in order to avoid the danger of an undue strain
upon the wires in attempting to rectify the condition afterward. It is
a good working rule that the wires should be subjected to no stress
other than the weights of their own spans after they have been attached
to the poles.
[Illustration: FIGS. 953 and 954.—Pay out reels. Fig. 953, type used
for telephone or telegraph work; fig. 954, type used for electric light
work.]
=Ques. Describe how the wires are strung.=
Ans. In stringing the lines, either one or the full number of wires
may be put up at the same time. When one line only is to be strung,
the operation consists simply in reeling the wire and running it off
from a hand reel, such as is shown in fig. 953 or 954. At each pole the
wire is drawn up to its place, pulled out to the desired tension, and
attached to the insulator.
In the operation of stringing a number of lines at once, the
method is different. The reels are placed at the beginning
of a section, each wire being inserted and secured through a
separate hole in a board, which is perforated to correspond
with the spacing of the insulators on the cross arms. A rope
is then attached to this running board, which is drawn by a
team of horses through the stretch to be wired, being lifted
over each pole top in turn. When a certain length has thus been
drawn out the wires are drawn to the required tension between
each pair of poles and secured to the insulators.
[Illustration: FIG. 955.—One form of "come along." The wire is
inserted between jaws and is held fast when tension is applied to the
ring.]
[Illustration: FIG. 956.—An improved form of "come along" or wire
stretcher. The jaws which grip the wire are smooth and remain parallel
in closing, thus the wire is not scratched or indented, as with
circular jaws having teeth.]
=Ques. How much tension must be put upon the wires?=
Ans. In applying tension to the wires as they are strung on the poles,
it is the rule to allow some sag. The amount of sag to be allowed
varies with different line hangers.
A typical case quoted by one or two authorities gives a sag of
four inches at the center of each 130 foot span for a given
size of wire, at a given temperature. A more general rule is to
make the tension on a wire as it is drawn up between each pair
of poles equal to one-third of its breaking weight. Thus No. 10
B.& S. gauge, would be drawn to about 163 pounds, and No. 12
to about 102 pounds. The temperature at the time of stringing
and the distance between the poles are, however, important
considerations in applying tension and allowing for sag. Thus,
one construction company specifies a dip of 10 inches in summer
and 8 inches in winter for spans of 130 feet, or 40 poles to
the mile. Several authorities specify figures about as given in
the above table for No. 14 iron or copper wire.
[Illustration: FIG. 957.—Wireman's "come along" with hook and tackle.]
SAG TABLE
+——————+————————————————————————————-+
| | Temperature Fahr. |
| Span +————————-+————————-+————————-+
| in | 30° | 60° | 80° |
| Feet +————————-+————————-+————————-+
| | Sag in Inches |
+——————+————————-+————————-+————————-+
| 75 | 1¾ | 2½ | 3⅛ |
+——————+————————-+————————-+————————-+
| 100 | 3 | 4¼ | 5⅜ |
+——————+————————-+————————-+————————-+
| 130 | 5⅛ | 7 | 8⅝ |
+——————+————————-+————————-+————————-+
| 150 | 6¾ | 9 | 11¼ |
+——————+————————-+————————-+————————-+
=Ques. How is the wire drawn out?=
Ans. In drawing out the wire, it is customary to use a wire clamp, or
"come along." This tool is attached to a block and tackle, or drawn in
by hand, and, as soon as the proper force has been applied, the wire is
held, while the lineman secures it to the insulator.
[Illustration: FIG. 958.—Lineman's block and fall with "come alongs"
for stretching wire and holding same when making splices.]
[Illustration: FIGS. 959 and 960.—Approved method of attaching wire to
an insulator; elevation and plan of insulator and tie. The line wire is
first laid in the groove of the insulator, after which a short piece of
the same size of wire is passed entirely around to hold it in place,
then it is twisted to the line at either side with pliers.]
Another contrivance for this purpose is the pole ratchet, by
which the wire is drawn tight and held until attached to the
pole.
=Ques. How are the wires attached to the insulators?=
Ans. An approved method is shown in figs. 959 and 960. Standard rules
specify that all wires shall be tied to the side of the insulators
toward the pole, except on the insulators next to the pole, where they
are to be attached on the opposite side. On curves, however, it is
required that all wires shall be arranged so that the strain shall be
against the insulator and not on the wire.
[Illustration: FIG. 961.—American wire joint. This is a simple method
of connecting the ends of the sections of wire by tightly twisting the
ends around each other for a few turns; it is _the standard Western
Union_ wire joint.]
[Illustration: FIGS. 962 and 963.—McIntire sleeve and sleeve joint.
An approved method of making the joints of telephone lines is by the
use of some form of sleeve, such as is shown in fig. 962. This consists
of two copper tubes of the required length, and of sufficient inside
diameter, to admit the ends of the wires to be joined, fitting tightly.
The tubes are then gripped with a tool, shown in fig. 964, and twisted
around one another, so that the wires are securely joined and locked,
as shown in fig. 963.]
=Ques. How are the wires spliced?=
Ans. There are several methods of splicing wires. Fig. 961 shows the
American wire joint, and fig. 963 the McIntire sleeve joint. In making
a joint, the two ends are gripped by come alongs and drawn up to the
proper tension with tackle as shown in fig. 958. The joint is then made
as shown in the illustrations.
=Transpositions.=—In some classes of circuit, as for instance
telephone lines, the current is often seriously affected by
electrostatic induction from other lines, and also from power circuits,
owing to the fact that the surfaces of the wires form, as it were, so
many charging plates of an electrical condenser, with the intervening
air as the insulating layer or dielectric.
[Illustration: FIG. 964.—McIntyre's twisting clamp for wires 00 to 16
B. & S. gauge.]
[Illustration: FIG. 965—Method of making a "transposition." This is
usually done by means of _transposition insulators_, which are either
double insulators, one being screwed to the pin above the other, or
else such caps as are shown in fig. 967. Such insulators are intended
to act as circuit breakers, the particular wire to be transposed being
cut and "dead ended," or tied around, on both the upper and lower
grooves of the cap. The free end of each length is then passed back and
around the insulator and twisted, or sleeve jointed to the other limb
of its own circuit.]
The telephonic current changes the pressure of its own charging
surface as frequently as it alternates, and this fact in itself is
amply sufficient to account for a vast weakening of the current
before it reaches its destination. The only practicable method of
overcoming this annoyance in pole lines is by the arrangement known as
"transposition," which is, briefly, _the practice of regularly shifting
the relative position of the two limbs of each circuit as regards other
wires in the same pole system_, as shown in fig. 965.
For short lines and pole systems with only a few wires it is
not necessary to transpose very frequently. On longer lines
it has been found amply sufficient to transpose once every
quarter mile; that is to say to change the relative position
of the wires of the different circuits at posts situated about
that distance apart. This does not mean, however, that each
pair of wires is transposed so often, but that on ordinary
sized systems, the transposition of some one circuit is amply
sufficient to secure balanced relations and effectually
counteract the effects of cross induction. It is a matter which
must be carefully calculated and planned in each particular
instance in order to secure the best advantages.
[Illustration: FIG. 966.—Telegraph and telephone line glass insulator.]
[Illustration: FIG. 967.—Type of insulator used in making a
transposition.]
=Insulators.=—Glass and porcelain are employed almost universally
for supporting overhead wires. Insulators made of these materials are
superior to those made of other material such as hard rubber, or
various compounds of vegetable or mineral matter, with the exception
perhaps of mica insulators used on the feeders of electric railway
lines.
[Illustration: FIG. 968.—Tree insulator. This type of insulator is
especially useful in connection with temporary or repair work, or where
the wires pass through trees having numerous branches. The illustration
shows a Cutler tree insulator lashed to the trunk of a tree. It is
made of a single piece of glass, and is provided with a slot which the
wire cannot leave accidentally. The back of the device is concave and
provided with ribs which prevent sliding. It can be readily slipped
over wires already in place, is available for electric light circuit,
and will take wires up to ½ inch, in diameter.]
[Illustration: FIGS. 969 and 970.—Overhead cable construction. In some
cases, particularly on short lines exposed to inductive disturbances
from power and other electrical circuits, it is usual to string the
cables on poles such as usually carry the bare conducting wires. It is
not necessary, however, to insulate the cable in any way; consequently
it is merely hung to a supporting wire rope or cable, called the
"messenger wire," being attached either with some form of hanger,
such as is shown in figs. 969 and 970, or by loops of tarred marline.
The marline is sometimes wound over the cable and messenger wire from
a bobbin, but frequently it is merely wound on by hand. Cables used
in such overhead construction consist of bundles of wires, the pairs
twisted together. The size most often used is No. 19, B. & S., which is
about .03589 inch in diameter, weighs 20.7 pounds, and has a specific
resistance of about 8 ohms to the mile.]
Glass insulators are generally used on low tension lines, and porcelain
insulators on high tension lines, the latter type being usually
stronger and less brittle. Porcelain is more expensive than glass, and
its opacity prevents the detection of internal defects which would be
readily observed through glass.
[Illustration: FIG. 971.—Clark's "antihum;" a device designed to
prevent the humming of telegraph wires.]
=Ques. What is a petticoat insulator?=
Ans. An insulator which has one, two or three deep flanges or
"petticoats" around the base for the purpose of increasing the leakage
path from the line to the pin.
Both glass and porcelain insulators may be the double or triple
petticoat type which may be cast or moulded solid, or made in
two or more parts which are subsequently cemented together.
=Service Connections and Loops.=—Whenever it is necessary to tap an
overhead conductor for service connection, the method of connection
will depend upon the character of the circuit. In the case of a
parallel circuit, an extra insulator must be placed on the cross arm
so as to prevent the service main putting a side strain on the main
line conductor. In the case of a series circuit the main line conductor
is usually dead ended at the nearest pole and a loop taken to the point
of service, as shown in fig. 972.
[Illustration: FIG. 972.—Method of making a series "loop" service
connection.]
[Illustration: FIG. 973.—Parallel service connection. Service wires
tapped to the main wires, are run to insulators on an auxiliary cross
arm, thence to insulators on the side of the building, and through the
drain tube to the service switch.]
[Illustration: FIG. 974.—Joint pole crossing, showing wires of two
lines crossing each other. Four guard wires (shown heavier than the
others) extend for one span either side of the joint pole parallel to
the wires of the lower circuits and protect them from contact in case
of a break in the wires of the upper circuits. These guard wires are
insulated. The minimum distance between high and low tension wires
should be three feet. Five is better. The end guards, which prevent
wires slipping off ends of cross arms and dropping on the lower wires,
should extend about six inches above the level of transmission line.]
=Ques. What are service wires?=
Ans. Wires which enter a building.
CHAPTER XL
UNDERGROUND WIRING
In large cities, the best method of running wires for all varieties of
electrical power transmission is to place them underground. Many city
authorities have made this method of wiring compulsory by law, because
of the difficulty in approaching a burning building, the danger from
crossed and falling wires, and the disfigurement of the streets where
there is a network of overhead wires.
The expense of installing an underground system is very great in
comparison with that of overhead construction, but the cost of
maintenance is much less and the liability of interruption of service
greatly reduced.
=Underground Systems.=—An underground system of electrical conductors
is composed of three essential elements:
1. The conductor itself, which is almost invariably of copper;
2. The insulation, which is either in the form of a complete covering
of insulating material, or simply insulated supporting points;
3. The tube or conduit, which constitutes the mechanical protection
against the effects of the severe shocks, weather conditions, etc., to
which the system is naturally exposed.
The various underground systems may be divided into three classes:
1. Lead encased cables laid directly in the ground;
2. Solid or built in systems;
3. Drawing in systems.
=Ques. What may be said of the first mentioned construction?=
Ans. Where cables are laid directly in the ground, the metallic
covering, consisting usually of a lead tube, which is placed over the
insulation is depended upon for mechanical protection. Such cables are
largely used for short private lines and the first cost is less than
that of the others, but in case of repairs it has to be dug up.
=Ques. Describe the drawing in system.=
Ans. In this construction the cables are drawn in after the conduits
are built. The conduit of the drawing in system may consist of various
forms of pipe or troughs of iron, earthenware, concrete, wood or fibre,
while those of the solid or built in systems are composed of either
iron tubes or concrete trenches.
=Conduits.=—The principal qualifications of a good conduit are freedom
from disintegration by the action of fire, water, acids, alkalies, or
electrolysis; second, a smooth interior surface so as to permit of the
easy drawing in of the cables; and third, a design which will permit
of its economical installation in crowded streets. There are numerous
kinds of conduit of which may be mentioned:
1. Vitrified clay pipe conduits;
2. Vitrified clay or earthenware trough conduits;
3. Concrete duct conduits;
4. Wooden duct conduits;
5. Wooden built in conduits;
6. Wrought iron or steel pipe conduits;
7. Cast iron pipe and trough conduits;
8. Fibre conduits.
[Illustration: FIG. 975.—A few forms of vitrified clay pipe conduits;
view showing single and multiplex types. The dimensions of each duct
are about 3½ × 3½. The lengths vary from two to three feet.]
=Vitrified Clay Pipe Conduit.=—Various forms of vitrified clay
conduit appear to possess the qualifications, desirable in underground
construction, to a higher degree than any other type. They are made in
both single and multiple duct, as shown in fig. 975, the single type
being about 3½ inches in diameter, or 3½ inches square, and 18
inches long. Multiple conduit is made in two, three, four, six and more
sections, ranging from 2 to 3 feet in length.
=Ques. For what conditions is the single conduit especially adapted?=
Ans. It is most suitable for use where the sub-surface conditions are
characterized by a great crowding of gas, water, and other pipes, as
the conduits can be divided into several layers so as to cross over or
under such pipes, and many other sub-surface obstructions which are
present in the streets of large cities and towns.
=Ques. What are the features of the multiple duct conduit?=
Ans. It can be laid somewhat cheaper than the single duct type,
especially in lines of about two to four ducts; it is, therefore,
most suitable for use in outlying communities where the streets are
comparatively free from many sub-surface obstructions.
=Ques. How is the conduit laid?=
Ans. In laying conduit, a trench is dug, usually sufficiently wide
to allow the placing of three inches of concrete on each side of the
ducts, and sufficiently deep to hold at least thirty inches of concrete
on top of the upper layer of concrete forming the conduit, and to
allow for three inches of concrete in the bottom. The trench is graded
from some point near the middle of the block to the manhole at each
intersection, or from one manhole to the next manhole, at a gradient
not less than 2 inches to 100 feet.
=Ques. How are single duct conduits laid?=
Ans. The tiles of the several ducts are placed close together, and
the joints plastered and filled with cement mortar consisting of one
part of Portland cement to one part of sand. When the conduit is being
laid, a wooden mandrel about four or five feet long, three inches in
diameter, and carrying a leather or rubber washer from three to eight
inches larger at one end is drawn through each duct so as to draw out
any particles of foreign matter or cement which may have become lodged
in the joints, and also to insure good alignment of the tiles, as shown
in fig. 977.
Single duct conduits are usually laid by bricklayers. This fact
accounts for the somewhat greater cost of the single over the
multiple conduit which is usually laid by ordinary laborers.
One good brick-layer and helper, however, will lay from 200 to
300 feet of single duct conduit per hour.
Practically the same standard of construction is maintained
on all conduit lines from two ducts up to twenty-five ducts,
as many of the smaller lines may extend for miles into the
outlying districts, and contain transmission lines of the
maximum working voltage.
[Illustration: FIG. 976.—Vitrified clay or earthenware trough conduit;
this type of conduit consists of troughs either simple or with
partitions, the latter type being shown in the figure.]
=Vitrified Clay or Earthenware Trough Conduit.=—It consists of troughs
either simple or with partitions as shown in fig. 976. They are usually
made in tiles 3 or 4 inches square for each compartment, with wall
about one inch thick. The length of the tiles ranges from two to four
feet. Each of the two foot form duct troughs weighs about 85 pounds.
When laid complete, the top trough is covered with a sheet of mild
steel, about No. 22 gauge, made to fit over the sides so as to hold it
in position, and then covered over with concrete.
=Joints in Multiple-duct Vitrified Clay Conduit.=—In laying multiple
duct earthenware conduit, the ducts or sections are centered by means
of dowel pins inserted in the holes at each joint, which is then
wrapped with a six inch strip of asphalted burlap, or damp cheese
cloth, and coated with cement mortar as shown in fig. 978. Economy of
space and labor constitutes the principal advantages derived from the
use of multiple duct conduit.
[Illustration: FIG. 977.—Method of laying single duct vitrified clay
conduit. The tiles of the several ducts are placed close together as
shown in the figure, and the joints plastered and filled with cement
mortar consisting of one part Portland cement and one part sand.]
=Concrete Duct Conduits.=—These are usually constructed by placing
collapsible mandrels of wood or metal in a trench where the ducts
are desired and then filling the trench with concrete. After the
concrete has solidified, the mandrels are taken out in pieces, leaving
continuous longitudinal holes which serve as ducts. Some builders
produce a similar result by placing tubes of sheet iron or zinc in the
concrete as it is being filled into the trench. These tubes have just
enough strength to withstand the pressure to which they are subjected,
and are, therefore, very thin and liable to be quickly destroyed by
corrosion, but the ducts formed by them will always remain unimpaired
in the hardened mass of concrete.
=Wooden Duct Conduits.=—In this type of conduit, the ducts are formed
of wooden pipe, troughing, or boxes, and constitute the simplest and
cheapest form of conduit. A pipe conduit consists of pieces of wood
about 4½ inches square, and three to six feet long, with a round
hole about three inches in diameter bored through them longitudinally.
As shown by fig. 979 a cylindrical projection is turned on one end of
each section, which, when the conduit is laid fits into a corresponding
recess in one end of the next section. The sections are usually laid in
tiers, those of one tier breaking joint with those of the tiers above
or below.
[Illustration: FIG. 978.—Method of laying multiple duct vitrified clay
conduit. The sections are centered by the dowel pins shown in the cut.]
The trough conduit consists of ducts about 3 inches square made of
horizontal boards and vertical partitions, usually of yellow pine about
one inch in thickness. This form of conduit can be laid in convenient
lengths of 10 or 12 feet, or it can be built along continuously.
=Ques. What is the objection to the use of wood for conduits?=
Ans. The decay of the wood tends to form acid which corrodes the lead
sheath of the cable.
[Illustration: FIG. 979.—Wooden pipe type of conduit. It consists of
pieces of wood about 4½ inches square, and three to six feet long,
with a wide hole about three inches in diameter, bored through them
longitudinally.]
=Ques. How can this be prevented?=
Ans. The decay of the wood can be prevented to a certain extent by the
application of sterilizing processes, thereby preserving it in fairly
good condition for about ten to fifteen years.
=Ques. For what service is wooden conduit best adapted?=
Ans. For temporary installations which will be discontinued before the
wood decays.
=Wooden Built-in Conduits.=—Within recent years several forms of
wooden built-in conduit have been designed and successfully used for
permanent work. They possess several advantages over any of the duct
systems, the chief of which are high insulating quality, the capability
of using bare wire and rods for underground conductors, and reduced
cost. An approved form of wooden built-in conduit is shown in fig. 980.
[Illustration: FIG. 980.—Perspective view of wooden built-in conduit.
It consists of an outer rectangular casing of wood which is lined
inside with impregnated felt.]
=Ques. How are wooden built-in conduits installed?=
Ans. A wooden trough is laid in a trench about 18 inches deep.
Porcelain carriers as shown in figs. 981 and 982 are placed in the
trough at intervals of 4 to 5 feet, to act as bridgework for supporting
the conductors. This bridgework is placed on and is surrounded by
impregnated felt or similar material, and the spaces between the
carriers, after the conductors have been placed in position on them, is
filled with voltax, which hardens rapidly and forms a solid insulating
material throughout the conduit.
=Wrought Iron or Steel Pipe Conduits.=—These are formed of pipes
similar to gas or steam pipes, with screw or other connections. They
are laid either simply in the earth, or in hydraulic cement, and are
the strongest and one of the most satisfactory forms of underground
conduit. An appropriate standard of this kind of work is shown in fig.
983.
[Illustration: FIGS. 981 and 982.—Porcelain bridgework or carriers for
supporting underground conductors.]
=Ques. What is the ordinary method of construction?=
Ans. A trench, the width of which will depend upon the number of pipes
to be laid, is first dug in the ground, and after its bottom has been
carefully leveled, is braced with side planking and filled to the
depth of two to four inches with a layer of good concrete, consisting
of two parts of Rosendale cement, three parts of sand, and five parts
of broken stone capable of passing through a one and one-half inch
mesh. This concrete is well secured in place and forms the bed for
the lowermost layer or tier of pipes. Ordinary wrought iron pipe is
employed, in 20 foot lengths about three to four inches in diameter,
depending upon the size and number of cables they are intended to
carry. After the last tier of pipes have been put in place, and a layer
of concrete from two to four inches placed over it, a layer of two inch
yellow pine planking is laid over the whole.
[Illustration: FIG. 983.—Cross section of wrought iron pipe conduit
laid in hydraulic cement.]
The pipe connections consist of a taper screw thread coupling
which can be easily made up as the pipes are laid, and which
forms a tight joint.
The pipes in each tier are usually laid from ½ to ¾ of
their diameter apart, and when the first tier is in place, the
spaces between and around the pipes are filled in with concrete
which is carried up over the pipes to a depth of about one-half
a diameter to form the bed for another tier of pipes.
=Ques. What is the principal object of the top covering of planks.=
Ans. To protect the conduit against the tools of workmen making later
excavations.
Practical experience shows that workmen will dig through
concrete without stopping to investigate as to the character
of the obstruction, but under similar circumstances, will
invariably turn away from wood.
=Ques. How are the pipes treated before being laid?=
Ans. They are dipped in tar to protect the outside surface from rust.
=Ques. What is the most satisfactory form of lined iron pipe?=
Ans. Pipe lined with cement. The internal surfaces of these pipes are
usually covered with a lining of pure Rosendale cement about ⅝ inch
thick and containing no sand. The internal surface of the cement lining
does not offer much friction to the introduction or withdrawal of the
conductors.
These pipes are laid in cement or concrete in the same manner
as plain iron pipe, and are given a coating of tar on the
outside to prevent rusting.
=Cast Iron Pipe and Trough Conduit.=—Cast iron pipe for underground
conduits is similar to ordinary wrought iron pipe, except that it is
thicker. The additional thickness is necessary to make the strength
equal to that of wrought iron; it is therefore heavier to handle and
more expensive.
=Ques. Describe a cast iron trough conduit.=
Ans. It consists of shallow troughs of cast iron in six foot lengths,
laid directly in the earth so as to form a system of continuous
troughing in which the conductors are placed and then covered over by
cast iron covers which are bolted to the trough.
=Ques. What advantages does this form of conduit possess over the duct
type?=
Ans. First, the cables can be laid directly in place, thus eliminating
any chance of injury during the process of drawing in, and second, the
cables are easily accessible at any point by simply removing one or
two of the sectional cast iron covers, thus permitting of their being
readily inspected and repaired.
[Illustration: FIG. 984.—Fibre conduit. It consists of pipes made of
wood pulp, having about the same thickness as cast iron pipe. Slip
joint conduit for electrical subways is three inches inside diameter.
The socket joints keep the lengths centered and make it easier to lay
than a mere butt joint. It is laid in cement like iron pipe.]
Branch connections can be made with greater facility than in
the case of any duct system, so that it is especially suitable
for distribution systems were it not for the fact that it is so
expensive as to be practically prohibitive.
=Fibre Conduits.=—This form of conduit consists of pipes made of
wood pulp impregnated with a bituminous preservative and insulating
compound. These pipes are laid in concrete in a manner similar to iron
pipe. Fibre conduits are made in sizes ranging from 1 inch to 4 inches
in diameter and from 2½ to 5 feet in length, with walls ranging from
¼ to ½ inch in thickness.
=Ques. Name the three types of fibre conduit.=
Ans. The socket joint type, as shown in fig. 984, the sleeve type, fig.
985, and the screw joint type, fig. 986.
=Ques. What is the usual method of laying the socket joint type of
fibre conduit?=
Ans. After the trench has been dug to the required width and depth,
depending upon the number or pipes to be placed in a tier and the
number of tiers, a bed of concrete about 3 inches deep is placed on
the bottom and a line drawn on one side for the alignment of the first
line of pipes. The other lines of pipe or ducts are laid parallel to
the first line, and are separated from it and from each other by means
of ¼ inch or ½ inch wooden or iron pegs. The pipes are well grouted
and covered with a layer of concrete to the depth of ¼ or ½ inch,
and the next tier laid in place in the same manner. When the final tier
of pipes has been installed, it is covered with a layer of concrete
about 2 to 3 inches deep.
[Illustration: FIG. 985.—Sleeve joint type of fibre. Both the socket
type (fig. 984), and the sleeve type here shown are easily aligned
without the use of a mandrel.]
=Ques. What is done when it is necessary to cut a length of pipe to
break joints, or to enter a manhole?=
Ans. The remaining part of the length may be utilized by using a fibre
conduit sleeve having an inside diameter ½ inch greater than the pipe
being used on the system.
These sleeves are furnished by the manufacturers at a nominal
charge per foot. They are about four inches in length and fit
over the ends of the abutting pipes, so that they make tight
joints and give perfect alignment.
Although its employment is not permitted where fireproof
regulations are in force, fibre conduit is now being
extensively used in other places, and is giving satisfactory
service. It is not affected by moist earth and is impervious
to the action of acids, alkalies, and gases. As it is not
subject to expansion and contraction, leakage is practically
eliminated, and since it is a very good insulator, troubles due
to stray currents are reduced to a minimum. It is extremely
light, comparatively non-breakable, and can be accurately laid
at the rate of 12,000 duct feet per day by a gang of common
laborers, consisting of two layers and three helpers.
[Illustration: FIG. 986.—Screw joint type of fibre conduit. This
method of connection will form a tight line and is suitable for running
under the lawns of private houses and parks, under the streets of towns
and villages, and in other places where the cost of building electric
subways is prohibitive.]
=Edison Tube System.=—Of the various built in or solid underground
conduit systems other than those already described under wooden conduit
systems, the most satisfactory are the Edison tube system, the Crompton
naked conductor system, the Kennedy system, which is a modification of
the Crompton and the Callender systems.
=Ques. Describe the Edison tube system.=
Ans. It consists of a series of iron tubes or pipes containing one or
more copper conductors which are placed therein before each complete
section or pipe leaves the factory, so that they only need to be
joined together to form a continuous line of underground conduit with
conductors in place. The arrangement of wires and the details of the
Edison tube system are shown in figs. 987 to 989.
[Illustration: FIG. 987.—Cross section of Edison "feeder" tube.
This runs from the power station to the centers of distribution, and
contains two principal conductors and a smaller conductor to serve as
a neutral wire, and also three insulated cables of seven strands of
No. 19 B. W. G. wire each. These cables form independent circuits and
enable the voltages at the distant end of the feeder to be read at the
central station. For this reason they are commonly called pressure
wires.]
