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■

I. c. s.

REFERENCE LIBRARY

A SERIES OF TEXTBOOKS PREPARED FOR THE STUDENTS OF THE

INTERNATIONAL CORRESPONDENCE SCHOOLS AND CONTAINING

IN PERMANENT FORM THE INSTRUCTION PAPERS.

EXAMINATION QUESTIONS. AND KEYS USED

IN THEIR VARIOUS COURSES

STORAGE BATTERIES

INCANDESCENT LIGHTING

, ARC LIGHTING

INTERIOR WIRING

MODERN ELECTRIC-LIGHTING DEVICES

ELECTRIC SIGNS

ELECTRIC HEATING

6322M

SCRANTON

INTERNATIONAL TEXTBOOK COMPANY

46B

Entered at Stationers' Hall, London.

Storage Batteries: Copyrijjht, lOW, by Intkrnational Textbook Company.

Entered at Stationers' Hall, London.
Incandescent Lighting : Copyright, 1905, by International Textbook Company.

Entered at Stationers' Hall, London.
Arc Lighting : Copyright, 1905, by International Textbook Company. Entered

at Stationers' Hall, London.
IntcriorWiring: Copyright, 11K)5, by International Textbook Company. Entered

at Stationers' Hull, London.
Modern Electric-Lighting Devices : Copyright, 1907, by In ternationalTextbook

CO.MPANY. Entered at Stationers' Hall, London.
Electric Signs : Copyright, 1907. by International Textbook Company. Entered

at Stationers' Hall, London.
Electric Heating: Copyright, 19l»7, by INTERNATIONAL TEXTBOOK COMPANY.

Entered at Stationers' Hall, London.

BURR printing HOUSE

FRANKFORT AND JACOB STREETS

NEW YORK

4428

46B

CONTENTS

Storage Batteries Section Page

General Description 27 1

Lead Accumulators 27 2

Bimetallic Accumulators 27 25

Installation and Care of Storage Cells . . 27 30

The Electrolyte 27 34

Charging 27 37

Discharging 27 39

Use of Accumulators in Central Stations . 27 54

Storage-Battery Regulating Appliances . 27 64

End-Cell Switches 27 64

Storage-Battery Boosters 27 68

General Data on Storage Cells 27 83

Incandescent Lighting

Incandescent Lighting 32 3

The Incandescent Lamp 32 3

Measurements and Lamp Calculations . . 32 12

Light Distribution 32 21

Recent Types of Incandescent Lamps .32 35

Systems of Distribution 33 1

Methods of Connecting Lamps 33 2

Direct-Current Constant-Potential System 33 6

Direct-Current Constant-Current System . 33 15
Alternating - Current Constant-Potential

System 33 15

Alternating-Current Constant-Current

System 33 34

Lamps 33 36

Line Calculations :^ZZ 44

111

8S£96

IV CONTENTS

Incandescent Lighting — Continued Section Page

Transformer Testing 33 62

Storage Batteries in Lighting Stations .33 62

Arc Lighting

The Arc 34 1

Arc-Light Carbons 34 11

Photometry of the Arc Lamp 34 15

Methods of Distribution 34 26

Arc Lamps 34 35

Special Applications of Arc Lamps ... 34 60

Care and Adjustment of Arc Lamps ... 34 64

Line Work for Arc Lighting 35 1

Testing Arc-Light Lines 35 10

Lightning Protection for Arc Circuits . . 35 16

Arc-Light Dynamos 35 17

Direct-Current Machines 35 17

Arc-Light Switchboards 35 32

Interior Wiring

Preliminary Considerations 43 1

Fires Caused by Electric Wiring .... 43 2

The National Electrical Code 43 2

General Rules 43 10

Wiring for Low-Potential Systems .... 43 16

Switches and Cut-Outs . 43 23

Open Work in Dry Places 43 32

Simple Example of Factory Wiring ... 43 32

Fuses 43 32

Uniform Drop in Feeder Lines 44 1

Calculating Sizes of Wire Required ... 44 1

Wiring in Damp Places 44 17

Concealed Wiring ,44 19

Wiring a Dwelling House 44 29

Specifications for Concealed Electric-Light

Wiring 44 36

Switches 44 38

Fixtures 44 43

Location and Distribution of Lamps . . 44 47

CONTENTS V

Interior Wiring — Continued Section Page

Conduit Wiring 44 48

Wooden Moldings 44 60

Tests 44 62

Marine Work 44 65

Wiring Estimates 44 69

Combining Several Wiring Systems ... 45 1

Store Lighting 45 1

Theater Wiring 45 4

Wiring for Special Purposes 45 5

High-Potential Systems 45 11

Wiring for Arc Lamps 45 13

Wiring for Electric Motors 45 17

Bell Wiring 45 20

Batteries 45 23

Annunciators 45 26

Bell and Annunciator Circuits 45 29

Special Appliances 45 38

Burglar Alarms 45 40

Electric Gas Lighting 45 44

Burners for Parallel System 45 44

Apparatus for Series Lighting System . . 45 49

Modern Electric-Lighting Devices

Luminous Efficiency 55 1

Incandescent Lamps 55 2

Metallized-Filament Lamps 55 2

Metallic-Filament Lamps .55 5

Tantalum Lamps 55 6

Osmium Lamps 55 10

Tungsten Lamps 55 13

The Nernst Lamp 55 16

Tube Lighting 55 27

Mercury- Vapor Lamps 55 28

Connections of Mercury- Vapor Lamps . . 55 31

Operation of Mercurj^- Vapor Lamps ... 55 36
Comparison of Mercury-Vapor Lamps With

Other Light Sources 55 37

vi CONTENTS

Modern Elkctric-Liguting Devices —

Contintud Sectioti Page

Moore Lighting Tubes 55 39

Flaming- Arc Lamps 55 47

Excello Flaming-Arc Lamps 55 50

The Beck Lamp 55 56

Characteristics of Flaming-Arc Lamps . . 55 58

Carbone Arc Lamps 55 61

Magnetite Luminous-Arc Lamp 55 62

Electric Signs

Fixed Electric Signs 56 1

Illuminated Signs 56 2

Transparent Signs 56 2

Exposed-Bulb Signs 56 5

Changeable Signs 56 10

Changes in Intensity of Light 56 10

Thermostats for Signs 56 10

Mechanical Flashers 56 15

Changes in Display 56 19

Talking Signs . . 56 21

Electric Heating

Heating Effects of Electric Currents ... 67 1

Applications of Electric Heaf 57 8

Thawing Frozen Water Pipes 57 10

Welding 57 13

Annealing 57 18

Electrolytic Forge 57 18

Electric Furnaces 57 20

Air Heating 57 21

Water Heating 57 23

Heating Appliances for Domestic Use . . 57 24

Miscellaneous Heating Devices 57 29

STORAGE BATTERIES

GENERAL DESCRIPTION

!• A storaf^e battery, secondary battery, or accu-
mnlator, as it is variously called, is an apparatus consisting
of certain materials so arranged that when they have under-
gone chemical action, due to the influence of a current of
electricity, the combination has acquired the properties of a
primary cell and is enabled to discharge into a closed circuit
approximately the same quantity of electricity as the original
charge. Strictly speaking, a storage battery is a group of
individual cells connected together, but the term battery is
often used when a single cell is meant.

Many forms of primary cell may, when exhausted, be more
or less regenerated by passing through them, in the opposite
direction to the current they produce, a current from some
external source. It is customary, however, to consider as
accumulators only those cells whose original construction is
similar to an exhausted battery; that is, they cannot be used
as sources of electricity until they have been charged by
passing a current through them.

Much confusion exists in the use of the terms positive and
negative when speaking of the plates of a secondary cell, for
in charging the cell the current is in the reverse direction to
that which flows when the cell is acting as a primary cell and
discharging; it is customary, however, to speak of the plate
at which the current enters the cell (while charging) as the
positive plate. In fact, whether charging or discharging, this
plate is at a higher potential than the other, which justifies
this use of the term, although with respect to the chemical

^fr mottct of copyright, see Page immediately following the title Page
127

483—2

STORAGE BATTERIES

i27

actions in the cell the positive and the negative plates are
reversed in the two operations-
Accumulators may be divided into two general classes;
(1) lead accumuiaiors, and (2) hi metal He accumuiai&rs; the
cells now in use are almost wholly of the first class-

XilSAD ACCUMUIiATOBa

PLANTE CELL

2. The origfinal lead accuiniilator, as made by
Plants, consists of two plates of lead, usually rolled
together in a spiral and separated by strips of rubber or
other suitable insulating material, placed in dilute sulphuric
acid. On sending a current from some external source
through this cell, the water becomes decomposed — the
oxygen combines with the positive plate, forming lead
oxide or peroxide, while the hydrogen collects at the
negative plate.

On disconnecting the source of the applied currenti and
completing the external circuit of the cell, the water is again
decomposed — the oxygen uniting with the hydrogen col-
lected at the negative plate and with the lead plate itself,
and the hydrogen uniting with the oxygen of the oxide of
lead at the positive plate— thus producing a current in the
opposite direction to the applied current.

Owing to the fact that the formation of the layer of oxide
prevents further oxidation, the amDunt of chemical change
due to the applied current is small, so the secondary current
from the cell is of short duration; after this current has
ceased, however, the surface of the positive plate is much
increased, owing to the removal of the oxygen from the lead
oxide ^ leaving the metallic lead in a spongy form. On
again sending a current through the cell a further oxidation
of this (positive) plate takes place, and by continuing this
process, reversing the current each time it is sent through,
both positive and negative plates become porous to a con-
siderable depth, thus very much increasing the surface on

§27 STORAGE BATTERIES 8

which the oxidation can take place. This process might be
carried on until the whole plate is reduced to spongy lead; in
that case the plate would not hold together, so a sufficient
amount of the original plate must be left for mechanical
strength. After the plates are so formed^ they are ready to
be used as an accumulator.

This forming process is, however, too slow and expensive
for commercial use. Batteries in which the Plants type of
plate is used are now formed by special electrochemical
methods, so that the active material can be produced in a com-
paratively short time.

FAURE CEI^Ii

3. Another method of preparing the plates is to apply
the active substance in the form of a paste. This process
was invented by Faure. The first charging current converts
the paste on the positive plate into lead peroxide, and that
on the negative into spongy lead. The substance applied
may be lead oxide (litharge) PbO, lead sulphate, minium
Pb^O^, lead peroxide PbO^, or mixtures of these substances.

The substances are applied in various ways; one method
is to make a paste of Pb^O^ (minium) with dilute sulphuric
acid for the positive and a similar paste with PbO (litharge)
for the negative. The sulphuric acid and the litharge com-
bine to form lead sulphate and water. On the positive plate
the acid combines with Pb^O^ to form lead peroxide, lead
sulphate, and water. In each case the action is only partial,
the amount of lead sulphate and lead peroxide formed
depending on the strength of the acid solution. These pastes
were originally applied directly to the surface of the plain
lead plate, but as they proved to be only slightly adhesive,
the plates were prepared by scratching or otherwise rough-
ening the surface, which process has been gradually extended
until the lead plates are now cast into grids, or latticework
plates, in the spaces of which the paste is applied.

The grids are usually designed to hold the active material
securely in position; to this end their perforations are not of
the same area throughout the thickness of the plate, but

4 STORAGE BATTERIES §27

wider or narrower in the center, so as to hold the filling of
active material by the dovetailin£ action of their shape.

After the grids have been filled with active material, they
are set up in pairs in suitable vessels and surrounded by an
electrolyte consisting of sulphuric acid diluted to about 1.17
specific gravity t which density corresponds to about 23 per
cent, of acid in the liquid. A charging current is then sent
through the cell from some external source; the action of
this current decomposes the water, the oxygen of which
further oxidizes the lead oxide (litharge or minium) to per-
oxide, at the positive plate, the hydrogen going to the nega-
tive plate, where it reduces the lead sulphate to spongy lead
by uniting with SO^, forming sulphuric acid. Thus, the
active material becomes lead peroxide on the positive plate
and spongy lead on the negative. By many investigators
this lead peroxide is thought to be hydrated lead peroxide;
that is, it contains a certain amount of hydrogen and oxygen
in excess of the normal peroxide, and is represented by the
formula H^Pb^O^, This, as well as many of the actions that
occur in accumulators, is not clearly established as yet.

Continuing the charging current when all the active mate-
rial is thus converted produces no effect, except to further
decompose the water; the resulting gases pass off through
the water, giving it a milky appearance. This phenomenon
is known as gassings or boilingi and is an indication that the
cells are fully charged,

4. On discontinuing the charging current at the gassing
point and completing the external circuit of the cell, a cur-
rent will flow in the opposite direction to that of the charging
current, the resulting chemical action being to change lead
peroxide to lead sulphate at the positive plate and the spongy
lead to lead sulphate at the negative. The sulphates thus
formed may not be all of the same proportions; one may
exist as red, another as yellow, and a third as white crystals,
of which the white sulphate is best known, as it is formed
when the cell is considerably discharged, and is extremely
troublesome. This discharge may be continued until all

§27 STORAGE BATTERIES 6

chemical action ceases and the E. M. F. consequently falls
to zero; but this is not advisable, since, if the discharge is
carried beyond a certain point, the red or yellow sulphates,
probably by combination with the litharge', PbO, form the
white insoluble sulphate; this, being a non-conductor, mate-
rially increases the internal resistance of the cell, and when
removed usually carries some of the active material with it,
as it is very adhesive.

The exact nature of the chemical reactions taking place in
a storage cell are not altogether understood. There are a
number of more or less complicated secondary reactions,
but it is now generally accepted that the main reaction
on charging is the formation of lead peroxide at the
positive plate and spongy lead at the negative; on dis-
charging, the final result is the formation of lead sulphate
on both plates, as explained above. The reaction may be
expressed as follows:

charzed condition dixharjged condition

-f plate electrolyte — plate + plate — plate

PbO. + 2H.SO^ -f /* = PbSO^-\-2H^O + PbSO, + electrical energy

^ — chararinff

The left-hand side of the equation represents the fully
charged condition. The active material on the positive plate
is lead peroxide and that on the negative, spongy lead. These
plates are immersed in the electrolyte containing sulphuric
acid, //,S0^, When the cell is discharged, it gives up elec-
trical energy and the substances are changed to those shown
on the right-hand side of the equation. Lead sulphate, PdSO^,
is formed on both plates and water is also formed. This water
mixes with the electrolyte and lowers its specific gravity.
When the operation is reversed and the cells charged, the
plates are in the initial condition represented by the right-hand
side of the equation. Electrical energy is supplied from an
outside source and the lead sulphate on the positive plate is
converted into lead peroxide, while that on the negative is
changed into spongy lead. Sulphuric acid is also formed and
this mixes with the electrolyte, causing the specific gravity
to increase as the charging progresses. When the cells have

STORAGE BATTERIES

§27

been properly charged, the positive plate is a chocolate color,
while the negative is a slaty ^ray.

The presence of the insoluble sulphate is made apparent
by the formation of a while coating or glaze over the plates,
which are then said to be suipkuied. If the cells are dis-
charged and left to stand with the electrolyte in place,
sulphating takes place rapidly.

5* It has been shown that sulphuric acid is formed during^
the charge and decomposed during discharge; thus, the pro-
portions of it in the electrolyte, consequently, the density of
the electrolyte, vary with the state of charge o£ the cell;
starting with a specific gravity of 1.150, the specific gravity
will be found to be about 1/20 when the cell is fully charged,
indicating the presence of about 27 percent, of sulphuric acid
in the electrolyte* The variation in density of the electrolyte
with discharge and charge is shown by the lower curves in
Figs. 1 and 2.

The E, M. P. of this cell is approximately 2 voltSi being
2.04 when the discharge starts, which gradually falls to 1.75
volts when nearly discharged; beyond this point, further dis-
charging causes the E. M. F, to fall more rapidly, the
decrease after 1.75 volts being very marked* The upper
curves in Figs. 1 and 2 show the variation in the potential
difference at the terminals of a cell, the curve in Fig* 1
showing the falling off during discharge and Fig. 2 the
rise during charge,

6, Buckling, — The rating of accumulators is usually
based on their capacity when discharged to an E. M. F. of
1,75 or 1.8 volts; cells should not be continuously discharged
to below 1.75 volts, as below this point injurious sulphating
will occur. This sulphating may lead to a distortion of the
positive plate, known as biiekllnf?, unless the grids are
strong mechanically. As the plates are located very close
together in the cells to reduce the internal resistance*
buckling is liable to cause the plates to touch, thus short-
circuiting the cell.

The cause of buckling seems to be the formation of sulphate

§27 STORAGE BATTERIES 7

in the plugs of active material that fill the spaces of the
grids, thus causing an expansion; lead having very little
elasticity, the grid is forced out of shape. As frequently
constructed, the edges of the grid are heavier than the inter-
mediate portion, so that the effect of the distortion is to
bulge the plate in the center. If the plates are not dis-
charged too far and too rapidly, the expansion of the active
material is gradual, causing the grid to stretch evenly.

7. Ratlngr of Cells. — The quantity of electricity that
may be taken from a completely charged cell depends on
the amount (weight) of material altered by the chemical
action, as in a primary cell; while the rate at which this
material is altered, consequently, the rate at which the elec-
tricity can be taken out (the rate of discharge in amperes),
and, to a large extent, the amount of material altered,
depends on the surface of the active material exposed to
the chemical action.