=Underground Cables.=—Electric light and power cables for use in
conduit may be divided into two classes: _moisture proof_, and
_non-moisture proof_, according to the character of the insulator. In
the moisture proof cables, the insulation consists of some form of
rubber, or of bitumen, and a metal sheath or covering, usually of lead,
is provided to protect the cable from mechanical or chemical injuries.
The non-moisture proof cables are insulated with paper impregnated with
oil, wax, or resinous compounds.
[Illustration: FIG. 988.—Cross section of Edison "main" tube. A number
of these tubes, which radiate from the center of distribution and loop
the ends of the feeders together, have three conductors of the same
size. These tubes are placed in the ground so as to bring the positive
and negative conductors on one side of the center of the tube, and the
neutral conductor on the other side. The mains are always laid with
the neutral conductor adjacent to the curb line, and for convenience
this side of the tube is commonly called the _inside_. The feeders are
always laid with the positive conductor on the right hand side, as
shown in fig. 989.]
=Metal Sheaths on Underground Cables.=—Metal sheaths are used on
rubber covered cables to protect the insulating compounds from the
deteriorating effects of electrolysis and various kinds of acids and
gases which, under present methods of construction, are ever present
in the underground conduits. It is a fact, however, that the lead
sheath on a low tension cable, which is used as one side of a grounded
circuit, has been, in some cases the cause of, instead of, cure for
electrolysis. The proper cure lies in the omission of the sheath
altogether, but as this is not practical except in the case of very
large conductors, the best thing that can be done is to interrupt the
continuity of the sheath by some form of insulating joint.
[Illustration: FIG. 989.—Method of laying Edison underground tube
system. The tubes are laid in trenches about 30 inches deep and 20
inches wide at the bottom, each trench usually containing two lines of
pipes—a _main_ adjacent to the curb and a _feeder_ on the outside. The
copper rods forming the conductors are uniformly 20 feet, 4 inches in
length and project from 2 to 3½ inches from each end of the pipes,
which are connected together by means of coupling boxes. The coupling
box usually employed consists of a two part egg shaped casting into
which the ends of the pipes enter through water tight sleeves at the
opposite ends of the oval. The projecting ends of the copper conductors
are joined by short pieces of flexible cable with sockets on each end,
which are drilled to fit easily over the conductor rods to which they
are thoroughly soldered in order to make a perfect electrical joint.
After the conductors have been thus properly connected the cover is
bolted down on the lower half, and the whole of the interior of the box
is filled with insulating compound through the small hole at the top
of the cover, thereby completely insulating the copper conductors, the
cable connectors, and the ends of the tubes. Finally, the hole in the
cover is closed with a cast iron cap. These coupling boxes are also
made in the form of tees for making branch connections, and in the form
of elbows for turning corners, the ball ends attached to the tubes and
the sockets into which they fit being designed to permit of variation
in direction through an arc of 18 degrees on either side of the central
position. _Services_ or branches to the consumers' premises consist
of short lengths of tube which tap the mains by means of three way or
four way service boxes, the latter readily permitting the taking of two
services from one joint. Services are never taken from the feeders, but
the latter are brought to distributing boxes containing three copper
rings to which the conductors are connected and branched out to one or
more mains which are led out through fuses to supply the districts.]
=Pot Heads.=—The upper end of a lateral cable is equipped with a
discharge bell, which is commonly called a pot head. The purpose of
a pot head is to hermetically seal the end of the cable and bring
the conductors out in such a manner as to permit of their being
conveniently connected to the primary service boxes.
[Illustration: FIG. 990.—Bottom of General Electric manhole junction
box; view from manhole interior. The cables enter the bottom of the box
as shown through composition nozzles to which the lead sheathes are
united by a wiped solder connection, forming a permanent water and gas
tight joint. Stuffing boxes are sometimes substituted, doing away with
the wiped joint, rendering the boxes suitable for use with unleaded or
braided cables. The normal position of the distributing cables is in
the upper ducts so that they may be brought to the junction box without
crossing other lines. The entrance nozzles and seats are so arranged
that all terminals are soldered to cables outside of box and any cable
may be removed without disturbing any soldered joint. The wiped joints
unite electrically the lead sheathes of all cables entering the box and
by connecting a single earth bond to the shell of the box all cable
sheathes are solidly grounded. Incombustible shields prevent the arc
from a blown fuse making a ground connection to the shell or inner
cover.]
=Ques. How are pot heads made?=
Ans. They are usually made in three parts, the base being of cast
brass, having a diameter depending upon the size of the conductors,
with a hole in the lower end threaded within in such a manner as to
make a tight fit on the cable.
=Ques. How is a pot head connected to a cable?=
Ans. After the cable has been bent in to the proper position, the brass
base is slipped down over it with the larger end up, and then screwed
down on the lead sheath. The threads cut down into the lead sheath to a
distance of about ½ inch along the sheath, thus making an air tight
connection without necessitating the making of a wiped joint.
The separate conductors are now bared of their insulation for
a distance of about two inches, and then spliced to heavy
rubber covered braided wire of sufficient length to reach the
primary service boxes. The joints connecting these rubber
covered wires and the cable conductors are spliced in the
same manner as straight splices, the paper sleeves used being
of sufficient diameter to be backed out of the way over the
rubber insulation. When the splice is completed a brass shell
threaded at one end to fit a female thread in the upper end of
the brass base, is slipped over the end of the rubber covered
wire and screwed into the base. A hood of sheet copper having
the form of a quarter section of a ball is slipped over the top
of the frame and its lower edge tracked in position below the
horizontal shelf. This hood makes the pot head water, snow, and
insect proof.
CHAPTER XLI
WIRING OF BUILDINGS
In laying out the circuits for a dwelling house, the cut out cabinets
should be located first. In many houses only one cut out cabinet is
necessary, but in large houses it is convenient to have one on each
floor, with vertical mains running through them from the top to the
bottom of the house.
If only one distributing point be used, it should be either in the
cellar or attic and risers run to the different floors.
=Ques. How should the distributing centers or cut out cabinets be
located?=
Ans. They should be installed near a partition that is so located as
to make the running of risers easy, and should be on an inside wall to
guard against dampness.
=Ques. What instructions are usually given the electrician who does the
wiring?=
Ans. In many cases simply a plan showing the location and number of
lights, from which he must figure out how to install them using the
least amount of material and labor consistent with a good installation
that will pass inspection.
=Ques. What provision should be made in rooms where lamps are suspended
from the ceiling?=
Ans. A switch should be placed at a point where it will be convenient
for any one entering to turn on the light.
=Ques. Where are receptacles usually placed?=
Ans. In the baseboard.
A receptacle is a convenient device which permits any one to
connect a lamp to the electric lighting system by inserting a
plug which is connected by flexible cord to the lamp.
[Illustration: FIG. 991.—Ceiling button. If a lamp be needed not more
than 3 feet from the direct line of the wires, it can be hung where
required by means of a _ceiling button_, as shown in the figure, but
the lamp cord must not be used to run lamps in this way more than two
or three feet from the rosette.]
=Ques. What provision should be made in wiring a hallway?=
Ans. The switching arrangement should be so designed that the lights
may be turned on or off either from the hall or floor above.
=Ques. What is this arrangement called?=
Ans. _A two way switch_, as shown in fig. 992.
=Ques. How can a two way switch be distinguished?=
Ans. It has three binding screws, two on one end and one on the other.
[Illustration: FIG. 992.—Two way lighting circuit permitting control
from two points. This is the usual arrangement for hall when it is
desired that the lights may be turned on or off from either floor. The
circuit contains two two way switches connected by "travellers." From
the diagram it is seen that the light may be controlled from either
switch. It is a bad arrangement to have travellers and return wire
located near each other, as it is possible by this method to connect
two individual circuits together and possibly overload one of the two
feed wires of each circuit. However, should each feed wire run to a
fuse direct, without any other lamps than those contained in the three
way circuit being connected, it is not objectionable and becomes a
convenient method in many cases.]
[Illustration: FIG. 993.—Four way lighting circuit, permitting
control from three points. This arrangement consists of a four way
switch connected between two two way switches as shown. In making the
connections it should be noted that the travellers connecting one side
of the four way switch to the two way switches should be crossed. On
the opposite side of the four way switch, the connections are direct.
For the various positions of the switches, the corresponding circuits
through them are as follows: ABDGHJ—ABDEIJ—ACFGHJ—ACFEIJ.]
=Ques. How may a group of lights be controlled from three points?=
Ans. By the use of a 4 way switch and two 2 way switches connected as
shown in fig. 993.
=Ques. Before laying out the wiring system for a building, what should
be done?=
Ans. It is necessary to ascertain whether power will be supplied from
the central station, or whether a private plant is to be installed.
[Illustration: FIG. 994.—Two wire multiple system as used with
isolated plant.]
=Ques. What wiring system should be used with a private or isolated
plant?=
Ans. The two wire multiple system as shown in fig. 994.
=Ques. When the central station is to supply power as an auxiliary in
case of break down, how should the connection be made?=
Ans. The supply from the central station should be connected to the
wiring system through a double throw switch, as in fig. 995, so that
either source may be thrown into circuit.
=Ques. How are the connections made when the auxiliary supply is
brought in through a three wire system?=
Ans. A double throw three pole switch is used as shown in fig. 995.
[Illustration: FIG. 995.—Double throw switch for use in isolated
plants when auxiliary power is used from the central station in case of
breakdown.]
=Ques. When power from an outside source only is to be used what must
be determined before wiring?=
Ans. The system of wiring of the supply. If a three wire system be
used, the general arrangement will be as shown in fig. 997.
[Illustration: FIG. 996.—Double throw three pole switch for use in
isolated plants where auxiliary power is brought in through three wire
system. The side of the switch controlling the current is bridged as
shown.]
=Ques. Would it be expensive to change a regular three wire system to a
two wire system?=
Ans. It would require the reinforcement of all mains and feeders by an
additional wire. This wire would be connected with the neutral wire so
as to make the capacity of the neutral equal to the sum of the other
two. If a three wire two wire system had been originally installed, no
change in the wiring system would be necessary. The only change would
be at the service end of the switchboard, and the doubling of the size
of the center fuses.
[Illustration: FIG. 997.—Three wire convertible, or three wire
two wire system; used to advantage where power is supplied from an
outside source and brought in through the three wire system. The only
difference between the three wire convertible, and the straight three
wire system is that the center, or neutral, wire of the mains and
feeders should have a current capacity equal to the other two. The
reason for this is that it allows the system to be readily changed
over to a two wire system for use in connection with a private plant.
It sometimes happens that after using power from the local electric
illuminating company for some time, conditions arise which make it
expedient for the owners to install a private electric plant. If a
straight three wire system had been originally installed, the mains and
the feeders when used on a two wire system would not be heavy enough
by 25 per cent., as the neutral wire of a straight three wire system
is the same in size as one of the two outer wires, and theoretically
carries one-half the current or less.]
=Ques. Is a three wire system desirable with an isolated plant?=
Ans. It is more expensive to install than one for a two wire system, as
it is necessary to add a balancer in connection with a 240 volt dynamo.
This balancer set should have one-tenth the capacity of the plant. Such
an equipment has its advantages when 240 volt motors and 120 volt lamps
are connected to the system. With this plant no changes in the motors
are necessary, whereas in a straight 120 volt system, the motors would
have to be changed from 240 to 120 volt machines.
[Illustration: FIG. 998.—Diagram showing reinforcement of neutral
wire necessary to change regular three wire system to two wire system.
The capacity of the neutral wire must equal that of the sum of the two
other wires.]
=Ques. After deciding on the system of wiring to be used, how should
the electrician proceed with the work?=
Ans. He should lay out the mains, feeders and branches of the wiring
system. The outlets are first located and then the distributing
centers. There is no fixed rule or plan by which to go, but the current
density and source of supply are the main points to be considered in
locating these centers. He must also consider the construction of the
building and select runways and shafts which provide easy runs for
feeders.
=Ques. How should panel boards be placed?=
Ans. Panel boards in loft buildings or in any building requiring 8
to 10 circuits to a floor should be distributed one to a floor. In
private houses it is sometimes advisable to install only one panel for
the entire house. This is good practice for a three-story house not
requiring over twelve circuits.
[Illustration: FIG. 999.—Diagram showing current required on each
floor of building. A sketch of this kind is useful in laying out the
feeder system. In the building here shown it will be seen that the
basement and first floor require the most power. In such a case a
feeder is run for these floors, and a sub-feeder from the basement
to the first floor. It is not worth while to reduce the size of the
sub-feeder unless the amount of current used on the sub-feeder be a
small percentage of that used in the feeder. Another reason is that
in changing the size of a wire, the underwriters require a fuse to be
inserted. This makes it necessary to install a larger panel with larger
trim, etc., and the consequent expense easily offsets any gain made by
installing a smaller wire.]
In a building covering a large area it is often advisable to
install two panels or centers to a floor, with two sets of
feeders. It is advisable to keep circuit lengths down to 100
feet or less, and the judicious laying out of circuit centers
will save many feet of wiring.
=Ques. How should the arrangement of feeders for a large building be
determined?=
Ans. A good method is to draw an elevation of the building as in fig.
999, and note on each floor the current requirements.
The best plan is to furnish a feeder for every floor,
especially in large installations. In smaller installations one
or two feeders are sometimes all that are required.
[Illustration: FIG. 1,000.—Diagram showing arrangement of switches in
wiring system where provision is made that any circuit can be fed from
an outside source in case of overload or accident.]
=Ques. How should feeders for motors be installed?=
Ans. They should be independent of the lighting feeders.
=Ques. What is the largest size of feeder that should be used?=
Ans. Feeders requiring over 2 inch pipe should not be used. It is
better to subdivide them, especially if there be many bends or offsets,
since two inch pipe is about the limiting size for economical handling.
=Ques. How should feeders be arranged?=
Ans. They should radiate from a distributing panel, having a proper
sized switch and fuse for each feeder.
If the system of wiring be such that auxiliary power is taken
from a local lighting company, it is a good plan to have each
circuit controlled by a double throw switch so that in case of
overload any circuit can be fed from the illuminating company's
mains as in fig. 1,000.
[Illustration: FIG. 1,001.—Sectional view showing method of cutting a
pocket or opening in floor for the insertion of wires.]
=Ques. How should feeders and mains be run?=
Ans. It is advisable to install them in iron pipe even though the
circuit wires be run otherwise. Since the former carry the main supply
of current it is important to have them well protected as they usually
run up side walls.
The underwriters make numerous restrictions against open or
moulding work on brick walls and require good protection, and
this is an additional reason for piping the mains and feeders.
=Ques. How much load should be placed on the branch circuits?=
Ans. In laying out the branch circuits, it is not good practice to use
up the underwriters' circuit allowance of 660 watts.
[Illustration: FIG. 1,002.—View of outlet pocket showing base board,
and cover supports in position.]
If a circuit be wired with the full allowance of lamps, no
additions could be made without violating the underwriter's
requirements.
=Ques. If concealed wiring is to be installed in a finished building
what should be done first?=
Ans. The outlets should be marked on the ceilings and walls with a
pencil cross at the spot, marking also the location of switches, etc.
=Ques. If an outlet is to be placed at the center of a room, how is the
center of the ceiling located?=
Ans. It is first located on the floor, then transferred to the ceiling
by means of a plumb bob.
=Ques. What is the first operation in making a ceiling outlet?=
Ans. A small hole is bored through the ceiling and the bit pushed up
till it comes in contact with the flooring of the room above, this
flooring is also bored, as in fig. 1,001.
[Illustration: FIG. 1,003.—View of completed pocket and ceiling outlet
showing method of bringing out the wires.]
A long bit about ¼ inch in diameter and about 18 inches long
is used. The hole bored in the floor above will show where to
take up the board to install the wires.
=Ques. How is a pocket opened above the hole bored for ceiling outlet?=
Ans. One-quarter inch holes are bored to insert a keyhole saw through
the joint between two boards at each end of the pocket, and as near
the beams as possible, then the board is cut at an angle as indicated
in fig. 1,001. Having sawed across the board at both ends, it is pried
out with a chisel as shown.
=Ques. How are the holes bored through the beams for the tubes?=
Ans. They are bored about two inches from the top with a 9/16 inch bit,
slanting downward just enough to give clearance for the brace.
[Illustration: FIG. 1,004.—Device for examining partition interiors. A
pocket flash lamp and a little mirror are the only apparatus required
to inspect the interior of a wall or partition which would ordinarily
be inaccessible. For fishing wires, retrieving cable and inspecting
finished work, the lamp and mirror will be found most useful. The
mirror has only to be introduced in the outlet hole in the wall, the
flash lamp and eye being held behind it as illustrated. The mirror
reflects the light of the lamp onto the place to be illuminated, at
the same time reflecting the image back to the eye near the lamp. The
usefulness of this little device is as great as its simplicity.]
=Ques. How are the knobs fastened?=
Ans. Screws may be used but stout wire nails are satisfactory and are
inserted with less labor.
Leather nail heads are slipped on the nails to protect the
porcelain.
=Ques. How is a ceiling outlet completed after the work has reached the
stage shown in fig. 1,002?=
Ans. A baseboard is next installed as in fig. 1,003 to have a secure
hold for the screws used in fastening the fixtures. Two holes are then
bored diagonally with a 11/16 inch bit inserting the bit in the small
hole bored in the ceiling as in fig. 1,001. The outlet wires are then
tied around the knobs and the upper ends being bared and tapped on to
the main wire. A piece of loom is slipped on each outlet wire after
which it is thrust through the outlet as in fig. 1,003.
[Illustration: FIG. 1,005.—Plan showing one floor of a dwelling house
wired with conduits. The numbers on the various outlets indicate the
number of lamps supplied. The wiring is carried out on the loop system,
and it will be noticed that no branches are taken off between outlets.
Four circuits are used in order that there may not be more than ten
lamps on any one circuit.]
=Ques. How are the mains secured to the knobs?=
Ans. By taking a turn around the intermediate knobs and a dead end
hitch at the end knobs, or they may be hitched at each knob. The main
may be secured also by use of a tie wire.
=Ques. What is the difference between a splice and a tap?=
Ans. A splice is the joining of two wires at their ends; a tap is the
joining of the end of one wire with an intermediate point of another
wire.
[Illustration: FIG. 1,006.—Wiring for heating appliances in two story
house; plan of basement.]
=Ques. What precaution should be taken in making joints?=
Ans. All wires joined together should be soldered as this insures good
electrical contact.
Unsoldered wires are both unreliable and dangerous, since they
will corrode from dampness, thus increasing the resistance of
the joint so that it may become heated.
=Ques. How should joints be finished after soldering?=
Ans. They should be covered with rubber tape twisted tightly while it
is hot. When the rubber has melted it will adhere to the joint and
can be moulded with the fingers. Adhesive tape is then wound over the
rubber, the insulation thus being made equal to that which was removed
to unite the wires.
[Illustration: FIG. 1,007.—Wiring for heating appliances; plan of
first floor.]
=Wiring for Heating Appliances.=—There are now on the market a great
number of heating appliances which absorb such small amounts of energy
that they can be used readily on the lighting circuit. These appliances
include the coffee percolator, chafing dish, heating pad, small water
heater, cigar lighter and many other miscellaneous devices. By adapting
these smaller devices to the lighting circuit, not only is the cost of
wiring decreased, but the convenience and cleanliness of the electrical
system is secured.
[Illustration: FIG. 1,008.—Wiring for heating appliances; plan of
second floor.]
The location of the outlets for the heating appliances is not of the
least importance. For many purposes, the flush receptacle in the
baseboard of the room answers many requirements. In other places, for
instance, a receptacle placed beneath the bracket lamp in the bathroom
upon the same circuit as the lamp, is very convenient as a connection
for the electric shaving mug or the massage motor. Similarly, a
suitable outlet placed near the head of the bed is most convenient for
operating a heating pad as it does not necessitate unscrewing a lamp at
night.
The house illustrated in figs. 1,006 to 1,008 is an example of
the use of a single electric heating circuit with a restricted
use of the lighting circuit for heating purposes.
[Illustration: FIG. 1,009.—Diagram illustrating wiring with
combination of moulding, flexible tubing or conduit in non-fireproof
building, where wiring had not been originally installed. In such cases
the moulding may be run in a cornice in the hall. When objectionable to
have the work exposed in the rooms, taps may be made in the moulding
opposite each room and the circuit extensions from the moulding to the
center outlets in the rooms may be run in flexible conduit, fishing
the wires from the moulding to the ceiling outlet. The use of wooden
moulding in new buildings is not to be recommended for the reason
that it is not usually fireproof, and it would be better to run the
conductors concealed in some form of conduit; if the circuit work
were installed at the time the building is erected, it would cost but
little more than moulding, and would be much more substantial. In some
cases, however, wooden moulding might be provided in a new building on
the ceiling as a means of affording facilities for making connections
to outlets over desks, tables, etc., where it would be impossible to
locate the outlet exactly before the building was plastered. In such
cases, the moulding could be installed on the ceiling at a distance of
18 to 24 inches from the walls, forming a rectangle on the ceiling.]
[Illustration: FIG. 1,010.—Feeder system for large hotel. The cellar,
basement, and ground floors are supplied by separate feeders, because
of the importance of having continuous and uninterrupted lighting
service at these floors. The three distributing centers at the cellar
are supplied by a single feeder. Three of the eight distributing
centers at the basement floor serve to supply the outside lights, as
described above. The distributing center for the outside street lamps
is supplied by a separate feeder from the main switchboard. Five of
the distributing centers at the basement floor serve for the basement
lights only; they are fed by two separate feeders, one of which serves
two centers and the other three centers as shown. Each of the three
centers at the ground floor is supplied by a separate feeder. The
upper floors, from the first to the fourteenth inclusive, are divided
into two symmetrical sections. Each section has its own distributing
center, and its own set of supply feeders. The feeder terminates at
the middle center of a group of three, and is extended by mains to the
corresponding centers at the floors immediately above and below. Each
feeder from the first to the twelfth floor inclusive serves to supply
three distributing centers.]
As can be seen in the basement plan, the main supply circuit enters
the basement and from this the heating circuit and lighting circuits
branch, as shown by the arrows. The heating circuit runs direct to
the basement laundry, a branch running to the flat iron. Connections
are made with the kitchen on the first floor and with the dining room
by branch circuits running through the partitions to the respective
rooms. The heating circuit at the dining room is provided with flush
wall receptacles, to which connection is made for the chafing dish and
percolator.
In the kitchen the electric baking outfit is arranged as shown. This
electric outfit is used for auxiliary cooking, such as a gas range
would be, and the oven, placed by itself on the opposite side of the
coal range, is controlled from the main table.
Upstairs the heating circuit, upon which the dining room appliances
are operated, is extended to supply current to the electric luminous
radiator, either in the chamber or bathroom.
The arrangements for the lighting circuits are shown in the figures.
Landing and basement lights are controlled by three way switches to
make them convenient.
In the living room a flush floor receptacle is installed so that the
reading lamp, chafing dish or coffee percolator can be operated without
necessitating the use of a long cord. A few of the electrical outlets
suitable for the purposes mentioned are illustrated.
Where several heating circuits are used it is essential that an
appliance taking a large current be not placed on the regular lighting
circuit. To guard against this possibility, special receptacles should
be installed, constructed for plugs which will not fit any other
receptacle.
CHAPTER XLII
SIGN FLASHERS
The devices used for giving the flashing and changeable effects to
electric lights in any form are called "flashers." The mechanism may be
constructed to flash a sign by spelling the words out, one letter at a
time, flashing border lights around a window, changing colors in glass
signs, or in fact in any way to attract the eye.
There are two advantages in favor of using a flasher: 1, it causes the
passerby to look at the sign, and 2, reduces the cost of electricity,
because the lamps are switched off periodically.
There are numerous kinds of flasher, and they may be classified,
according to construction of the switch contacts, as:
1. Carbon type;
2. Brush type;
3. Knife type.
Again, with respect to operation or the electrical effects, they may be
classified as
1. Simple on and off flashers;
2. High speed flashers;
3. Lightning flashers;
4. Script breakers;
5. Chaser flashers;
6. Thermo flashers;
7. Carriage calls;
8. Talking signs;
9. Electric clocks.
[Illustration: FIG. 1,011—Dull's carbon type flasher. This is a
main line flasher; that is, it is set into the main wires instead of
carrying down each circuit. The circuits are opened and closed on
carbon contacts, reinforced with standard knife switches. The blades
are opened and the current broken by gravity alone. Each switch can be
made to hold the lights for any period from 18% to 81% of a revolution
of the shaft. They can throw on the circuits progressively or all on
and all off together. Again, the circuits may be closed progressively,
remain on a few seconds, and then be opened progressively. No circuit
or circuits can be closed more than once per revolution.]
=Carbon Flashers.=—In this type of flasher, carbon breaks are
provided, that is, the arc which is formed when the circuit is broken,
falls on carbon, while metal switches are provided to carry the load.
Thus the carbon gets the arc which prevents the switches burning, while
the switches carry the load to prevent the carbons becoming heated and
disintegrated. The carbons must be adjusted occasionally according to
the load they are carrying. Carbon machines are made either double,
triple, or series break.
[Illustration: FIGS. 1,012 to 1,014.—Wiring diagrams for Dull's carbon
flashers. Fig. 1,012, usual method of wiring. The load is balanced by
running the neutral wire around the machine, to the cut outs, breaking
the outside "legs" only of a 220-110 volt system. While this method
of wiring is entirely feasible, it is no harder on the contacts, and
permits the use of a cheaper machine, but it is technically a violation
of the underwriters' rules, which say that all circuits of more than
660 watts must be broken double pole. If the load be balanced there
would be double pole break at 220 volts, and the lamps would be in
series, but if the load be not exactly balanced, there would be single
breaking to the extent of the amperes over the average balance.
In other words, it is a double break and it is not according to
circumstances, and the use of this machine wired as above is a matter
that should be taken up with the local inspector before installing.
Fig. 1,013, diagram for connecting a straight two wire carbon flasher
on a two wire system. Fig. 1,014, diagram for connecting a straight
three wire carbon flasher on a three wire system and breaking the
neutral.]
[Illustration: FIG. 1,015.—Reynolds' brush type flasher. The brush
type, as its name indicates, is of brush construction and is limited to
5 amperes capacity on each switch. The cams constituting a drum are of
heavy construction while the brushes are of fine copper several leaves
thick. It is most commonly used for spelling signs, that is, for letter
by letter flashing.]
[Illustration: FIG. 1,016.—Reynolds' knife type of flasher with metal
contacts. The construction is cheaper than the carbon type. It is
mounted on a slate base, and is heavily built throughout. The switches
are designed for 15 amperes capacity double break.]
=Brush Flashers.=—These machines are provided with brush contacts.
These bear on cams constituting a drum, and they are usually made
of several strips of copper. Brush flashers are generally used for
spelling out signs one letter at a time, or work of a similar nature.