Cells are rated at a certain number of ampere-hours
capacity, depending on both the weight and the surface area
of the active material in the cell; a certain economical dis-
charge rate is also recommended, depending on the surface
of the plates exposed to the electrolyte. If this discharge
rate be continually exceeded, the chemical action goes on
too rapidly, the white sulphate is formed in the active
material of the positive plate, finally causing disintegration
of the active material, even if the discharge is not carried
beyond the point (1.75) given above. With the ordinary
construction, the normal discharge rate is about .04 ampere
per square inch of surface (both sides) of positive plate, and
the discharge capacity about 4 ampere-hours per pound of
plate (both positive and negative plate included).

8. Changre of E. M. P. With Dischargee. — The upper
curve in Fig. 1 shows the manner in which the E. M. F. of an
accumulator falls as the discharge proceeds. In this case the
cell was connected to a variable external resistance, such that
about the normal discharge current, as advised by the manu-
facturers, was maintained throughout the test in the external

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STORAGE BATTERIES

§27

circuit. The state of potanzatton of the dight surface layer
of both plates resulting from the charge causes the E. M. F.
to be high at first, but as this is quickly disposed of^ the
E. M. F\ falls in the first b minutes or so to 1,98 volts; on
continuing the discharge, the E. M* F. falls slowly and evenly
imtil after 8 hours of discharging the E* M* F. falls to
1.75 volts. If the discharge is continued beyond this pointi
the nature of the chemical action changes somewhat, and the
fall of E, M. F. becomes mure rapid.

This falling off of the E. M, F, is due to the weakening of
the acid solution and to the gradual changing of the spongy
lead on the one plate and the peroxide on the other to
sulphate. As this reduction can only go on at the points
where the acid is in contact with the spongy lead or the
peroxide^ it is evident that the interior portions of the active
material are affected much more slowly than the surface, as
the acid penetrates the active material oijly at a comparatively
slow rate* On this account, discharging at slow rates allows
the active material to be more uniformly and thoroughly
acted on^ thus giving a greater output »

This also accounts for the fact that on discontinuing the
discharge at any point the E. M, F, will soon rise to practi-
cally its original value, 2.04 volts; for unless the cell is
entirely discharged there is always some unconverted active
material in the interior of the plate, which serves to give the
original E* M, F. when reached by the acid. If the discharge is
r^sumedj this acid is soon exhausted, and the E. M. F. rapidly
falls to the value it had when the discharge was stopped*

In the above case, the product of the amperes and the hours
will give the output of the accumulator in ampere-hours; if
the discharge rate had been greater, the output in ampere-
hours would have been diminished, the discharge being
continued until the E, M. F, falls to the same value in each
case. Conversely, if the discharge rate had been lower, the
output would have been increased*

For example, assume the limiting E, M* F* to be U5 volts.
In a certain cell, with a dischargee current of SO amperes,
the E. Mi F. reaches its limit in 8 hours, giving an output of

S 27 STORAGE . BATTERIES 11 .

240 ampere-hours. If the discharge current were 40 amperes,
the limiting E. M. F. would be reached in about 6 hours,
giving an output of only 200 ampere-hours, while if it were
20 amperes, the limiting E. M. F. would not be reached for
about 13 hours, giving an output of 260 ampere-hours.

For the sake of uniformity, the rating of the capacity of
accumulators is made on the basis of a discharge current
that will cause the E. M. F. to fall to 1.75 volts in 8 hours,
although most manufactiu"ers give tables showing the com-
parative capacity of the various sizes of cells at other rates of
discharge. The rate of charge (charging current) for accu-
mulators of this class should be about the same as the nor-
mal (8-hour) discharge rate, although much smaller currents,
continued for a proportionately longer time, may be used.

EFFICIENCY OF STORAGE CEL.LA

9. Although storage batteries do not store electricity,
they certainly do store energy by converting the kinetic
energy of the electric current into chemical potential energy,
which may be realized as kinetic energy again. The efficiency
of the accumulator (or of any other means of storing or
transforming energy) is the output divided by the input.
This quotient is always less than 1, as the accumulator is
not a perfect storer of energy; that is, there are certain losses
in the transformation of kinetic electrical to potential chem-
ical energy, and victe versa, besides the loss of the energy
required to force the current through the cell, that is, the loss
due to the resistance of the plates and electrolyte.

10. Ampere-Hour Efficiency. — The input and output
of an accumulator may be expressed either in ampere-hours
(the quantity of electricity) or in watt-hours (the work done
by the current). If secondary cells of this class be fully
charged at normal rate, after a discharge to 1.75 volts, and
then discharged to the same point, also at normal rate, the
ampere-hour efficiency will be ordinarily from .87 to .93, or
87 to 93 per cent. If charged and discharged to the same point
at very slow rates, this efficiency may rise to 96 or 97 per cent.

STORAGE BATTERIES

§27

11. Watt-noiir Efricleucj-*— The watt-honr effi-
ciency at normal rates of charge and discharge is lower,
being from 70 to 80 per cent*, depending on the constraction

of the celh When batteries are used for regulatings purposes
to take up rapid load fluctuations, the battery is alternately
charged and discharged and the chemical action is confined
largely to a thin surface film on the plates. Under such
circumstances the watt-hour efficiency becomes considerably
higher than when the battery charges and discharges con-
tinuously, and the watt*hour efficiency may be as high as
from 92 to 94 per cent*

The cause of the loss represented by the foregoing figures
is^ for the ampere-hour efficiency, due to the fact that the
charging current must perform several chemical decompo-
sitions, the elements of which either do not recombine or,
recombiningi do not give up their potential energy in the
form of electrical energy*

The loss shown in the watt- hour efficiency figures is due
partly to the fact that the E. M. F. of charge is higher than
that of discharge, partly to the E, M. F. required to per-
form the wasteful chemical actions referred to above, and
partly to the drop in volts caused by the passage of the cur-
rent against the resistance of the plates and electrolyte.
This drop adds to the E. M. F, required to perform the
chemical decompositions in charging, and subtracts from the
E. M, F. due to the chemical recom positions, and its amount
depends more on the construction of the cell than does the
loss represented by the ampere-hour efficiency, as it varies
wnth the shape and size of the plates, their distanee apart,
their state of charge (on account of variations of the resist-
ance of the electrolyte as the percentage of acid varies), the
rate of charge and discharge, and other conditions.

The loss due to the internal resistance in well-designed
cells usually amounts to about S per cent, at normal rates of
charge and discharge; the loss is correspondingly less at low
rates and more at high rates, being proportional to the square
of the current flowing.

These efficiency figures, as stated, are given for a discharge

§27 STORAGE BATTERIES 13

to 1.75 volts E. M. F., the usual manufacturers' rating; if
the cells are not discharged to so great an extent, both
ampere-hour and watt-hour efficiencies are higher.

12. Resistance of Cells. — In a good modem cell
exposing about 1,100 square inches of positive-plate surface,
and listed as having 400 ampere-hours capacity, the internal
ohmic resistance is about .0007 ohm when charged. Cells of
greater capacity have a proportionately lower resistance.

CHARGING E. M. F.

13. The E. M. F. required to send a given charging
current through a secondary cell varies with the state of
charge of the cell. Fig. 2 shows the E. M. F. required to
charge the same type of cell that gave the discharge E. M. F.
curve, Fig. 1. The curve shows the voltage across the ter-
minals of the cell when it is being charged at the normal rate.

This curve shows that the charging E. M. F. during the
first hour rises at a comparatively rapid rate from 2.04 to
2.13 volts. During the next 5 hours the rise in voltage is
slower and practically uniform, having become 2.19 volts at
the end of 6 hours. For the next 2i hours the rise in voltage
becomes more rapid and at the end of 8 hours reaches 2.38
volts, and at Si hours 2.48 volts. On continuing the char-
ging current beyond the 8i-hour period the E. M. F. rises a
little more, and then remains practically constant at about
2.50 volts; as the only action that now takes place is the
decomposition of the electrolyte, giving off gas, further
charging will only result in a waste of energy.

From this curve it appears that the cell became completely
charged in practically 9 hours; as the discharge curve. Fig. 1,
shows that with the same number of amperes the discharge
is complete (to 1.76 volts) in 8 hours, the ampere-hour
efficiency of this cell is 1^, or nearly 90 per cent.

CONSTRUCTION OF LEAIKSITLPHURIC ACID CELLS

14. The usual construction of lead-sulphuric acid
cells is as follows: The plates and electrolyte are contained
in a vessel of approximately cubical form; this vessel is of

STORAGE BATTERIES

§27

glass, if the cells are not intended to be portable, the glass
allowing the examination of the condition of the plates white
the cell is in operation. If the cells are intended to be port-
able, the vessel is usually made of hard rubber, or of wood
lined with rubber or lead* Very large accumulators for
central-station use are set up in lead-lined wooden tanks.
The plates are usually approximately square, except in
large cells, and from } inch to i inch thick, according to size-
To get a large surface area without using single large plates,
and to allow of one size of plate being used for cells of

various capacities, each cell
contains a number of pos-
itive and negative plates
arranged alternately side
by side a short distance
apart. The number of
negative plates is always
one more than the number
of positive plates, so that
each side of each positive
plate has presented to it
the surface of a negative.
All like plates are con-
nected together by a con-
necting strap, usually at
one comer of the plate.
The arrangement of a
widely used type of cell
that vnW be described more
in detail later is represented in Fig. S, where a, a are the
positive plates and b, b the negative. From a corner of
each plate a lug projects; those on the negative plates are
joined to a connecting strap, and those on the positive
plates to another; the projections on the plates rest on
the edges of the jar so that the bottoms of the plates are
some distance from the bottum of the jar* This is done in
order to prevent any active materia! or foreign matter that
may accumulate in the bottom of the cell, from short-circuiting

STORAGE BATTERIES 15

the plates. The joints are made by a process called buminj^,
which consists in melting: the lug^s and straps tog:ether by a
hydrogen flame; this flame absorbs the oxygen from the
film of lead oxide with which the lead is usually covered,
thus making a clean and solid joint. The connecting straps
are extended beyond the limits of the cell, and serve to
connect the various cells of the battery, the connection being
made by a lead-covered brass bolt in the case of small cells.
Large cells are nearly always joined together by burning
the connections.

TYPES OF LEAIKSULPHURIC ACID CELL

15. A great many different styles of storage cell of the
lead-sulphuric acid type have been brought out both in North
America and in Europe. The operation of all of them is
substantially as described, their distinguishing features lying
in the style of grid used and the methods of preparing or
applying the active material. As it is impossible to here
consider all the different types, we will confine our attention
to a few of those that have been used most widely in America.

16. The Chloride Accumulator. — The Chloride accu-
mulator made by the Electric Storage Battery Company is a
type that is extensively used. Fig. 8 shows one of these
cells in which the elements are mounted in a glass jar. The
large cells used for central-station work arc mounted in lead-
lined wooden tanks. In the Chloride cell, the positive plate
is of the Plants type and is known as the Manchester type of
plate. The active material is formed from metallic lead. The
negative plate is made by a special process. Fig. 4 shows
the construction of the positive plate. The supporting grid A
is a casting made of a mixture of lead and antimony and the
holes in which the active material is placed are tapered from
each side, as shown in the sectional view. This grid is not
acted on by the acid and takes no part in the chemical
changes that take place in the cell. It is strong mechanic-
ally, and serves to hold the active material /? which is in the
form of round plugs about J inch in diameter, made by roll-
ing up a corrugated ribbon of pure lead, as shown at [b)\ the

STORAGE BATTERIES

§27

strip is slightly wider than the thickness of the supporting
grid so that, when pressed in place, the plug projects a little
on each side. The coiled-up piece of lead expands in the
forming process^ so that there is no possibility of its falling
out. After the lead ribbon is in place it is converted into
lead peroxide, as described, thus forming the active material.
This construction gives a rigid plate, and, since the active
material in each hole is free to expand and contract a certain
amount, buckling is avoided.

(h)

The Chloride cell Is so called because ^inc chloride was at
one time used in the construction of the negative plate*
Though it is not used in the present type of plate the name
is retained p Fig. 6 shows the construction of the negative
plate known as the box ne^itlve. It is made of two parts
A^ B riveted together* Each part is made by casting lead-
alloy ribs f , r on a sheet of perforated sheet leadt these ribs
divide the sheet into a number of squares about li inches
each way. When the halves are riveted together, as shown
in the sectional view, a number of small bo^es, or recesses.

§27

STORAGE BATTERIES

are formed; the halves are firmly held together by cast pro-
jections, at the rib intersections, that project from one half
through corresponding holes in the other half. Before the
halves are riveted together, the active material, litharge or
lead monoxide, is placed in the recesses. The litharge is first
made into a paste and molded into pellets, which are slowly
dried. Four of these pellets are placed in each compartment
of the plate, and as they fit in loosely they are free to expand
and contract. The first charge given the battery after it is

'•■*■*«* I V* *«>■>*»« BVB ■'■■■■I

I IT i '' ^ — I - ir^ i aa ar ' - ^ ■ ■ a

Secff'ofta d

Pio. 5

installed converts the litharge into spongy lead, which con-
stitutes the active material of the negative plate. This con-
struction allows free access of the electrolyte to the active
material and it is not possible for the latter to fall away
from the plate as it did in some of the older types.

The requisite number of these prepared plates, positive
and negative, are then set up together to form a cell, some

4«B— 3

STORAGE BATTERIES

§2?

form of separator being mualljr placed between them. In
the Chloride accumulator a number of different kinds of sep*
arators have been used* In the earlier cells the plates were
separated by sheet asbestos, but the separator now generally
used is a board diaphragm used in connection with wooden
strips. The arrangement of these diaphragms and separators
will be explained in detail in connection with the setting up
of cells.

Fig. 6 shows the general arrangement of some large
Chloride cells used with a central-station lighting system.
Each cell here contains 87 plates 15i in. X 32 in. The lugs /, /
on the plates are burned on to the channel'shaped pieces r, c
that form the connections between the cells; d is the edge
of the lead lining of the tankj and e, e are glass rods for-
merly used for separating the plates. The heavy bar m forms
one terminal of the battery and is connected to the last set
of plates by means of the copper cross-piece n*

17. The E. M, F, and action of the Chloride accumulator
are the same as that of the Faure (pasted) type or the
Plants* It is claimed by the manufacturers that^ from
the solidity of the construction, buckling and loosening of the
active material are practically impossible, so that the cells
may be occasionally discharged to a low E. M. F. or at high
rates without serious injury. Its output per poimd of ele-
ment is greater than that usually assigned to lead accumu-
lators, being from 4 to 6 ampere-hours, according to the type
of cell, per pound of plates (both positive and negative) at
normal discharge rates,

18. The Gould Storafre Battery. — The Gould battery
is of the Plants type: Both positive and negative plates are
made of rolled sheet lead, and the distinguishing feature of
the cell is the method of increasing the active surface of the
plates. Fig. 7 shows a Gould plate before it has been sub-
jected to the forming process; the sheet lead is spun up so
as to form thin ridges with grooves between them in which
the active material is formed. Sheet-lead blanks are placed
in steel frames and made to move back and forth between

STORAGE BATTERIES

§27

two rapidly revolving shafts on which are mounted steel
disks alternating with steel washers* The thickness of the
disks and washers determines the width of the ^rrooves and
the thickness of the ribs* The pressure maintained between

PlQ. 7

the rolls and lead causes the latter to be spun up in thin
ridges, as shown in Fig. S {a}. No lead is removed from
the blank; the form is merely changed so as to give a greatly
increased surface. In all except the smallest plates the spun

r«;

portion is divided into sections, as shown in Fig. 8 (d), and
the imspnn parts a,b,c form bars of solid conducting material
to which the thin webs are anchored. There is also a thin
dividing line d in the center of the plate. The width of the

§2Y

STORAGE BATTERIES

^ooves is governed by the kmc! of work that the cell has to
perfomi, and varies (rom .005 to .024 inch. By spinning tip the
lead, the superficial area is increased from ten to twenty times,
and gives from 200 to 400 square inches per pound of lead.
This permits a low current density at the contact surface
between acid and* plate, the density at normal discharge rate
being about 1 ampere for each 250 square inches of contact

surface. The thickness of the ribs varies from .006 to ,040
inch on the positive plate, and is about .012 inch on the nega-
tive. The active material is formed electrochemically, and
fills the narrow spaces between the ribs; these spaces are so
narrow that there is little chance for the material to fall out*
After the plates have been formed^ the thin ribs do not
appear as distinctly as shown in Fig, 7«

STORAGE BATTERIES

§27

Fig. 9 shows a Gould cell arranged for central-station
work. The elements are mounted in a lead-lined wooden
tank, and are separated by glass rods a, a. This cell has 41
plates — 20 positive and 21 negative — and has a capacity of
400 amperes for 8 hours, 560 amperes for 5 hours, or 800 '
amperes for 3 hours. It is covered by heavy glass, half of
which b is sho\^Ti in the figure, in order to prevent acid spray
beinjT thrown off when the battery gases^ The whole cell is
supported on porcelain insulators c^ c*

19, The Wlllard Storage Batter? .— The WiUard bat-
tery is of the Plants type, the active material being held in
narrow grooves cut in a rolled lead plate. Fig. 10 (a) show^s
a Willard plate; its grooves are inclined upwards in order to
hold the active material more effectively in place. Fig* 10 {b)
shows a complete cell of the WiUard type. The action of the
cell is the same as the Plants cell, so that furtlier comment is
unnecessary.