[Illustration: FIG. 1,017—Sign flasher transmission gearing. The view
shows an oil tight gear case with cover plate removed. The gears are
equipped with ball bearings and run in graphite grease. By means of the
worm gear the large speed reduction necessary between the flasher shaft
and motor is obtained without a multiplicity of gear wheels.]
=Knife Flashers.=—This type of construction is cheaper than the carbon
type. The switches are of the knife type with metal contacts. One
manufacturer states that it is not advisable to build knife flashers
for more than 15 amperes per double pole switch, as they cannot be
depended upon to break a greater load for any length of time.
=Simple On and Off Flashers.=—These are used for flashing whole signs
or heavy loads on and off. A flasher of this type consists essentially
of a revolving double pole switch with reducing gear and connection to
a small motor for operating same.
[Illustration: FIG. 1,018.—Simple on and off double pole flasher for
"all on" or "all off" sign flashing. The machine is furnished with any
number of switches ranging from 5 amperes up.]
The machine may have only one switch or any number of switches. The
connection to motor may be by belt or chain, or the motor may be
directly connected to the worm gear.
* * * * *
=Flash System of Gas Lighting=—This system for simultaneously lighting
a large number of gas burners, is used in large halls, churches,
theatres, etc. Two sparking points, each insulated one from the other
and from the burner, are arranged at each burner, so that a spark
between the points passes through the jet of gas and ignites it. A
number of sparking points and the secondary of an induction coil
are connected in series. When the circuit through the primary of
the induction coil is closed, sufficient pressure is induced in the
secondary to cause sparks to jump across every jet in the series. Since
the voltage is high, the wires must be installed with great precaution.
The wire should be enclosed in glass tubing wherever it comes within
less than 1¼ in. from the gas piping, except where purposely
grounded.
=High Speed Flashers.=—Machines of this type are used for giving what
is generally known as _high speed effects_, such as fountains, water,
steam, smoke and fire effects, whirling borders, revolving wheels and
work of a similar nature.
[Illustration: FIG. 1,019.—Dull's high speed flasher. It is mounted on
a slate base 12 inches wide, the length being governed by the size of
the machine. Motion is given to the rotary switches through worm and
belt gearing. Iron cams are used, the current being taken therefrom by
six-leaf brushes, provided with stiffeners. The wiring for the machine
is simple; 4 c.p. lamps can be run on one wire. A border or ornament
containing 160 lamps requires 12 wires between the sign and flasher.
The flasher is made in 4 switch sizes only, viz.: No. 4, 8, 12, 16,
etc. This is due to the fact that there are three parts of light to one
of darkness.]
=Lightning Flashers.=—These machines are for giving the appearance
of a streak of lightning going across a display. There is very little
expense attached to their operation, because not more than two-thirds
of the lamps are turned on at one time, and this number for only about
one-sixth of the time, as compared with the sign burning steadily.
Lightning strokes can be utilized in various ways, either alone or with
other advertising pieces. Alone they can be placed along a cornice,
across the front of a building, up and down the corners leading to a
doorway, etc. They can be used in the center of a sign with letters
above and below. In this case, it is best to alternate the stroke with
the letters, that is, flash the wording on and then off. As soon as it
goes out, the stroke flies across in the darkness, then the wording
comes up again, say six times a minute.
[Illustration: FIG. 1,020—Wiring diagram for flags. These may be
wired for high speed flashers by gradually increasing the lamp centers
between the vertical rows from the flag staff to the end.]
[Illustration: FIG. 1,021.—Diagram showing method of wiring for high
speed effects on single lines. This wiring diagram would be carried out
the same in the case of a travelling border, whether it be straight or
otherwise. In the case of a fountain, begin numbering each stream at
the bottom and carry out the same scheme to the end of that stream.
When several streams are parallel, all the lamps may be connected in
a row the same as though they were an individual lamp. Care should be
taken not to get more than twenty No. 1 lamps on a circuit. Among the
effects that may be obtained are a revolving wheel, a column of flame,
and a straight travelling border with part of the No. 1 lamps from
each effect to the same No. 1 wire, carry it back to any No. 1 switch
on the machine, and the effect will come out right. For instance, in a
flame effect with sixteen No. 1 lamps, four No. 1 lamps could be taken
in the straight border, and put on the same wire, and the effect would
come out right. The spacings for high speed effects vary, according
to the size of the sign. Travelling borders around an ordinary sign 3
x 10 feet should have their lamps spaced about six inches apart. In
a fountain fifteen feet high, the lamps should be spaced about nine
inches apart.]
[Illustration: FIG. 1.022.—Method of wiring for a torch. This wiring
diagram gives the correct method of wiring smoke, flames, steam, and
water effects. It may be the flame in the top of a torch as here shown,
liquid pouring out of a bottle, smoke rising from a cigar, or dust
behind an automobile wheel. The only difference being in the direction
each goes and the outline of the bank of lamps. Wire the lamps in
unequal lines across; avoid any straight lines because it gives a
mechanical effect which is not natural. If the effect be to rise, mark
the lower row No. 1, the next row above No. 2, etc. Pick up all the
No. 1 rows until there are twenty lamps, and attach them to No. 1 wire
which will go back to any No. 1 switch on the machine. Do the same with
the other numbers. Do not overload line as this will decrease the life
of the contacts.]
[Illustration: FIGS. 1,023 and 1,024.—Wiring diagrams for high speeds.
Where a high speed flasher is used on a spoked wheel containing more
lamps in the rim than the number of spokes, the extra rim lamps must
be connected to the spoke circuits, so that the number of rim circuits
will equal the number of spokes; otherwise, the rim will appear to
travel slower than the spokes.]
In the case of a sign already in use, on the front of a building or
over the sidewalk, a stroke can be placed leading to the sign from any
point above. The flash goes down and when it hits the sign the latter
lights up, holds a few seconds, goes out, and repeats about four times
a minute.
[Illustration: FIG. 1,025—Dull's lightning type flasher for giving the
appearance of a streak of lightning going across a display.]
Lightning flashes are not usually constructed for heavy loads, the one
shown in fig. 1,025 being designed for two amperes.
=Script Breakers.=—Flashers of this type are used for breaking large
script signs, one socket at a time; that is, each lamp is lighted one
after another until all are on. After a few seconds they all go out
simultaneously and repeat. This gives the appearance of an invisible
hand, writing the name in the darkness, and is very effective. The
result can be accomplished only with script, and to get the proper
effect the smallest letter in a sign should be not less than two feet
high; the larger the letter, the better the effect.
[Illustration: FIG. 1,026.—Betts' script breaker (brush type). This
flasher is especially designed for spelling out signs one letter at a
time, or work of a similar nature, The brushes for the revolving cam
contacts are of copper, several leaves thick and provided with special
brush holder to prevent loose contact and abnormal burning.]
Script breakers are also used for fancy border signs of other kinds,
and in order to produce these results, it is necessary that the return
wire of every lamp go back to the flashers independently, which means a
wire for each lamp.
=Chaser Flashers.=—This class of flasher is designed to operate signs
whose lamps are arranged to give the effect of snakes chasing each
other around the border. This peculiar effect is produced by having a
separate wire and a separate switch on the flasher for each two lamps
in the border, and the mechanism so arranged that when the tenth lamp
is lighted (assuming the snake to be ten lamps long) the first lamp
goes out; when the eleventh is lighted, the second goes out, etc.,
progressing in this way around the entire border.
[Illustration: FIG. 1,027.—Reynolds chaser type of flasher, as used on
electric signs whose lamps are arranged to give the effect of snakes
chasing each other around the border of a sign.]
In operation, the lamps are turned on and off so rapidly that it
produces the effect of snakes.
It is not advisable to build these signs small nor cheaply, as
in order to produce the desired effect, the curved path taken
by the snake should cover at least 10 inches width, which
would mean a total of 20 inches lateral space for the snake in
addition to the electric letters in the center. In order to get
the proper effect, the sign should be at least ten feet long.
=Ques. Why are chaser signs expensive?=
Ans. It is on account of the care required in their construction, large
amount of wiring necessary and large flasher required.
A sign four by ten feet outside dimensions, would require in
the neighborhood of 150 lamps in the border alone on each side.
This would require a flasher with 75 switches and about 82
wires to run between the sign and flasher.
[Illustration: FIG. 1,028.—Chaser wiring diagram for two snakes.
Draw a line diagonally through the sign (as shown in dotted line) so
that one-half the total lamps will be on either side. Begin to number
from one consecutively to the line. Over the line commence again at 1
and number as before. For three snakes, divide total lamps into three
parts and number as before. In each case, connect all lamps of the same
number to the same wire whether the sign be single or double face. The
wire containing all the No. 1 lamps goes to the No. 1 switch on the
flasher, and the remaining sets are connected similarly.]
=Ques. How are chaser signs worked?=
Ans. There are several ways of operating these signs. The border is
generally working continuously, while the center can be flashed or not,
as may be desired. Flashing the wording reduces the current expense,
which offsets in a measure the extra cost of the sign.
The border, although working continuously consumes very little
current.
=Ques. What is the relative cost of a one snake sign as compared with a
two snake sign?=
Ans. One snake running around the border would cost twice as much for
flasher and wiring as a two snake flasher.
Three snakes would cost about 25 per cent. less for flasher and
wiring than for two snakes. The smaller the number of snakes
travelling around the border at one time, the greater the
expense of wiring and flasher.
[Illustration: FIG. 1,029.—Thermo flasher. It consists of two metal
strips, one of brass and the other of iron, about 5"x ½" x 1/32" each.
The brass strip is provided with a winding of fine wire over asbestos
and the two strips are connected to the base as shown. One terminal of
the winding is connected to J, and the other end to M. At the end of
the strips is a small contact screw N with locknut O, and below is a
contact plate L, fastened to the base and terminal post R. The flasher
is connected at P and R in series with the lamp it is to flash, and
N adjusted so that it clears the plate about 1/32 inch when there is
no current flowing in the winding. When the switch is turned on there
will be a current through the lamp and winding in series. The brass
strip will be heated more than the iron and it will expand more, thus
forcing the point of the screw N down upon the brass plate, which will
result in the winding about the brass strip being shorted and the full
voltage will be impressed upon the lamp, and it will burn at normal
candle power. When the coil is shorted there will of course be no
current in its winding and the brass strip will cool down, the screw
N will finally be drawn away from contact with the brass plate, and
the winding again connected in series with the lamp. The lamp will
apparently go out when the winding is in series with it, as the total
resistance of the lamp and winding combined will not permit sufficient
current to pass through the lamp to make its filament glow. The time
the lamp is on and off may be varied to a certain extent by adjusting
the screw N.]
=Ques. How many snakes should there be for best effect?=
Ans. Two is considered best. Three may be used on some signs, but more
than four would, in most cases, so crowd them as to spoil the effect
entirely.
=Thermo Flashers.=—These flashers work on the thermo or heat expansion
principle, that is, the movement of the contact points of the flasher
necessary to open and close the circuit is obtained automatically by
the alternate heating and cooling of the metal of the flasher, which
causes it to expand and contract.
[Illustration: FIG. 1,030.—Thermal flasher. This simple flasher
consists of a brass strip fixed at each end to a porcelain base and
slightly arched upwards. The amount of this arching, however, is much
less than is shown in the figure. The center of the strip carries a
platinum contact on its upper surface, and opposite this is a platinum
tipped contact screw which is carried in a brass angle piece fixed
to the base. One terminal is fitted on one end of the strip, and the
other is connected, through the angle piece, with the contact screw.
The strip is wound from end to end with an insulated resistance wire,
one end of this being soldered to the strip, and the other connected
to the right hand terminal. When this device is switched into circuit
with the lamps, the current first flows through the resistance, which
cuts it down so much that the lamps are not visibly affected. The heat
generated in the resistance causes the strip to curve still more, till
at length contact is made, the resistance short circuited, and the
lamps lighted.]
[Illustration: FIG. 1,031.—General Electric thermal flasher. It
consists of a small brass cylinder fixed at its left hand end to one
of the terminal blocks. The junction between the two is hidden by a
portion of the cover, which is shown broken away. The right hand end
of the cylinder carries a cross piece bearing a platinum contact; and
opposite this is the platinum tip of a contact screw carried in the
other terminal block. The cylinder is wound with a heating coil of
manganin resistance wire, one end being soldered to the cylinder and
the other to the right hand terminal. When the current is switched
on, the coil and the cylinder warm up and the cylinder elongates
sufficiently to make contact and light the lamps. The coil being then
short circuited, it and the cylinder cool down, and contact is broken,
whereupon the coil is put in circuit once more, and warms up again.
In some sizes of this flasher, the contact gap is shunted by a small
condenser fitted beneath the base. This helps to eliminate the sparking
at the contacts.]
=Carriage Calls.=—These are used to avoid the confusion and noise at
the theatre, club house or department store when vehicles are called by
a megaphone.
[Illustration: FIG. 1,032.—Monogram or unit for carriage call or
talking sign. It consists of a collection of metal compartments
each arranged to receive an incandescent lamp. The purpose of these
compartments is to confine the light to a certain space, thus forming a
clearly defined number or letter which can be read from a distance.]
[Illustration: FIG. 1,033 and 1,034.—Wiring diagrams showing proper
methods of wiring for illuminating a painted sign. The lamps are placed
about one foot apart in an overhead inverted trough. They should
project out in front of the sign one-half its width, but no sign should
be more than eight feet wide, as ordinary 16 c.p. lamps will not carry
any farther. Black and white paint only should be used. The lamps may
be flashed on and off as a whole, saving one-half the current, or they
can be flashed in different colors as desired. For flashing in colors,
only red and amber should be used. No other colors, such as green,
blue, etc., will give sufficient light to produce a good effect.]
The call itself consists of two or more sheet steel boxes, one of which
is shown in fig. 1,032, with incandescent lamps arranged in metal
compartments in such order that any number may be produced by lighting
the proper lamps.
[Illustration: FIG. 1,035.—Operating keyboard for three number
National carriage call. The keyboard here shown is designed to control
a three number call, there being a row of keys for each monogram or
unit of the call. Its dimensions are 4 inches deep, 18 inches wide and
19 inches long. The base is of slate. There are fourteen wires for each
monogram and one return wire, coming out of the call.]
The flashing of the number is controlled by a keyboard or switch which
may be placed in any convenient location. When the switch and call
are connected together, any numeral may be flashed by pressing the
corresponding key. The numeral automatically remains lighted until the
releasing button is pressed.
[Illustration: FIG. 1,036.—Clock monogram or electric sign clock,
operated by the mechanism shown in fig, 1,037.]
[Illustration: FIG. 1,037.—Betts' clock mechanism for operating
electric monogram time flasher. The secondary mechanism consists of
a three cylinder flasher and is controlled by a master clock which
transmits an electric impulse through a relay switch one each minute.
This flashes the time in figures on the monogram, viz.: 11.45, 11.46,
11.47, 11.48, etc. The first monogram to the left consists simply of a
vertical row of lights representing the figure one. Each of the other
monograms of metal compartments so arranged that any figure may be
produced by lighting the proper combination of lamps.]
=Talking Signs.=—This type of electric sign automatically flashes out
in brilliant letters, different phrases or announcements. These are
flashed out repeatedly and continuously during the operation of the
sign and the changes follow each other without intermission of darkness.
[Illustration: FIG. 1,038.—Two way thermal flasher. The moving portion
consists of a rocking arm _A_ pivoted at _p_, and carrying two sealed
bulbs, _B_, _B'_, whose bottoms are united by the tube _T_. Inside
there is sufficient mercury _M_ to fill _T_ and the bottoms of the
bulbs, the remainder containing air. At each end of _A_ is fixed an
insulating block _I_, _I'_, carrying two contact prongs _P_ and _P'_,
which are connected together at the top through heater wires _H_, _H'_
sealed in the bulbs _B_ and _B'_ respectively. _MC_, _MC'_ are pairs
of mercury cups, the further one of each pair whose stud is marked +,
being connected together to the positive pole of the circuit, while
the front ones are joined up to the respective groups of lamps. The
action is as follows: If the apparatus be in the position illustrated,
when the circuit is closed at the time _P_ is down, lamp group No. 1
will light up, the current passing through _H_ on its way. The air
in _B_ consequently expands, and gradually forces the mercury down
in _B_, along _T_, and up in _B'_. The arm _A_ will gradually become
horizontal, and will then overbalance, _P_ being withdrawn from _MC_,
and _P'_ dipped into _MC'_. Lamp group No. 1 will consequently be
extinguished and lamp group No. 2 lighted; _H_ will cool down, and _H'_
will warm up. Thus, in due course, _A_ will be tilted the other way
again.]
The talking sign consists of any desired number of monograms or units,
in each of which any letter or figure can be formed by lighting
certain combinations of incandescent lamps. A unit is shown in fig.
1,032. The lamps are controlled by a simple mechanical arrangement
operated by a small motor. Any reading matter can be flashed by
properly setting the mechanism.
The flashing of the letters or numerals in the monogram is controlled
by commutators, one commutator being required for each monogram, except
for a double faced sign where the corresponding monogram on each side
is controlled by the same commutator.
CHAPTER XLIII
LIGHTNING PROTECTION
A lightning arrester is an apparatus designed to provide a path by
which lightning disturbances or other static discharges may pass to
earth. Lightning arresters may be divided into three classes, according
as their action depends upon the effects of:
1. Sharp points;
2. Air gaps;
3. Sharp turns.
=Lightning Rods.=—This form of arrester consists of a conducting rod
or cable erected on the outside of a building and connected to earth,
in order to afford protection from lightning by carrying the lightning
discharge into the ground; or to prevent lightning by leading the
electricity from the earth to the cloud without disturbance.
=Ques. Why do lightning rods terminate in sharp points?=
Ans. The action of the rod depends on the discharging effect of a sharp
point as follows: When an electrically charged cloud approaches a
building provided with a lightning rod, it induces an opposite charge
in the earth and in the rod which is connected to the earth. As soon
as the charge on the point becomes strong enough to break apart the
molecules of the air in front of it, a stream of electrified particles,
opposite in sign to that of the charge on the cloud, passes from the
neighborhood of the rod to the cloud and thus neutralizes the charge of
the cloud.
=Ques. How should a lightning rod be erected?=
Ans. The conductor should be carried to all high points of the building
it is to protect and should be well insulated from the latter and
grounded in deep wet earth, independent of gas or water pipes. Sharp
bends and corners should be avoided.
[Illustration: FIG. 1,039.—Diagram showing principle of air gap
arrester: lightning discharges more readily at sharp points than along
flat surfaces.]
=Ques. Why have lightning rods fallen into disfavor?=
Ans. On account of numerous failures due to faulty installations, and
non-maintenance of the rod in good condition, also because of the
excessive prices charged by unscrupulous dealers for rods and their
erection.
A lightning rod with defective insulation or broken ground
connection is a danger rather than a protection.
=Air Gap Arresters.=—Many of the lightning arresters used for the
protection of electrical apparatus depend upon the fact that lightning
discharges will jump across air spaces that are good insulators for the
regular working current, while they find difficulty in passing through
circuits containing electromagnets.
[Illustration: FIG. 1,040.—Union lightning arrester and ground wire
switch for telegraph lines. Two line wires are attached to the two
plates provided with points. The ground wire being connected to the
third or central plate. The pin serves as a ground wire switch and cut
out. This is a good form for short lines.]
The principle of air gap arresters is illustrated in fig. 1,039. There
are two brass plates slightly separated; one is connected to the line
and the other is grounded. The air gap between the plates is very
small and the resistance thus interposed, while sufficient to prevent
the regular working current jumping across, is not great enough to
interfere with a lightning discharge which readily jumps the gap and
passes off to earth.
=Ques. Why are teeth provided on the plates?=
Ans. For the same reason that points are used on lightning rods. That
is, when electricity at high pressure accumulates at such points the
surrounding air is electrified and the charge escapes by means of the
charged air particles.
[Illustration: FIG. 1,041.—Mason multi-discharge lightning arrester.
The construction of this arrester is based on the well known principle
that lightning discharges more readily at points or angles than
elsewhere. The wire is wound around square carbon rods, which are
connected to the ground, the line being insulated from the rods by
sheets of mica. The wire itself being square, instead of round, adds to
the efficiency of the arrester, by increasing the number of points or
angles.]
=Ques. For what kind of service is the form of arrester just described
used?=
Ans. It is suitable for telegraph and telephone lines where currents of
very low voltage are employed.
=Ques. Why is it not used on lines employing higher voltage, such as in
electric light and power stations?=
Ans. Current at high pressure would follow the lightning across the
gap and establish an arc or continuous flame from one plate to the
other thus quickly destroying the plates and causing other more serious
damage.
=Ques. What provision is made to prevent the destruction of arresters
by the line current?=
Ans. Lightning arresters used on heavy duty circuits are designed to
rupture the arc as soon as formed.
[Illustration: FIG. 1,042.—Diagram showing operation of variable gap
arc breaker used on heavy duty lightning arresters. When a lightning
discharge passes across the gap to earth, the dynamo current follows it
and energizes the magnet M, which attracts the short arm of the double
lever, thus quickly jerking the terminal B away from C. The wider air
gap thus interposed between B and C greatly increases the resistance
which breaks the arc.]
=Ques. How is this done?=
Ans. There are several methods, of which may be mentioned the variable
gap method described in fig. 1,042, and the magnetic blow out method
shown in fig. 1,043.
=Ques. Where should lightning arresters be placed?=
Ans. They should be placed as near as possible to the point where
wires enter a building, and in an easily accessible place away from
combustible material.
=Ques. What should be avoided in installing lightning arresters?=
Ans. Kinks and sharp bends in the wire running from the outdoor lines
to the arresters and from arresters to ground should be avoided as far
as possible.
=Ques. Why should kinks and sharp bends be avoided?=
Ans. Because they offer resistance to the lightning discharge.
[Illustration: FIG. 1,043.—Horn type lightning arrester. In this type
of arrester, two wires, after approaching within a short distance
of one another, are bent divergently. These wires are supported on
insulators. One of them is connected to the line to be protected
and the other is earthed. The normal line pressure is insufficient
to bridge the gap, even at its narrowest portion, but an extra high
pressure whether due to lightning or to other disturbing phenomena,
will bridge the gap at its narrowest point and establish a path to
earth. When, however, the main current attempts to flow across,
phenomena of electromagnetic repulsion force the arc upward along
the horns, lengthening and attenuating it, until it finally becomes
extinguished.]
=Ques. How should lightning arresters be grounded?=
Ans. They should be connected to ground with No. 6 B. & S. gauge copper
wire or larger. Gas pipes within a building must not be used for a
ground connection.
[Illustration: FIG. 1,044.—Ground connection for lightning arrester.]
[Illustration: FIG. 1,045.—Carbon lightning arrester with fuses as
used on telephone lines. The arrester consists of two blocks of carbon
separated a small distance by a thin sheet of insulating mica, which is
perforated with one or more holes; a high voltage charge on the line
will jump through the hole in the mica from the carbon on the line side
to the lower carbon, which is connected with the ground; the fuses
protect the instruments against foreign currents which might damage,
although not of sufficiently high pressure to jump to earth; sometimes
the connections are reversed so that the fuse is between the line and
the earth.]
Ground connections may be made with a one inch galvanized iron
pipe driven about 8 feet or until it reaches permanently moist
earth, and extending at least 7 feet above ground. The ground
wire should be securely soldered to a brass plug firmly screwed
into the pipe, and both strongly stapled to the pole so there
will be little danger of the connection being broken.
A good ground is important, as the efficiency of the protection
would be impaired if the ground connection were poor. Wherever
the earth is dry and a good ground cannot surely be obtained,
an excavation 4 or 5 feet deep should be made, and after
placing the copper ground plate or iron pipe in the hole, it
should be filled with crushed coke or charcoal about pea size.
This improves the electrical connection between pipe or plate
and earth.
=Ques. Does lightning often strike telephone or electric light lines?=
Ans. No, the lines become charged to a high pressure by induction
from lightning flashes or from the passing of clouds that are highly
charged.
CHAPTER XLIV
STORAGE BATTERIES
=Introduction.=—The practical development of the storage battery is
comparatively recent, although a knowledge of the phenomena upon which
its actions are based, dates back to 1801. In 1800, the year made
memorable by Volta's discovery of the galvanic battery, Nicholson and
Carlisle found that a current from Volta's cell could decompose water.
In 1801, Gautherot discovered that if two plates of platinum or
silver, immersed in a suitable electrolyte, be connected to the
terminals of an active primary cell and current be allowed to
flow, a small current could be obtained on an outside circuit
connecting these two electrodes as soon as the primary battery
had been disconnected.
Erman found that the positive pole of such a cell, was the pole
which had been connected to the positive pole of the battery.
In 1803, Ritter observed, with gold wire, the same phenomenon
as Gautherot, and constructed the first secondary battery, by
superposing plates of gold, separated by cloth discs, moistened
with ammonia.
Volta, Davy, Marianini, and others added somewhat to the
knowledge on the subject, and in 1837, Schoenbein found that
peroxide of lead could be used in secondary batteries.
Sir William Grove next came forward with the discovery that
metal plates, with a layer of oxide on them, acted better
than the plain metallic plates, and Wheatstone and Siemens
found still later that peroxide of lead was the best for such
purposes.
In 1842, Grove constructed a gas battery, in which the
electromotive force came from the oxygen and hydrogen evolved
in the electrolysis of water acidulated with sulphuric acid. By
means of fifty such cells, he obtained an arc light.
Michael Faraday, when electrolyzing a solution of lead
acetate, found that peroxide was produced at the positive, and
metallic lead at the negative pole, and in his "Experimental
Researches," he comments on the high conductivity of lead
peroxide, and its power of readily giving up its oxygen.
Although he made no apparent use of this discovery, it may be
considered as the next important step in the development of the
storage battery.
According to Niblett, Wheatstone, de la Rue, and Niaudet were
well aware that peroxide of lead was a powerful depolarizer,
but nobody appears to have made use of this fact until 1860,
when M. Gaston Plante constructed his well known cell with
coiled plates. Plante's researches extended up to 1879, and
practically determined the state of the art.
[Illustration: FIG. 1,046.—One plate or "grid" of a type of storage
cell constructed by inserting buttons or ribbons of the proper chemical
substances in perforations. Some such cells use crimped ribbons of
metallic lead for inserting in the perforations, others pure red lead
or other suitable material.]
As to the theory at this time, it may be stated that Clerk
Maxwell, although the leading electrician of his time, speaks
of the storage battery as storing up a quantity of energy in a
manner somewhat analogous to the ordinary condenser; hence the
use of the word "accumulator" for storage battery.
In 1879, R. L. Metzer did away with the tedious forming
process, by mechanically applying the active material. This
important discovery was not, however, generally known, until
1881, when Camille Faure obtained important patents concerning
the method of shortening the time of formation.
Charles F. Brush, working independently of either Faure or
Metzer, arrived at the same result, and the United States
courts have decided, after long litigation, that to him belongs
the priority of invention in this country.
[Illustration: FIGS. 1,047 to 1,050.—Electric Storage Battery Co.
plates. Fig. 1,047, "Manchester" positive plate; fig. 1,048, box
negative plate; fig. 1,049, "Tudor" positive plate; fig 1,050, pasted
negative plate.]
=Ques. To what use is the storage battery sometimes put in electric
lighting or power stations?=
Ans. To carry the "peak" of the load; that excessive portion of the
load which, for instance, in electric lighting stations has to be
carried only for two or three hours a day. To carry the entire load at
minimum hours. To act as equalizer or reservoir. Also for equipment of
annex or substations.
[Illustration: FIG. 1,051.—"Unformed" plate of one pattern of Gould
storage cell. The particular plate shown has total outside dimensions
of 6×6 inches. The clear outline of the grooves indicates absence of
oxides, due to action of "forming" solutions, or charging current.]
=Theory of the Storage Battery.=—The action of the storage battery
is practically the same as that of the primary battery and it is
subject to the same general laws. The cells of a storage battery are
connected in the same way as primary cells, and when charged is capable
of generating a current of electricity in a manner similar to that
of a primary battery. It differs, however, from the primary battery
in that it is capable of being recharged after exhaustion by passing
an electric current through it in a direction opposite to that of
the current on discharge. This difference constitutes the principal
advantage of the storage battery over the primary battery.
[Illustration: FIGS. 1,052 and 1,053.—Electric Storage Battery Co.,
type H "exide" plates. This form of plate is used for large "stand by"
batteries. Fig. 1,052, positive plate; fig. 1,053, negative plate.]
=Ques. Describe a storage cell.=
Ans. A storage cell consists of plates or of grids in an electrolyte,
of such a character that the electrical energy supplied to it is
converted into chemical energy (a process called charging). The
chemical energy can be reconverted into electrical energy (a process
called discharging).
=Ques. Describe the electrolyte generally used.=
Ans. It consists of a weak solution of sulphuric acid which permits
ready conduction of the current from the primary battery, the greater
the proportion of acid within certain limits, the smaller the
resistance offered.
[Illustration: FIG. 1,054.—Elements of 6 volt 40 ampere hour "Aplco"
portable (3 cell) storage battery. The grids are made from an alloy of
lead and antimony; hard lead straps which are burned together, are used
for joining the plates. Specially treated separators are used.]
=Ques. What is the effect of the current passing through the
electrolyte?=
Ans. It decomposes the water into oxygen and hydrogen; this is
indicated by the formation of bubbles upon the exposed surfaces of
both plates, these bubbles being formed by oxygen gas on the plate
connected to the positive pole of the primary battery, and hydrogen on
the plate connected to the negative pole.
Because, however, the oxygen is unable to attack either
platinum or silver under such conditions, the capacity of such
a device to act as an electrical accumulator is practically
limited to the point at which both plates are covered with
bubbles. After this point the gases will begin to escape into
the atmosphere.
=Ques. What is the prime condition for operation of a storage battery?=
Ans. The resistance of the electrolyte should be as low as possible in
order that the current may pass freely and with full effect between
the electrodes. If the resistance of the electrolyte be too small, the
intensity of the current will cause the water to boil rather than to
occasion the electrolytic effects noted above.
=Ques. What happens when the charging current is discontinued, and the
two electrodes joined by an outside wire?=
Ans. A small current will flow through the outside circuit, being due
to the recomposition of the acid and water solution. The process is
in a very definite sense a reversal of that by which the current is
generated in a primary cell.
Hydrogen collected upon the negative plate, which was the
cathode, so long as the primary battery was in circuit, is
given off to the liquid immediately surrounding it, uniting
with its particles of oxygen and causing the hydrogen, in
combination with them, to unite with the particles of oxygen
next adjacent. The process is continued until the opposite
positive plate is reached, when the oxygen collected there is
finally combined with the surplus hydrogen, going to it from
the surrounding solution.
This chemical process causes the current to emerge from the
positive plate, which was the anode, so long as the primary
battery was in circuit. The current thus produced will continue
until the recomposition of the gases is complete; then ceasing
because these gases, as before stated, do not combine with the
metal of the electrodes.
=Types of Storage Battery.=—There are three classes of storage cell
which are commercially important:
1. Plante cells;
2. Faure cells;
3. Alkaline cells.
According to construction secondary cells may be classified as follows:
1. Lead sulphuric acid cells;
2. Lead copper cells;
3. Lead zinc cells;
4. Alkaline zincate cells.
The lead sulphuric acid type includes all those cells belonging
to the Plante and Faure groups.
Lead copper cells consist of sheets of metal coated with lead
oxide, serving as the positive electrode, and copper plates
for the negative electrodes. These plates are immersed in a
solution of copper sulphate. Cells belonging to this class are
not employed in commercial practice, being useful only for
laboratory experiments.
Lead zinc cells are similar to the preceding type, but differ
by having zinc for the negative electrode, and zinc sulphate
for the electrolyte. The voltage of these cells is slightly
higher than that of the ordinary cell, and their capacity per
unit of total weight is high, but they are apt to lose their
charge on open circuit, besides they possess most of the
disadvantages of the Plante cells.
Alkaline zincate cells have copper for the positive, and iron
for the negative electrode. The electrolyte is composed of
sodium, or potassium, zincate. Cells of this type are used to
some extent for traction purposes.
In addition to the above there are some special forms of cell
which do not belong to the four preceding types.
=Ques. Describe the Plante type.=
Ans. In the Plante type the lead is chemically attacked and finally
converted into lead peroxide, probably after it has gone through
several intermediate changes. The plates are all formed as positive
plates first and then all that are intended for negative plates are
reversed, the peroxide being changed into sponge lead.
[Illustration: FIGS. 1,055 and 1,056.—Willard plates; fig. 1,055,
negative plates; fig. 1,056, positive plates. Both positive and
negative plates are of the Planté type, made from one integral piece
of rolled lead. These are grooved plates. The projections are tapered,
that is, they are wider at the base than at the surface, for strength.
The center web of each positive plate is tapered from the top of the
plate downward to secure uniform distribution of the current all over
the surface of the plate.]
[Illustration: FIG. 1,057.—Wood separator for spacing the plates, as
used in the Willard storage cells.]
[Illustration: FIG. 1,058.—Positive plate.]
[Illustration: FIG. 1,059.—Perforated rubber separator.]
[Illustration: FIG. 1,060.—Wood separator.]
[Illustration: FIG. 1,061.—Negative plate.]
[Illustration: FIG. 1,062.—Hard rubber cover.]
[Illustration: FIG. 1,063.—Vent plug.]
[Illustration: FIG. 1,064.—Pillar connecting strap.]
[Illustration: FIG. 1,065.—Hard rubber jar.]
[Illustration: FIG. 1,066.—Complete element.]
[Illustration: =Figs. 1,058 to 1,066.—Parts of the Willard "Autex"
automobile cells.=]
=Ques. What is done to make the Plante plate more efficient?=
Ans. The surfaces are finely subdivided, the following methods being
those common: scoring, grooving, casting, laminating, pressing, and by
the use of lead wool.
=Ques. Describe the Faure or pasted type.=
Ans. This form of plate is constructed by attaching the active material
by some mechanical means to a grid proper. The active material first
used for this purpose was red lead, which was reduced in a short time
to lead peroxide when connected as the positive or anode, or to spongy
metallic lead when connected as the cathode or negative, thus forming
plates of the same chemical compound as in the Plante type.
The materials used at the present time by the manufacturers
for making this paste are largely a secret with them, but in
general they consist of pulverized lead or lead oxide mixed
with some liquid to make a paste.
=Ques. How do Faure plates compare with those of the Plante type?=
Ans. They are usually lighter and have a higher capacity, but have a
tendency to shed the material from the grid, thus making the battery
useless.
Many ways have been tried for mechanically holding the active
material on the grid, the general method involving a special
design in the shape of the grid. Some of these designs are:
1, solid perforated sheets of lattice work; 2, corrugated and
solid recess plates not perforated; 3, ribbed plates with
projecting portions; 4, grid cast around active material; 5,
lead envelopes, and 6, triangular troughs as horizontal ribs.
=The Electrolyte.=—Sulphuric acid is generally used as electrolyte;
the acid should be made from sulphur and not from pyrites, as the
latter is liable to contain injurious substances.
=Ques. How is the electrolyte prepared?=
Ans. One part of chemically pure concentrated sulphuric acid is mixed
with several parts of water. The proportion of water differs with
several types of cell from three to eight parts, as specified in the
directions accompanying the cells.
[Illustration: FIGS. 1,067 to 1,079.—Willard connecting straps and
connectors.]
=Ques. What test is necessary in preparing the electrolyte?=
Ans. In mixing the water and acid, the hydrometer should be used to
test the specific gravity[6] of both the acid and the solution. The
most suitable acid should show a specific gravity of about 1.760 or 66°
Baumé.
[6] NOTE.—_Specific gravity_ is the weight of a given substance
relative to an equal _bulk_ of some other substance which is taken as
a standard of comparison. Water is the standard for liquids. In the
laboratory the _specific gravity bottle_ is often used in determining
the specific gravity of a liquid. The capacity of the bottle is 1,000
grains of pure water. When it is filled with spirits of wine and
weighed in a balance (together with a counterpoise for the weight of
the bottle, which of course is constant), it will weigh considerably
less than 1,000 grains; in fact, the bottle will contain only about 917
grains of proof spirit; therefore, taking the specific gravity of water
as unity, 1 or 1.000, the specific gravity of spirits of wine is 0.917.
If, on the other hand, the bottle be filled with sulphuric acid, it
will weigh about 1,850 grains; hence, the specific gravity of sulphuric
acid is said to be 1.850. A more convenient method for the automobilist
is by the use of the hydrometer.
=Ques. In preparing the electrolyte, how should the water and acid be
mixed?=
Ans. The mixture should be made by pouring the acid slowly into the
water, _never the reverse_. As cannot be too strongly stated, in
mixing, the liquid should be stirred with a clean wooden stick, the
acid being added to the water slowly; the latter is corrosive and will
painfully burn the flesh.
Distilled or rain water should be used in preparing the
electrolyte. When made, the solution should be allowed to cool
for several hours or until its temperature is approximately
that of the atmosphere (60 being the average). At this point it
should have a specific gravity of about 1.200 or 25° Baumé. If
the hydrometer show a higher reading, water may be added until
the correct reading is obtained; if a lower reading, dilute
acid may be added with similar intent.
The electrolyte should never be mixed in jars containing the
battery plates, but preferably in stone vessels, specially
prepared for the purpose. Furthermore, it should never be
placed in the cell until perfectly cool.
=Ques. What is the effect of mixing the acid and the water?=
Ans. The mixture becomes hot.
Before using, the mixture should be allowed to cool.
=Ques. What kind of a vessel should be used?=
Ans. The vessel should be of glass, glazed earthenware, or lead.
=Ques. At what density is the resistance of dilute sulfuric acid at a
minimum?=
Ans. At 1.260.
The percentage of concentrated sulphuric acid and of water per
100 parts of the electrolyte for various specific gravities is
given by the following table:
SPECIFIC GRAVITY TABLE
+——————————————+————————————+————————————————+
|Sulphuric acid| Water |Specific gravity|
| (Per cent.). |(Per cent.).| of Mixture. |
+——————————————+————————————+————————————————+
| 50 | 50 | 1.398 |
| 47 | 53 | 1.370 |
| 44 | 56 | 1.342 |
| 41 | 59 | 1.315 |
| 38 | 62 | 1.289 |
| 35 | 65 | 1.264 |
| 32 | 68 | 1.239 |
| 29 | 71 | 1.215 |
| 26 | 74 | 1.190 |
| 23 | 77 | 1.167 |
| 20 | 80 | 1.144 |
| 17 | 83 | 1.121 |
| 14 | 86 | 1.098 |
| 10 | 90 | 1.068 |
+——————————————+————————————+————————————————+
The electrolyte of the desired specific gravity may be
purchased ready for use, but in cases where it is desirable
to save freight, the acid may be diluted at the point of
installation.
=Ques. What is the effect of a deep containing vessel?=
Ans. Parts of the plate surface may do more than their share of the
work due to the difference in the density of the electrolyte at the top
and bottom. The containing vessel should, therefore, never be deeper
than about 20 inches unless some artificial means of acid circulation
be used.
=Ques. What is the effect of changes in temperature on the electrolyte?=
Ans. The resistance of the electrolyte is changed, being less for
increase of temperature.
[Illustration: FIGS. 1,080 to 1,084—Acid hydrometers for liquids
heavier than water. Fig. 1,080, standard storage battery hydrometer
with guiding points designed for "hydrometer syringe," shot bulb, with
red line at 25 Baumé, 5 inches long, double scale 10 to 40 Baumé, 1.050
to 1.400 specific gravity. Fig. 1,081, plain hydrometer with shot bulb,
5 inches long, double scale 10 to 40 Baumé, 1.050 to 1.400 specific
gravity. Figs. 1,082 and 1,083, hydrometer with small flat bulb, used
in car lighting batteries, shot bulb, 4½ inches long, single scale,
reading from 1.100 to 1.250 specific gravity. Fig. 1,084 jar for
hydrometers.]
=Ques. How should the cells be filled?=
Ans. Enough of the electrolyte should be poured into the jars to
completely cover the plates, or to within about a half inch of the top
edge of the jar. Large cells should be filled by means of an acid proof
pump and rubber hose.
=Ques. What change takes place after filling the jars?=
Ans. The specific gravity of the electrolyte will fall considerably,
but will rise again when the battery is charged.
=Ques. What may be said with respect to the density of the electrolyte?=
Ans. It should never exceed 1.200 when the battery is fully charged.
=Ques. How much electrolyte is used per 100 ampere hours battery
capacity, on an 8 hour rating?=
Ans. About ten pounds; in automobile batteries, about four pounds is
sufficient.
[Illustration: FIG. 1,085.—The hydrometer syringe; a convenient device
for testing electric vehicle cells. By slightly compressing the bulb
and inserting the slender tube through the vent hole in the cover of
the cell sufficient acid may be drawn up to float the hydrometer within
the large glass tube, and the reading can be made at once. The acid is
returned to the cell by again compressing the bulb, and the reading of
the next cell taken. The laborious and uncleanly method of drawing out
sufficient acid by a syringe is thus avoided.]
=Ques. What may be said with respect to impurities in the electrolyte?=
Ans. The electrolyte should be free from chlorine, nitrates, acetates,
iron, copper, arsenic, mercury, and the slightest trace of platinum.
Mercury alone has no injurious effect unless it be present
in sufficient quantity to amalgamate the plates, but in
combination with any other metal, may cause local action.
[Illustration: FIGS. 1,086 to 1,089.—The "Champion" Accumulator;
views showing parts and assembly. Fig. 1,086, empty plate; fig. 1,087,
filled plate; fig. 1,088, complete element, small type; fig 1,089, cell
assembled. The plates are of the envelope type and are made thick. The
active material is held firmly in place by a covering of lead. A few
thick plates are used instead of many thin ones.]
The following tests should be made for impurities before the
electrolyte is poured in the cells:
=Chlorine.=—To a small sample of the electrolyte add a few
drops of silver solution (20 grains of silver dissolved in
1,000 cu. cm. of water). A white precipitate indicates chlorine.
=Nitrates.=—Place some of the electrolyte in a test tube,
and add 10 grains of strong ferrous sulphate solution.
Carefully pour down the side of the test tube a small amount of
chemically pure concentrated sulphuric acid. A brown stratum
between the electrolyte and the concentrated acid indicates the
presence of nitric acid.
=Acetic acid.=—Neutralize the electrolyte with ammonia,
then add ferric chloride. If the solution turns red, and is
afterwards bleached by the addition of hydrochloric acid,
acetic acid is present.
=Iron.=—Neutralize a sample of the electrolyte with ammonia;
boil a small portion with hydrogen peroxide, and add ammonia or
caustic potash solution until the mixture becomes alkaline. If
a brownish red precipitate forms, it indicates iron.
=Copper.=—If copper be present, a bluish white precipitate
will be formed when ammonia solution is added to the
electrolyte.
[Illustration: FIG. 1,090.—One cell of the Gould storage battery for
electric vehicle use. According to the data given by the manufacturers,
this cell, containing four negative and three positive plates, has a
normal charging rate of 27 amperes; a distance rate of 22 amperes for
four hours; a capacity of 81 ampere hours at 3 hours discharge, and of
90 ampere hours at 4 hours discharge. Forty such cells are generally
used for an average light vehicle battery.]
=Mercury.=—This is indicated by an olive green precipitate
when a solution of potassium iodide is added to the
electrolyte, or by a black precipitate when lime water is added.
=Platinum.=—A rough test for traces of platinum is made by
pouring the electrolyte into a cell in which the battery plates
are immersed. If gassing take place for some time on open
circuit, it is an indication of the presence of platinum.
=Ques. What should be done with old electrolyte?=
Ans. When a battery is taken down the electrolyte may be saved and used
when re-assembling the battery, providing great care be exercised when
pouring it out of the jar, so as not to draw off with it any of the
sediment. It should be stored in convenient receptacles, preferably
carboys, which have been thoroughly washed and never used for any other
purpose.
[Illustration: FIG. 1,091.—Phantom view of an "Exide" sparking or
ignition battery. It contains three cells. In this type, the terminal
lug has been designed to obviate the creeping of the electrolyte with
its accompanying corrosion. The positive and negative terminals are for
identification.]
The electrolyte saved in this manner will not, however, be
sufficient to refill the battery, and as some new electrolyte
will be required, in general it is recommended that the old
supply be thrown away and all new electrolyte (1.200 specific
gravity) be used when re-assembling.
=Voltage of a Secondary Cell.=—This depends on the density of the
electrolyte, the character of the electrodes and condition of the cell;
it is independent of the size of the cell.
The voltage of a lead sulphuric acid cell when being charged is from 2
to 2.5 volts. While the cell is being discharged, it decreases from 2
to 1.7 volts. The voltage due to the density of the electrolyte may be
calculated from the following formula:
V = 1.85 + .917 (S - s)
in which
V = voltage;
S = specific gravity of the electrotype;
s = specific gravity of water at the temperature of observation.
[Illustration: FIG. 1,092.—The Exide storage cell. The positive and
negative plates are separated by thin sheets of perforated hard rubber,
placed on both sides of each positive plate. The electrolyte and plates
are contained in a hard rubber jar.]
[Illustration: FIG. 1,093.—An Exide battery of five cells. The box
which holds the cells is usually made of oak, properly reinforced,
with the wood treated to render it acid proof. The terminals as shown,
consist of metal castings attached to the side of the box and plainly
marked.]
=Connection for Charging.=—The dynamo cable connections may be made
either before or after filling the cells. In making these connections
great care should be taken to be sure that the positive terminal of the
battery is connected to the positive lead of the dynamo, and that the
negative terminal of the battery is connected to the negative lead of
the dynamo. In order to insure that the reverse connections are not
made accidentally, the dynamo leads should be tested by a pole tester,
and the positive and negative poles marked red and black respectively.
[Illustration: FIGS. 1,094 to 1,109.—Parts of the "Exide" sparking
battery. A, positive plate; B, negative plate; C, wood separator; D,
positive strap; E, negative strap; F, terminal lug; H, connector; I,
terminal bolt connector, stud, thumb nut and hexagonal nut; J, copper
washer for bolt connector; L, hard rubber jar; M, hard rubber cover;
N, hard rubber cylinder vent; O, vent plug for cylinder vent; R,
wood case; S, strap handle; T, fitting for strap handle. The "Exide"
sparking battery is also adapted for electric lighting of automobiles,
for head lights, tail lights, side and interior lights.]
The polarity of the dynamo wires being determined, they may be joined
to the proper terminals by means of suitable clamps or by solder.
Wherever possible the dynamo should be of the direct current, shunt
wound, or special compound type, but in cases where only alternating
current can be obtained, suitable rectifiers or converters should be
used for changing it to direct current.
=Charging.=—Before beginning to charge a storage battery, it should
be gone over carefully, and any cell that is not up to the standard
should be disconnected and put in working order before being replaced.
In general, if the current used in charging be too large, it will
waste energy by evolving an excess of heat and gas; if too small,
an insulating deposit of white lead sulphate will be formed on the
positive plate, thereby preventing the formation of the proper amount
of lead peroxide.
[Illustration: FIGS. 1,110 and 1,111.—Switchboard and motor dynamo
circuit connections for charging a battery from direct current mains.]
=Ques. How should a battery be charged for the first time?=
Ans. It is essential that the current be allowed to enter at the
positive pole at about one-half the usual charging rate prescribed, but
after making sure that all necessary conditions have been fulfilled, it
is possible to raise the rate to that prescribed by the manufacturers
of the battery.
=Ques. What is the usual period for charging a new battery?=
Ans. With several of the best known makes of storage battery the
prescribed period for the first charge varies between twenty and thirty
hours.
[Illustration: FIGS. 1,112 and 1,113.—Switchboard and motor generator
circuit connections for charging a battery from alternating current
mains. The connections of a third wire are shown, for use in case a
three phase circuit is available.]
=Ques. How is the electrolyte affected by the first charge?=
Ans. A change of specific gravity occurs. The specific gravity should
be about 1.200 when the solution is poured into the cells.
At the completion of the first charge, it should, on the same
scale be about 1.225. If it be higher than this, water should
be added to the solution until the proper figure is reached, if
it be lower, dilute sulphuric acid should be added until the
hydrometer registers 1.225.
At the first charging of a cell, when the pressure has reached
the required limit, the cell should be discharged until the
voltage has fallen to about two-thirds normal pressure, when
the cell should again be recharged to the normal voltage (2.5
or 2.6 volts).
The manufacturers of a well known cell of the Plante genus
prescribe for the first charge, half rate for four hours, after
which the current may be increased to the normal power and
continued for twenty hours successively.
[Illustration: FIG. 1,114.—Plates of Edison storage battery. The
positive or nickel plate consists of one or more perforated steel
tubes, heavily nickel plated, filled with alternate layers of nickel
hydroxide and pure metallic nickel in excessively thin flakes. The
tube is drawn from a perforated ribbon of steel, nickel plated, and
reinforced with eight steel bands, equidistant apart, which prevent the
tube expanding away from and breaking contact with its contents. The
tubes are flanged at both ends and held in perfect contact with a steel
supporting frame or grid made of cold rolled steel, nickel plated. The
negative or iron plate consists of a grid of cold rolled steel, nickel
plated, holding a number of rectangular pockets filled with powdered
iron oxide. These pockets are made up of very finely perforated steel,
nickel plated. After the pockets are filled they are inserted in the
grid and subjected to great pressure between dies which corrugate the
surface of pockets and force them into good contact with the grid.]
=Ques. What strength of current should be used in charging a cell?=
Ans. It should be in proportion to the ampere hour capacity of the
cell.
Thus, as given by several manufacturers, the normal charging
rate for a cell of 40 ampere hours should be five amperes, or
one-eighth of its ampere hour rating in amperes of charging
current.
=Ques. What should be the voltage of the charging current before
closing the charging circuit?=
Ans. The voltage should be at least ten per cent. higher than the
normal voltage of the battery when charged.
[Illustration: FIG. 1,115.—Complete element of Edison storage battery
with insulators. After the plates are assembled into a complete
element, narrow strips of treated hard rubber are inserted between the
plates, thereby separating and insulating them from each other. The
side insulator is provided with grooves that take the edges of the
plates, thereby performing the dual function of separating the plates
and insulating the complete elements from the steel container. At the
ends of the element, that is between the outside negative plates and
container, are inserted smooth sheets of hard rubber. At the bottom,
the element rests upon a hard rubber rack or bridge, insulating the
plates from the bottom of container.]
[Illustration: FIG. 1,116.—Four Edison cells (type A-4) in wooden
tray.]
=Ques. What indicates the completion of a charge?=
Ans. When a cell is fully charged the electrolyte apparently boils and
gives off gas freely. The completion of a charge may be determined by
the voltmeter, which will show whether the normal pressure has been
attained.
=Ques. How should the voltage be regulated during the first charge?=
Ans. It should be allowed to rise somewhat above the point of normal
pressure.
Electrical Data Edison Cell
+——————————————————————————————————————————————————————————————+
| =B-2= =B-4= =B-6=|
|Normal output, ampere hours 40 80 120 |
| |
|Maximum output, ampere hours 48 95 142 |
|Normal rate of discharge, amperes for |
| five hours 8 16 24 |
| |
|Average voltage on normal discharge 1.2 1.2 1.2 |
| |
|Normal rate of charge, amperes for |
| seven hours 8 16 24 |
| |
|Maximum rate of "boosting charge" |
| (for short time only) 50 100 140 |
| |
|Length of containing can (determined |
| by number of plates) 1½ 2⅝ 3-13/16 |
| |
|Width of containing can 5⅛ 5⅛ 5⅛ |
| |
|Height " " " 7-15/16 7-13/16 7¾ |
| |
|Height over all 8¾ 8¾ 8⅞ |
| |
|Weight of each cell alone, lbs. 4.6 7.4 10.5 |
| |
|Average weight per cell of battery, |
| assembled in trays 5.5 8.7 11.8 |
+——————————————————————————————————————————————————————————————+
[Illustration: FIG. 1,117.—Cell of Edison storage battery. The jar or
container is of nickel plated sheet steel with welded seams; the walls
are corrugated to give strength. The cell cover, of sheet steel, has
four mountings, two being pockets to contain stuffing boxes about the
terminal posts. One of the other two is a separator which separates
spray from the escaping gas while the battery is charging. The fourth
mounting is for filling with electrolyte. The electrolyte consists of
a 21% solution of potash in distilled water with a small per cent. of
lithia. The density of the electrolyte does not change on charge or
discharge.]
=Ques. How often should a battery be charged?=
Ans. At least once in two weeks, even if the use be only slight in
proportion to the output capacity.
In charging a storage battery, it is essential to remember the
fact that the normal charging rate is in proportion to the
voltage of the battery.
Thus, a 100 ampere hour battery, charged from a 110 volt
circuit at the rate of ten amperes per hour, would require ten
hours to charge, and would consume in that time an amount of
electrical energy represented by the product of 110 (voltage)
by 10 (amperes) which would give 1,100 watts, or 1⅒ kw.
[Illustration: FIG. 1,118.—Diagram illustrating method of charging
storage battery of stationary gas engine ignition system; the system
is simple to install and will give satisfactory results. Two storage
batteries are used, one being charged while the other is operating
the sparking coil. Where charging current is available at the point
where the batteries are used, the following diagram shows the system
of connections, which can be easily followed, A represents the source
of charging current and B the bank of lamps (or other resistance, such
as an ordinary rheostat) sufficient to cut down the charging voltage
to that required by the battery. C and D are two double pole double
throw knife switches connected at their hinges to two batteries, E and
F, each consisting of a group of cells. G represents the leads to the
sparking coil terminals. From the diagram, it will readily be seen
that by throwing the switches in opposite directions one battery will
be charging while the other battery is discharging to the engine, thus
giving a constant source of supply, and insuring that the spare battery
will be full and ready for service by the time the other is discharged.