527

STORAGE BATTERIES

20, The {oregoing will give a fatr idea as to the con-
strue tioti ot storage batteries* The list might be prolonged
almost indefinitely, for many makes that are perfectly satis*
factory in operation are not mentioned here- As before
stated, nearly all of these cells operate on the same principlep
the only difference being in the method of making the plates.
A vast amount of time and money have been spent in the
improvement of storage-battery elements and in perfecting
the manufacturing details. The above ^ however, will be
sufficient to show the general construction of such batteries
as are made at the present time. It seems as if the Plants
type were used most largely in America, especially for
stationary work; in Europe, the Faure, or pasted type^ is
more common. The Faure type is used by some makers for
automobile batteries, because, in generals the pasted cell
gives a greater output per pound of weight than the Plants
type. On the other hand» it has been found that pasted plates
are more liable to disintegration, so that where weight is not
an objection, the Plants type is favored.

AtJTOMO»n.K BATTEHIES

21* In batteries intended for automobiles, electric
launches, or similar class of service, every effort must be
made to secure a large output with a minimum weight.
The cells must at the same time have sufficient mechanical
strength to withstand the jarring to which they are sub-
jected. The grids used in these cellsi are of lighter con-
struction than those used for stationary batteries and carry
a larger proportion of active material.

Fig. 11 shows the general construction of the plates used
in the "Exide'* battery made for automobile use by the
Electric Storage Battery Company. The foundation for
the positive plate is a light but stiff cast grid made of a
mistture of lead and antimony; the general form of the grid
is indicated in Fig. 11 (a). These grids are pasted with red
lead, which is afterwards converted into lead peroxide; the
Staggered arrangement of the cross*ribs, shown in the

STORAGE BATTERIES

§27

sectional view, insures a firm locking of the active material.
The negative plate* shown in (^), is of lighter construction
than the positive. It is made up of a sheet of lead a with .
p stifiE frame b cast around it. This sheet has a number of
holes punched in it, half of these € being pimched through
from one side and the other half d from the other side.
The metal is not removed but is torn or burred up as
indicated- The torn projections are pressed down flush with
the edge of the cast frame and the plate is then pasted on
both sides with litharge, which is afterwards converted into
spongy lead. The torn projections » when pressed down^

3ecf/Qfi tt-fr

^Bctfoft m*^

form a series of hooks that lock the material securely to the
plate. This cell is, therefore, of the Faure type, both plates
being pasted-

The Porter automobile battery is also of the pasted type,
while the Willard and Gould automobile batteries are of the
Plants type, and have plates made in practically the same
way as those used for stationary batteries. The elements of
automobile batteries are usually mounted in hard-rubber
cells in order to avoid breakage, and are separated from each
other by perforated hard-rubber diaphragms- The output of
automobile batteries is usually from 5 to 6.5 ampere-hours

§27 STORAGE BATTERIES 26

per pound total weight when discharged at a 4-hour rate.
However, it is difficult to compare such batteries simply by
their capacity per pound weight. The ability to withstand
rough usage and constant jarring is of more importance than
mere lightness for this class of service.

BIMETAIililC ACCUMUIiATORS

22. Owing to the great weight of lead accumulators many
attempts have been made to produce a storage cell that
will be equal or superior to the lead cell and a great deal
lighter. A vast amount of experimenting has been done
along this line, but so far the lead cell has proved the most
economical in t^he long run. In bimetallic cells, the ele-
ments consist of two metals, the electrolyte being a salt
of one of the metals or a hydroxide. Though many com-
binations of metals have been proposed for these cells, the
most satisfactory are the zinc-lead, capper-lead, copper-zinc,
and, later, the nickel-iron cell of Edison. The principal
trouble with bimetallic accumulators has been due to local
action, which soon causes deterioration of the plates; also,
many of these cells will not work well at ordinary tempera-
tures, making it necessary to keep the electrolyte hot in
order to secure satisfactory action. A few of these cells are
described in order to show what has been done in this line,
though few of them have been used to any great extent.

23. Zine-Liead Cell. — The zinc-lead cell usually con-
sists of plates of zinc and lead in a solution of zinc sulphate..
On sending a charging current through this cell (the zinc
being the negative plate) the zinc sulphate is decomposed,
depositing zinc on the zinc plate and forming free sulphuric
acid with the hydrogen of the water, which is also decom-
posed, its oxygen uniting with the lead plate, forming
peroxide of lead. On open circuit and while charging, the
free sulphuric acid in the solution slowly attacks the deposited
zinc, reforming zinc sulphate, so that the efficiency of this form
of cell is low; it will not retain a charge more than a few days.
The E. M. F. is high, being about 2.35 volts to 2.5 volts.

STORAGE BATTERIES

S27

By substituting^ copper sulphate for zinc sulphate, and
copper plates for the zinc or other negative plates in this
type of cell, the acid formed during charge cannot attack the
copper, so that this loss is obviated; the E, M, F:, however,
is but L2r> volts under these ci ream stances, so the watt out*
put is materially reduced* Fig* 12 shows a zinc-lead cell

made by the United States
Battery Company, The
positive element a is per-
forated lead, and the neg-
ative element b gran-
ulated zinc amalgam*
The amalgam is placed
in the bottom of the cell
and the lead plate ar*
ranged horizontally above
it in order to avoid short-
circuiting by any particles
that may drop off the
positive plate; by thoroughly amalgamating the zinc it is
claimed that local action is avoided. This type of cell gives
an average E, M. F. about 15 per cent, higher than that of
the lead-sulphuric acid cell, and is somewhat lighter. The
electrolyte is a i^ohition of zinc sulphate.

Owing to the variations in the composition of the electro-
lyte, the internal resistance of these cells is variable, being
lowest when charged and increasing during discharge as the
sulphuric acid forms sulphate of copper or zinc.

Fio. 12

24, Copper-Zlnc Cells, — The copper-zinc accumulators

were at one lime in commercial use to a limited extent, the
beat known being the Phillips-Entz accumulator ^ made by
the Waddell-Entz Electric Company. This accumulator
employed the same active materials as the Lalande-Chaperon
or Edison-Lalande primary cell, modified in mechanical coti-
struction to adapt them for accumulator use* The positive
plate was made of porous copper on a solid foundation. ^ The
negative plate was a thin sheet of steel, and the plates were

§27 STORAGE BATTERIES 27

mounted in a jar made of steel. The electrolyte was a solution
of potassium zincate and potassium hydrate (caustic potash).

The reactions in a cell of this kind are complicated, but
when the cell, is charged zinc is deposited, from the potassium
zincate, on the steel plates and the porous copper is oxidized.
On discharge, the action is the same as in the Edison-Lalande
primary cells; that is, the zinc is dissolved, the potassium
zincate is reformed, and the copper oxide reduced to metallic
(spongy) copper.

The efficiency of this type of accumulator is about the
same as that of the lead accumulator, while its output is very
much greater, weight for weight, the ampere-hour output
being about five times that of a lead cell. The E. M. F. is
much lower than that of the lead accumulator, averaging
.75 volt during discharge, so that the comparison on a basis
of watt-hour output is not so favorable; still, the copper-zinc
accumulator will show an output of about 15 watt-hours per
pound of plates, while the lead accumulators seldom exceed
from 7 to 10 watt-hours per pound of plates, the latter figure
being seldom reached at normal rates of discharge.

The efficiency and internal resistance of the copper-zinc
accumulator vary quite largely with the temperature, on
account of the considerable variations in the density of
the electrolyte; on this account the cells are ordinarily
charged and discharged at a temperature of about 54° C.
(130° F.), at which point the resistance is about the same as
in a similar lead accumulator.

These cells are not much affected by the rate of discharge,
there being no such occurrence as sulphating or buckling;
but on account of the difficulty of depositing the zinc in a
solid form, the charging must be done at a low rate, and the
action of the cells is improved by intermittent charging.
The E. M. F. required to charge one of these cells varies
from .9 volt at the start to 1.05 volts at the finish. On
account of these features the copper-zinc accumulator can be
used only in installations where it is charged and discharged
daily, thus preventing local action, and when it can have the
necessary appliances, care, and attention in charging, to

STORAGE BATTERIES

§27

insure proper charging rate, teniperature^ etc.; so, io spite
of its large output per unit of weight> it can hardly come into
general use. Another serious objection to this type of ceU is
its low voltage^ for a system operating at a given voltage
nearly three limes as many cells would be required as would
be sufficient if lead-sulphuric acid cells were used* This
objection, of course, applies to any cell that gives a low
voltage. Like all cells using caustic potash or other
hydroxide for the electrolyte, the air must be kept from the
electrolyte to prevent the absorption of CO^ (carbonic -acid
gas) from the atmosphere, and the fonnation thereby of
carbonates- The necessity of excluding the air by means of
a layer of oil or by other means constitutes quite a serious
drawback in the practical operation of these cells. Although
this type of accumulator has many good points, it has never
been able to displace the lead-sulphuric acid cell in commer-
cial work on account of the above-mentioned drawbacks and
has, in fact, never been used to any great extent-

25* Edison Nlekel-Iron CeU, — A bimetallic cell has
been developed by Edison that* it is claimed, is lighter and
more durable than the lead type and does not have the
disadvantages of other bimetallic cells. The cell has been
developed with particular reference to the requirements of
electric vehicle service, but at present it has not been used
to a sufficient extent commercially to indicate whether or not
it will be able to displace the lead type of celL The active
material of the positive plate is peroxide of nickel and that
of the negative plate, finely divided iron. Both plates are
constructed as indicated in Fig, 13. The active material is
held in flat stamped steel boxes, or pockets, made by shallow
halves that fit tightly together. These boxes are perforated
with narrow slits that allow the electrolyte to come in con-
tact with the material contained within. The plate proper is
made of steel, nickel plated, and is punched with twenty-four
rectangular openings, as shown at a. Fig, 13. The boxes b
are held in the openings as shown in the complete plate c.
The plates are quite thin and the number required for a cell

§27

STORAGE BATTERIES

are assembled with rubber separators between adjacent
plates. The electrolyte is a 20-per-cent. solution of caustic
potash iiCOH), and as the amount required for the cell is
small, the plates can be placed close together. The nest of
plates is placed in a sheet-steel containing vessel. The regular
attlomobile cell measures 13 in* X 5.1 in, X 3*5 in. and weighs

^^_^_^_-...n/6^

I17.B pounds. The E, M, F. of the cell is 1.33 volts, and the out-
put varies from 173 to 142 ampere-hours on discharges ranging
I from 30 amperes to 200 amperes. This corresponds to about

IS watt*hours per pound at the lower discharge rate* Like all
other cells using a hydroxide for the electrolyte, the air
must be excluded to prevent the formation of carbonates.

Fm. 13

STORAGE BATTERIES

§27

INSTALLATION AND CARE OF STORAGE

CELLS

SE-rriNG UP CELLS

26. The following instructions regarding the installation
and care of storage cells are an abstract of those furnished
by the Electric Storage Battery Company, and refer to the
Chloride cell as used for stationary work. However, the
instructions may be taken as applying for the most part to
any of the ordinary types of lead-sulphuric acid cell. Manu-
facturers send out instructions regarding their cells and give
any special recommendations that may relate to their par-
ticular type. For the most part these instructions apply also
to automobile or other portable cells.

27. Loeatlon. — Storage cells should be located in a
well-ventilated room of moderate temperature, say from 50^
to 7-^° F, The floor should be of cement with drainage
facilities, and the room should be light enough to allow
easy inspection of the cells. Generally, the battery room is
located somcw^here near the dynamo room In case the battery
is used In connection with a central station, as a near-by
location cuts down the length of conductors between the
battery and station, and also allows the outfit to be watched
to better advantage*

28. Method or Supporting Cells- ^The cells are

usually mounted on racks made of heavy wooden framework
securely braced. It must be remembered that these cells are
heavy, and sagging of the framework is not allowable, as it
may result in broken cells. If there is plenty of space avail-
able* the cells should be in a single tier, in which case all the
framework that is necessary is a set of stringers properly

§27

STORAGE BATTERIES

29. Placing Ele-
ments in Jar. — The

elements and jars are
shipped separately,
so that the battery
usually has to be as-
sembled at the place '^ ^
where it is to be used. The plates should be unpacked
carefully, because if handled roughly they may be bent or

Omm

fastened together. Fig. 14 shows a framework recom-
mended by the Electric Storage Battery Company for
those places where it
is necessary to ar-
range the cells in
two tiers. Each cell
is placed in a shal-
low wooden tray a
partly filled with
sand, and each tray
is set on four single
petticoat glass insu-
lators. The sand dis-
tributes the strains
on the glass jar and
avoids breakage.
Where wooden tanks
are used, these trays
are not necessary.
Fig. 15 shows the
shape of the glass
insulators. Any cur-
rent leakage from the
cells has to take place
over the petticoat a,
taking the long path
indicated by the dot-
ted line.

e'!—

jej— a.^--..--ijfee)^

STORAGE BATTERIES

§27

otherwise damaged. The positive and negative plates are,
except in the case of very large cells » connected together
in groups; the positive group is easily distinguished by

its dark-brown, color. Fig. 16
shows the various parts of a
Chloride accumulator after
they have been unpacked and
separated; a is the negative
group, b the positive, c the
Jar, d the wood diaphragms
for placing between the plates, c the slotted wood sep-
arators for slipping over the diaphragms and holding
them up in place, and / one of the diaphragms with its pair
of slotted wood separators in place. The block g^ is used
in raountiog and arranging the elements and the lead-covered
brass screws h are for bolting the terminals of the cell

Fig. 15

together. Before placing the board diaphragms between the

plates, the grain of the wood always being parallel to the
edges or sides of the plates, two of the slotted wood sep-
arators must be slipped over each board and spaced 1* inches
from the edge. The elements are then slipped together, as
shown in Fig. 17 (a)^ and the diaphragms adjusted in place.
The whole group of elements is then lifted, by means of
a broad piece of webbing, on to the block mentioned above.

§27

STORAGE BATTERIES

This allows the diaphragms to be pushed down into place,
and the elements further adjusted, as shown in Fig» 17 (^),
The elements are then lifted by means of the webbing, as
shown in (c), and gently lowered into the jar.

Though this method of placing plates refers particularly
to the Chloride accumulator it can be used with almost any
of the ordinary tj^pes of storage cell. After the cells have
been assembled the lead terminals should be well scraped at
the point where they are bolted together in order to secure
good electrical contact.