The method of determining the necessary resistance for cutting down the
line voltage for charging the battery is illustrated by the following
example: If a battery require about 3 amperes for charging, how is this
current obtained from a 110 volt circuit? Each 16 candle power carbon
filament lamp in the lamp bank would give approximately ⅓ ampere with
the cells in series in the lamp circuit. Therefore, 3 x 3 or 9 lamps
should be used in parallel to give 3 amperes.]
=Ques. If in charging a battery, one or more of the cells do not boil
at the completion of the charge, or fail to show the proper voltage,
what should be done?=
Ans. The charging must be continued until the cadmium test shows the
required voltage, but if the prolonging of the charge be liable to
damage the plates in the other cells, the defective cell or cells
should be cut out of circuit when the battery discharges and then
placed in circuit again when the battery is recharged. If the desired
result cannot be attained by this method, the plates which require
additional charging may be charged in a separate cell.
[Illustration: FIGS. 1,119 and 1,120.—Emergency connections for weak
ignition battery. It sometimes occurs through carelessness or neglect,
that the storage battery is discharged so low that the engine explosion
will not take place, and it is necessary to run somehow or other for a
short time. In such cases the following suggestion may be followed: If
there be two storage batteries, connect them in series. If there be one
storage battery and a set of dry cells, connect the positive terminal
of the storage battery to the negative or outside terminal of the dry
cell; set and connect to the coil leads as if they were one battery.
The above suggestions should only be followed in emergency, for it may
injure the coils, and is harmful to the battery.]
=Ques. How is the cadmium test made?=
Ans. A plate of cadmium is mounted in a hard rubber frame and immersed
in the electrolyte. The test consists in taking voltage readings
between the cadmium plate and the positive or negative plates of the
cell. During charge the cadmium plate reads negative to the negative
plate, until the cell is about full, when the reading should be
zero; the charge should be continued until the cadmium reads 0.2 volt
positive to the negative while charging at the normal rate.
=Ques. Name some portable instruments that should be provided for
testing batteries.=
Ans. 1, a hydrometer syringe (specific gravity tester); 2, an acid
testing set (can be used instead of the syringe); 3, a low reading
voltmeter; 4, suitable prods, and 5, a thermometer.
=Ques. What precaution should be taken in charging a battery?=
Ans. Care should be taken not to have a naked flame anywhere in its
vicinity.
To either charge or discharge a battery at too rapid a rate
involves the generation of heat. Thus, while this is not liable
to result in a flame under usual conditions, the battery may
take fire, if it be improperly connected or improperly used.
=Ques. What is the effect of varying the charging current?=
Ans. In charging a storage cell, particularly for the first time, a
weaker current than that specified may be used with the same result,
provided the prescribed duration of the charge be proportionally
lengthened. The battery may also be occasionally charged beyond the
prescribed voltage, ten or twenty per cent. overcharge effecting no
injury, although if frequently repeated, it shortens the life of the
battery.
=Ques. What are the charge indications?=
Ans. The state of the charge is not only indicated by the density of
the electrolyte and the voltage of the cell, but also by the _color of
the plates_, which is considered by many authorities as one of the best
tests for ascertaining the condition of a battery.
[Illustration: FIGS. 1,121 and 1,122.—Two methods of charging from a
direct current lighting system. The simplest method of charging is from
an incandescent light circuit, using lamps connected in parallel to
reduce the voltage to that of the battery, the current being adjusted
by varying the number of lamps in circuit. The group of lamps is in
series with the battery to be charged, and the combination is connected
across the circuit furnishing the current. If the charging source be a
110-120 volt circuit, and the rate required be 6 amperes, twelve 16 c.
p. or six 32 c. p. lamps, in parallel, and the group in series with the
battery, will give the desired charging rate, unless high efficiency
lamps be used, when more will be required. In case a lower charging
rate, say 2 amperes be used, then a proportionately fewer number of
lamps will be needed; but the length of time required to complete
the charge will be correspondingly increased. Instead of lamps, as
in fig. 1,121, a rheostat is sometimes used, as shown in fig 1,122.
Its resistance should be such as to produce, when carrying the normal
charging current, a drop in volts equal to the difference between the
pressure of the charging source and that of the battery to be charged;
thus, if a battery of three cells, giving 6 volts, is to be charged
from a 110 volt circuit at a 6 ampere rate, the resistance would be,
according to Ohm's law,
(110 - 6) ÷ 6 = 17.3 ohms.
The carrying capacity of the rheostat should be slightly in excess
of the current required for charging. An ammeter with suitable scale
should be inserted in the battery circuit to indicate the current.
For charging more than one battery at a time from a 110 volt circuit,
the batteries should be connected in series (positive terminal of one
battery to the negative of the next, and so on). The charging rate
should be that of the battery with the lowest rate. The resistance to
be inserted will be less than if only one battery is being charged;
where lamp resistance is used, _this means more lamps in parallel_.
Care should be taken to remove each battery from the circuit as it
becomes charged, inserting additional resistance to take its place.]
=Ques. What are the colors of the plates?=
Ans. In the case of formed plates, and before the first charging, the
positives are of a dark brown color with whitish or reddish gray spots,
and the negatives are of a yellowish gray. The whitish or reddish gray
spots on the positive plates are small particles of lead sulphate which
have not been reduced to lead peroxide during the process of forming,
and represent _imperfect sulphation_.
As a general rule, the first charging should be carried on
until these spots completely disappear. After this the positive
plates should be of a dark red or chocolate color at the end of
the discharge, and of a wet slate or nearly black color when
fully charged. A very small discharge is sufficient, however,
to change them from black to the dark red or chocolate color.
If the battery has been discharged to a pressure lower than 1.8
volts, the white sulphate deposits will reappear, turning the
dark red color to a grayish tint in patches or all over the
face of the plate, or in the form of scales of a venetian red
color.
_The formation of these scales_ while charging indicates that
the maximum charging current is too large and should be reduced
until the scales or white deposits fall off or disappear, after
which the current can be increased again.
During charging, the yellowish gray color of the negatives
changes to a pale slate color which grows slightly darker at
the completion of the charge. The color of the negatives always
remains, however, much lighter than that of the positives.
=Ques. How are the best results obtained in charging?=
Ans. The rate of charge should be normal, except in cases of emergency.
At such a rate, unless the constant voltage method be employed, the
cell may be considered full when the voltmeter reads 2.5 volts during
charge. The electrolyte should be kept at uniform density throughout
the cell; when water is added, because of evaporation, it should be
added by means of a funnel reaching to the bottom of the cell. Care
should be taken never to add acid after evaporation; otherwise the
electrolyte will be too heavy. Hydrometer readings should be taken
regularly; the reading is an excellent indication of the amount of
charge in the battery. Hydrometer readings are useless, however, unless
the precaution be taken to keep the electrolyte of uniform density.
=Ques. What voltage should be used in charging?=
Ans. At the beginning of the charge the voltage should be about 5 per
cent. higher than the normal voltage of the battery, unless the latter
has been overdischarged, in which case the difference of pressure
should not exceed 2 per cent., otherwise the current might be too large.
[Illustration: FIG. 1,122.—Diagram showing charging connections for
"Exide" duplex sparking battery. C, charging source; D, double pole
single throw switch; E, single pole single throw switch; M, lamp
resistance "main" battery; R, lamp resistance "reserve" battery.]
=Ques. In what two ways may batteries be charged?=
Ans. They may be charged either at constant current or at constant
voltage.
Although the latter method is considered the better one by many
authorities, it is a fact, nevertheless, that if the charging
current be normal at the beginning of the charge, and no means
be provided for keeping it constant, it will diminish as the
charging progresses, thereby greatly increasing the length of
the time required for charging, and resulting in serious injury
to the plates.
=Ques. How may the charging current be kept constant?=
Ans. Its voltage should be gradually increased, first to about 10 or
15 per cent. above the voltage of the battery, and kept at that point
nearly to the end of the charge, where in consequence of the rapid rise
of pressure in the battery it might become necessary to increase the
voltage of the current to 30 or 40 per cent. above the normal of the
battery.
[Illustration: FIGS. 1,124 to 1,126.—Electric Storage Battery Co.
chloride cells. The voltage of cells of all capacities is slightly
above 2 volts on open circuit, and during discharge at the 8 hour rate
it varies from that point at the beginning to 1.75 volts at the end.]
=Ques. What tests should be made while charging?=
Ans. Occasional voltage and cadmium readings of each cell should be
taken for the purpose of ascertaining their condition and the behavior
of the separate plates.
=Ques. What tests should be made after charging?=
Ans. Each cell should be tested with a low reading voltmeter and
hydrometer about once a week. If any cell read low, it should be cut
out and examined to see if any material has been introduced which
would cause a short circuit. If this trouble do not exist, the cell
should be given an independent charge.
=Charge Indications.=—The state of the charge is not only indicated by
the density of the electrolyte and the voltage of the cell, but also by
the _color of the plates_, which is considered by many authorities as
one of the best tests for ascertaining the condition of a battery.
In the case of formed plates, and before the first charging,
the positives are of a dark brown color with whitish or
reddish gray spots and the negatives are of a yellowish gray.
The whitish or reddish gray spots on the positive plates are
small particles of lead sulphate which have not been reduced
to lead peroxide during the process of forming, and represent
_imperfect sulphation_.
As a general rule the first charging should be carried on until
these spots completely disappear. After this, the positive
plates should be of a dark red or chocolate color at the end
of a discharge and of a wet slate or nearly black color when
fully charged. A very small discharge is sufficient, however,
to change them from black to the dark red or chocolate color.
If the battery has been discharged to a pressure lower than 1.8
volts, the white sulphate deposits will reappear turning the
dark red color to a grayish tint in patches or all over the
surface of the plate, or in the form of scales of a venetian
red color.
The _formation of these scales_ during charging indicates that the
maximum charging current is too large and should be reduced until the
scales or white deposits fall off or disappear, after which the current
can be increased again.
=Ques. Describe the behavior of the electrolyte during discharge.=
Ans. There is a definite change in the density of the electrolyte for a
given amount of discharge.
The density of the electrolyte is, therefore, one of the best
indications of the state of charge, provided, of course, no
internal discharge due to local action takes place. If, when
the cell is charged, it show a density of 1.200, and when
discharged 1.130, the difference .07 represents the total
charge. If at any time the density be 1.165, then just one half
the amount of capacity has been taken from the cell.
It is necessary to stir the electrolyte well, in order for
these observations to be reliable.
If the discharge has taken place at a high rate, the cell
must stand for an hour or more before the electrolyte will
completely diffuse so that the density readings are correct.
[Illustration: FIG. 1,127.—Electric Storage Battery Co., arc lead
burning outfit. In assembling a storage battery element, a negative
plate is laid down with a separator on it, then a positive plate,
separator, negative plate, etc. The plates are so placed that all the
lugs of the positive plates are on one side and all the lugs of the
negative plates are on the other side. A strip, consisting of flat
strips of lead or lead alloy, having rectangular openings in it of the
same dimensions as the cross section of the lug of the plates, these
openings being spaced to register with the lugs, is then placed over
the plate lugs of the positive plates and a similar strap is placed
over the lugs of the negative plates. The lugs are then burned into
integral union with the straps.]
=Ques. Define the term "boiling."=
Ans. Boiling means the rapid evolution of gas when a cell is nearly
charged.
=Ques. What causes boiling?=
Ans. The amount of sulphate to be converted into peroxide becomes less
and less as the charge progresses and the plates therefore become
virtually smaller, so that the current becomes too large for the work
demanded of it. The result is, that part of the current not actually
used in the formation of peroxide decomposes the electrolyte into its
constituent elements.
=Ques. Why do the gases evolved produce a less milky appearance of the
electrolyte when a battery has been in use for a considerable time?=
Ans. The plates are better formed; consequently a larger charging
current can be used without producing "boiling".
[Illustration: FIG. 1,128.—Hydrogen gas generator for lead burning.
A complete lead burning outfit consists of the following parts: 1,
hydrogen gas generator; 2, trap for cleaning the gas and for preventing
the flame getting back in the generator; 3, air pump; 4, air tank; 5,
blow pipe; 6, lead burner's mixing tee; 7, length of 150 feet 5/16 inch
soft rubber tubing. When the generator is to be used for lead burning,
connect up the different parts of the apparatus as shown. Fill the trap
⅔ full with water and be sure to connect the gas generator to the
nipple on the bottle marked B. The stop cocks N and C must be closed.
See that the rubber plug at D is secured in place. Put the required
amount of zinc in the opening at H. (No. 1 generator requires: 15 lbs.
zinc, 9 gals, water, 3 gal. vitriol. No. 2 generator requires: 20 lbs.
zinc, 15 gals. water, 5 gals. vitriol). After putting in the zinc, add
the water and then the sulphuric acid, _and note that the water must
always be put in before the acid_. When making the connection be sure
that there are no low points in the hose between E and N, as water
is liable to accumulate at these low places, which will make the gas
damp which is detrimental to the burning. If water get into the line,
kink the hose between F and B, detach the hose at E and blow out the
water with air by opening the cocks, N, C and V. The length of the hose
between T and X must not be longer than five feet as the cocks N and C
must always be within the reach of the man who is using the flame. When
ready to use the flame, open N which allows the hydrogen gas to escape.
Light the same with a match and adjust the air cock C until the desired
flame is obtained. Different classes of work require different flames,
which can be obtained by changing the tips and by varying the amount of
gas and air with the cocks N and C. When the generator is laid up for
the night, or when the charge is exhausted, pull the hose off at F and
draw off the solution by removing the plug at D. The generator should
then be thoroughly washed by pouring water in A.]
=Ques. What may be said of charging a battery as quickly as possible?=
Ans. As a general rule, such a procedure should not be adopted unless
the battery be thoroughly discharged.
=Ques. What precaution should be taken?=
Ans. The danger to be avoided in rapidly charging a cell is its
tendency to heat.
=Ques. What apparatus is necessary in charging a battery?=
Ans. The battery may be charged from direct current mains having the
proper voltage. A current as near uniform as possible is required,
and existing conditions must be met in each separate case. Sometimes
a motor dynamo set with a regulating switchboard is used. Such an
apparatus consists of a direct current dynamo, driven direct from the
shaft of a motor, which, in turn, is energized by current from the line
circuit.
With a direct current on the line, a direct current dynamo may
be used; but with an alternating current an induction motor is
required. The speed of the motor is governed by a rheostat, and
the output of the dynamo is thus regulated as desired.
=Charging Through the Night.=—If an electric vehicle, after a late
evening run, is to be used in the morning, the battery may be charged
during the night without an attendant being present; but in doing this
great care must be taken not to excessively overcharge.
A careful estimate of the amount of current required should be made and
the rate of charge based on this estimate.
If, say, 72 ampere hours be required to recharge, and the time
available is nine hours, the average rate of charge must be 8
amperes.
If charging from a 110-volt circuit, the rate at the start
should be about 10 amperes; if from a 500-volt circuit, about 9
amperes; as, in charging from a source with constant voltage,
such as a lightning or trolley circuit, the rate into the
battery will fall as the charge progresses. This also applies
if the charging be done from a mercury arc rectifier without
attendance.
=Ques. What precautions should be taken in charging a battery out of a
vehicle?=
[Illustration: FIG. 1,129.—Interior view Northwestern storage battery.
The positive plate is of double grid construction, and the negative
plate consists of a special staggered grid. The separators used between
the plates are hard rubber, ribbed on one side so as to prevent the
positive plate from buckling. It is perforated so as to allow a free
circulation of the electrolyte and to decrease the internal resistance.
Rubber separators are better than the commonly used wood or paper
separators because they prevent local action. The flat side of each
separator is placed against a positive plate, preventing shedding or
jolting of the active material of the plate. This checks deterioration.
The jars are made of rubber composition; the walls are thick and the
covers well fitted to avoid spilling the electrolyte. All Northwestern
batteries are contained in rubber composition jars. The walls are thick
and the covers fit tightly to prevent spilling the acid. A hard wood
box, treated with a moisture repellant is used for the outer case.
These batteries are made in any voltage desired, the ampere capacity
ranging from 25 amp. hrs. to 300 amp. hrs.]
Ans. When a battery is being overhauled, the cells must be connected
together in series and to the charging source in relatively the same
manner as if they were in the vehicle; that is, the positive (+)
terminal of one group of cells must be connected to the negative (-)
terminal of the next group, and the two free terminals, one positive
and the other negative, must be connected respectively to the positive
and negative terminals of the charging circuit, but not until all of
the groups have been connected in series. Great care must always be
taken to have the polarities correct and the wire or cable for the
connections of ample size to carry, without heating, the heaviest
current used in charging.
=Charging Small Cells.=—For cells of the portable type, having
capacities from 10 to 100 ampere hours, the normal charging and
discharging rate should be about one-tenth the stated capacity, but
the discharging rate may be increased to double this value, in case of
necessity.
If the cells be provided with formed plates and not charged, the jars
should be filled with the proper electrolyte, and then charged for at
least 10 hours steady, or until they boil, then they may be discharged.
In the case of unformed plates, the charging should be from 30 to 40
hours, until the cells boil, and the plates assume their proper color.
=Ques. How are small cells easily charged from 110 or 220 volt
circuits?=
Ans. This may be conveniently done by inserting in one of the charging
leads an incandescent lamp which will pass the required quantity of
current. If the current required be as large as 10 amperes, a suitable
resistance or 10 lamps in parallel, each passing one ampere, may be
used. Great care should be taken to see that the battery is connected
properly.
=Period of Charging a New Battery.=—In the case of batteries provided
with formed plates, the first charge should extend over a period of
not less than 30 consecutive hours, without stopping, if possible,
or for periods of not less than 10 hours a day for three consecutive
days. The electrolyte will then commence to "boil" or "gas," assuming
a milky appearance due to the ascending bubbles of gas. At this stage
the density of the electrolyte as shown by the hydrometer placed in
each cell should be at least 1.200; it is essential that the charging
should be continued until every cell boils equally. From this point the
charging should be prolonged until the pressure, as determined by a
voltmeter or a cadmium tester, rises to about 2.55 volts.
[Illustration: FIG. 1,130.—The Willard underslung battery box for
automobiles. The general tendency in automobile design, is to keep
everything off the running board as far as possible, and to get tool
boxes, battery boxes, etc., placed somewhere under cover. To meet
these conditions the box here illustrated is arranged so that it can
be underslung beneath the rear footboard or supported on auxiliary
cross members made of strap iron and attached to the side members of
the chassis. It is usually suspended under the rear footboard or the
rear seat. The box has a chemically treated wood lining to make it
acid proof. The lining is so made that there is air space between the
battery and the sides of the box, except at the corners. Ventilation
is thus obtained and the battery kept dry. Accumulation of water or
spilled electrolyte in the bottom of the box is prevented by grooves in
the bottom board, extending downward from the corners to an outlet at
the center of the board. The box is also fitted with rubber bushings in
the holes where wire leaves the battery box.]
The charging of unformed plates is similar in all respects to
that of formed plates, except that the first charging should
extend over a period of at least 70 consecutive hours without
stopping, at the end of which time the plates should have the
characteristic colors of those of a fully charged battery. If
they do not, the charging should be prolonged and the cell
tested for density of electrolyte, and voltage, as already
described until the desired conditions are attained. Then the
battery may be discharged and recharged.
It is probable that a total of 300 to 400 hours of charging
with intervening discharges will be required to form the
plates until they acquire a good color, and the density of the
electrolyte becomes stable.
In regular charging, the rate should be rapid when the battery is
nearly exhausted, but it should be greatly reduced at the end of the
charge after passing the point of boiling. Charging at too low a rate
is always injurious.
=Ques. What may be said with respect to the capacity of a new battery?=
Ans. A new battery will never give its full capacity till after about
twenty discharges. During this time it should be given about 25%
overcharge. After that, 10% overcharge, that is, 10% more charge than
was taken out, will be sufficient for ordinary work.
=High Charging Rates.=—Occasionally it is desirable to charge a
battery as quickly as possible. As a general rule, such a procedure
should not be adopted unless the battery be thoroughly discharged, and
not then, unless done by a person who thoroughly understands what he is
about; battery makers will always furnish data and directions to meet
emergencies.
In charging a battery at a high rate, the danger to be avoided
is the tendency of the cells to heat. The troubles that might
arise from this cause may be prevented by immediately reducing
the current strength. The proper rate of charge for a given
battery of cells may be thus discovered by experiment. A
battery should never be charged at a high rate unless it be
completely exhausted, since it is a fact that the rate of
charge that it will absorb is dependent upon the amount of
energy already absorbed.
[Illustration: FIG. 1,131.—Instructions for taking voltage readings
("National" batteries). The batteries are made up of several cells,
usually two or three, each cell representing approximately 2 volts when
battery is on "open circuit" (neither charging nor discharging). It
is sometimes advisable to take individual readings of the cells, both
to determine on charge if all the cells be evenly charged, and also
on discharge to be sure that the cells are evenly discharged. To do
this, a low-reading voltmeter must be used with prods attached to the
voltmeter leads that can be forced into the terminals so as to insure
good contacts. To test the positive end cell, put the positive prod on
the positive terminal of the battery and the negative prod into small
hole back of positive terminal in hard rubber cover. Middle cell (in
6 volt, type "Y" batteries) is tested by inserting the positive prod
in the small hole back of the positive terminal, and the negative prod
in small hole back of negative terminal. In the 120 ampere hour, Auto
type of battery, the middle cell is tested by inserting the positive
prod in the small hole back of the positive terminal and the negative
prod on the middle terminal. The negative end cell is tested by putting
the negative prod on the negative terminal and the positive in the
small hole in rubber cover back of the negative terminal. A charging
cell at end of charge should read about 2.55 volts. A fully charged
cell on open circuit should read about 2.1 volts. Since open circuit
readings vary under different conditions, as to age, acid, etc., little
significance should be attached to them. A discharged cell voltage will
vary considerably with the many different coils, engines, etc., but in
the majority of cases should read between 1.8 to 1.9 volts, while motor
is in operation.]
For rapid charging, when a battery has to be charged in four hours, the
current should vary about as follows:
40 per cent. of total 1st hour
25 " " " " 2nd "
20 " " " " 3rd "
15 " " " " 4th "
For quick charging in three hours the rates should be: 50 per
cent. 1st hour; 33⅓ per cent. 2nd hour; 16⅔ per cent. 3rd
hour.
=Mercury Arc Rectifier.=—This is a device for obtaining direct current
from alternating current for use in charging storage batteries. The
transformation is obtained at a low cost, because the regulation is
obtained from the alternating side of the rectifier, while the current
comes from the direct current side.
[Illustration: FIGS. 1,132 to 1,134.—Mercury arc rectifier outfit,
or charging set. The cuts show front, rear, and side views of the
rectifier, illustrating the arrangement on a panel, of the rectifier
tube with its connection and operating devices.]
The theory is as follows: In an exhaust tube having one or more mercury
electrodes, ionized vapor is supplied by the negative electrode or
cathode, when the latter is in a state of "excitation." This condition
of excitation can be kept up only as long as there is current flowing
toward the negative electrode.
If the direction of the voltage be reversed, so that the formerly
negative electrode is now positive, the current ceases to flow, since
in order to flow in the opposite direction it would require the
formation of a new negative electrode, which can be accomplished only
by special means. Therefore, the current is always flowing toward one
electrode—the cathode, which is kept excited by the current itself.
Such a tube would cease to operate on alternating current voltage
after half a cycle if some means were not provided to maintain a flow
of current continuously towards the negative electrode.
[Illustration: FIG. 1,135.—Elementary diagram of mercury arc rectifier
connections. A, A´, graphite anodes; B, mercury cathode; C, small
starting electrode; D, battery connection; E, and F reactance coils; G
and H, transformer terminals; J, battery.]
=Ques. Describe the construction and operation of a mercury arc
rectifier.=
Ans. Fig. 1,135 is an elementary diagram of connections. The rectifier
tube in an exhausted glass vessel in which are two graphite anodes
A, A´, and one mercury cathode B. The small starting electrode C is
connected to one side of the alternating circuit, through resistance;
and by rocking the tube a slight arc is formed, which starts the
operation of the rectifier tube. At the instant the terminal H of
the supply transformer is positive, the anode A is then positive, and
the arc is free to flow between A and B. Following the direction of
the arrow still further, the current passes through the battery J,
through one-half of the main reactance coil E, and back to the negative
terminal G of the transformer. When the impressed voltage falls below
a value sufficient to maintain the arc against the reverse voltage of
the arc and load, the reactance E, which heretofore has been charging,
now discharges, the discharge current being in the same direction as
formerly. This serves to maintain the arc in the rectifier tube until
the voltage of the supply has passed through zero, reversed, and
built up such a value as to cause the anode A to have a sufficiently
positive value to start the arc between it and the cathode B. The
discharge circuit of the reactance coil E is now through the arc A'B
instead of through its former circuit. Consequently the arc A'B is now
supplied with current, partly from the transformer, and partly from the
reactance coil E. The new circuit from the transformer is indicated by
the arrows enclosed in circles.
=Ques. How is a mercury arc rectifier started?=
Ans. A rectifier outfit with its starting devices, etc., is shown in
figs. 1,132 to 1,134. To start the rectifier, close in order named
line switch and circuit breaker; hold the starting switch in opposite
position from normal; rock the tube gently by rectifier shaker. When
the tube starts, as shown by greenish blue light, release starting
switch and see that it goes back to normal position. Adjust the
charging current by means of fine regulation switch on the left; or, if
not sufficient, by one button of coarse regulation switch on the right.
The regulating switch may have to be adjusted occasionally during
charge, if it be desired to maintain the charging current approximately
constant.
=Capacity.=—The unit of capacity of a storage cell is the _ampere
hour_, that is, the ability to discharge one ampere continuously
for one hour. For instance, a 100 ampere hour battery will give a
continuous discharge of 12½ amperes for eight hours. It should
theoretically give a discharge of 25 amperes continuously for four
hours, or 50 amperes for two hours, but in reality, the ampere hour
capacity decreases with an increase of discharge rate.
It requires, theoretically .135 ounces of metallic lead on either
element reduced to sponge lead or to lead peroxide to produce one
ampere hour; in practice, from four to six times this amount is
required.
The reason for this is because it is impossible to reduce all
the active material, to bring every particle in contact with
the electrolyte, or to cause every part to be penetrated by the
current.
Experiments show that from .5 to .8 ounces of sponge lead, and from .53
to .86 ounces of metallic lead converted into peroxide, are required on
their respective elements to produce a discharge of one ampere hour at
ordinary commercial rates.
The capacity increases with the temperature, being about one per cent.
for each degree Fahr. increase in temperature.
Battery capacity depends on the size and number of plates; the quantity
of active material present, and the quantity of electrolyte.
For an eight hour rate of discharge and 60 degrees temperature, the
capacity of American batteries varies from 40 to 60 ampere hours per
square foot of positive plate surface ( = 2 × number of positive plates
in parallel × length × breadth).