34 STORAGE BATTERIES §27

THE EIjECTBOIjTTE
30. Miiclngr the Elect rolyte.^The electrolyte used

in storage batteries differs slightly with different makes of
cell; it is always dilute sulphuric acid, but the specific gravity
of the solution recommended by different manufacturers
varies somewhat. The electrolyte should have a specific
gfravity of 1/20 to 1,24, as indicated by the hydrometer when
the cells are charged. The specific gravity is taken at nor-
mal temperature of about 60^ F, Most manufacturers of
storage ceils furnish electrolyte ready mixed, but it can be
prepared by diluting suitable commercial sulphuric acid
{oil of vitriol) with pure water. In selecting sulphuric acid
none but the sulphur or brimstone acid should be used;
acid made from pyrites is liable to contain impurities, such as
iron or arsenic* It is absolutely essential that the acid and
water be free from impurities, such as iron, arsenic, and
nitric or hydrochloric acid. When diluting, the acid must be
poured slowly and with great caution into the water; do not
pour water into the acid because the sudden evohition of heat
and the consequent boiling action may throw acid into the
operator's face. The proportions of acid (of 1,84 specific
gravity or 66^ Beaurne) and water are 1 part of acid to 5 of
water (by volume)* The vessel used for the mixing must
be a lead*lined tank, or one of wood that has not been used
for other purposes; a wooden wash tub or spirits barrel
answers very welL The electrolyte when placed in the cell
should come i inch above the top of the plates. Before put*
ting the electrolyte in the cells, the circuits connecting the
battery with the charging source should be complete. The
positive pole of the charging source must be connected to
the positive pole of the battery. Also, care must be taken
in placing the cells to see that positive and negative poles of
adjacent cells are connected together. It is an easy matter
to connect one or more cells backwards if the terminals are
not closely inspected when the cells are being connected.
After the electrolyte has been placed in the jars, the battery
shi^uld be charged at once^ iif possible; in any event, the cells

827

STORAGE BATTERIES

I
I

should never be allowed to stand more than 2 hours after the
electrolyte has been placed in them, before they are charged.
The value at which the density of the electrolyte should be
maintained is usually specified by the manufacturer, but it is
generally in the neighborhoud of
1.2; automobile batteries are usually
supplied with an electrolyte having
a sUghtly higher density. During
regular operation of the battery, the
density of the electrolyte changes;
as the battery is charged the specific
gpravity rises until it reaches a max-
imum not necessarily fixed; when
the battery is discharged the spe-
cific g^ravity lowers. The acid does
not evaporate so that any evapora-
tion of the electrolyte should be
made tip by the addition of water;
however* a certain small amount of
acid may be thrown off in the form
of fine spray or be absorbed by
sediment in the bottom of the cell.
The addition of some acid every
1 or 2 years is, therefore, necessary
in order to maintain the specific
gravity at the standard density.
The most convenient way of adding
the acid is to prepare a mixture of
acid and water having a density of
about '1.4 J and add as much of this
as may be necessary ♦ As men-
ttoned above » it is particularly im-
portant that the acid be free from
impurities; if there is any doubt on
this score a sample should be analyzed

formance of a battery depends very much on the condition
of the electrolyte, hydrometer readings should be taken at
regular weekly intervals*

Fio. la

As the proper per-

STORAGE BATTERIES

127

31. nydrometers, — In order to facilUate the deter-
mination of the density of the electrolytet special forms of
hydrometers are used in connection with storage-battery
work. Fig. 18 shows two styles of battery hydrometer
suitable for use in stationary cells where there is plenty of
room around the plates for placing^ the hydrom*
eier in the liquid. The larger size is preferable,
as the density can be determined more easily and
more closely than with the smaller, which is only
used in cells where there is not sufficient room
for the larger size. Each of the hydrometers has
a small bnlb at the lower end and that contains a
quantity of fine shot. Some hydrometers have
mercury in the bulb, but shot is preferable because,
if the bulb becomes broken, no mercury as an
impurity is introduced into the electrolyte. More-
over, if mercury grets into a lead-lined tank it
attacks the lead lining or rather amalgamates with
it and a leak is likely to result. The air in the
large bulb floats the hydrometer, which, when
placed in the electrolyte, stands upright, and the
reading on the stem Is taken at the point where
it emerges from the Hquld.

fFij?* 19 shows a style of hydrometer more par-
ticularly adapted to cells where it would be difficult
to place a hydrometer directly in the liquid, as,
for example, in automobile batteries. The hydrom-
eter a is placed within the glass tube ^, and by
means of the rubber bulb sufficient electrolyte can be drawn
up to float the hydrometer. Enough liquid is drawn up to
fill the tube up to the mark d ground on the glass, and the
reading is taken at the point where the floating tube m
emerges from the liquid*

S27

STORAGE BATTERIES

CHARGING

82, After the battery has been set up, it should be given
a full charge at the normal rate. The rale of charging is
usually the satne as the 8-hour rate of discharge as specified
by the manufacturers. It is desirable that the charging be
continued uninterruptedly, though this is not absolutely essen-
tiaL The charge should be continued until it is certain that the
charging is complete according to the signs given below. It
should not be repeatedly carried t>eyond the full -charge point,
because it entails an unnecessary waste of energy, causes a
rapid accumulation of sediment, wastes acid through spray-
ing, and what is still worse, shortens the life of the plates.
It is advisable to overcTiarge the batteries slightly, about
once a week, in order that the prolonged gassing may
thoroughly stir up the electrolyte, and also in order to cor-
rect any inequality in the voltage of the cells that may have
developed. At the end of the first charge it is advisable to
discharge the battery about one-half, and then immediately
recharge it. Repeat this operation two or three times, and
the battery will then be in condition for regular use,

33* Indleatlotis of a Complete Chargre,-^A complete
charge should exceed the previous discharge, in anipere-
hourst from 12 to 15 per cent. The principal indications of
a complete charge are; ( 1 ) The voltage and specific gravity
reach a maximum value, which value is not necessarily
fixed; for example, the voltage at the end of a charge may
be from 2.4 to 2.7. (2) The amount of gas given off at
the plates also increases when the cells are fully charged*
(3) The positive plates become a dark brown, and the
negatives a light gray. (4) With all the cells of the battery
in normal condition, with pure electrolyte and no material
lodged between the plates or sediment touching them at the
bottom, the maximum voltage and specific gravity are
reached when» with the charging current constant at the
normal rate, there is no further increase in either during a
period from i to 1 hour; for example, if the charge has been

STORAGE BATTERIES

§27

carried oo for 5 hours with a gradual rise in the voltage
and specific gravity during^ that time and with an additional
i hour of charging, there should be no further rise in either,
then the charge is complete.

34, Yoltagre at Eiia of Cliarisre,— The voltage at the
end of a charge is not always the same. It depends on the
age of the plates and the temperature of the electrolyte^
hence, both of these must be taken into consideration when
determining the completion of a charge. When the battery
is first installed, the voltage at the end of the charge will be
2,5 volts per cell or higher, at normal rate of charge and at
normal temperature. As the age of the battery increases »
the point at which it will be fully charged is gradually
lowered and may drop as low as 2 A volts at normal rate
and temperature. With charging rates lower than the nor-
mal, the voltage at the end of the charge will be approxi-
mately .05 volt less for each 25 per cent, decrease in the rate.
For example, if the final voltage were 2.50 at the normal
rate, say, of 1,000 amperes, it would be 2,45 at 750 amperes,
and 2,40 at 500 amperes* If the temperature is increased
above normal, the final charging voltage is noticeably
lowered, and vice versa, irrespective of the age of the plates.
It is understood in the preceding that all voltage readings
are taken with the current flowing; readings taken with the
battery on open circuit are of little value and are frequently
misleading. After the completion of a charge and when the
current is off, the voltage per cell will drop to about 2,15
volts and then to 2 volts, or slightly less, when the discharge
is started* If the discharge is not begun at once^ the pres-
sure will quite rapidly drop to 2,05 volts and remain there
while the battery is on open circuit. Cells should never be
charged at the maximum rate except in cases of emergency;
if charged at the maximum rate, the final voltage per cell will
be about ,05 volt higher than if charged at normal rate.

§27 STORAGE BATTERIES 39

DISCHARGING

35. One of the most valuable features of a storage
battery is its ability to deliver large currents for short
intervals. While such is the case, repeated heavy overdis-
charges are almost sure to injure the cells if maintained for
a considerable time. Batteries should, therefore, be dis-
charged at about the normal rate as nearly as possible.
The amount that a battery has discharged can be determined
in the same manner as the amount of charge, i. e., from
voltage and specific-gravity readings. During the greater
part of a complete discharge the drop in voltage is slight
and very gradual until near the end, when the falling off
becomes much more marked. The limit of discharge is
reached when the voltage has fallen to 1.7 volts per cell;
a battery should never be discharged below this point, and
in ordinary service it is advisable to stop the discharge con-
siderably above it. Cells, as a rule, are not discharged below
1.75 volts, and 1.7 represents the limit that should not be
passed under any circumstances. If a reserve is to be kept
in the battery for use in case of emergency, the discharge,
must be stopped at a correspondingly higher voltage. The
fall in density of the electrolyte is in direct proportion to
the ampere-hours taken out, and is, therefore, a reliable
guide as to the amount of discharge. In this respect it
differs from the drop in voltage, which varies irregularly for
different rates of discharge; consequently, the specific gravity
of the electrolyte is the more satisfactory guide. The actual
amount of variation in the strength of the electrolyte between
full charge and full discharge depends on the quantity of
solution compared with the bulk of the plates in the cell.
If a cell contains the full number of plates, the change in
specific gravity is about 85 points. With fewer plates in the
same size containing vessel, the range will be lessened.
Also, at higher rates of discharge than normal the drop in
specific gravity will be less because of the smaller number
of ampere-hours discharged. As the discharging pro-
gresses, the positive plates become somewhat lighter and

STORAGE BATTERIES

|2t

the negatives darker, so that the color of the plates is a
rough indication of the amount of discharge.

After a battery has been completely discharged it should
be immediately charged again. It should be allowed to
stand but a very short intervali if at all, before recharging*

36,

MISCEIitANEOUS POINTB

Infipectlon of Cells, — In order to secure satis-

factory operation of a battery each of the cells should be
inspected at regular intervals. The voltage of individual
cells may become lowt the electrolyte may not be of the
proper specific gravity, or foreign substances may become
lodged between the plates or in the bottom of the cell, and
regular inspection is necessary to locate any such defects
that may develop. Such readings as are taken from the
cells should be recorded in such a way that consecutive read-
ings can be easily compared; i£ a cell is acting irregularly,
the fact will then be at once apparent. Each cell should be
thoroughly inspected at least once a month. This can be
easily done by examining a certain number of cells each day .
in case the battery is too large to examine all the cells in a j
single day*

For the inspection of individual cells, a portable lamp
should be used so that any tendency for an accumulation or
lodgment of material between the plates can be at once
noticed. If the elements are in glass jars, an ordinary lamp
with extension cord will be found most convenient? by hold-
ing the lamp behind the jar and looking through between the ,
plates, the condition of the cell can at once be seen. If
wooden tanks are used, a lamp suitable for immersion to the
bottom of the electrolyte will be needed. When examining
a cell great care should be taken to look between all the
plates, and any accumulation of material should be removed
at once. If the accumulation is from the plates themselves,
it may be pushed down to the bottom of the containing ves-
sel by means of a stick of hard rubber or wood; if it is any

foreign substance it should be removed from the celL A

§27 STOkAGfi BAttERIES 41

metal rod should never be used for removing obstructions in
a storage cell; it is sure to cause short circuits and do
damage.

In addition to the examination of the cells with the lamp,
an examination should be made near the end of each charge
to see if all the cells are gassing equally, and readings of
voltage and specific gravity should be taken at the end of a
prolonged charge, while the current is still flowing. If any
of the cells show readings lower than normal and do not gas
freely at the end of the charge, they should be examined at
once with a cell lamp to determine the cause of the falling
off. Very likely it is due to short-circuiting between the
plates, caused either by a lodgment of material in the inter-
vening space or else by an accumulation of mud in the
bottom of the cell.

37, It is advisable, in storage-battery installations, to use
recording instruments to show the variations in voltage or
current. There are many types of these instruments, but
in most of them a paper chart is moved at a uniform
rat^ by means of clockwork and on it the pointer of the
ammeter or voltmeter draws a line showing the variations in
voltage or current. Sometimes the record is made on a
straight strip of paper but more often it is made on a circular
chart, as in the Bristol recording instruments. Records
of this kind are valuable because they show just what the
battery has been doing; and if it is not performing sat-
isfactorily, steps can at once be taken to remedy the
defect. The most generally useful instrument is a recording
voltmeter. Recording wattmeters are sometimes used where
the expense is warranted. A special type of Thomson
recording wattmeter is made for this purpose. The instru-
ment is provided with two recording dials, one of which is
moved by the meter mechanism when the battery is charging
and the other when it is discharging. The amount of charge
given to the battery during any given period can thus be
compared with the amount of discharge and the watt-hour
efficiency thereby determined.

STORAGE BATTERIES

38« (Jetting: Low Cells luto Normal Coudltioii. — ^A
cell that has become low will generally require more than
the usual amount of charging to get it into condition again ^
after the cause of the trouble has been removed* The
simplest way of doing this is to overcharge the whole battery
until the low cells are brought up to the proper point, but
care must be taken not to carry this to excess* Another
method is to cut the low cells out of circuit over one or two
discharges, and then cut them in on the charges* A third
method is to give the faulty <!:ells an individual charge while
the other cells are on the discharge; the most convenient way
of doing this is by means of a small motor-driven dynamo.
Before putting a cell that has been defective into service
again, care should be taken to see that all the signs of a full
charge are present.

39. Setllmetit In Cells. — After cells have been in
service for some time there is an accumulatioh of sediment
in the bottom caused by small particles dropping from the
plates* This sediment should never be allowed to touch the
bottom of the plates and thus short-circuit them; it should be
carefully watched, especially under the middle plates, as it
accumulates there more rapidly than under the side plates*
If there is any free space at the end of the cells, the sediment
can be raked from under the plates and then scooped up; the "
device used for this purpose must have no metal in its make-
up. If this method is impracticable, the electrolyte should be
drawn off into clean containing vessels after the battery has
been fully charged. The cells should then be thoroughly
flnshed with water, from the local water supply, in such a
way as to stir up the sediment thoroughly and get it out of
the cells. All the water should then be drawn off; if the
cells are too low for siphoning, a rotary pump with bron;5e
parts should be used. After the cells have been thoroughly
cleaned, the electrolyte should be at once replaced before the
plates have had a chance to become dry* and thus necessitate
the long charge required by dry plates* In addition to the
electrolyte withdrawn^ new electrolyte must be added to make

§27

STORAGE BATTERIES

I
I

good Ihat displaced by the sediment^ this should be of 1*8 or
I A specific gravity to counteract the effect of the water
absorbed by the plates during the washing process, and also
to reduce the bulk of the new supply. The electrolyte must
be kept free from impurities; if it is known that any impurity,
especially any of the metals other than lead, or other acid
has got into a cell in any except very minute quantities, the
electrolyte should be renewed immediately.

40p Battery Used Occasionally.^ — When the battery is
used but occasionally, or if the discharge is at a very low
rate* the battery should be given a weekly freshening charge.

41. Puttlngr Battery Out of Commission,— If the use

of the battery is to be discontinued for a considerable time,
say 6 months or more, it is usually best to take it entirely
out of service by withdrawing the electrolyte. This should
be done as follows: After giving a complete charge, siphon
off the electrolyte into convenient receptacles, preferably
carboys that have previously been cleaned and have never
been used for other kinds of acid. As each cell is emptied,
immediately refill it with water. After water has been placed
in all the cells, begin discharging and continue until the volt-
age falls to or below 1 volt per cell at normal load. Then
draw off the water; the battery may then stand without
further attention until it is needed again.

42. PuttI nir Battery Into Commission*— To put a

battery into commission proceed in the same manner as when
giving the battery its first charge. First make sure that the
polarity of the charging source has not been altered during
the interval that the battery has been out of use, and that the
positive pole of the battery connects to the positive pole of
the charging source. Put in the electrolyte and begin char-
ging at once at the normal rate, and continue until the charge
is complete; from 25 to 30 hours at this rate will be required*

43. Cadmium Test.— ft may sometimes happen that
the plates of a cell are unevenly acted on; that is, the mate^
rial on one plate may be wholly changed during the charge ^

44 STORAGE BATTERIES §27

while that on the other plate may be only partially changed.
When the cell is discharged, it is evident that under these
conditions the voltage will fall off sooner than it should
because the capacity of the cell will be limited by the capacity
of the partially converted plate. In order to determine the
existence of such a condition it is necessary to test each of
the plates separately because the voltage of the cell as a
whole will not indicate the relative condition of the plates.
In order to make the test, a third electrode, consisting of a
piece of cadmium, is used; a piece of zinc could be used If it
were chemically pure. The cadmium test piece is dipped
into the electrolyte and the voltage between it and the plates
of the battery measured by means of a low-reading voltmeter.
Care should be taken to see that the cadmium is not allowed
to touch either plate. If both plates are fully charged, and
the normal charging current flowing through the battery, the
voltage between the positive and negative plates will be
about 2A6 to 2.5 volts. The voltage between the cadmium
and the negative plate will be about AB or *19 and between
the cadmium and positive plate about 2*3 volts, the voltage
of the cell being the sum of the two readings. When the
battery has been discharged until the voltage per cell is
reduced to 1.8 or 1*75 volts, the voltage between the cadmium
test piece and the positive plate will be about 2.05 and
between the cadmium and negative about ,25, the voltage
of the cell being the difference of the two readings. When
the cell is fully discharged, the cadmium is positive to both
plates; when it is fully charged, the cadmium is positive with
regard to the positive plate and negative with regard to the
negative plate. All the readings given above and the state-
ments regarding the polarity of the cadmium with respect to
the plates assume that the normal charging or discharging
current is flowing when the readings are taken,

44. Snlphatln^.^ — ^Unless a battery is properly looked
after, sulphatiu^r Is liable to set in, and if allowed to go too
far may cause a great deal of trouble. As already explained »
lead sulphate » PbSO^, is formed during each discharge of a

127

STORAGE BATTERIES

^
^
^

celL This sulphate does no harm; in fact, it is essential to
the operation of the cell. However, under certain conditions
a white insoluble sulphate, J%SO^, may be formed, and it is
this that is credited with the action known as stdphaiing.
When a cell is sulphated, the plates, more particularly the
positive, become covered in spots with this white insoluble
sulphate, which is difficult to remove* As the sulphate
usually accumulates in patches and as it prevents, to a lar^
extent, chemical action on the active material underneath it,
the capacity of the cell is reduced and the uneven action is
liable to lead to buckling unless the mechanical structure of
the plate is such that buckling is practically impossible* The
most frequent causes of sulphating are overdischarging",
wrong specific gravity of electrolyte, and allowing the battery
to stand for a considerable length of time in a discharged
condition; if a battery is looked after » as it should be» there
will be little trouble from this source. If cells are repeatedly
discharged below L7 volts, sulphating may be expected; too
strong an electrolyte will also cause it. At the end of a
complete charge, a lodgment of white powder that may easily
be brushed off will sometimes be noticed on top of the plates;
pro\nded the body of the plates is the proper color, no atten-
tion need be paid to this powder as it is composed of particles
from the plates thrown off by the gassing at the end of the
charge; these particles become sulphated and of a light color
while in sxispension in the electrolyte.

lu case w^hite insoluble sulphate appears on the plates, the
battery should be given a long continued charge at a low
rate, somewhat below the normal 8-hour rate until the cells
give all the signs of a full charge, and the plates have
resumed their normal color. In case of badly sulphated cells,
the color of the positive becomes lighter than normal and the
negatives considerably darker,

45# Treatment of End Cell». — In order to allow the
voltage of a battery to be varied, a number of cells at one
end are frequently arranged so that they may be cut into or
out of circuit. These are called end celle. Owing to the

STORAGE BATTERIES

§27

fact that these cells are cut in and out of circuit, they are
specially liable to become unevenly discharged and, there-
fore, require more attention than the remainder of the cells.
They are successively cut into service on the discharge;
hence, on the charg^e they should be successively cut out in
the reverse order, otherwise the ones that were last cut in will
be overcharged^ Special care should be taken in regard to
this, as it is easy to forget that a number of the cells were
not cut into circuit until probably near the end of the dis-
charge, and thus require but a small proportion of the amount
of charge required for the main battery. As an aid in deter-
mining the state of charge of the end cells, there is usually
installed on the switchboard a multi -circuit voltmeter switch
by which the voltage of each end cell can be obtained.
If any of the end cells are not used regularly or stand idle,
they should be given a complete charge once a week.

SIMPLE CONNBCTIONS FOR CMARQINO

46, Where cells are used for portable purposes it is
necessary to provide some convenient means for charging
them from the ordinary sources of electrical supply. The
best method of doing this will depend on the available source
of charging current* It goes almost without saying that
alternating current, as such, cannot be used for charging a
battery, and when it is the only available source, some means
must be provided for changing it to direct either by means
of an alternating-current motor coupled to a direct-current
dynamo, or by a rotary or mercury-vapor converter* If the
ordinary 110- volt, direct-current, lighting circuit is avail-
able, it is an easy matter to charge the cells as indicated in
Fig, 20 (rt). A double- pole switch a with fuses b is connected
between the mains and the battery as shown. In series with
the battery c are a number of lamps by means of which the
charging current is limited to the proper amount* It is
advisable to connect an ammeter d in circuit, though this is
not absolutely necessary. The number of lamps required
depends on the line voltage and on the charging rate of the

§27

STORAGE BATTERIES

cells. If the line pressure is 100 to 120 volts and but three or
four cells are to be charged with a current of 5 amperes,
then five 32-candlepower lamps connected as in Fig:. 20 (a)
will be sufl&cient. If 16-candlepower -lamps are used, it will

(I n

■^sjini

<It-

(a)

-^>-^0-N

-HWfr

(e)

Pio. 20

be necessary to connect ten in parallel. If the line pressure
is 500 volts it will be necessary to connect twenty-five
32-candlepower lamps in five rows of five lamps in series in
each row, or fifty 16-candlepower lamps in ten rows, five

STORAGE BATTERIES

§27

lamps in series in each row as shown id (^). Incase it is
convenient to charge at a lower rate, fewer lamps will be
needed, but the time for charging will be proportionately

increased*

Lamps form a convenient resistance as they are easily
obtained, but an adjustable rheostat r is frequently used, as
shown in (c). The amount of resistance required in the
rheostat can be easily obtained as follows: Let N be the num-
l>er of cells to be charged in series, then 2 N will be the
approximate voltage for charging, since each cell may be
taken as requiring 2 volts at the beginning of the charge.
If E is the line E. M. F., then £'-2A^ is the number of
volts effective in forcing current through the circuity because
the E* M. F. of the cells is opposed to that of the line* If / is
the charging current, then the resistance of the circuit will be

R ^

(1)

and this will be practically equal to the amount of resistance
required in the rheostat, because the resistance of the cells
i? very low.

Example. ^Twenty storage cells are to he charged from a 220- volt
circuit. How much resistance should be coanected in series with them
if the charging current is to be 5 amperes?

Solution ,~Froni formula 1, ^ = 220, A^= 20, and /= 5; hence,

220-2x20

*• 36 ohms. Aqs.

This resistance should be adjustable so that some of It can be cut
out as the voltaf^e of the cells iccrea^eSt and it must be made of wire
lar^e enough to carry at least 5 amperes without overheating.

Charging with resistance in series is at best a makeshift
because it involves a largfe loss of energy; as a rule, it is
used only where a few cells are to be charged and where no
other method is available, A resistance is not used with
regular batteries because the number of cells is such that
the battery can either be connected directly across the
charging circuit or else used in cnnnectinn with a booster
in power or lighting stations or with motor generators in

§27 STORAGE BATTERIES 49

telephone or teleg:raph stations. The use of a resistance
involves a waste of energy, but in the case of small portable
batteries this waste is not a very serious matter, especially
as the use of the series-resistance gives the most convenient
and simple means of charging from existing circuits.

47. Cbargringr From Constant-Current Arc Circuit.

Sometimes cells are charged from constant-current arc-light
circuits, but the practice is dangerous and this source of
charging current should never be used if any other is avail-
able. Constant-current arc-light dynamos generate a very
high pressure, and as arc-light lines are nearly always
grounded to a greater or less extent, there is quite an
element of danger in working around a battery that is being
charged from such a source. Great care must be taken to
see that the arc-light circuit is not opened when the battery
is being switched on and off. This method of charging is
shown in Fig. 20 (t/), where /, / represent arc lamps. In this
kind of circuit the current is maintained at a constant value,
usually from 6 to 10 amperes, so that when the battery is
to be charged it must be placed in series with the lamps.
The battery is cut into circuit by means of a special switch
called a consumer's switch, which is constructed so that it
will neither open the circuit nor short-circuit the battery.
This is done by means of a contact point c connected to
a resistance r. When the broad blade is moved to the
dotted position, the resistance is first placed in series so
that the line is not opened, and at the same time there is
no short-circuiting of the battery. It will be noticed that
when the switch is in the dotted position, the resistance is
in parallel with the battery so that part of the main current
is shunted around the battery. For example, the main cur-
rent might be 9 amperes and the required charging current
5 amperes, in which case the resistance should be such that
the difference between the two, i. e., 4 amperes, will flow
through it. The pressure between the terminals of the
resistance is equal to the E. M. F. of the cells; hence, if /is
the current shunted through the resistance, E the voltage of

46B— 6

STORAGE BATTERIES

127

the series of ceUs, and R the resistance, then ^ is eESil]^
obtained from the relation R = --.

48- nirectiou of Current.*— When charging a battery
from any source, especiaUy when there is any doubt as to the j
direction of flow of the current, a test should be made to
determine whether or not the positive plates are connected
to the positive pole, so that the current fiows in at this
pole when the battery is charging. A simple method
of doing this is to attach two wires to the mains, connect
some resistance in series to limit the current, and dip the
free e!>ds into a glass of acidulated water, keeping the ends
about 1 inch apart. The end from which bubbles of gas are
given off most freely is connected to the negative main, so
that the main to which the other end connects is the one to
be attached to the positive pole of the battery* Another
convenient method of testing the polarity is by means of a
Weston voltmeter, or instrument of similar type, which will
give a deflection over the scale only when the terminal
marked -h is connected to the positive line,

49, Battery Charged F^om DynamOp^Fig. 2t shows

about the simplest possible arrangement of connections for
charging a storage battery from a dynamo^ all appliances
that are not absolutely necessary having been left out in
order to avoid confusion. A is a dynamo, usually either of
the shunt- wound or compound- wound type; / is the rheostat
in the shunt field, by means of which the voltage of the
machine may be varied throuj3:h a considerable range; Vis a
voltmeter connected to the voltmeter switch S, which is so
arranged that the voltmeter may be connected to either the
battery C or the dynamo A\ E is a double-pole knife switch,
by means of which the battery may be thrown in connection
with the dynamo; F is an ammeter that shows the amount
of the charging current. The ammeters used with storage
batteries are usually made with their zero point at the
middle of the scale. When the battery is charijin^, the needle
is deflected to one side of the zero mark; when discbargingj

n r

§27

STORAGE BATTERIES

it is deflected to the other side, thus showing: at a gflance
which way the cells are acting. It should be noted that the
+ side of the dynamo is connected to the + side of the
battery when the switch is thrown in, the direction of
the charging current being indicated by the arrows. In this
case, we have assumed that the number of cells to be
charged is sufficiently great to take up the voltage of the

''6G(5m

Pio. 21

dynamo; if this were not the case, a resistance would have
to be inserted in series with the battery. Charging is
effected as follows: Having made sure that the connec-
tions are all right, and that switch E is open, get the dynamo
up to speed. Then measure the voltage of the cells and
adjust the field rheostat of the dynamo until the voltage of
the latter is from 6 to 10 per cent, higher than that of the

STORAGE BATTERIES

1 27

cells. Throw in the main switch and adjust the rheostat
until the ammeter indicates the charg^ing current called for
by the makers of the cells.

The outfit shown in Fig, 21 is sufficient where a battery is
simply to be charged and where a fairly close watch can be
kept on it while the charging process Is going on. Gen-
erally, however, the connections
must be arranged so that the cells
may be either charged from the
dynamo or allowed to discharge
into the line. It is also neces-
sary to have fuses or an automatic
circuit-breaker of some kind to
protect the battery against over-
loads. An underload switch is
also connected between the cells
and the dynamo, as indicated by
the dotted outline IC, Fig. 21. The
duty of this switch is to prevent
the ceUs from discharging into the
dynamo and running it as a motor;
it is, usually, an automatic switch
controlled by an electromagnet
connected in series between the
dynamo and the battery* If for
any reason the current drops to a very low value, the elec-
tromagnet releases its armature, thus opening the switch and
disconnecting the cells from the machine.

Fig. ^

50- Cutter Automatic Overload and Underload
Switch. — Fig. 22 shows a special automatic switch designed
to protect the dynamo from any backward rush of current
and also to protect the battery from overloads. Two coils
a^ b are connected in series between the battery and dynamo,
as indicated at K, Fig. 21 ♦ If the current becomes excessive,
coil b pulls lip a core that releases a trip and allows a spring
to throw the arm out, thus breaking the circuit at d, d. When
the battery is charging^ coil a holds its armature, but if the

§27

STORAGE BATTERIES

current becomes very small, as it must do before it begins to
reverse and flow back from the batteries, the armature is
released and causes the switch to open. The instrument is
therefore a protection against both underload and overload.
For example, a battery might be charging and the speed
of the dynamo might drop or the belt fly off. In either case,
the voltage of the dynamo would drop and the charging

current fall to zero. 1 1 1 1 ti ft_

If the circuit were,
not opened, a cur-
rent would flow from
the battery through
the dynamo and
run it as a motor.
Another instance
in which damage
might result if an
underload switch
were not used is in
case the field cir-
cuit of the dynamo
should become
broken. This would
reduce the E. M. F.
of the dynamo to
zero and a large
rush of current could
take place through
the armature, be-
cause the cells
would be unable to
excite the field so as to e^able the machine to generate any
counter E. M. F. as a motor. In the case of a compound-
wound dynamo, a backward rush of current might result in a
reversal of the dynamo field. In the case of a simple shunt
dynamo, the current flows around the shunt in the same
direction no matter whether the dynamo is charging the
battery or whether the battery is forcing current back

Pio. 23

STORAGE BATTERIES

§27

through the dynamo. Fig. 23 shows a simple switchboard
suitable for a small plant where a battery^ is used in conjunc-
tioii with a dynamo for lighting or other purposes; k and s
are double-pole knife switches provided with fuses, k con-
trols the lighting circuit while s Is connected to the dynamo
through the underload circuit^breaker c. The ammeter A is
connected in series with the battery b and indicates the
charging or discharging current. Fis a voltmeter connected
to a switch p, by means of which it may be connected across
either the dynamo or the battery; r is the handle "of the fielt'
rheostat that is connected in series with the shunt field of tht
dynamo. When the battery is being charged t the switch k
is open and the switch s closed* When the battery alone is
furnishing current to the line, $ is open and k closed. If it
is desired to have both battery and dynamo furnish current
to the line, both switches are closed.

In Fig. 2S, it win be noticed that no provision is made for
varying the E. M- F. of the battery, either by cutting cells
in or out or by any other means. In all but small installa-
tions such provision is usually necesfiary.

USE OF ACCTJMTrLATORB IX CENTRAI/ STATIONS

51. In central stations furnishing current for lighting
or other purposes, the demand for current varies greatly at
different periods in the day; lor example, a lighting station
in a large city will probably be called on to furnish, from
6 to 8 p- M., ten times the amount of current that is required
from 5 to 6 A. M., and in small stations the disproportion
is even greater. As economy of operation demands that
the engines and dynamos be worked at or near their full
capacity, especially if the engines be compound or triple
expansion, both of these conditions can be met only by
dividing the machinery into a large number of small units, or
by using some system of storage of the electrical energy.
In the first case, the small units require more attention and
are much less efficient than larger ones, so that most mod-
em large stations have their machinery divided into a few

§27

STORAGE BATTERIES

large units, employing
large compound en-
gines. Storage batteries
can be used to great
advantage, therefore, in
connection with stations.
The way in which they
are used will, however,
depend largely on the
nature of the load, and
the following will point
out the more common
methods.

52. Battery Ta-
king: Peak of lioad.

Probably the most com-
mon method of using a
central-station battery is
to charge it during inter-
vals of light load and
discharge it when the
heavy load comes on; in
other words, make it
take the peak of the
load. Fig. 24 shows the
load line of a lighting
station where a battery
is used in this way. The
full line shows the varia-
tion in the output of
the station for a period
of one week beginning
on a Sunday at 12:30
A. M. Each horizontal
division represents 3
hours and each vertical
division 260 amperes.

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8 )»

STORAGE BATTERIES

127

On Sunday, the load is light and the battery is allowed to
charge, as shown by the double-shaded area, from 12:30 <
until about 10 a. m. All the generating plant is then shut
down and the whole load carried by the battery for about
8 hours. The generators are again started about 4 p- M-
and in addition to carrying the load, they charge the bat-
tery until a little after 3:30 on Monday when the heavy load
begins to come on. The load rises very rapidly between
3:30 and 6:30 and reaches a maximum of 4,600 amperes— of
which nearly 1,750 amperes is supplied from the battery ^ as
indicated by the single-shaded area. After the load has
dropped to about 2^600 amperes, the charging is again
started and so on throughout the week. On Saturday, the
peak of the load is not as high as on the other week days, but
it is broader on account of the earlier closing of offices and
later closing of retail stores.

By examining Fig. 24, the great advantage of the battery
is at once apparent. If no battery were provided, generating
equipment capable of supplying the maximum output of
4,600 amperes would be necessary* With the battery, the
generator output never exceeds 2,950 amperes, approxi-
mately, so that the battery takes the place of engines, boilers,
and dynamos equivalent to an output of 1,650 amperes. The
combined areas in Fig. 24 representing the charge, must of
course be somewhat greater than the combined areas of
discharge, because the ampere-hour efficiency is less than 1-

There are many advantages incident to the use of the
battery other than the saving In generating equipment. The
battery is valuable as an insurance against complete shut-
downs in case of serious accident to the generating equip-
ment. It also holds a supply of energy that is instantly
available in case of a sudden demand for current caused, for
example, by darkness due to a storm. It is of very great
benefit in preventing voltage fluctuations on the system as a
whole, thus making the lights burn steadier and last longer.
By installing a battery in a station of given generating equip-
ment, the output of the station and the revenue obtained
therefrom can be considerably increased without additional

§27 STORAGE BATTERIES 57

expenditure for generating equipment. Moteover, the
equipment already installed will be worked to the best
advantage, because the load on the engines and dynamos
can be kept more nearly uniform and also more nearly at the
full capacity of the units employed, thus securing maximum
efficiency of operation. Against these various advantages
must be set the cost of the battery, the expense of looking
after it, and the allowance for deterioration which with
storage batteries is greater than with engines or dynamos.
The fact, however, that so many large central stations are
installing storage batteries or are adding to their present
installations, is the best proof that they are desirable and
that a distinct saving is effected by their use.

53. Battery Used to Carry Whole Lioad. — In Fig. 24,
a case was shown of where the battery is used to carry the
whole load on Sunday. This allows all the machinery to be
shut down for 8 hours and gives a good opportunity for
inspection or repairs, besides allowing the operation of the
station with a small working force.

54. Battery Used to Take Up Fluctuations In Ijoad.

In street-railway power stations of small or moderate size, or
in substations supplied from a large central station, the out-
put varies between wide limits owing to the starting and
stopping of the cars, and if a storage battery is not used
the station machinery must stand these wide and rapid
fluctuations. This is liable to strain the engines and
dynamos to say nothing of its being an uneconomical
method of working. Also, wide and rapid variation of load
on the generating outfit is almost sure to cause considerable
variation in voltage. Storage batteries are now largely used
in railway power stations to take up these fluctuations, dis-
charging when the load is heavy and charging when it
becomes light. Regulating appliances make this action
automatic, so that the load on the generating outfit is kept
nearly uniform.