The following table gives the variation of capacity for different rates
of discharge:
Capacity Variation for Different Discharge Rates
+——————————-+——————————————————————+
| Discharge | Per cent of capacity |
| rate | at 8 hour rate |
+——————————-+——————————————————————+
| | =Plante= | =Faure= |
| 8 hour | 100% | 100% |
| 6 hour | 96% | 96% |
| 4 hour | 80% | 88% |
| 2 hour | 61% | 70% |
| 1 hour | 56% | 48% |
+——————————-+——————————+——————————-+
[Illustration: FIG. 1,136.—"Exide" connector puller for removing
connectors.]
=Ques. How may the capacity of a battery be increased?=
Ans. By mixing organic materials with the lead oxide, _but any such
mixture is always accompanied by a rapid deterioration of the plates_.
=Discharging.=—In discharging a battery its voltage should never be
allowed to fall below 1.8 volts, under load, thus leaving about 30 per
cent. of the total capacity unused. The normal discharging current
may be equal to the normal charging current, but a discharge equal to
3 or 4 times the normal may be given without injury to the plates.
Some types may be discharged at even six or seven times the normal
rate. In such cases, however, the capacity will be reduced in the same
proportion, as before explained in the paragraph dealing with battery
capacities.
[Illustration: FIGS. 1,137 to 1,151.—Parts of the Witherbee battery.
1, jar; 2, inside cover; 3, cover; 4, handle; 5, vent cap; 6, cover,
screws, nuts and washers; 7, handle eyes, nuts and washers; 8, rubber
covered nut; 9, spannernut; 10, plate strap for positive plates;
11, plate strap for negative plates; 12, rubber separator; 13, wood
separator; 14, positive group of plates; 15, negative group of plates;
16, positive plate; 17, negative plate; 18, cell connector. An element
consists of a complete set of plates bound together on strap, with wood
and rubber separators for a single cell. Positive plates are brown,
negative plates, gray.]
=Ques. What is the effect of discharging too rapidly?=
Ans. It tends to break the plates, and in the case of pasted plates, a
very sudden discharge will dislodge the paste.
=Ques. How is the discharge capacity of a storage battery stated?=
Ans. In ampere hours. This, unless otherwise specified, refers to
its output of current at the eight hour rate. Most manufacturers of
automobile batteries specify only the amperage of the discharge at
three and four hours. Thus, at the eight hour rate, a cell which will
discharge at ten amperes for eight hours is said to have a capacity
of eighty ampere hours. It does not follow that eighty amperes would
be secured if the cell were discharged in one hour. It is safe to say
that not more than forty amperes would be the result with this rapid
discharge.
As a general rule, the one hour discharge rate is four times
that of the normal, or eight hour discharge, and considerations
of economy and prudence suggest that it should never be
exceeded, if, indeed, it ever be employed. The three hour
discharge, which is normally twice that of the eight hour,
is usually the highest that is prudent, while the four hour
discharge is the one most often employed in vehicles for the
average high speed riding.
=Ques. What should be the maximum rate of discharge?=
Ans. The one-hour rate; this when used, should not extend over fifteen
or twenty minutes. In the case of regulating batteries a forty-five
minute rate of discharge may be allowed for one or two minutes during
great fluctuations of load.
=Ques. How does the capacity decrease?=
Ans. It decreases with the increase in current output.
An 80 ampere hour cell, capable of delivering 10 amperes for 8
hours, would, when discharged at 14 amperes, have a capacity of
70 ampere hours; when discharged at 20, its capacity would be
60; and when discharged at 40, its capacity will have decreased
from 80 to 40 ampere hours.
[Illustration: FIG. 1,152.—The Edison alternating current rectifier.
It consists of an electro-mechanically operated valve which allows
current waves of only one polarity to pass through it from the
alternating current circuit to the battery which is to be charged. An
indicating snap switch of the usual form controls the starting and
stopping of the charging current. The rectifier gives any desired
charging rate within its capacity. The illustration shows the rectifier
connected up and charging an ignition battery of five Edison cells.
The connections consist of the usual connecting cord and plug and a
charging lead running from the plus side of the charging terminals
on the rectifier to the plus pole of the battery, and another lead
connecting the negative terminals as shown. In turning the snap switch
to the "on" position, the proper charging current will flow into the
battery. When charging is completed, the switch is turned to the "off"
position and the battery leads disconnected.]
=Ques. What, in general, are the indications of the quantity of
electricity remaining within a cell?=
Ans. The voltage, and the density of the electrolyte.
=Ques. What should be done after discharging?=
Ans. Whenever possible the battery should be immediately charged.
=The Battery Room.=—Precautions should be taken to prevent any direct
sunlight falling on the battery cells in glass jars, as the breakage
of such jars due to unequal expansion of the different portions of the
glass, is a source of constant trouble and danger.
[Illustration: FIG. 1,153.—Permanent connections for Edison rectifier.
As shown, the rectifier is connected to a small switch and cutout.]
The exclusion of direct sunlight also tends to keep the evaporation of
the electrolyte at a minimum.
[Illustration: FIG. 1,154.—Edison Alternating Current rectifier; view
with cover open showing parts. B, primary circuit cord; C, condenser;
E, primary relay; F, secondary switch; S, alternating circuit switch;
T, transformer.]
[Illustration: FIG. 1,155.—Vibrating unit of Edison alternating
current rectifier. M, permanent magnet; N, carbon vibrating contact; O,
comb radiator; P, primary circuit coil; Q, vibrator adjustment screw.]
Operation of Edison Rectifier
The operation of the Edison rectifier may be explained as
follows with the aid of figs. 1,154 to 1,156 (the parts being
uniformly lettered in the figures): The primary circuit taken
from the alternating current mains by the cord B, embraces the
primary winding of the transformer T, a condenser C, and the
coils P, of the vibrating units, fig. 1,155.
The secondary circuit from the transformer embraces the
massive carbon and copper contacts (N and O, fig. 1,156) which
pass only the positive waves of the alternating current, for
charging batteries or other duty.
An ammeter and rheostat may be placed in this charging circuit
if the current is to be varied, or a fixed connection may be
substituted on the base of the rectifier if it is to be used
for the maximum duty of 8 or 16 amperes.
The vibrating unit (fig. 1,155), which operates in a manner
similar to the well known action of a polarized relay, includes
a permanent magnet M; the coil in the primary circuit P; the
vibrating armature of steel with removable carbon contact N;
the stationary copper contact with comb top for heat radiation
O, and the screw Q for adjusting the amplitude of the armature
vibration.
The vibrating armature of each unit is divided into two parts,
which gives flexibility, affords increased current capacity
and minimizes sparking, the two leads shown being connected
together in one circuit.
A primary relay and a secondary switch (E and F, figs. 1,154
and 1,156), close their contacts when current is flowing.
Upon failure of the main alternating current line they operate
to open the charging circuit. A storage battery is thus
prevented discharging through the rectifier.
Upon resumption of the main alternating current, the rectifier
starts automatically.
[Illustration: FIG. 1,156.—Elementary diagram of connections.]
Every battery room should be provided with a water tap and sink. The
floor should be paved with vitrified brick, preferably blue or yellow
in color, of diamond pattern and sloping in all directions toward
suitable drains. A floor of this type can be easily washed by flooding
with water, and its patterns tend to keep it dry under foot at all
times. Wooden floors are rotted very quickly by acid spillings and by
the spray.
The room should be kept absolutely clear of everything, which may be
injured, by the sulphuric acid fumes and it should be well ventilated
to insure the safety and good health of the attendants.
A battery, even at rest, gives off hydrogen which when diluted with air
forms a mixture which is very liable to explode if brought in contact
with any kind of flame. Unless proper ventilation be provided, the
breaking of the connection when a current is flowing, or the lighting
of a bare flame lamp in the battery room would be dangerous.
=Battery Attendants and Workmen.=—Those employed in setting up
batteries are liable to suffer from soreness of hands and the
destruction of clothing unless proper precautions be taken to prevent
the same. In order to avoid these troubles, the boots should be painted
with paraffine mixed with an equal quantity of beeswax.
The clothing should be of woolen material, which, unlike cotton, is
practically unaffected by the acid. If cotton shirts be worn, they
should be dipped in a strong solution of washing soda and then rough
dried.
An apron of sacking, backed with flannel should be worn over all the
other clothes. A bottle of strong ammonia should be kept in the
battery room at all times, and in case of an accidental splash of acid
on the clothes, the immediate application of a small quantity of the
ammonia, by means of the stopper, will at once neutralize the acid and
prevent it burning a hole in the material. A pail containing water made
strongly alkaline with washing soda should also be kept conveniently
at hand during all operations in the battery room. The hands should be
dipped occasionally in this water in order to prevent the skin smarting
and becoming sore under the action of the acid.
[Illustration: FIG. 1,157.—Interior of storage battery room showing
arrangement of cells. A, are the cell insulators; B, wooden stringers;
C, supporting pieces.]
If a splash of acid should happen to enter the eye, it should
be washed at once with clean water, warm water preferably, and
then put one or two drops of olive oil into the eye. If olive
oil be not immediately available, any kind of engine oil is
better than none at all.
=Points on Care and Management.=—In setting up storage cells, they
should be placed in as few tiers as possible, and in such a manner that
the direct rays of the sun are not allowed to fall upon the cells. The
rays of the sun are likely to crack the glass. This is probably due to
the unequal expansion of the glass, for it has been found that jars
which are carefully annealed never crack in this manner. Of course, the
latter precaution does not apply to large batteries, where lead lined
wooden tanks or solid lead boxes are used.
In installing plants where expert attendance is not to be had, it is
well to place in the circuit two magnetic cut outs, one set for maximum
current, and the other for minimum voltage, so that the battery cannot
be discharged too low.
=Ques. How should the cells be placed?=
Ans. They should be placed as shown in fig. 1,151, on insulators A,
resting on wooden stringers B, and supporting pieces C placed on the
floor. The insulators are usually of glass or porcelain, which in
certain patterns may be filled with oil, to insure better insulation as
shown in figs. 1,165 and 1,166.
In setting up a battery, it should be remembered that plates
deteriorate on standing exposed to the air. They should,
therefore, be unpacked and set up immediately on arrival. When
they are entirely connected up, they are ready for the addition
of the electrolyte, and for the forming charge, which they
should receive immediately.
=Ques. How should the wooden stringers, shelves, cell boards, and trays
be treated?=
Ans. They should be thoroughly varnished to insure cleanliness as well
as good insulation.
Outside of each cell and close to the mouth, melted paraffine
should be applied by means of a brush, so as to form a
band about an inch wide, for the purpose of preventing the
electrolyte creeping over the top of the jar, wetting the
outside, and thereby impairing the insulation.
=Ques. What should be done to avoid waste of current by leakage?=
Ans. Each cell of the battery must be thoroughly insulated.
=Ques. What is the effect of verdigris which forms on the terminals?=
Ans. It is a poor conductor and should therefore be removed and the
terminals kept bright and clean to insure the proper flow of the
current.
[Illustration: FIG. 1,158.—Charging "Champion" battery with charging
plug. Where direct lighting current is available, recharging may be
done by means of the charging plug. First insert the plug in a regular
socket. Then screw a 50 c.p. lamp into the plug and turn on. To tell
the positive from the negative, lay both wires on a small piece of red
litmus or test paper moistened. The negative wire makes a mark on the
paper. This wire must go to the negative post of battery. This will
fully charge the "6-25-G" battery in 15 to 20 hours.]
=Ques. What precautions should be taken in unpacking cells?=
Ans. The plates should be handled carefully. When they are sent out
from the factory already built into sections, they should be unpacked
without disturbing a single plate. In all cases, every particle of
packing, straw, hay and any chips and bits of parts should be carefully
removed, and all the dust should be blown out of the spaces between the
plates by means of a bellows or other similar device.
NOTE.—_Champion directions for repairs._ To replace broken
jars in a battery remove the lid and lift out elements bodily.
Empty the good jars with a syringe or by tilting the battery
over. Never put the acid in any vessel except glass, stone
or lead. Put new jars in place same as others and run melted
paraffine around the edges. The wax must be broken off the
elements that are to go into new jars and be poured on again.
Fill the jars with acid to ¾" from tops. Melt the broken wax
in a tin ladle and pour over the acid about ½" thick. Do not
fill with wax to tops of jars. When the wax gets cold it will
be found to have shrunk away from the edges of the jars. Fill
up the opening with a little melted paraffine wax by means of a
squirt can. Cut a small hole in the middle of the wax seal for
a vent. Smear the brass posts and terminals and inside of case
with vaseline to prevent creeping of the acid. The "6-25-G"
requires one-half gallon of acid and the "6-50-G" one gallon.
Although such particles are good non-conductors, the action of
the sulphuric acid electrolyte carbonizes them, giving them
conducting properties which tend to produce leakage.
[Illustration: FIGS. 1,159 to 1,161.—"Champion" electric light
equipment designed especially for use on launches, yachts, and
country residences. The outfit consists of three essential parts: 1,
a dynamo run by belt from main engine; 2, a storage battery, and 3, a
switchboard to regulate, measure and control the current.]
=Ques. How should the cells be assembled?=
Ans. In placing the plates or plate sections in the containing jars
or tanks, care should be taken to see that the supporting frame of
paraffined wood bears evenly on the bottom of the jar. If they do not,
wedges of paraffined wood should be placed under the frame, so as to
distribute the weight of the section equally. Each section should be
lowered gently into the jar until it rests fairly upon the frame, and
care should be taken to see that none of the plates have shifted, and
that the section is situated centrally in the jar, with a small clear
space all around.
=Ques. How should the cells be arranged?=
Ans. They should be so placed that the battery attendant can see the
edges of the plates and consequently the spaces between them at the
same time.
=Ques. Describe the method of connecting the cells.=
Ans. This is accomplished by means of solder, bolts and nuts, or
clamps, according to circumstances. The use of solder is not essential
if there be a good surface of the lead strip of one cell in contact
with that of the next, and provided these contact surfaces have been
well cleaned. Usually, the ends of the lead strips are turned up so
that the junction of two cells takes the form of an inverted T as shown
in fig. 1,162.
[Illustration: FIG. 1,162.—Two storage cells; view showing the
inverted T form of connection.]
=Ques. What precaution should be taken in joining the terminals of the
cells?=
Ans. The contact at the junctions should be very thorough, otherwise
they will become heated when a current is flowing, and it is desirable
that the connections should include as little lead strip in the circuit
as possible, thereby reducing the amount of useless resistance.
Brass or gun metal clamps may be kept clean by brushing them
over with melted paraffin after they have been screwed up
tightly. When thus treated they serve to indicate points of bad
contact by heat, generated at such points, when the current is
flowing, softening the paraffin and changing its normal color.
Vaseline and different kinds of anti-sulphuric acid varnishes,
or preparations that are not attacked by the electrolyte, may
also be used for this purpose. It is a good plan to color the
varnish with vermillion or lamp black and paint the positive
connections red and the negative connections black, and
also other parts of the installation for distinguishing the
polarities.
=Cell Connections.=—The cells may be connected together either
in series or parallel, or in parallel-series or series-parallel
combinations, according to the requirements, but in all cases it is
best to use the simplest arrangement practicable.
For instance: if the cells employed in an installation
requiring 110 volts, have only half the capacity required, and
55 cells give the desired voltage, then the number of cells
must be increased to 110, and theoretically the required number
of amperes hours at 110 volts may be obtained in one of two
ways: 1, by connecting the cells in pairs in parallel and then
coupling the pairs together in series, and 2, by arranging the
110 cells in two complete batteries of 55 cells each connected
in series, then coupling the two batteries in parallel.
The first method is quite impracticable, however, as the
slightest difference between the voltages of the two cells of
any pair will result in the one having the greater pressure
discharging into the other, thereby causing the entire battery
to quickly deteriorate.
NOTE.—_To determine the positive wire._ Without a voltmeter,
the positive terminal of the charging circuit can be determined
by attaching a piece of clean lead to each wire which is to be
connected to the battery, and immersing them, without touching
each other, in a glass or other insulating vessel containing
water to which is added a drop or two of sulphuric acid. After
the current has passed through the circuit for a short time,
the positive lead will commence to discolor, and, if left
long enough, will turn brown. Bubbles will arise from the two
terminals immersed, the larger and more frequent ones being
from the negative, the smaller ones from the positive.
NOTE.—_Method of disconnecting "National" cells._ There
are two methods of disconnecting the cells employing link
connectors. First a ⅝ inch bit or twist drill may be used,
boring down into the top of the posts about ¼ inch. The link
will then be loosened and can be removed. This leaves the link,
as well as the post, in good condition for reburning. Second
the link may be cut in the center. A flame should be played on
the top of the post, at the same time grasping the end of the
half link firmly with pliers. When the connection has become
warmed (care being taken not to melt the lead) the half link
can be twisted loose from the port. New links may be used if
desired in re-assembling the cells. It is not necessary to
remove the covers from the element, the links may be cut in the
center and the plates removed from the jars without removing
the links from the ports. The links can be afterwards reburned
together in the center. When the cells are equipped with "T" or
"L" straps, they should be cut apart with hack saw or chisel
midway between the cells, and in re-assembling, burned together
at this point.
=Battery Troubles.=—To successfully cope with faults in storage
batteries, there are two requisites: 1, a thorough knowledge of the
construction and principle of operation of the battery, and 2, a well
ordered procedure in looking for the source of trouble. The faults
which are usually encountered by those who operate storage batteries
are here given.
[Illustration: FIG. 1,163.—Arrangement of battery cells and stand.
A, cable lugs; B, bus bars; C, glass tanks; D, plate; E, glass
insulators; Q, vitrified brick; O, lead washers. Battery cells are
set up on stands; the one shown being built for a 100 ampere battery.
Larger sizes would, of course, require heavier stands, and if space be
limited, the cells may be set in rows, one above the other. However,
it is evidently much better to place the cells in single rows, where
they will be convenient for inspection and repairs or any work that has
to be done on them. There are several other ways of setting a battery,
one of which is to place the stringers on the floor, on vitrified
brick or some other insulator, and then place trays filled with sand
on the stringers, setting the cells in the trays on glass insulators.
The battery room should be dry, clean, well ventilated and free from
metal work, also neither too hot nor too cold. Too high a temperature
in the battery will shorten the life of the plates, and although there
is no danger of the battery freezing, a low temperature, while it is
maintained, reduces the capacity; otherwise cold has no ill effect on
the battery. A good temperature for the battery room is about 60° F.
A damp, dirty room is conductive to grounds and surface leakage, and
there is danger of impurities getting into the cells. If the room be
very damp the electrolyte may absorb enough moisture to cause the cells
to overflow. Strong floors are necessary to support a battery, as one
of a 100 ampere, 125 volt capacity weighs from 12 to 13 tons. A wood
floor may be used, but a cement floor is better, and a glazed vitrified
brick floor is better still. Wooden floors will rot quickly from the
acid, which is sure to get onto it more or less; a cement floor will be
disintegrated if too much acid get onto it. This kind of floor forms
a first class ground if there be any chance for one; the glazed brick
floor is not affected by the acid and is an insulator.]
=Short Circuiting.=—A form of derangement that may occasionally affect
storage batteries is short circuiting. It may be caused by some of the
active material—if the cell be of the pasted variety—scaling off and
dropping between the plates, or by an over collection of sediment in
the bottom of the cell.
Should the operator suspect trouble with his battery he may
discover a short circuited cell by the marked difference
in color of the plates or of the specific gravity of the
electrolyte, as compared with the other cells. No particular
damage will be caused, if the trouble be discovered and removed
before these symptoms become too marked.
If a foreign substance has become lodged between the plates, it
may be removed by a wood or glass instrument.
If some of the active material has scaled off, it may be forced
down to the bottom of the jar. If excessive sediment be found,
the jar and plates should be washed carefully, and reassembled.
A cell that has been short circuited may be disconnected from the
battery and charged and discharged several times separately which may
remedy the trouble.
=Ques. How are internal short circuits indicated?=
Ans. Short circuits in a cell are indicated by short capacity, low
voltage and low specific gravity, excessive heating and evaporation of
the electrolyte.
=Ques. How are internal short circuits located?=
Ans. If the trouble cannot be located by the eye, the battery should be
connected in series and discharged at the normal rate through suitable
resistance. If a suitable rheostat be not available, a water resistance
may be used.
This consists of a receptacle (which must not be of metal)
filled with very weak acid solution, or with salt water in
which are suspended two metal plates, which are connected by
wires through an ammeter. The current may be regulated by
altering the distance between the plates, or by varying the
strength of the solution. As the discharge progresses the
voltage will gradually decrease, and it should be frequently
read at the battery terminals; as soon as it shows a sudden
drop, the voltage of each cell should be read with a low
reading voltmeter.
While the readings are being taken, the discharge rate should
be kept constant and the discharge continued until the majority
of the cells read 1.70 volts; those reading less should be
noted. The discharge should be followed by a charge until the
cells which read 1.70 volts are up, then the low cells should
be cut out, examined, and the trouble remedied.
=Overdischarge: Buckling.=—On account of unequal expansion of the two
sides of a plate, or certain portions thereof, the strains thus set up
may distort it and cause it to assume a buckled shape, that is, bent so
one side is concave.
[Illustration: FIG. 1,164.—Method of straightening a buckled plate.
Buckling is caused by the unequal expansion of the plates which is due
to the sulphate lodging on the plates, thus preventing action taking
place at that point; and by excessive charging. If the plates be not
badly buckled, they can be placed between 2 boards and with a little
pressure, can be straightened out.]
Buckling is due always to over discharge on either the whole,
or some portion of the plate. Occasional buckling may occur
with too rapid charge and discharge.
=Sulphation of Plates.=—During discharge a storage cell deteriorates
on account of the formation of lead sulphate over the surface of the
plates. This lead sulphate is the product of the chemical combination
of active material with the electrolyte. It is a non-conductor, white
in color and of greater volume, in proportion than the active material.
When the discharge is over prolonged, sulphation is evidenced by the
electrodes becoming lighter in color, because of the sulphate which
lessens the active surface.
[Illustration: FIGS. 1,165 and 1,166.—Oil Insulator; fig. 1,165,
general view; fig. 1,166, sectional view. Whenever a number of open
cells are in use, unless precautions be taken, electrical leakage
between the cells invariably occurs. This leakage is due chiefly to the
semi-conducting nature of the thin layer of moisture which frequently
covers not only the glass containing cells, but the unimmersed parts of
the elements, and even the shelves on which the cells rest. To prevent
this waste of energy, the outside of the cells should occasionally be
well cleaned and thoroughly dried. A little vaseline or tallow may
then be rubbed over them to advantage. The shelves or supports for
the cells, should either be well varnished or coated with paraffin
wax. Electrical leakage is greatly reduced if each cell be mounted
on a glass or earthenware insulator, as shown in the illustrations.
The insulator here shown is in two parts and of a mushroom shape. The
lower cup contains a small quantity of some non-evaporating oil, and
as the conducted moisture cannot bridge across this, a nearly perfect
insulating medium is obtained. These insulators are made in various
sizes and may be obtained in earthenware or glass. Those made of glass
are found to give the best results.]
=Ques. Name some causes of sulphation.=
Ans. It is sometimes caused by a too weak or too strong acid solution,
but more generally by continued over discharging, or too rapid
discharging of the batteries, or by allowing them to remain uncharged
for long periods of time.
=Ques. What is the effect of sulphation?=
Ans. It tends to cause shedding of the active material, buckling
of plates, loss of capacity, increase of resistance and consequent
reduction of efficiency, and increase of temperature with flow of
current. A sufficient amount of lead peroxide and sponge lead must
be retained on the plates to reduce this resistance, otherwise the
charging current cannot flow through the active material and regenerate
the battery.
[Illustration: FIG. 1,167.—Illustrating method of placing plates in
glass jars.]
=Ques. What should be done in case of sulphation?=
Ans. Charge the battery below the maximum rate, necessarily prolonging
the charge, until the plates assume the proper color. This is a tedious
task, but it must not be hastened, as rapid charging will cause serious
buckling.
* * * * *
NOTE.—_How to destroy acid vapor in storage battery rooms_:
The best remedy is a good system of thorough and rapid
ventilation; failing this the evil effect of the acid may be
minimized by the fumes of a powerful alkali such as ammonia,
which will readily combine with the sulphuric acid to form
sulphate of ammonia, an inert and harmless salt. If the use
of liquid ammonia be objectionable, the granulated carbonate
of ammonia will do equally well. The ammonia fumes are best
obtained by placing dilute ammonia in shallow dishes, so that
an extensive evaporating surface is obtained. In the same way
the corroding dew which is so frequently deposited on the lugs
and connectors of storage battery elements may readily be
neutralized by the application of a solution of ammonia, or
even common washing soda. A good method of protecting metal
work in battery rooms is to smear it over evenly with vaseline.
The charging should be done at low rates. Discharge should not
be carried below 1.8 volts per cell, and the charging current
should be stopped when each cell shows 2.4 volts.
If the plates be in a very bad condition, a little of the white
sulphate deposit on each of the positive plates may be removed
with a stick, thus exposing a part of the good surface to the
action of the electrolyte.
If the positive plates cannot be restored to their proper color
as directed, it is cheaper to replace them by a new set, rather
than to attempt their recovery by means of reversals.
Electrical Data on "National" Cells
(Size of plate 4⅞" × 8⅝")
======================================+=======+=======+========+========
Number of Plates per cell | 5 | 7 | 9 | 11
——————————————————————————————————————+——————-+——————-+————————+————————
{for 4 hours |12 |18 | 24 | 30
Discharge in amperes {for 5 hours |10¼ |15¼ | 20½ | 25½
{for 6 hours | 9¼ |13¾ | 18½ | 23
| | | |
{at 4 hour rate|48 |72 | 96 |120
Ampere hour capacity {at 5 hour rate|51 |76 |102 |127
{at 6 hour rate|55 |83 |110 |138
| | | |
Outside measurements of rubber {Length| 1⅞ | 2⅝ | 3⅜ | 4-3/16
jar, in inches {Width | 5-5/16| 5-5/16| 5-5/16| 5-5/16
{Height|11¾ |11¾ | 11¾ | 11¾
| | | |
Weight of cell complete, in lbs |14¼ |19¼ | 24¼ | 29¾
| | | |
Weight of electrolyte, in lbs | 1 | 2 | 3½ | 5
——————————————————————————————————————+——————-+——————-+————————+————————
=Lack of Capacity.=—This is usually due to the clogging of the pores
in the plate with sulphate which is invisible because the surface of
the plate is maintained in proper condition but the interior portions
of the active material have not been thoroughly reduced. To correct
this condition, the battery should be given a prolonged overcharge at
low current rates, say about one fourth the normal 8 hour charging rate.
NOTE.—_Oxide of lead_, _litharge_, or _plumbic oxide_ is
sometimes found native as lead ochre, and may be artificially
made by heating the carbonate or nitrate. It is usually
prepared on a larger scale by heating the lead in air. When
the metal is only moderately heated, the oxide forms a yellow
powder which is known as massicot, but at a higher temperature
the oxide melts, and on cooling, it forms a brownish scaly
mass, which is called flake litharge. The scaly pieces are
afterwards ground between stones under water, forming buff
or levegated litharge. The litharge of commerce often has a
reddish yellow color, due to the presence of some of the red
oxide of lead, and frequently from one to three per cent. of
finely divided metallic lead is found mixed with it. When
heated to dull redness litharge assumes a dark brown color, and
becomes yellow again on cooling. At a bright red heat it fuses
and readily attacks clay crucibles, forming silicate of lead.