Fig. 25 shows the current output from a street-railway
station equipped with a battery of 258 Chloride cells. The

V 58 STORAGE BATTERIES §27

^M full line shows the station output, which varies from a

^m minimum of less than 100 amperes to a maximum of over
^m 850 amperes. It will be acted that this load diagram is for
H an interval of 15 minutes only, so that the variations are
H very sudden. In spite of these sudden variations , the load
^m on the dynamos is kept within 350 and 400 amperes, as shown
^M by the dotted line, the double-sectioned areas above this line
^M representing discharge mtervalsj and those below the line
^H charge intervals. The ampere-honrs discbarge » indicated in
^H Fig, 25 by the combined double-sectioned areas, is con-
^B siderably greater than the charge, as represented by the
^B single-shaded areas. It must be rem eon be red, however, that
^^L the interval of time represented is only 15 minutes. If the

^^^^^^H

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^V load curve were drawn for a

^m the charge would likely be in
^M the regulating appliances are
^m cient charge is given to the b
^B tion to make up for the dis
wK charging unnecessary.
[ The curves in Fig. 26 ar(
^m substation from which ciirre
^M converter used in conjunction
^1 up the load ^uctuations. In
^B charge areas of the battery cu
H in Fig. 25. The load on the i
^B separately and the lowest eui

longer period, say 24 hours,

excess of the discharge, since

usually adjusted so that suffi-

attery during its regular opera-

scharge and thus render extra

B taken from a street-railway
nt is supplied from a rotary
with a storage battery to take
this case the charge and dis-
rve are more nearly equal than
-otary converter is here plotted
-ve represents the total output

§27

STORAGE BATTERIES

99^l9lfmf

STORAGE BATTERIES

%91

of the substation obtained by adding the battery and rotary-
converter load curves together, charging currents being taken
as negative and hence subtracted from the converter output
to obtain the current dehvered to the line* The load on the
converter remains comparatively steady, between 75 and
100 amperes, while the line current varies from below
25 amperes to over 325 amperes- The readings only cover
a period of 20 minutes and the fluctuations in load are very
rapid, yet the load on the converter and hence the current
supplied to the substation from the line is kept fairly steady

and is small compared with the maximum that would be

required if the battery were not used.

55* Battery Out on Line. — Batteries are frequently
placed at the end of feeders supplying certain sections. By
this means the voltage at the distributing center is main-
tained at a nearly uniform value, the variations of load in the
central station are reduced ^ and the feeders are worked to the
best po*isible adv^antage. This method of using a battery will
be understood by referring to Fig. 21, which shows a three-
wire network /> of incandescent lamps supplied from a dis-
tributing center or substation C which is in turn supplied by

§27

STORAGE BATTERIES

feeders B running: to the main
station A. Under normal con-
ditions, the battery EF is con-
nected across the outside lines,
but a connection to the neutral
wire from the middle point is
provided so that it can be used
if necessary. The load of
lamps represented by D may
be much in excess of what
could be supplied over the
feeders B without giving rise
to a prohibitive drop in volt-
age. If, however, a battery is
installed, it may be charged
during the daytime when the
demand on the feeders is small,
and thus relieve the feeders at
night when the heavy load
comes on; in other words, by
using the battery, the feeders
are worked at an approximately
uniform rate throughout the
day. Looking at it in another
way, the installation of the
battery out on the line allows
a larger amount of work to
be done without increasing
either the feeder or generator
capacity, and the further im-
portant gain is made that a
heavy drop in voltage in the
feeders is eliminated, thus ren-
dering the service much more
satisfactory.

A battery installed on the
line regulates automatically.
When the demand is large, the

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IP !l* !

STORAGE BATTERIES

§27

drop in the feeders becomes greater than normaU thus lower-
ing: the pressure at the battery terminals and allowing: it to
discharge into the line. Wheo the load is lights the drop in the
feeders is small, the pressiue applied to the battery is higher
than that of the battery, and a charging current flows into it-
Fig. 28 shows the variation in output of a Chloride battery
placed on a street-railway line 4 miles from the power house.
This shows how the battery takes up the fluctuations and
supplies the peak of the load between 4 and 7 P* M, Since
this large current is supplied from the battery and not brought
over the longf feeders from the power house, it follows that
the voltage is maintained much better than if the battery were
not used* After 11 p, m, the load on the feeders becomes
so light that the battery charges most of the time, and
between 7 and 9 a< m. it again takes a peak, though in this
case the peak is smaller than in the evening.

The curves in Fig, 2d show the effect that a battery, used
at the end of the line, has on the voltage regulation of a
railway system. Curve A shows the current delivered by
the battery when discharging or taken by it when charging.
Curve B shows the variation in voltage when the battery
is in use and curve C shows the variation when the battery is
cut of service. When the battery is not used, the voltage
varies from 550 to 325 volts, owing to the heavy momentary
currents that must be transmitted over the line. When the
battery is in use the voltage varies between 450 and 525
volts, thus maintaining a much better pressure on the system
and enabling the cars to make better time. When the load
is lights voltage high, the battery charges, hence the maxi-
mum voltage with the battery on is not as high as with the
battery off because of the drop in the line due to the char-
ging current. When the battery is ofiE there are instants when
there is practically zero current in the line and the pres*
sure at the end of * the line then becomes equal to the
station pressure*

56. Selection of Battery for Given Service, — The
only way to arrive at an intelligent conclusion regarding the

§27

STORAGE BATTERIES

-^=:

:f^=±:::^b::

^'i

§ S I S g I

^ «« ^ ^ s s

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^iOA

9HiJ

moj.

99A9dUty

STORAGE BATTERIES

§27

size of battery to be used for any given case is to determine
as nearly as possible the load line of the station in question.
The generating capacity is usually known, so that by laying
out a diagram and measuring up the probable discharge
areas on it, a fairly close idea as to the capacity needed can
be obtained* As the output of most plants is always
increasing, it is common practice to install jars or tanks
somewhat larger than required at the start. The capacity of
the cells can then be easily increased by simply adding more
pairs of plates to each cell.

The number of cells required for a given installation will
depend on the voltage of the system, and also on the range
of voltage regulation that is desired by cutting cells in or
out* Assuming that the cells are discharged down to 1,76
volts, the minimum number of cells required would be the
voltage of the system divided by 1.75. For example, a

battery for a 110-volt system would require —— = 63 cells.

l*7o

STORAGE-BATTERY REGULATING
APPLIANCES

67- In order that the charging and discharging of a bat-
tery shall be under control, it is necessary to use auxiliary
apparatus that will allow the effective voltage of the battery
to be varied at will. The appliances used in any given case
will depend on the nature of the work that the battery has to
do. For example, the regulating devices necessary with a
slowly changing lighting load are not adapted to the opera-
tion of a battery on a rapidly fluctuating railway load.

ENB-CBLL eWlTCOES

58# The simplest device for varying the effective volt-
age of a battery is the end-coll sT?^Itcli, the use of which
will be understood by referring to Fig. ."^O; ^^ is the main
battery and B a number of cells from each of which connec-
tion is made to the contacts d of the end-ceU switch. A

§27

STORAGE BATTERIES

contact piece a is arranged so that it can be slid from a to a'
by means of a suitable mechanism, and the number of cells
in use thereby varied. When the battery has been fully
charged, the end cells are cut out of circuit and the contact a
occupies the position a'. As the voltage runs down, a is
moved to the left and fresh cells cut in, thus maintaining the
voltage E at the desired amount. Fig. 31 shows a horizon-
tal type of motor-driven, end-cell switch made by the Electric
Storage Battery Company; this switch accommodates 20 end
cells. The traveling laminated contact is shown at a a, and
the cells are connected to the terminal blocks byb mounted
on a slate slab. The bar c connects to the line, the ter-
minal connection being attached at d. The cross-head is

mmrn^

Fio. 30

operated by the screw s driven by a small series-motor my
which is controlled from the switchboard and can be run in
either direction, the motion being transmitted to the Jscrew
through the worm w. An electric brake b is provided to
stop the motor promptly when the current is turned off. In
some of the later switches this braking action is effected by
short-circuiting the armature of the series-motor while the
field is fully excited. An automatic switch, not shown in the
figure, is operated by the shaft 5 so that after the motor has
been started in either direction by the switchboard attendant,
the screw will revolve until contact a has .moved to the next
cell contact and will then stop. Insulated bearing pieces e, e
are provided between the blocks b, b for the contact a to slide
on. The laminated contact a is not wide enough to bridge

MH^— 0

^^^ 60 STORAGE BATTERIES §27 W

n over the space between contacts A, and H

thereby short -circuit a celL In order to ■

H ^JIK^^^

, avoid interruption of the circuit while a '

fjl is passing from one cell lo another,

^1 *P^^^^^r^ auxiliary carbon contacts are carried on

^ the cross'head; the resistance of these h

^^^^3

> is sQfRcient lo prevent short-circuiting ■
of the cell during the movement* and at H

the same time keep the battery in con- ^

r&^~:ra

nection with c. Gear ^ is used when
two or more end-cell switches are geared

1 nSs

together so as to be operated simul-

1 jW^

taneously. End-eel! switches are fre-
quently equipped with end-ceii indkaiors.

which, by means of small signal lamps.

,j^i^j

g a traveling pointer, or other device oper-
1 a ted from the end-cell switch, show the

s»^

switchboard attendant at all times the

^ exact position of the switch and the num-

£ ber of cells in service.

• ri

59i Battery With SliiRle End-

[^Sd

Cell Switch, ^Fig. 32 shows about the
simplest possible arrangement for a bat-

'vl

tery with an end-cell switch operated in
parallel with a dynamo* In this figure
all minor devices, such as voltmeter

' r^l

switches , circuit- breakers » etc, have been
omitted. An automatic circuit-breaker

» ^;m

* should be provided in series with the

dynamo, and an overload and under-

load circuit-breaker should be connected

\ between the dynamo and battery.

J In Fig. 32, A Is the dynamo, either

1 _jn

, shunt or compound wound, but usually
^^ the latter type in America, ^ is the

K .4 1 f

?P main battery, and C the end-cell switch

connected to the end cells, as shown.

■

§27

STORAGE BATTERIES

Switches are provided at d, e, f,g,h, and k. An ammeter /
connected to its shunt o indicates the output of A^ and
ammeter m indicates the output of the battery; this ammeter
has its zero point in the center of the scale. When
the battery is working on the load in parallel with the
dynamo, all switches are closed; and as the battery becomes
discharged fresh cells are cut in by means of the end-cell
switch. When the battery is to be charged, all switches are
first opened and the end-cell switch placed in the extreme
left position. The dynamo is then brought up to a volt-
age slightly higher than that of the battery, and switches
d, €y h, and k closed. The field is then adjusted further
until m shows the correct charging current. The pressure

.♦ c

wm^

ToLoaJ

Pig. 32

required for charging the battery is considerably higher than
the normal line voltage; hence, it is not possible with this
arrangement to use the dynamo, running at a high voltage,
for charging purposes, and also for furnishing current to the
line unless a resistance is connected in series with the line
to take up the surplus voltage. This involves considerable
waste of power, so that with the arrangement shown in
Fig. 32 the charging is done at such times as cvurent is not
required on the line.

60. Battery With Double End-Cell Switch.— Fig. 33

shows a battery with two end-cell switches C /?. By using
a double arrangement as shown, the normal voltage may be
supplied to the line while at the same time the battery is

STORAGE BATTERIES

§27

being charged by a current supplied at high voltage from the
dynamo. In Fig. 33 switches i, 2, and 3 are closed and
the double-throw switch 4,5 is thrown to the upper position;
the battery is charging and the path of the charging current
is represented by the dotted arrows. At the same time the
dynamo is furnishing current to the line, as indicated by the
full-line arrows. From the position of end-cell switch D it
is seen that the pressure between the outgoing Imes is equal

i»i#i*i#bJ

Tffla*/

•»— U

Pio. 88

to that of the main battery B plus that of two end cells,
while from the position of C the pressure furnished by the
dynamo must be high enough to charge the whole battery.
When it is necessary to arrange a battery so that the gen-
erator can furnish current for charging purposes, and at the
same time furnish current to the line, it is usual to provide
a booster for increasing the generator voltage the desired
amount.

STORAGE-BATTERY BOOSTERS

61. A storage-battery booster is an auxiliary dynamo,
generally of small size compared with the main-station gen-
erators, the armature of which is usually, though not always,
connected in series with the storage battery. The voltage of
this dynamo may be either added to or subtracted from that
of the battery, thus increasing or decreasing its effective
voltage. For example, in Fig. 34, A is a battery working
in parallel with a dynamo, and B is the armature of the

§27 STORAGE BATTERIES 69

booster connected in series with the battery. Suppose that
the booster is, for the present, generating no voltage and
that the voltage of both battery and dynamo is 110 volts.
Under these circumstances the battery would neither charge
nor discharge. If the field of the booster is excited so that
its brush a, which is connected to the negative pole of the
battery, is positive, it is seen that whatever voltage is
generated in the booster is added to that of the battery, and
the pressure between points
c and d is raised above 110
volts; the battery, therefore,
discharges and the rate of
discharge depends on the
pressure generated by the
booster. If the polarity of
the booster were reversed,
brush a being — and h +»
the booster voltage would be opposed to that of the battery,
and the pressure between d and c would be less than 110
volts by the amount of the booster voltage. Or, looking at
it in another way, the pressure of the booster is added to
that of the dynamo, so that the pressure applied to the ter-
minals of the battery is raised above the battery voltage, and
a charging current therefore flows. With this explanation
in mind the student will more readily understand the explana-
tions of the following types of storage-battery booster.

Storage-battery boosters may be divided into four classes:
shunt ^ compound^ differential^ and constant current.

SHUNT BOOSTER

62. The shnnt booster is so called because its field is
provided with a plain shunt winding similar to that of a shunt
dynamo or motor. Boosters are usually driven at approxi-
mately constant speed by means of a shunt motor mounted
on the same base and directly coupled to the booster arma-
ture, though in some special cases they might be driven by
an engine. The shunt booster is used in those places where

STORAGE BATTERIES

§27

the battery is intended to take the peak of the load or for
other work where it does not have to be continually charging
and discharging. It is, therefore, well adapted for use in
lighting stations where the load changes gradually, and
where the battery charges or discharges for fairly long
intervals of time.

Fig. 35 shows the general arrangement of a shunt booster.
A is the main generator and B the armature of the booster
driven by means of a motor not indicated. C is the storage

Pio.85

battery, and c the end-cell switch by means of which the
effective voltage of the battery may be varied. In order to
charge the battery to its full capacity, it is necessary to have
a voltage considerably higher than that generated by A\ this
increase in voltage is supplied by the booster B, Suppose
that the battery is to be charged; switches a, b, and d are
closed and the double-throw switch c' is thrown to the lower
position. The end-cell switch is placed on the last point, as

§27

STORAGE BATTERIES

shown, so that all the cells will be included in the circniiL
When d and c^ are closed, the armature B is connected in
series with the battery and the two are across the line. The
polarity of the booster voltay;e is such that it assists A in
forcing current through the battery; or, in other words,
B increases the E. M. F» applied to the battery terminals.
The voltage of B can be adjusted by means of a field
rheostat B until the battery ammeter m indicates the proper
charging current. When the battery is fully charged, the
E* M, F. of all the cells will be greater than that of /f, but
the voltage with the end cells cut out will be about equal to
that of A.

When the battery 19 to discharge into the line, switches
d and ^ are opened and e^ is thrown to the position e. End
cells are then cut out until the voltage of the battery agrees
with that of the line and switch ^ is closed, thus connecting
the battery across the line. The ammeter m indicates the
discharge current. As the voltage of the battery falls, due
to the discharge, end cells are cut in by means of switch c.

In many cases shunt boosters are arranged so that they can
be made to assist the battery to discharge as well. as charge.
In order to do this, provision must be made for reversing
the shunt-field current so as to reverse the polarity of the
brushes. The field winding of the booster Is here shown
connected across the brushes of the booster, though it may
be connected across the bus-bars or battery, provided the
winding is designed for the voltage impressed on it. In
Fig. 35, ammeter / indicates the load on the generator, and
the voltmeter K may be used to indicate the voltage of A by
inserting a plug at i. The voltage of the battery is indicated
by inserting a plug at 2, and the voltage of the battery plus
that of the booster is indicated by inserting a plug at 3.

63 ■ Reverslnjy Ittieoetnt for Booster Field. — Pig. 86
illustrates a special type of field rheostat used when the
voltage of the booster is to be reversed and controlled by
gradual steps in either direction. A, B are equal resistances
split into a number of sections and connected to the insulated

STORAGE BATTERIES

i2?

segments g, g as shown; </, e are contact arcs and a lever
pivoted at h carries contacts <z, b that bridge over between
the contacts and the contact arcs. Terminals x^ y are con-
nected either to the bus-bars or to the battery, and the
arcs dy e are connected to the field winding C of the booster.
The whole scheme of connections is, in fact, the same as a
Wheatstone bridge where the galvanometer is replaced by
the field C. It is evident that, when the lever is in the
vertical position a b, there is no difference of potential

■n56(5mm5m(35^ — ^

FiO.86

between the field terminals and the field is unexcited. As
the lever is moved over to the position a'^ b", the pressure
across the field terminals is gradually increased until the
extreme position of the lever is reached and c is connected
directly to the + terminal and d to the — terminal. A move-
ment of the lever in the reverse direction, i. e., from the
vertical position toward a' ^', gradually increases the pressure
across the field but in the reverse direction. This rheostat,
therefore, allows the booster to be used as an aid either in

§27

STORAGE BAttERlES

charging or discharging, and also allows close regulation of
the charging and discharging current. In order to make the
waste of energy small, the central sections of the rheostat
have a high resistance.