Litharge is a most powerful base, and has a strong tendency to
form basic salts. Hot solution of alkalies, as potash or soda,
readily dissolve it, and on cooling, it crystalizes out in the
form of beautiful pink crystals.
Falling off in the capacity may be caused by a dry cell, due
to a leaking jar; some or all of the cells may be in a state
of incomplete charge, due to the battery having been run too
low and not sufficiently charged; or the plates may be short
circuited, either by the sediment (deposit in the bottom of the
jar) getting up to the bottom of the plates or by something
that has fallen into the cell.
Electrical Data on "American" Cells
+————————+——————————————————————————————————————————-+
| Normal | Number of 30 volt Tungsten lamps that can |
|Capacity| be run with 16 cells in series for |
| | 2, 4, 6 or 8 hours |
+————————+——————————+——————————+——————————+——————————+
| Ampere | | | | |
| hours | 2 hours | 4 hours | 6 hours | 8 hours |
| 40 | 14 | 9 | 8 | 7 |
| 60 | 17 | 14 | 12 | 10 |
| 80 | 28 | 18 | 15 | 14 |
| 120 | 42 | 27 | 24 | 21 |
| 160 | 57 | 37 | 31 | 28 |
| 200 | 71 | 45 | 40 | 35 |
| 250 | 88 | 56 | 50 | 44 |
| 300 | 106 | 70 | 60 | 52 |
| 350 | 124 | 81 | 71 | 62 |
| 400 | 142 | 91 | 81 | 71 |
+————————+——————————+——————————+——————————+——————————+
[Illustration: FIG. 1,168.—"American" cell.]
=Ques. What action takes place when a battery stands idle for some
time?=
Ans. It loses part of its charge, due to local losses in the cells.
=Ques. How should batteries be treated, when used but occasionally?=
Ans. If a battery is not to be used for several days, it should first
be fully charged before standing; if it continue idle, a freshening
charge should be given every two weeks, continuing the charge when the
cells begin to gas freely.
=Ques. What should be done in case of lack of capacity?=
Ans. If the current consumption be normal, there may be poor
connections or trouble in the battery; there may be a dry cell, due to
a leaking jar; some or all of the cells may be in a state of incomplete
charge, due to the battery having been run too low and not sufficiently
charged, or the plates may be short circuited, either by the sediment
(deposit in the bottom of the jar) getting up to the bottom of the
plates or by something that has fallen into the cell.
Electrical Data on "Autex" Cells
(Standard plates; size, 5¾" x 8⅝")
+————————————————————————————————+————————+————————+————————+————————+
|Number of Plates | 7 | 9 | 11 | 13 |
+————————————————————————————————+————————+————————+————————+————————+
|Discharge in Amperes for 4 hours| 21 | 28 | 35 | 42 |
+————————————————————————————————+————————+————————+————————+————————+
| {Length | 2¾ | 3½ | 4¼ | 5 |
|Outside Measurements { +————+————+————+————+
| {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ |
|Rubber Jars in inches. { +————+————+————+————+
| {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ |
+————————————————————————————————+————————+————————+————————+————————+
| {Element | 15¾ | 20¼ | 24¼ | 29¾ |
| { +————————+————————+————————+————————+
|Weight in Pounds {Electrolyte | 4½ | 5 | 5¾ | 6¼ |
| { +————————+————————+————————+————————+
| {Complete Cell | 22 | 28 | 34¼ | 40½ |
+————————————————————————————————+————————+————————+————————+————————+
Electrical Data on "Autex" Cells(continued)
(Standard plates; size, 5¾" x 8⅝")
+————————————————————————————————+————————+————————+————————+————————+
|Number of Plates | 15 | 17 | 19 | 21 |
+————————————————————————————————+————————+————————+————————+————————+
|Discharge in Amperes for 4 hours| 49 | 56 | 63 | 70 |
+————————————————————————————————+————————+————————+————————+————————+
| {Length | 5¾ | 6½ | 7¼ | 8 |
|Outside Measurements { +————————+————————+————————+————————+
| {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ |
|Rubber Jars in inches. { +————————+————————+————————+————————+
| {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ |
+————————————————————————————————+————————+————————+————————+————————+
| {Element | 34 | 38½ | 43 | 47½ |
| { +————————+————————+————————+————————+
|Weight in Pounds {Electrolyte | 7 | 7¾ | 8½ | 9¾ |
| { +————————+————————+————————+————————+
| {Complete Cell | 47 | 53¼ | 59½ | 66 |
+————————————————————————————————+————————+————————+————————+————————+
NOTE.—_Peroxide of lead, pure oxide or plumbic dioxide_ is the
true active material in all forms of lead storage cell. This
lead salt is found native as the mineral plattnerite. It is
a heavy lead ore, forming black, lustrous, six sided prisms.
It may be prepared from the red oxide by boiling it in fine
powder, with nitric acid diluted with five parts of water, or
by treating the carbonate when suspended in water with a stream
of chlorine gas, and then thoroughly washing and drying it. It
is reduced to a lower oxide on heating or by exposure to bright
sunlight. This salt readily imparts oxygen to other substances;
it becomes heated to redness when thrown into sulphuric
dioxide, and takes fire when triturated with sulphur—hence
this oxide is a common ingredient in lucifer match composition.
When used in primary or secondary batteries it readily imparts
its oxygen to nascent hydrogen, forming water, and thus it
acts as a powerful depolarizer. When robbed of its oxygen,
it readily becomes reoxidized, if subjected to the action of
nascent oxygen liberated by the electrolytic decomposition of
water.
If the trouble cannot be located by the eye, connect the
battery in series, and discharge it at the normal rate, through
suitable resistance. If a suitable rheostat be not available, a
water resistance may be used.
This consists of a receptacle (which must not be of metal)
filled with very weak acid solution or salt water in which
are suspended two metal plates, which are connected, by wires
through an ammeter.
Electrical Data on "Autex" Cells
(Light weight plates; size, 5¾" × 8⅝")
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Number of Plates | 7 | 9 | 11 | 13 | 15 |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Discharge in Amperes for | | | | | |
5 hours | 15¾ | 21 | 26¼ | 31½ | 36¾ |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Outside {Length | 1-29/32 | 2-7/16 | 3-31/32 | 3½ | 4-⅟32 |
Measurements { +——————————+————————-+——————————+————————+————————-+
{Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | 6⅛ |
Rubber { +——————————+————————-+——————————+————————+————————-+
Jars in in. {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ | 12⅜ |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Weight {Element | 11½ | 14¾ | 18 | 21¼ | 24½ |
in { +——————————+————————-+——————————+————————+————————-+
Pounds {Electrolyte | 2¼ | 2½ | 3 | 3¾ | 4¼ |
{ +——————————+————————-+——————————+————————+————————-+
{Comp. Cell | 15¾ | 20 | 24¼ | 28½ | 33¼ |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Number of Plates | 17 | 19 | 21 | 23 | 25 |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Discharge in Amperes for | | | | | |
5 hours | 42 | 47¼ | 52½ | 57¾ | 63 |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Outside {Length | 4-9/16 | 5-3/32 | 5⅜ | 6-5/32| 6-11/16 |
Measurements { +——————————+————————-+——————————+————————+————————-+
{Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | 6⅛ |
Rubber { +——————————+————————-+——————————+————————+————————-+
Jars in in.|{Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ |12⅜ |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
Weight {Element | 27¾ | 31 | 34¼ | 37¼ | 40½ |
in { +——————————+————————-+——————————+————————+————————-+
Pounds {Electrolyte | 4¼ | 5½ | 6 | 6¾ | 7¼ |
{ +——————————+————————-+——————————+————————+————————-+
{Comp. Cell | 38 | 42 | 46¼ | 51½ | 56 |
——————————————————————————+——————————+————————-+——————————+————————+————————-+
The current may be regulated by altering the distance between
the plates or by varying the strength of the solution. As the
discharge progresses, the voltage will gradually decrease and
it should be frequently read at the battery terminals. When it
shows a sudden drop, the voltage of each cell should be read
with a low reading voltmeter.
While the readings are being taken, the discharge rate should
be kept constant and the discharge continued until the majority
of the cells read 1.70 volts; those reading less should be
noted. The discharge should be followed by a charge until the
cells which read 1.70 volts are up; then the low cells should
be cut out, examined and the trouble remedied.
NOTE.—_How to prevent lead poisoning._ Workmen employed in
the manufacture of lead or lead salts are always liable to
lead poisoning, both by inhaling the dust and by contact of
the materials with the hands. Various preventives for this
have been employed, and of these, the most simple seems to be
a careful washing of the hands in petroleum. It is said that
three washings a day are sufficient to prevent all serious
danger of poisoning. The benzole in the petroleum appears
to scour the skin and remove the loose lead dust, and the
fatty substance in the oil fills up the pores of the skin
and prevents the absorption of the deleterious salts. The
employment of petroleum has given such good results that it has
been proposed to use this material as a guard against poisoning
in other industries where the salts of copper or mercury are
employed.
=Ques. What causes low specific gravity when there are no short
circuits?=
Ans. 1, sloppage or a leaky jar (the loss having been replaced with
water alone), 2, insufficient charge, 3, over discharge, or 4, a
combination of these abuses. Any of these mean that there is acid in
combination with the plates.
In this case the acid should be brought out into the
electrolyte by a long charge at a quarter of the normal
discharge rate.
[Illustration: FIGS. 1,169 and 1,170.—The "National" storage battery;
views showing methods of assembling cells. Fig 1,169, end assembling;
fig 1,170, side assembling.]
=Ques. How should weak cells be treated?=
Ans. They should be grouped by themselves and charged as a separate
battery, care being taken that the positive strap of one cell, is
connected to the negative strap of the adjoining cell and that the
charging connections are properly made. If there be not sufficient
resistance in the charging rheostat to reduce the current to the proper
point, a water resistance should be used.
NOTE.—_Pole testing paper._ Make a thin solution of white
starch and soak strips of thin white blotting paper in it,
and set aside in a clean, dry place to dry. Dissolve ½ oz.
of potassium iodide in one pint of water. Immerse the strips
in the solution for a few seconds and again dry. This paper,
when moistened and used in the usual way, turns violet at the
positive pole.
While a cell is being treated, when possible, the cover should
be removed (if sealed, the compound can be loosened by using a
hot putty knife).
[Illustration: FIGS. 1,171 to 1,177.—"National" battery bolt connector
and parts. The connector is equipped with grease cups and antimonious
lead washers.]
=Disconnecting Cells.=—The best method of disconnecting cells
assembled with pillar straps, for the purpose of replacing broken jars,
cleaning or taking out of commission, is to use a five-eighth inch
twist drill, in a carpenter's brace, boring down into the top of the
pillar about one-quarter inch; then pull off the connector sleeve from
the pillar. By following this method, all parts may be used again.
When cells are equipped with top straps, the straps should be
cut with a sharp knife or chisel midway between the cells.
=Taking Batteries out of Commission.=—Where a battery is to be out of
service for several months, and it is not convenient to give it the
freshening charge every two weeks, it should be taken out of commission.
COMPARISON OF THE BAUMÉ AND SPECIFIC GRAVITY
SCALES AT 60° FAHRENHEIT
+————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+
|_Degrees_|_Specific_|_Degrees_|_Specific_|_Degrees_|_Specific_|_Degrees_|_Specific_|
| _Baume_ |_Gravity_ | _Baume_ |_Gravity_ | _Baume_ |_Gravity_ | _Baume_ |_Gravity_ |
+————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+
| 0 | 1.000 | 17 | 1.133 | 34 | 1.306 | 51 | 1.542 |
| 1 | 1.007 | 18 | 1.142 | 35 | 1.318 | 52 | 1.559 |
| 2 | 1.014 | 19 | 1.151 | 36 | 1.330 | 53 | 1.576 |
| 3 | 1.021 | 20 | 1.160 | 37 | 1.342 | 54 | 1.593 |
| 4 | 1.028 | 21 | 1.169 | 38 | 1.355 | 55 | 1.611 |
| 5 | 1.036 | 22 | 1.179 | 39 | 1.368 | 56 | 1.629 |
| 6 | 1.043 | 23 | 1.188 | 40 | 1.381 | 57 | 1.648 |
| 7 | 1.051 | 24 | 1.198 | 41 | 1.394 | 58 | 1.666 |
| 8 | 1.058 | 25 | 1.208 | 42 | 1.408 | 59 | 1.686 |
| 9 | 1.066 | 26 | 1.218 | 43 | 1.421 | 60 | 1.707 |
| 10 | 1.074 | 27 | 1.229 | 44 | 1.436 | 61 | 1.726 |
| 11 | 1.082 | 28 | 1.239 | 45 | 1.450 | 62 | 1.747 |
| 12 | 1.090 | 29 | 1.250 | 46 | 1.465 | 63 | 1.768 |
| 13 | 1.098 | 30 | 1.261 | 47 | 1.479 | 64 | 1.790 |
| 14 | 1.107 | 31 | 1.272 | 48 | 1.495 | 65 | 1.812 |
| 15 | 1.115 | 32 | 1.283 | 49 | 1.510 | 66 | 1.835 |
| 16 | 1.124 | 33 | 1.295 | 50 | 1.526 | | |
+————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+
NOTE.—The characteristic properties of concentrated sulphuric
acid are very marked. Its freedom from odor, oily appearance,
and its great weight, distinguish it from other liquids. The
pure concentrated commercial acid has a density which usually
reaches 1.842, and its boiling point is about 640° F. The
absolutely pure acid is perfectly colorless, but usually even
that used in laboratories has a peculiar grayish color, due to
slight traces of organic matter. Sulphuric acid is exceedingly
hydroscopic, and when exposed to the air it rapidly increases
in bulk, owing to absorption of atmospheric moisture.
NOTE.—Clamps not made of metal similar to that of the
connecting strips, frequently give trouble from the galvanic
action due to the contact of dissimilar metals in the presence
of moisture which causes the destruction of either the
connecting strip or the clamp. Such troubles can be avoided
by placing a thin strip of sheet zinc between the lead strip
and the clamp. Under these circumstances the zinc will crumble
away, and can be replaced without much inconvenience and very
little expense, while the clamps and connecting strips will
remain uninjured.
Strength of Dilute Sulphuric Acid
of
Different Densities at 59° Fahr.
+————————————————+——————————+————————————————+——————————+
| Per cent. | Specific | Per cent. | Specific |
| of | | of | |
| Sulphuric Acid | Gravity | Sulphuric Acid | Gravity |
+————————————————+——————————+————————————————+——————————+
| 100 | 1.842 | 23 | 1.167 |
| 40 | 1.306 | 22 | 1.159 |
| 31 | 1.231 | 21 | 1.151 |
| 30 | 1.223 | 20 | 1.144 |
| 29 | 1.215 | 19 | 1.136 |
| 28 | 1.206 | 18 | 1.129 |
| 27 | 1.198 | 17 | 1.121 |
| 26 | 1.190 | 16 | 1.116 |
| 25 | 1.172 | 15 | 1.106 |
| 24 | 1.174 | 14 | 1.098 |
+————————————————+——————————+————————————————+——————————+
=Ques. Describe the method of taking a battery out of commission.=
Ans. The battery is charged in the usual manner, until the specific
gravity of the electrolyte of every cell has stopped rising over a
period of one hour (if there be any low cells, due to short circuits
or other cause, they should be put in condition before the charge is
started, so that they will receive the full benefit of it). The cells
may now be disconnected and covers and elements removed from the jars,
(if sealed, the compound is loosened with a hot putty knife). The
elements are placed on their sides with the plates slightly spread
apart at the bottom, the separators withdrawn, and the positive and
negative groups pulled apart. The electrolyte is washed off with a
gentle stream of water and the plates allowed to drain and dry.[7] The
positive plates are ready to be put away. When dry, the negatives are
completely immersed in electrolyte (of about 1.275 specific gravity),
and allowed to soak for three or four hours. The jars may be used for
this purpose. After rinsing and drying, they are ready to be put away;
wash also the rubber separators.
[7] NOTE.—If the active material in the negative plates extend beyond
the ribs of the grid (the supporting frame), it should be at once
pressed back into place, care being taken to prevent the plates drying
before this is done. The most suitable and convenient method for
pressing, is to place between the plates smooth boards of a thickness
equal to the distance between the plates and then put the groups under
pressure.
Wood separators, after having been in service, will not stand
much handling and had better be thrown away. If it be thought
worth while to keep them, they must be immersed in water or
weak electrolyte, and in re-assembling, the electrolyte must be
put into the cells immediately, as wet wood separators must not
stand exposed to the air.
[Illustration: FIG. 1,178.—The "Witham" charging board, for charging
from any electric outlet on a direct current system. The instrument
shows the direction of the current, and the candle power of the lamps
used as resistance indicates approximately the strength of the current
passing. Operation: From any convenient electric light fitting remove
one of the lamps, replacing it by the plug attached to the flexible
cord. Screw the lamp into one of the sockets on the charging board.
Connect a wire to each binding post, and before joining up to the
battery, hold the ends of the two wires together. The lamp will then
light up and the indicator needle will point to that binding post which
must be connected to the positive (+) terminal of the battery. The
other binding post must, of course, be connected to the negative (-) of
the battery. The charging current can be increased by inserting another
lamp into the second socket on the charging board and by using lamps of
higher candle power. If, when the lamp lights up, the indicator needle
do not point to one of the binding posts, but retain its position
midway, then the current is an alternating one and will not charge the
battery.]
=Ques. What precaution should be taken with the jars?=
Ans. They should be thoroughly cleaned with fresh water, no sediment
being allowed to remain.
=Putting Batteries into Commission.=—When re-assembling a battery, it
should be treated in the same manner as if it were new and the regular
instructions for assembling and putting a new battery into commission
followed.
=Cleaning Jars.=—The jars should be thoroughly cleaned with fresh
water, no sediment being allowed to remain.
Table of Voltage Change as Affected by Discharge Rate[8]
[8] NOTE.—The voltage increase or decrease with change in current is
practically constant in a given type of cell for any size of cell when
the current is referred to a given time rate of charge or discharge;
that is, the drop in a large cell or in a small cell, when each is
discharged at its four, six or eight hour rate, will be the same. The
drop varies somewhat for the condition of the battery charge. For
batteries which are one-third discharged, the temperature 60° Fahr.,
and plates in good condition, the changes in pressure which may be
expected between open circuit voltage and the voltage on charge or
discharge are given in the above table.
8 hour rate .05 volt
6 " " .065 "
4 " " .09 "
3 " " .11 "
2 " " .14 "
1½ " " .18 "
1 " " .21 "
=Condensed Rules for the Proper Care of Batteries.=—The following
general instructions should be followed in the care and maintenance of
batteries:
1. A battery must always be charged with "direct" current and
in the right direction.
2. Be careful to charge at the proper rates and to give the
right amount of charge; do not undercharge or overcharge to an
excessive degree.
3. _Do not bring a naked flame near the battery while charging
or immediately afterwards._
4. Do not overdischarge.
5. Do not allow the battery to stand completely discharged.
6. Voltage readings should be taken only when the battery is
charging or discharging; if taken when the battery is standing
idle they are of little or no value.
7. Do not allow the battery temperature to exceed 110° Fahr.
8. Keep the electrolyte at the proper height above the top
of the plates and at the proper specific gravity. Use only
pure water to replace loss by evaporation. In preparing the
electrolyte _never pour water into the acid_.
9. Keep the cells free from dirt and all foreign substances,
both solid and liquid.
10. Keep the battery and all connections clean; keep all bolted
connections tight.
11. If there be lack of capacity in a battery, due to low
cells, do not delay in locating and bringing them back to
condition.
12. Do not allow sediment to get up to the plates.
CHAPTER XLV
STORAGE BATTERY SYSTEMS
Storage batteries are used for many purposes, such as to supply current
for electric vehicles, gas engine ignition, lighting, and in connection
with power stations and distribution work.
* * * * *
The latter is an important field, the storage battery being used in
connection with the power station for the following purposes:
1. To carry the peak load, during hours of maximum demand;
2. To carry the entire load during hours of minimum demand, or for a
short time in case of emergency;
3. To act as an equalizer;
4. For regulation of load and voltage;
5. As compensation for feeder drop;
6. As a preventive against shut downs.
In almost every electric lighting plant there are long periods during
the day and late at night when the number of lamps lighted is so small
that it may not pay to run the generating machinery. In such cases,
storage batteries may usually be used to advantage to aid in carrying
the maximum load and to supply the entire current at minimum load as
illustrated in fig. 1,179. In other words, batteries are substituted
for a certain portion of the machinery plant or are used in place of
the latter.
=Ques. What provision must be made in power plants when storage
batteries are not used?=
Ans. The capacity of the generating machinery must be sufficient
for the heaviest overloads which may occur, and it must be operated
continuously for 24 hours a day in the majority of central stations
supplying current for lighting and power.
=Ques. What results are obtained with this method of working?=
Ans. The engines working under very variable loads, not only operate
at low efficiency, but are continually subjected to severe mechanical
strains.
[Illustration: FIG. 1,179.—Load curve showing use of storage battery
as an aid to the generating machinery. In the diagram, it is seen that
the battery discharges at minimum and maximum loads and is charged at
other times, the battery furnishing current for the entire minimum load
and part of the maximum load.]
=Ques. How may greater efficiency be secured with steam engines under
variable loads?=
Ans. Judicious selection of the number and sizes of the engines enable
them to be worked in most cases at a considerable fraction of their
full capacity nearly all the time.
=Ques. What further improvement is secured in most cases with the
storage battery?=
Ans. The plant is made more flexible, and the economy of the engines
is increased by making their loads nearer uniform, and nearer to full
capacity while they are running.
=Ques. What is the effect of a battery connected in parallel with a
dynamo, as in fig. 1,180?=
Ans. It is not necessary for the dynamo to have a capacity exceeding
that which is sufficient for the average daily load, at which it may be
worked practically all the time.
[Illustration: FIG. 1,180.—Storage battery connected in parallel with
a dynamo. This arrangement enables the dynamo to be stopped for a
considerable portion of the time, and thus save labor and attention. It
also acts to prevent fluctuations as in a dynamo driven by a gas engine
whose speed varies periodically because of the nature of its cycle of
operation.]
When the load is below the average, the dynamo charges the
battery, and when the load rises above the average, during the
hours of maximum demand, the battery discharges into the line
in parallel with the dynamo. During the hours of minimum demand
the engines may be shut down and the necessary current supplied
from the battery alone, thus not only increasing the efficiency
of the plant, but serving to maintain a steadier pressure under
fluctuating loads.
=Ques. What is understood by the expression "floating the battery on
the line"?=
Ans. A storage battery is said to _float_ on a line when connected
across the circuit at some distance from the power station, so that
a heavy load on the line, within the range of the battery influence,
causes sufficient line drop to allow the battery to discharge, while
with a light load on the line, the drop is small and the impressed
voltage at the battery high enough to charge the battery. This usage
is confined chiefly to electric railway service, where large voltage
changes are permissible.
[Illustration: FIG. 1,181.—Diagram showing effect of storage battery
in regulating the dynamo load in a combined railway and lighting plant.
In this case the average and line loads are about equal and the battery
covers the instantaneous fluctuations. It will be noted that while the
line load fluctuations vary between 780 and 1,420 amperes, those of the
dynamo load are kept at an average between 1,030 and 1,160 amperes.]
=Ques. When the battery is floated on the line, how may the amount of
charge be made to approximately equal the amount of discharge?=
Ans. By properly proportioning the number of cells in series.
=Connections and Circuit Control Apparatus.=—When a storage battery is
used in an electric lighting plant, provision must be made for feeding
the lamps, etc., from either the dynamo or battery separately, or from
the two working in parallel, and it should be possible to charge the
battery at the same time the lamps are being supplied. To accomplish
these results requires three switches, for the following connections:
1. To connect the lamps to the dynamo;
2. To connect the lamps to the battery;
3. To connect the battery to the dynamo.
[Illustration: FIG. 1,182.—Diagram showing action of storage battery
as a reservoir of reserve power. The figure shows an actual load curve
from an Edison station for 24 hours. A sudden storm caused the load
to be thrown on very quickly, the peak of the load being higher than
usual.]
In some plants, the first switch is omitted, because the lamps are
always fed by the battery alone, the latter being charged during the
day, when no lamps are in use.
It is desirable, however, to have all three switches in every plant in
order to be able to supply lamps and charge the battery at any time.
In the battery circuit there should be an ammeter having a scale on
both sides of zero, to show whether the battery is being charged
or discharged, as well as the value of the current. Another similar
ammeter is required in the circuit between the dynamo and the battery,
to show the direction and amount of current. A third ammeter is
desirable in the lamp circuit, to show the total current supplied to
the lamps, but it need only indicate on one side of zero, since the
current there always flows in the same direction.
[Illustration: FIG. 1,183.—Diagram showing three wire system with one
dynamo and storage battery. A 220 volt dynamo charges a storage battery
of corresponding pressure, which in turn subdivides the pressure and
supplies a three wire system, the neutral wire of which is connected to
the middle point of the battery as shown.]
A voltmeter is required with a three-way switch to connect it to the
dynamo, battery or lamps, and a circuit breaker must be inserted in the
battery circuit in order that it may be opened when the current becomes
excessive.
A discriminating cut out or reverse current circuit breaker is required
between the dynamo and the battery to open the circuit when the
charging current falls below a certain value, and thus avoid any danger
of the battery discharging through the dynamo, if from any cause the
voltage of the latter drop below that of the battery. This completes
the ordinary measuring and circuit controlling apparatus employed with
storage batteries.
=Methods of Control for Storage Batteries.=—As the external voltage
of a storage battery varies with the amount of charge it contains and
with the direction of the current, it is necessary to employ some means
for compensating this variation in order to maintain a constant voltage
on the line supplied by the battery. The various devices used for this
purpose are as follows:
1. Variable resistances;
2. End cell switches;
3. Reverse pressure cells;
4. Boosters.
[Illustration: FIG. 1,184.—Diagram showing connections for ignition
outfit. The charging switch has four indications—"Off," "Battery,"
"Dynamo" and "Charge." When engine is at rest switch is turned to
"Off." The first turn brings it to "Battery," enabling the engine to be
started. Next turn cuts battery off and puts "Dynamo" direct on engine.
The next turn brings the switch to "Charge." Dynamo then charges the
battery and surplus current is stored up. Next turn is "Off," which
stops engine and disconnects battery from dynamo. Test the dynamo
wires with test paper (negative makes mark). Put positive of dynamo to
positive of battery. Dynamo should be regulated to charge at about four
amperes.]
The particular method selected will depend upon the size of the
battery, the purpose for which it is used, the allowable limits pf
current and voltage variations, the cost of the system, etc.