COMPOUND BOOSTER

64. When the load fluctuates rapidly, as in electric rail-
way or power plants, and the battery is used to even up
these fluctuations, it is not practicable to regulate the charge
and discharge by means of an end-cell switch, because the
regulation cannot be effected quickly enough. For work of
this kind the charge and discharge is usually regulated by
means of either a compound or a differential booster. A
number of patents have been taken out relating to various

-Bu9-bar or Onm/n^l

Pio. 87

arrangements of these boosters, but the general operation
of a conii>oiind booster will be understood by referring to
Fig. 37. A is the armature of the main dynamo, B the
armature of the booster, and C the battery. The field of
the booster is provided with two windings, one of which is
in series with the armature. The other winding is excited
from the battery, or bus-bars, and has a rheostat R in series
with it; this rheostat is usually of the reversing type so

74 STORAGE BATTERIES §27

that the current in the shunt winding: can be made either to
oppose or aid that in the series-winding.

Under normiil conditions of operation the shunt winding^
aids the series-winding in magnetizing the field of the
booster* It is necessary for the operation of this type of
booster that the voltage of the generator should drop with
increasing load. If A is compound wound, the series-cuils
may be cut out of service or shunted when the machine is
used in conjunction with the battery. The operation of the
booster is as follows: The rheostat ^ is adjusted so tliat
when the generator is delivering its normal load at normal
voltage, the voltage of the booster plus that of the battery
just equals the voltage of the dynamoj under these condi-
tions there will be neither a charging nor a discharging
current. If the load on the line increases, the voltage of A
tends to drop on account of the increased load momentarily
thrown on it. This allow^s the battery to discharge, and the
discharging current flowing through the series-coils of the
booster raises the combined E. M. F. of the battery and
booster, thus making the battery at once take such a share
of the load that the E, M, F, across the lines is restored to
Its nonnal amount. On the other hand, a decrease in the
external load below the normal tends to make the dynamo
voltage increase. The battery then charges, and the char-
ging current flowing back through the series-coils of the
booster opposes the shunt coils, thus lowering the booster
voltage and allowing the charging current to increase until
the generator voltage comes down to the normal amount.
In actual working, the voltage changes very slightly, as any
tendency to change is checked by the operation of the
battery and its booster*

DIFFERENTIAT. BOOSTER

65. The ellfferentlal boof^tor is used on systems where
a load subject to wide and rapid fluctuations is handled. It
has two sets of field windings, series and shunt, as in the
compound booster, but is distinguished from it by the fact
that under normal conditions of operation the magnetising

STORAGE BATTERIES

effects of the series and shunt coils are opposed to each
other. A number of types of differential booster have been
patented, their differences consisting principally in the
method of arranging and connecting the field windings.
Fig. 38 shows a scheme of connections very commonly
used. A is the generator, B the booster armature, and C
the battery. The field of the booster is provided with
two sets of series-coils Z?, E connected as shown; the
shunt field is connected across the line. The effect of
the shunt field can be varied by means of the rheostat R.
Coils D, E are connected so that their magnetizing effect is
opposed to that of the shunt coil. The battery C is con-
nected in series with the booster by throwing switch cd \!o

-But t>mr or Ground
PlO. 88

the upper position; by throwing to the lower position ^ and
also closing switch d, the battery is connected directly across
the line and the booster thereby thrown out of service.
Coil D, when battery C is discharging, carries the combined
output of the battery and dynamo; coil E carries the dynamo
output only. The magnetizing effect of D will therefore
vary with the lead on the line, and that of E will vary with
the current delivered by the dynamo; this latter is supposed
to be nearly constant, so that coil E may be considered as
furnishing an approximately constant magnetizing force.
The coils are adjusted (in case of the series-coils, by adjust-
able shunt resistances across their terminals) so that when
the normal load is delivered there is neither charge nor

76 STORAGE BATTERIES §27

discharge from the battery, because the effects of the magneti-
sing coils neutralize each other, making the booster E, M, F,
zero and allowing the battery E. M. F. to balance that of the
generator. If the load increases above normal, the mag-
netizing effect of D is increased, thus causing the booster to
generate an E, M. F. in such a direction as to assist the
battery to discharge and take tip the surplus load. H the
load falls below normal, the magnetizing effect of the shunt
field predominates, thus making the booster generate an
E, M, F, in the reverse direction and allowing the battery to
charge. The load on the dynamo is therefore kept practi-
cally constant in spite of the fluctuations of the current
delivered from the station*

The connections shown in Fig. 38 have been simplified as
much as possible in order to bring out the main points con-
nected with the operation of the booster; in practice^ a
number of additional connections might be used. For
example, switches are often provided so that the series-coils
may be cut out of service and the machine operated as a
plain shunt booster. The hattery is occasionally charged
up when the load is light, as the intermittent charging
that it receives during its regular operation may not be
sufficient- In case the battery were used on a fairly steady
load, the machine would ^ of coin^se, be operated as a plain
shunt booster and whatever regulation was necessary to
control the battery current would be obtained by varying
the field rheostat,

66» Fig. 39 shows a scheme of switchboard connections
for a differential booster. A is the generator armature,
B the booster armature, D an underload-and-overload battery
circuit-breaker, E the generator circuit*breaker, F the gener-
ator ammeter, G the battery ammeter with its zero point in
the center of the scale, and H the voltmeter. The voltmeter
is connected to a voltmeter switch, so that readings may be
taken of the generator voltage, the battery voltage, or the
voltage of the battery plus that of the booster; the voltmeter
connections have been omitted in order not to confuse the

§27

STORAGE BATTERIES

figure. K is the generator-field rheostat, L the reversing

rheostat in the shunt field of the booster, M a starting

. rheostat for the shunt motor N that drives the booster, and

■^Bua ^*^

— Bi/s tof

— ^Tb /WoSf/3

Illlll|l|illlllllllllllll|

Pig. 89

OP the series-fields of the booster. Single-pole switches
I, 2, 3^ etc. are connected as shown; switches 4-5, ^-7, 8-9^

78 STORAGE BATTERIES §27

are siugfle-pole double-throw, and are used for making the
various combinations described later. Switch 10 connects the

shunt field of the booster to the bus-bars, and J/ is the main
switch for the motor* The curabiriations that tnay be effected
are as follows:

(a) Generator workinj^ alone on bns-bars with battery and
booster cut out of service. Switch 2 is closed, and switches
5 and 7 thrown to the upper position. All other switches
are open*

(d) Battery working^ alone on bus-bars, E:enerator and
booster cut out of service. Switch / is closed, and switch 9
thrown to the upper position, all other switches open*

(c) Battery and generator operating in parellel on' bus-
bars with booster in service. Switches I and 2 are closed,
and switches I, 6, and 8 thrown to the lower position*
Switches JO and 11 are also closed because the booster is
now in operation.

{(/) Battery in parallel with generator, series-coils of
booster cut out. In this case B is operated as a shunt-wound
booster and the battery is being charged. Switches i; 2 and 3
are closed; switch 8 is thrown to the lower position and
switches 5 and 7 to the upper position* Switches 10 and 71
are also closed and L is adjusted so that the booster helps
the battery to charge.

CONSTANT-CURRENT BOOSTER

67* The constant-current booster is used principally
in office buildings or manufactories where the feeders are
not long and where a considerable portion of the load, such
as motors and elevators, is of a fluctuating nature. It is also
used to some extent for street-railway systems instead of the
compound or differential types. Its object is to maintain an
approximately constant current delivery from the generators,
the fluctuations of the load being taken up by the battery. It
therefore accomplishes the same purpose as a compound or
differential booster as far as keeping the dynamo current at a
constant value is concerned* while on account of the way in
which it is used, the machine can be smaller and cheaper than

§27

STORAGE BATTERIES

either of the other types. This booster can be used to advan-
tage where constant voltage on the power circuit is not
essential. Fig. 40 shows a common arrangement of connec-
tions. A is the generator supplying current to the bus-bars
E, Fio which the steady load is connected. The fluctuating
load is connected to bus-bars G, H, and the booster arma-
ture B and series-field are connected in series between E
and G. That is, the fluctuating load does not pass through
any of the booster windings as in the case of the compound
and differential boosters. The booster carries only the
average current supplied by the generator to the power

1 1

7b Hftih or of her stesdy loti

I I

7b motors orofherifsritible tosi

Pio.40

system and can be of comparatively small output; more-
over, the steady load is connected between the generator
and the booster so that this part of the load current
does not pass through the booster. The battery is
usually provided with an end-cell switch D so that, if
desired, it may be operated on the lighting load only, the
c6lls being cut in as the voltage drops. The booster is pro-
vided with a shunt winding, which sets up an E. M. F. in the
armature in a direction such as to aid the generator E. M. F.
The series-coils oppose the shunt coils and set up an E. M. F,

STORAGE BATTERIES

§27

opposed to that of A. It will be noticed that the curreot
through the booster is not reversed, because the only current
that flows through it is that supplied by the generator.
Under ordinary operatiug conditions switches 1,2,5,6^, and 7
are closed, at which time the operation is as follows: In case
a heavy load comes on the power circuits, the tendency is for
a heavy current to be delivered by the generator through the
booster. Now the voltage across the terminals of the battery
is equal to the generator voltage plus that of the booster; any
increase of current in the series-field causes a lowering of the
booster E, M. F., because the series-winding opposes the
shunt winding. The result is that the pressure across
the battery terminals decreases, thus causing the battery to
discharge and supply the extra demand for current. Con-
versely, a decrease in the fluctuating load causes the battery
to charge. The dynamo, therefore! delivers an approxi-
mately constant current. Of course, the generator current
does not remain absolutely constant, but the irregularities
due to the heavily fluctuating motor load are so smoothed out
that the pressure supplied to the lamps is practically uniform
and the objectionable flickering, so often apparent where a
variable load is operated from the machine, is done away with.
If both loads must be operated directly from the dynamo
without the use of the battery or booster, these may be cut
out as follows; The booster is shut down and switch 3
closed. Switch 3 cannot be closed while the booster is
generating, because armature B would be short-circuited.
Switch 5 is then opened and the booster thereby cut out of
service. By opening switches 6 and 7 and closing switch 8,
the battery is cut out and the dynamo supplies all the current.
Note that switch 7 must be opened before 8 is closed, other*
wise the end cells will be short-circuited. If it is desired to
cut off the fluctuating load and run the lights from the battery
alone, switches 8 and 9 are opened ^ and switch € closed.
This cuts off the fluctuating load and places the battery, with
its end cells, in parallel with the generator, it being under-
stood that the booster is now out of service* By opening
switches 1 and 2 the generator is cut off and the whole

STORAGE BATTERIES

iightin^ load is carried by the battery, the regulation being
effected by means of the end-cell switch. When the battery
is to be given a full charge, B can be operated as a plain
shunt booster by cutting out the series-coils by means of the
short-circuiting switch i,

CAPACITY OF HOOSTEHS

68* The maximum amount of power that a booster has
to deliver depends on the circumstances under which it is
used. Generally speaking, the voltage generated by a battery
booster is comparatively low, while the current capacity must

be Uir^e, The maximum outpiit, in watts, \^ obtained by mul-
tiplying the maximum number of volts by which the current
must be raised or lowered by the maximum current that is
likely to pass through the boos ten In actual work this max-
imum demand is made but seldom, and then only for short
intervals, so that if a machine of 70 or 8*3 per cent, of the above
capacity is installed, it will be large enough. The amount of
current that the booster will probably be called on to handle can
only be determined by carefully noting the demand for current
from the battery, as indicated by the load line of the station*
Fig. 41 shows a differential battery booster made by
the General Electric Company for street-railway work.
The differentially wound generator A is driven by a direct-
coupled, shunt-wound motor B which is wound for 500 volts
and has a capacity of 150 horsepower; the generator is
wound for 11-5-180 volts and has a maximum output of
115 kilowatts at 525 revolutions per minute. It will be
noted that the booster does not differ much in construction
from an ordinary com pound- wound generator. The com
mutator is somewhat larger than usual on account of the
large current sent through the machine, though the size of
the commutator, as compared with the output of the gener-
ator, does not in this case appear so excessive as in
the case of boosters designed for lower voltage and larger
current. On low- voltage boosters it is sometimes necessary
to use two commutators, one at each end of the armature,
in order to provide sufficient current-carrying capacity. The

40Ii— 7

STORAGE BATTERIES

§27

two sets of field windings are indicated at a and d. In order
to accommodate the special field windings required for a
machine of this kind the field-magnet cores have to be
unusually lon£^; this makes the booster field magnet of
large diameter as compared with that of the motor.

Fig, 41

These descriptions will give a general understanding of
the me th od s u se d f o r s t or a ge-ba 1 1 e r y r e g ul at io n . T h e co ndi-
tions under which batteries are used vary so much that the
switchboard connections for scarcely any two installations
are alike in all particulars. However, if the foregoing
methods are kept well in mind there should be little difficulty
in tracing out the connections for any particular installation.

§27 STORAGE BATTERIES 83

GBNERAIi DATA ON STORAGE CEIiliS

69. In order to give an idea as to the size, capacity,
weight, etc. of storage cells Tables I, II, and III are here
given. These tables do not show all the sizes of each type
because cells can be made up with almost any number of
plates desired. In each table, the first cell of a given type
is the smallest size made in that type and the last given is
the largest. The number of plates per cell is always an odd
number because there is always one less plate in the group
of positives than in the group of negatives. For example,
a 13-plate cell would be made up of six positives and seven
negatives. The capacities of cells with a number of plates
different from that shown in the tables can be easily calcu-
lated. For example, in Table I, the 9-plate, type F cell has
an 8-hour capacity of 40 amperes and a 15-plate cell of the
same type has a capacity of 70 amperes. The addition
of six plates or three pair of plates increases the capac-
ity 30 amperes; hence, the capacity per pair of plates is
10 amperes. A 27-plate cell has thirteen pair; hence, its
capacity is 13 X 10 = 130 amperes for 8 hours. In making
estimates of the room occupied by a given battery, about
Ik inches clearance should be allowed between glass jars,
2? inches between metal tanks, and 2 inches between
wooden tanks.

STORAGE BATTERIES

§27

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STORAGE BATTERIES

§27

TABIiK III

GENERAL DATA ON KLECTRIC VEHICLE CELLS

Of CeU

Size of
Plates

Inches

Number

of
Plates

Discharge

for
4 Hours

Amperes

Weisrht of

Cell
Complete
With Acid

Pounds

DimcnKlons of Hard-
KubbcrJar

Inches

Width

LenfTth

Hciirht

ExideMV

5* X8i

I9i

Exide M V

5f X8|

ExideMV

5f X8S

ExideMV

5f X8J

44i

ExideMV

5i X8S

56i

II A

Exide P V

4flX8S

Exide P V

4ttX8j

17*

Exide P V : 4rt X 85

274

Gould E V i 5 J X 9

20i

Gould EV 5* X9

Gould EV

SJ X9

57i

59*

INCANDESCENT LIGHTING

(PART 1)

INTRODUCTION

1. The subject of electric lighting involves a considera-
tion of the different methods used for carrying out artificial
illumination by means of electrical energy. Thus, not only
must the actual means of converting the electrical energy
into light be considered, but the methods used for its
generation and distribution must also be given due attention.
The general subject of electric transmission has already been
considered, so that it will only be necessary to take up such
features regarding distribution as relate more particularly to
lighting work.

2. There are two methods in common use for producing
light by means of electricity: (a) By means of incayidescent
lamps, and {b) by means of arc lamps. Both methods are
extensively used, the arc light being especially adapted for
street lighting, although it is largely used for interior light-
ing as well. The principal field for incandescent lighting is
interior illumination, but incandescent lamps are also used
for street lighting, especially in places where the streets
are thickly shaded by trees, or in cases where a uniform
distribution of light is desired.

3. In the incandescent electric lamp, light is produced by
bringing a continuous conductor of high resistance to a very
high temperature by passing a current through it. If a cur-
rent is sent through a conductor, there will be a certain loss
of energy in the conductor due to the resistance that the

For notiu of copyright , seepage immediately following the title Page
232

2 INCANDESCENT LIGHTING §32

current encounters in flowing through It, and this loss reap-
pears in the form of heat* In the incandescent lamp the
heating effect is so intense that it raises the conductor to
incandescence and so produces the desired illumination,

4. The illumination produced by the arc lamp is brought

about in a different manner. The current is made to pass
between two electrodes (usually carbon) that are held a short
distance apart. The points of these electrodes become
heated to an exceedingly high temperature and a very bril-
liant light is produced. The arc lamp was first publicly
exhibited by Sir Humphry Davy, in London, in the year 1810,
when he used a battery of 2,000 cells for its operation; but it
did not come into commercial use imtil a much later period,
because current could not be supplied cheaply enough by
means of batteriesi and the introduction of the light was not
accomplished until the dynamo-electric machine had been
developed sufficiently to insure the generation of electrical
energy at reasonable cost.