=Variable Resistance.=—Regulation by variable resistance may be used
advantageously only with batteries of small capacity, and in small
lighting plants such as those of yachts, where the space available for
battery auxiliaries is limited, and where the cost of energy is so low
that the loss of power in the resistance is not objectionable.
[Illustration: FIG. 1,185.—Variable resistance method of regulation
for storage battery; diagram showing connections for charging two
halves of a battery in parallel.]
The connections for one of the simplest methods is shown in fig. 1,185.
The battery is divided into two halves, which are connected in series
for discharging and in parallel for charging. Since the voltage of each
cell at the end of a discharge should not be lower than 1.8 volts, a
battery intended for use on a 110 volt lighting circuit will require
110 ÷ 1.8 = 62 cells. The voltage necessary, however, for each cell at
the end of a charge is about 2.6 volts, or a total of 2.6 × 62 = 161
volts for the battery, a value which is far above the line voltage. By
dividing the battery into two halves and connecting them in parallel
only 80.5 volts are necessary for charging. The excess voltage of the
line, 29.5 volts is taken up by the resistance, which also controls the
output of the battery on discharge.
=End Cell Switches.=—These may be used to advantage in small
installations where there is not demand for current during the day, or
where the charging is done by means of _boosters_.
[Illustration: FIG. 1,186.—Diagram of connections of a battery
equipment for a residential lighting plant. In the diagram the
voltmeter and voltmeter connections have been omitted. The bus bars on
the battery panel are connected directly to the bus bars on the dynamo
panel. In this installation the dynamos are run during the afternoon on
discharge, being regulated by means of an end cell switch. On charge,
the pressure above that of the bus bars, required to bring all cells
up to full charge, is supplied by means of a motor driven charging
booster, the voltage at the armature being suitably varied by changing
the field excitation.]
=Ques. What is an end cell switch?=
Ans. A form of switch employed in connection with a storage battery in
order to control the end cells for regulating the voltage.
=Ques. Describe the construction of an end cell switch.=
Ans. This is shown in fig. 1,187. The switch contact arm is made in
two parts, A and B, which are insulated from each other as shown, and
connected with each other through the protective resistance R. The end
cell contacts are so spaced that when the main current carrying part
A of the switch arm is squarely on one end cell contact such as X,
the part B, does not touch any other contact such as Y, but when the
switch arm is advanced for cutting into circuit another end cell, the
part B, reaches the contact Y before the part A, leaves the contact X,
thus keeping the battery circuit closed, while the resistance R, limits
the current in the short circuited cell at the instant the switch arm
passes from one end cell contact to the next.
[Illustration: FIG. 1,187.—Diagram of end cell switch. This form of
switch controls several cells at one end of a storage battery and
is used for regulating the voltage. The requirement of an end cell
switch is that in switching from one end cell contact to another, the
discharging circuit must not be opened, neither must the moving arm
touch one contact before leaving the one adjacent, since the joining
of two contacts will short circuit the cells connected thereto. To
accomplish this, the spacings of the two arms and contacts are such
that when the main arm A is squarely on an end cell contact, the
advance or auxiliary arm B touches no other contact, but in passing
from one point to the next, the advance arm reaches the contact
toward which it is moving before the main arm leaves its contact. The
resistance X, between the two points prevents short circuiting, and the
current to the main circuit is never broken.]
=Ques. How should the conductors joining the end cells to the end cell
switch contacts be proportioned?=
Ans. They must have the same sectional area as the conductors of the
main circuit.
The reason for this is that when any end cell is in use, the
conductor connecting it to the switch becomes a part of the
main circuit. An allowance of 1,000 amperes per sq. in., when
the battery is discharging at the two-hour rate, is considered
good practice.
=Ques. Describe some of the features of end cell switch construction.=
Ans. Those of small capacity are made circular; the larger sizes are
made horizontal in form, and both types may be either operated by hand
or motor driven.
[Illustration: FIG. 1,188.—End cell switch control for storage
battery; connections showing main line open when the battery is being
charged.]
=Ques. Where are end cell switches of large capacity located?=
Ans. Generally they are placed as near the battery room as possible to
avoid the cost of running the heavy conductors, and when such switches
are motor driven, the usual practice is to control their operation from
the main switchboard.
In fig. 1,188 is shown the method of regulation with an end
switch. The diagram shows the battery being charged with the
main switch open, and the voltage of the dynamo raised to the
charging pressure. During discharge the cells are connected
in series, and as the voltage of each cell at the beginning
of discharge is at least 2.1 volts, only 52 or 53 cells are
required to give the desired pressure of 110 volts, but as the
discharge continues, and the voltage of each cell decreases,
the end cells, 1, 2, 3, 4, etc., are cut into circuit
successively by means of the end cell switch, thereby adding
to and compensating the drop in the total voltage until, at
the end of discharge when the voltage of each cell has fallen
to 1.8 volts, the entire 62 cells are in series to supply the
required line pressure.
[Illustration: FIG. 1,189.—Diagram of connections arranged for
charging battery in two parallel groups and discharging in series, the
charge and discharge being controlled by variable resistances. In yacht
lighting the limited space generally prohibits the use of a charging
booster, and in such instances this method of charge and discharge
control is the usual practice. In case the dynamo from which the
battery is charged has sufficient range in voltage to charge all cells
in series, a charging booster is not required, nor is it necessary
to connect groups of cells in parallel, as the dynamo voltage may be
varied as charge proceeds.]
For a 110 volt circuit, the number of cells required is 110 ÷
1.8 = 61, and the number in series when the battery begins to
discharge is 110 ÷ 2.1 = 52. Hence, in a 110 volt circuit an
arrangement must be provided whereby 61 - 52 = 9 cells may be
cut out or switched in, one by one.
The number of end cells for any voltage may be obtained by the
following formula:
Number of end cells = (E/1.8) - (E/2.1)
E = voltage of supply circuit;
1.8 = minimum voltage of cell during discharge;
2.1 = voltage of fully charged cell.
=Reverse Pressure Cells.=—These consist of unformed lead plates
immersed in the ordinary electrolyte of dilute sulphuric acid. As
they have no active material, they possess no capacity, but are
capable of setting up an opposing pressure of about 2 volts each to
the discharging current flowing through them, thereby cutting down
the total voltage of the battery, so that the net voltage across the
line depends on the number of reverse current cells in series in the
battery circuit. As the voltage of the battery falls during discharge,
the reverse pressure cells are cut out, successively, thus keeping the
external or line voltage constant.
[Illustration: FIG. 1,190.—Regulation with reverse pressure cells.
These cells are merely lead plates placed in an electrolyte of dilute
sulphuric acid. They have no capacity but set up an opposing or reverse
voltage of approximately 2 volts per cell if current be passed through
them. In using these cells for controlling discharge, the total number
of active cells in the battery will be the same as if the method of
end cell control had been used. Reverse pressure cells represent an
increase in equipment of about 8 per cent. or more. These cells, as
shown, are connected in the circuit in opposition to the main battery,
and conductors are run from each of them to points on a switch similar
to an end cell switch. At the beginning of discharge, all the reverse
cells are in circuit, acting in opposition to the main battery. As
discharge proceeds and the battery voltage falls, the reverse cells
are gradually cut out of circuit. The only advantage in this method of
regulation is that the discharge throughout the battery is uniform, but
this fact alone does not warrant such means of regulation on account of
the additional expense involved, and the energy loss when discharging
against reverse cells is the same as if resistance had been placed in
the circuit.]
It is obvious, that as these cells do not possess any capacity, the
number of active cells required in the battery will be the same as
when end cell control is employed. Therefore, the reverse pressure
cells represent an increase in equipment, which entails an additional
expense of at least 8 per cent. For this reason, and also on account
of the fact that the amount of energy lost in discharging against
reverse pressure cells, is the same as when the resistance methods
of controlling the discharge are employed, the use of cells for this
purpose is now practically obsolete.
[Illustration: FIG. 1,191.—Holzer-Cabot dynamotor (type K). A
dynamotor is a combination of dynamo and motor on the same shaft,
one receiving current, usually of different voltage, the motor being
employed to drive the dynamo with a pressure either higher or lower
than that received at the motor terminals. A machine of the dynamotor
form, with its windings exactly alike, is often used in three wire
systems to balance or equalize the two halves of the circuit as in fig.
798.]
=Boosters.=—In general, a booster may be defined as _a dynamo inserted
in series in a circuit, to change its voltage_. It may be driven by an
electric motor, in which case it is sometimes called a _motor-booster_.
The function of a booster is to add to an electric pressure derived
from another source.
For instance, if a storage battery be used in conjunction with
one or more dynamos to supply current to an electric light
installation, the battery cannot be charged from the machines
which are feeding the lamps, because it requires a pressure
higher than that required for the lamps to complete the
charge. A small dynamo is therefore connected in series, with
the main machines and the battery, acting in conjunction with
the former to provide the necessary pressure.
[Illustration: FIG. 1,192.—Dayton launch lighting outfit. It consists
of an "Apple" dynamo, switchboard and storage battery. The dynamo is
fitted with a bevel friction drive governor. The dynamo gives a three
ampere charging rate on a six volt battery at its normal speed of 1,050
R. P. M. The switchboard is provided with a combination volt-ammeter
which shows the voltage of the battery, the ampere charging rate
of the dynamo and the ampere discharging rate of the battery. The
automatic cut out in the back of the switchboard automatically severs
the connections between the dynamo and the storage battery when the
engine stops and so prevents the storage battery current running back
through the dynamo when the dynamo is not generating current. A 6 volt,
60 ampere hour battery, consisting of 3 five plate units connected in
series, is used with the size dynamo shown in the illustration.]
The power for running such a dynamo is obtained in various ways.
The dynamo or charging booster may be belt driven or arranged on an
extension of the armature shaft of the main dynamo; again, it may
consist of a single armature with a double winding (fig. 1,191), or a
motor and dynamo coupled together on one bed plate as in figs. 800 and
805. Boosters may be divided into several classes as follows:
1. Series boosters;
2. Shunt boosters;
3. Compound boosters;
4. Differential boosters;
5. Constant current boosters;
6. Separately excited boosters.
=Series Boosters.=—The series booster acts so as to compound the
battery, and tends to maintain a constant voltage on the line, whatever
the load may be. Its operation depends on the fact that the dynamo
voltage must rise and fall with the load. It can, therefore, be used
only with a shunt dynamo or its equivalent as the source of supply.
=Ques. What use is made of the series booster system?=
Ans. It is suited to power, but not to incandescent lighting purposes,
being similar in operation to a floating battery. It is not extensively
used as the other types give better service, under the same conditions.
[Illustration: FIG. 1,193.—Diagram of Joseph Bijur's storage battery
system (General Storage Battery Co.). The booster field winding has
one terminal connected to the middle point of the battery and the
other terminal, to the wire joining the resistances A and B. A lever,
pivoted at L, carries at either end a number of contact points which
dip into troughs of mercury when one end of the lever moves upward
or downward. These points are connected to corresponding points on
their respective resistances, and therefore all of the resistances
connected to contact points which are immersed in the mercury are short
circuited. The points are of various lengths, so that when the lever
operates, they contact progressively with the mercury. If more of the
A points than the B points be immersed in the mercury, the resistance
of B is less than that of A, more sections of it being short circuited.
Current will therefore flow from the middle point of the battery,
through the booster field, and through B to the negative side of the
system, exciting the booster field and producing a booster voltage
to charge the battery. Again, if more of the A points be immersed,
the A resistance becomes the smaller, and current then flows from the
positive side of the system through resistance A, through the booster
field to the middle point of the battery, the field excitation and the
booster pressure produced being in a direction opposite to the first
described, and tending to discharge the battery. When the resistances
A and B are equal, there is no pressure to send current in either
direction through the booster field coil. When the load on the external
circuit is normal, the lever is in a horizontal position, A and B being
equal, no current flows through the booster field hence, no current
passes into or out of the battery. With increase of external load, the
pull of the solenoid is strengthened by a small increase in dynamo
current passing through the winding. This draws down the left end of
the lever producing a current in the booster field such as to discharge
the battery and assist the dynamo to supply the load demand. A decrease
in external load is attended by a slight diminution in dynamo current,
the solenoid is weakened and the pull of the spring predominates. This
results in a downward movement of the right side of the lever causing
excitation of the booster field to produce a pressure to send charge
into the battery.]
=Ques. Describe some characteristics of the series booster.=
Ans. It is automatic and adjusts its voltage to produce the proper
ratio of charge or discharge with varying external load, and it also
tends to maintain a constant voltage across the line, under all
conditions of change in circuit.
[Illustration: FIG. 1,194.—Load diagram, showing kind of service to
which the shunt booster is adapted.]
=Shunt Boosters.=—This type of machine is simply a shunt dynamo,
having its armature circuit in series with the line from the main
dynamo to the battery. A rheostat controls the field excitation. Its
function is to send charge into the battery. It is used in plants
where the battery is not designed to take up load fluctuations, but is
in service only to carry the peak of the load, being charged during
periods of light loads and discharged in parallel with the dynamo.
The shunt booster acts to increase the voltage applied to the battery
so that the charging current will flow into the latter.
=Ques. How is a battery used with a shunt booster proportioned?=
Ans. Usually sufficient battery is provided to carry the entire load
during the light load period.
=Ques. Explain the use of the rheostat controlling the field
excitation.=
Ans. It is used to vary the booster voltage so as to hasten the
charging of the battery if desired.
[Illustration: FIG. 1,195.—Entz' carbon pile booster system (Electric
Storage Battery Co.). The booster field winding is connected at one
end to the middle point of the battery. The other end is connected to
the upper contact points of two carbon pile resistances, A and B. The
lower end of A is connected to the negative side of the battery, and
the corresponding end of B, to the positive side. This arrangement
constitutes in effect a potentiometer. If the resistance of A be
equal to that of B, there is no pressure in the booster field to
establish current through it. The drop through A + B is equal to the
total battery voltage, and if A = B, the drop from either side of the
battery through A or B is one-half the total drop, hence the end of the
booster field winding, connected to the upper ends of A and B is also
at the pressure of the middle point of the battery which is likewise
the pressure of the other side of the booster field coil. Accordingly
when A = B, there can be no current through the coil. When the two
resistances are unequal, there will be current through the booster
field, its direction depending on which of the resistances is the less,
and its magnitude will be proportional to the difference between the
two resistances. Variations in the pressure on a carbon pile causes
variations in its resistance and the solenoid, M, opposed by spring S,
both pulling on lever L which rests on the two piles A and B, controls
the relative resistances of the two piles to cause charge and discharge
of the battery. The solenoid winding is in series with the dynamo
circuit and when the load is normal, the spring pull is just equal to
the magnet pull, and the resistance of A and B are equal. When external
load varies, a small but proportional variation in the pull of P
charges the relative resistances of the piles and the booster field is
energized to produce a voltage to cause battery charge or discharge.]
=Ques. For what service is the shunt booster not suited?=
Ans. It is not adapted to circuits where there are sudden fluctuations
that are great compared with the capacity of the dynamo.
=Ques. What is its action in changing from charge to discharge?=
Ans. It is not automatic, the switching must be done by hand.
[Illustration: FIG. 1,196.—Diagram showing usual connections of a
non-reversible shunt booster and battery system. In charging, the
switches A and B are closed, and C put on contact _m_; the end cell
switch D is put on the last contact. Part of the dynamo current will
go into the line and part through the booster into the battery. The
charging current is adjusted by the field rheostat E. To discharge,
throw the end cell switch D to first contact; next turn switch C to
contact _s_. The battery is then in parallel with the dynamo with all
end cells cut out. As the voltage of the battery falls, end cells are
cut in by the end cell switch D.]
=Ques. How may it be used reversibly?=
Ans. It will give a pressure to assist the battery to discharge when
excited from the bus bars and provided with a reversing rheostat.
In this case it will assist the battery to discharge when
the direction of the field magnetization is changed. When so
used, no end cells are necessary, but the booster must be run
continuously during the entire period of discharge.
=Ques. What should be the battery capacity on a 110 volt circuit with a
reversible booster?=
Ans. 56 cells will be sufficient.
The voltage to fully charge is 56 × 2.6 = 146, or 36 volts
above dynamo voltage. Minimum voltage of discharge = 1.8 × 56 =
100 volts, or 10 volts less than that of the line. Hence, the
booster need give only 36 volts maximum, and is required to
add 10 volts to the battery voltage toward the end of battery
discharge. In this case, the booster voltage is only 36/49 or
about ¾ of that required in the preceding case; five cells
less of battery are necessary and the end cell switches and
leads are eliminated.
[Illustration: FIG. 1,197.—Diagram of compound booster connections.]
The machine will be larger, however, than it would be if used
only for charging, because the discharge current is unusually
greater than that of charge, and the current carrying of the
armature must be great enough to take care of the heaviest
currents.
=Compound Boosters.=—These machines are used on railway and power
circuits where there are great fluctuations in load, the battery acting
to prevent excessive drop and to assist the generating machinery in
carrying the load, relieving it from the strain of sudden rushes of
current.
The connections are shown in the diagram fig. 1,197. Under ordinary
working conditions, the shunt field of the booster creates an electric
pressure in the same direction as that of the battery, tending to
discharge it.
[Illustration: FIG. 1,198.—Fairbanks-Morse lighting outfit. The above
cut illustrates a 2 horse power vertical special gasoline or kerosene
oil engine belted to a .9 kw. compound wound 32 volt dynamo. It will
supply a maximum of 42-20 watt, or 50-15 watt 32 volt Tungsten lamps
and is built and balanced, so that current can be taken direct from
the dynamo without flicker in the lights. The storage battery has 16
cells and a capacity of 4½ amperes for 7½ hours at 32 volts. This
will supply seven 20 watt Tungsten lamps for 7½ hours, or nine 15
watt lamps for 7½ hours. The switchboard is arranged so as to give
24 hours service. It is customary to run the engine during most of the
lighting period and to use the battery for lights late at night. If the
whole number of lights be not used when the engine and dynamo are in
operation, the surplus is used to charge the battery.]
When no current is flowing into or out of the battery, the following
relation exists:
Dynamo voltage = booster voltage + battery voltage
In this case the dynamo carries the whole external load. If the load
increase, the dynamo voltage decreases, so that the booster voltage
+ battery voltage is greater than the dynamo voltage, and the battery
begins to discharge.
In discharging, the current passes through the series field of the
booster and produces a proportional pressure acting with the shunt
field to raise the voltage of the booster, thus increasing the battery
discharge and shifting more of the load from the dynamo, until the
system becomes balanced.
[Illustration: FIG. 1,199.—Diagram showing method of charging a
storage battery at one voltage and supplying lights at a different
voltage. As may be seen, two end cell switches are required. The
voltage of the supply current is adjusted by the number of cells in
series on switch S', while switch S is moved to cut out cells as they
become fully charged. In this instance the end cells included between
the contact arms of the two end cell switches must be of sufficient
size to receive the charging current, plus the current to the supply
circuit. If the battery can be charged at times when the dynamo is
supplying no other load, only one end cell switch is required.]
If the load on the external circuit be small, the dynamo
voltage rises and current flows into the battery. In this case
the series field acts against the shunt field and decreases the
booster voltage so that the pressure at the dynamo is greater
than booster and battery voltage combined, thus increasing the
rate of charge of the battery until the load causes the dynamo
voltage to drop to normal and the system is again balanced.
The battery and booster can be placed at the power house or
where the greatest drop is likely to occur. As this system,
like the series booster, depends for its action upon the drop
of voltage with increase of load, it is only adapted to shunt
wound dynamos.
From the foregoing description it will be seen that the
compound booster is automatic within certain limits of battery
charge. Any marked change of battery voltage will be followed
by a corresponding change in dynamo current, unless the
rheostat be manipulated to bring battery voltage + booster
voltage back to normal.
While the theoretical dynamo current variation is small for
a given change of load, there is always a sudden, momentary,
current rush from the dynamo on increase of load, the duration
of which is equal to the time lag of magnetization of the
booster field.
Lights on a circuit with variable load will "wink" on sudden
changes of load. In this respect the compound booster is not so
satisfactory as the constant current booster, as in the latter
_all_ dynamo current passes through the series fields, which,
by reason of their self-induction, oppose and check any sudden
current rush, giving the booster field time to change its
magnetization to the proper degree.
[Illustration: FIG. 1,200.—Diagram of connection of one form of
differential booster. In operation, the dynamo current passes through
the series winding of the booster, and the current in this winding
is to remain practically constant. The shunt coil produces a field
which opposes the field produced by the series coil, the resulting
magnetization being, in direction and amount, the resultant of the
two field strengths. The adjustments are so made that when the normal
dynamo current is passing through the series coil, the shunt field
just neutralizes its effect, and the resultant magnetization is zero.
Since the open current voltage of the battery is equal to that of
the system, neither charge nor discharge takes place. With increased
demand on the line, the slight increase in dynamo current in the series
coil overpowers the shunt field, and causes a pressure in the booster
armature in such direction as to assist discharge. If the external load
fall below the average demand, the current in the series coil decreases
slightly so that the shunt field predominates, producing a booster
armature pressure in a direction to assist charge. Although the voltage
of the battery falls while discharging by an amount proportional to the
outflowing current the increased excitation due to this current through
the series coil is also proportional to it, and the booster voltage
rises as that of the battery falls, their sum being always equal to
that of the system. In other words, the booster serves to compound the
battery for constant pressure.]
=Differential Boosters.=—In this type of booster, a series coil
energized from the main current, tends to discharge the battery, and
a shunt coil, excited from the battery, tends to charge the cells.
These two coils are opposed to one another, and the difference in
their respective strengths represents the net strength available for
boosting. In order to produce quicker reversal, additional compound
coils are sometimes added.
[Illustration: FIG. 1,201.—Diagram of differential booster system
with compensating coil. In operation, the compensating field coil
of the booster opposes the shunt coil and prevents the variation of
the battery voltage disturbing the equilibrium of the system. If the
battery pressure be lower than normal, it will not discharge rapidly
enough to relieve the dynamo from overload fluctuations, unless the
booster voltage be increased, and the dynamo will therefore have
to supply a current greater than normal. If a current greater than
normal flow through the compensating coil, the effect of the shunt
coil opposed by the series coil is decreased, and the compensating
coil, acting in the same direction as the series coil, causes a higher
booster pressure tending to discharge the battery, and thus brings down
the dynamo load to normal. Should the battery voltage be above its
normal value, the battery would discharge too rapidly and carry more
than its share of the load. In operating this system, the varying load
must be beyond the booster equipment. The series and compensating coils
may be temporarily short circuited so that the battery may be charged
more rapidly.]
=Ques. For what service is the differential booster adapted?=
Ans. It is suited to power and railway circuits where the load
fluctuates widely and suddenly.
There are several varieties of this type of booster, and many
patents have been issued covering the different methods of
varying the voltage of the machine.
=Constant Current Boosters.=—In installations where it is desired
to supply both an approximately constant load and a fluctuating load
from the same dynamos (as for instance, in office buildings or hotels,
where it is necessary to supply lights and elevators from the same
source), the fluctuations in the power circuits must not interfere with
the lighting circuits and to prevent this, two sets of bus bars are
provided.
[Illustration: FIG. 1,202.—Diagram of non-reversible or constant
current booster system. The booster armature and field are in series
between one side of the lighting and power bus bars. A shunt field
is also provided, which acts in opposition to the series field. This
booster carries a practically unvarying current from the lighting to
the power bus bars, regardless of the fluctuations of the external
load, which current is equal to the average required by the fluctuating
load. Except under abnormal conditions the shunt field always
predominates giving a voltage which is added to that of the lighting
bus bars, so that the voltage across the power busses is always higher
than that across the lighting by an amount equal to the booster
voltage. If an excessive load come on the power circuits, the increased
excitation of the series coil, due to a slight increase in current from
the lighting to the power bus bars, lowers the booster voltage and
consequently reduces the voltage across the power bus bars. The battery
discharges, furnishing an amount of current equal to the difference
between that required by the load and the constant current through the
booster. If the power load decrease below normal, the slight decrease
in current in the booster series field increases the booster armature
voltage and the excess current goes into the battery. The booster,
therefore, does not in reality give a constant current, but by proper
design the variation may be kept within a few per cent.]
The dynamos are connected in the usual manner to one set of bus bars,
and the lighting circuits are connected across these.
Across the other set of bars are connected the circuits supplying the
fluctuating load, and the battery is also connected directly across
these power bars.
The power bars are supplied with current from the lighting bars, a
non-reversible or so called constant current booster being interposed
between the two as shown in fig. 1,202. Since this permits only a
constant current to pass from the lighting bus bars, the load on the
dynamo does not vary, although the load on the power busses may vary
widely.
[Illustration: FIG. 1,203.—Hubbard's separately excited booster system
(Gould Storage Battery Co.); diagram showing general arrangement.]
=Separately Excited Boosters.=—In some forms of booster the field
excitation is secured by a small exciting dynamo. An example of this
class is shown in fig. 1,203. The exciter is provided with a single
series coil, through which the station output or a proportional
part thereof passes. The armature of the exciter is connected to the
exciting coil on the booster, and thence across the mains as shown.
NOTE.—Reversible boosters should be used where the average
total current to the fluctuating load is greater than the
battery discharge current, and where the pressure of the power
bus bars must not fall off with increase in load. Electric
railway and lighting plants having long feeders are examples
of the systems to which reversible boosters are suited.
Non-reversible boosters should be used where the average total
load is less than the battery discharge current, and where a
drop in the voltage of the power bus bars is of advantage.
Examples of such plants are hotels or apartment houses where
electric elevators are operated from the lighting dynamos.
Boosters are usually driven by electric motors directly
connected to them, though any form of driving power may be used.
With the average current passing through the field coil or the exciter,
its armature generates a voltage which is equal to that of the system,
and in opposition to it. These two opposing pressures balance, and no
current flows in the booster field coils.
[Illustration: FIG. 1,204.—Battery system with regulation for long
feeders, for installing where it is desirable to locate the battery
at a point remote from the station and avoid any equipment requiring
constant attention at the battery end. The compound wound motor,
constant current booster is used and keeps constant the current flowing
through the feeder, the battery taking up all load fluctuations.]
With an increase in external load above the average, the tendency
is for an increase to take place through the exciter series coil,
augmenting its field strength and consequently the exciter armature
voltage. This latter now being higher than that of the line, causes
current to flow in the booster field coil in such a direction as to
produce a pressure in the booster armature which assists the battery
to discharge, and is of a magnitude to compensate for the battery drop
occasioned thereby.
[Illustration: FIG. 1,205.—Diagram illustrating storage battery
system, as applied to an automobile for lighting.]
When the load decreases below the normal, the current in the exciter
field is decreased, and its armature voltage falls below that of the
system. Current will now flow in an opposite direction in the booster
field coil, generating a voltage in the booster armature to assist
charge. Since the exciter always generates a voltage in opposition to
that of the line, this system is known commercially as the counter
pressure system.
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=ELECTRICAL GUIDE, NO. 1=
Containing the principles of Elementary Electricity, Magnetism,
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