5. Arc and incandescent lamps may be operated by
means of either alternating current or direct current. Arc
lamps have, in the past, been operated principally by direct
current, but alternating current is now largely used for this
purpose. Incandescent lamps will operate quite as well with
alternating as with direct current, provided the frequency is
not too low* The heating effect in a conductor is independ-
ent of tlie direction in which the current flows; hence, an
alternating current ^ which periodically reverses its direction
of floWi will operate an incandescent lamp just as well as
direct current* The reversals of the current are so rapid
that the conductor in the lamp does not have time to cool off
perceptibly, and hence there is no flickering noticeable to
the eye. If, however, a frequency below 30 cycles per
second is used, the lamps are apt to flicker, and if alternating
current is to be used for incandescent lighting work, the
frequency should not be below this value.

6. In taking up the subject of electric lighting, there will
then be the four following divisions to consider;

S3S

INCANDESCENT LIGHTING

L Incandescent Itghtinjj by direct current.

2, Incandescent liirhting by alternating current-

3, Arc lighting by direct current.

4, Arc lighting by alternating current.

These main divisions of the subject cover broadly the
numerous systems in common use; tbey may be still further
subdivided, but the various modifications will be taken up
when each of the above divisions is considered by itself*

INCANDESCENT LIGHTING

THE INCANDESCENT LAMP

7, The iTicanclcftt't^iit lamp is naturally the first thing
to be considered in connection with the subject of incan-
descent lighting, as it is by means of this lamp that the
electric energy is made to furnish the required illumination.
Fig* 1 shows a typical incandescent
lamp with which every one is familiar.

In order that the lighting service sup-
plied from an incandescent plant shall
be satisfactory* it is highly important
that the lamps be efficient* If poor
lamps are used, or if the lamps are
burned beyond their useful life, poor
service will result, no matter how
efficient the system may be in other
respects* It is useless to install the
best generating machinery available and
then expect to give a good service with
old or cheap lamps that soon run down
in candlepower* Central-station man-
agers are coming to realize this point
more than \vas once the case, and are
devoting more attention to the quality of the lamps that
they buy; in fact, most progressive companies now provide
means for testing their lamps.

Fia.l

INCANDESCENT LIGHTING §32

CONSTRUCTION OF LAMPS

8, Early Experiiiietits.— It was not long after the
invention of the arc lamp until inventors turned their atten-
tion to the production of electric light by heating continuous
conductors to a high temperature by means of the current,
instead of using the arc, because the early forms of arc
lamps were not well suited to interior illumination. The
first experiments were made with platinum or iridium wire.
These wires were mounted in the open air and current sent
through them, the current bringing the wire to a white heat
and thus causing light to be given off. All these lamps
proved failures because the wire very soon burned out.
The temperature to which it had to be raised was very near
the melting point of the metal, and if great care were not
exercised the wire would fuse. In later experiments, the
wire was enclosed in a glass globe from which the air was
exhausted. This was a great step in advance^ because it
prevented the conductor from becoming oxidized and thus
destroyed by the action of the air; it also prevented the wire
from cooling so fast* and thus allowed the high temperature
to be maintained by a much smaller ciirrent than would be
required were the wire heated in the open air. Even when
the platinum or iridium wire was enclosed in a globe from
which the air had been exhausted, it was found that, although
the lamps were very much im proved » they were not suitable
for commercial use. It became evident that some substance
that would be cheaper and capable of standing a higher tem-
^ perature would be necessary. Carbon was finally selected

as the substance most suitable and is now universally used.

9» Filaments. — Edison tried a great many experiments
to determine the best substance for the coniluetor, or
fllameut, as it is usually called. The material that he
finally selected was bamboo fiber, which was cut to the
proper size and then carbonized. Maxim made lamps with
filaments of carbonized paper. These lamps embodied all
the essential parts contained in the modem lamp shown

S33

INCANDESCENT LIGHTING

in Fig, 1, but lamps as now made are very much improved
in efficiency and are decidedly dieaper. Fig, 2 shows the
general shapo of one of the early bamboo filaments. The
ends a, a were enlarged so that the heating at the joint
between the leading* in wires and the filament was much
less than that of the filament proper. Lamp filaments as
now made are usually in the forms shown in Fig, 3 {«)» (b),
and (r), («) is the plain loop filament, (b) the spiral,
and (f) the oval. In Fig. 3 (r), the filament is fastened at ^
to a small iron or nickel wire fused into the glass, and is
called an anchored fiiamtni. This is done to prevent violent
vibrations of the filamenti which would tend to shorten the

Fio.a

life of the lamp, and lamps of this type should be used in
any place where they are subjected to vibration, as, for exam-
ple, on street cars,

10* Filaments have been made of carbonized stlk or cot-
ton thread, hut the usual method of manufacture at present
is by the so-called squiriittg^ process* The raw material of
which the filaments are made is usually a fine grade of cot-
ton, though filter paper is sometimes used. This is dissolved
in a strong solution of zinc chloride made acid by the addi-
tion of hydrochloric acid; the solution digests the cotton, at
first producing a jelly-like substance and finally a complete
solution* While hot, the solution is filtered and subjected to

6 INCANDESCENT LIGHTING §82

a vacuum treatment to remove all traces of air. The mix-
ture is then forced through small holes, or dies, and thus
squirted into the form of threads which, as they emerge from
the dies, run into jars containing wood alcohol; the alcohol
hardens the squirted thread, which coils up in the bottom of
the jars. When a jar is full, the alcohol is removed and the
white cellulose thread washed thoroughly for several hours
to remove all traces of zinc chloride, after which the thread
is wound on drums and dried. In the drj^ing process the
thread shrinks greatly; If squirted through a .023-inch hole,
it will shrink to about *008 inch. The carbonized filarnents
are made by winding bunches of the dried thread on carbon
forms, which are then bedded in charcoal or graphite in a
crucible and subjected to a high temperature for several
hours. During the carbonizing process there is a further
_ shrinkage, the diameter being reduced to about .0035 inch.

After carbonization, the filaments vary more or less in
diameter and they are sorted into lots having like diameters
before being subjected to the treaiijt^^ or fiashing- process^
which is carried out as follows: After having been cut to the
proper length, the filaments are held in suitable clamps in an
air-tight receptacle from which the air has been exhausted,
and a thin vapor of gasoline substitutedi Sufficient current
is then passed through the filaments to bring them to incan-
descence» thus decomposing the gasoline vapor and causing
a dense layer of carbon^ in a form similar to graphite, to be
deposited on the filament. This deposit greatly lowers the
resistance, and when the proper resistance is attained
the current is cut off automatically; uniformity of resistance
is thus secured. With the older styles of filament made from
bamboo or thread, the object of flashing was to even up thin
places and make the filaments uniform. Thus, thin parts of
the filament would become more highly heated than the
parts of lower resistance and there would be a greater deposit
of carbon on the hotter parts. In squirted filaments, the
flashing is not necessary so far as securing a uniform cross-
section is concerned, but it is found that the layer of dense
graphitic carbon greatly strengthens the filament and results

§32

INCANDESCENT LIGHTING

in 2. longer-lived lamp. Also, heat is not so readily radiated
from this deni>e outer layer as from aa untreated filament,
consequently a smaller current is sufficient to maintain the
treated filament in a state of incandescence and the Bashing
results in an increase in efficiency • It is this layer of
graphitic carbon that gives the filaments their familiar
steeMike appearance,

1 1 . The size of the filament depends altogether on the
candlepower of the lamp and the voltage and current with
which it is to be supplied. The lamp shown in Fig. 1 is one
of 16 candlepower, such as would ordinarily be used on a
110- volt circuit. Such a lamp would require about i ampere;
hence, from Ohm's law, its resistance
when hot must be in the neighborhood
of 220 ohms. In order to get this
high resistance, the filament must be
long and fine. Lamps designed for
low voltage and large current would be
provided with short, thick filaments.
Fig* 4 shows a low-voltage lamp de-
signed to take about 3i amperes. In
this case the filament is short and cor-
respondingly thick.

Fig. 3 shows the way in which the
filament is usually mounted; it is
fastened to the platinum wires a^ a,
which are sealed into the glass and thus render the globe air-
tight* The junction between the filament and the leading-in
wire is effected by means of carbon paste; this paste also
enlarges the cross-section of the joint, so that the heating
is small compared with that which takes place in the filament
itself, and the leading-in wires are therefore kept cool.

12* The Ijeadtn^^In Wires, — These are made of plati-
mim, because this metal has almost exactly the same coeffi-
cient of expansion as glass^ and also because it does not
oxidize. If the glass and platinum did not expand at the
same rate when heated, cracks would form at the point

PX€*. f

8 INCANDESCENT LIGHTING §32

where the wires are sealed into the glass. This would let
in the air and the filament would soon burn out* A film of
oxide on the leading-ln wires would also tend to let air
leak into the globe, and platinum does not oxidize. Only
enough platinum is used to pass through the glass, as shown
at a, a, Fig. 3. Connection is made to the base by means o£
small copper wires b,b fused to the platmum at c^c. In
early lamps, the whole length of the leading-in wires was of
platinum, but this is unnecessary and the practice was soon
discontinued, owing to the high price of the metal. Substi-
tutes for platinum for the leading-in wires have been
brought out from time to time, but none of them have dis-
placed it as yet*

13, The Bulb, — The style of bulb used to enclose the
filament is familiar to almost everybody. Different shapes
are in use, but by far the most common is the pear-shaped
bulb shown in Fig, 1. Bulbs should not be made too small,
because, as the lamp bums, the filament gradually undergoes
disintegration and small particles of carbon are thrown off
and deposited on the globe. This causes the well-known
blackening of the lamp, and if the bulb is very small the
blackening is aggravated, because the surface is smaller and
the deposit* for that reason, more dense.

14, Kxlmustlou.^ — Fig. 5 shows a lamp after the stem
carry tng the filament and the leading-in wires have been
sealed into the bottom. The lamp is now ready to be
exhausted. In order to accomplish this, the bulb is first
iubidatedy i. e,> a small glass tube with a narrow neck at a is
sealed into the top of the bulb.

Numerous methods have been devised for the exhaus-
tion of lamps. Ordinary mechanical air pumps, those that
exhaust the air by the operation of a plunger in conjunction
with valves, are not capable of producing a sufficiently high
degree of exhaustion. Mercurial air pumps were formerly
used for the purpose ^ but have been superseded by the
so-called chemical method* which is very 'much quicker.
Id this process a finely constructed mechanical air pump is

i32

INCANDESCENT LIGHTING

used to exhaust the greater part of the air find the remaining
oxygen is then removed by introducing a chemical that will
combine with It and render it incapable of oxidizing the fila-
ment. In the pump used for this purpose the valves and
piston work in heavy oij, which forms a seal and permits a
rather high de^ee of exhaustion to be obtained. A small
quantity of red phosphorus is painted in the *'tubulation"
before the lamp is connected to the pump* A few seconds
suffice to obtain a fairly good vacuum
and current is sent through the lamp*
The filament is burned at a very high
temperature, thus driving off air from
the ^lament, carbon paste, and inside
surface of the bulb, A bluish mist fills
the lamp, and when this appears a gas
flame is applied to the part of the
tubulation painted with the red phos-
phorus, thus converting some of it into
active phosphorus, which combines with
the remaining oxygen in the bulb form-
ing phosphoric anhydride — a solid* The
instant this combination takes place the
blue mist vanishes and the operator at
ODCe * 'seals off'' the bulb by heating the
contraction a. Fig. 5, in the glass tube,
thus forming the tip on the lamp. The
vacuum is tested by holding the lamp
by the bulb and touching the terminal
wires to one terminal of an induction
coiL If the vacuum is perfect ^ no glow will be observed in
the bulb; if the vacuum is poor, a bluish glow will appear*

Fm. 5

15* BaseB. — After the lamp has been exhausted, it is
complete with the exception of the base N^ Fig. 1, with
which it must be provided in order that it may be readily
attached to the socket. These bases are usually made of
brass and porcelain, the lamp being held in them by a setting
of plaster of Paris or cement*

INCANDESCENT LIGHTING

§32

In Fig. 5, the lower part of the lamp is made of such
shape that the base will be held securely when the plaster of
Paris is put in place. The rib b prevents the base from pull-
ing off* The base must, of course, provide two terminals for
the leads from the filament, these terminals being arranged
so that when the lamp is placed in the socket contact will
be made with two corresponding terminals. There are
three different bases commonly used in America; these are
the Eiiis&n; the Thomson-Hoiistayt, or 7". //., as it is more
commonly called; and the IVesHnghouse, or Sawyer- Man,

Fig, 6 (a) shows the Edt^on tMise, of which there are
more in use than all the others put together. One end of
the filament is attached to the outer shell /^ which is pro-
vided with a coarse screw thread. The other terminal is

connected to the projecting centerpiece A the two brass pieces
being separated by means of a porcelain piece r. When the
lamp is screwed into the socket, the screw shell makes one
connection and the centerpiece the other. Fig. 7 shows a
lamp screwed into an ordinary Edison key socket.

Fig. 6 {b) shows the T. U. bane, so called because it was
brought out by the Thomson-Houston Company. In this
base, one terminal is connected to a brass centerpiece t in
which a hole is drilled and tapped. The other terminal
is connected to the brass ring /'. This base has the advan-
tage that the outer shell* if one is used, is in no way con-
nected to the circuit, and there is therefore less danger of
receiving a shock by touching the lamp; it has been, and

las

INCANDESCENT LIGHTING

still is, used to a considerable extent, though it is gradually
going out o£ use, as it is more expensive to make than the
Edison base. It works loose in the socket a little more
easily than the Edison base when the lamp is subjected to
vibration. When placed in the socketi terminal / screws
on a projecting stud, thus making one connection; the other
connection is made by the ring /' coming into contact with a
corresponding ring or terminal
in the socket. The later types
of T. H. base are made of
porcelain with a brass center-
piece and outside ringp as de-
scribed above.

Fig, 6 (c) shows the West*
Ingrhouse or Baw^^er-Man
baBi^ as it is sometimes
called, because it was orig-
inally brought out by The
Sawyer-Man Company. This
base is similar in some re*
spects to the Edison, but the
outer shell is not threaded; the
lamp is pushed into the socket,
the outer shell slipping into a
split bushing that is provided
with an annular groove* The
rib d slips into this groove
when the lamp is in position
and prevents the lamp slipping
out. The other connection is
made by the projecting pin / coming into contact with a
spring in the socket. This base has the fault that it some-
times allows the lamp to drop out of the socket if the split
bushing does not grip the rib d properly. It also makes
comparatively poor contacts, which become worse with use.

16. When incandescent lamps were first broughl into
use on a commercial scale, each difiEerent maker had his

Cff/tfoefm

Fig- 7

4«n^«

INCANDESCENT LIGHTING

§32

own style of lamp base, and the result was that over a dozen
different types were in use. The number has^ however,
been gradually reduced until the three mentioned above
probably include over 99 per cent, of all the
bases in use in America. The chances are
that in a few years the Edison base will
have replaced the others, because, taking
everything into consideration, it is the best
base of the three. Even plants that are
equipped with sockets of other makes are
fitting them with adapters so that they
may be able to use Edison base lamps*
Fig. 8 shows an adapter for changing T, H, sockets to
take lamps with the Edison base.

FiO, S

MEA8UEEMENT8 AND I^AMP CAIiCUL-ATIOKS

LIGHT MEASUREMENTS

17, Incandescent lamps are usually designated by their
candlepower. For example, a !amp is spoken of as giving:
16 candlepower when it produces an intensity of light equal
to that produced by 16 standard candles.

The unit of light intensity commonly used is a spermaceti
candle of standard dimensions* Standard candles are ,9 inch
in diameter at the base» ,8 inch in diameter at the top, and
10 inches long; they bum 120 grains of spermaceti and wick
combined, per hour. Six candles weigh 1 pound. The
candle is not a very satisfactory standard, as it is subject
to considerable variation, and other standards have been
brought out to replace the candle in practical work. Various
kinds of gas and oil lamps have been used for this purpose,
which, although less liable to fluctuations than the candle,
have not yet superseded it.

18* The Mcthven screen is a convenient standard that
has been largely used. It consists of an Argand gas burner
provided with a screen that cuts off all the light from the

§32

INCANDESCENT LIGHTING

flam« except a small portion that is allowed to come through
a thin-edged standard opening in the screen. The size of
the opening is ,233 inch wide and 1 inch lon^. The height
of the flame is 3 iuches and the screen is placed li inches
from the axis ol the flame. The light given by a standard
of this kind will vary considerably with the quality of the
gas used, and while it may not be reliable as an absolute
standard^ it makes a very good working standard after its
candlepower is known by comparing it with a standard
candle. A slit of the above size should emit about
2 candlepower,

19, One of the best light standards is the ain^ri acetate,
or Hefiiert unit. This lamp consists of a small reservoir
provided with a wick tube of standard size. The lamp burns
amyl acetate and the flame is adjusted until its tip is 40 milli-
meters above the top of the wick tube. This standard is
very reliable and is subject to little variation, but it has the
disadvantage of giving a light of reddish tinge. The Hefner
unit is not quite as large a unit of light as the English
candle, the relation being 1 candle = 1*136 Hefner units.

20, For photometric tests connected with electric-light
stations, neither the candle nor the amyl acetate lamp is
used as a working standard. The general practice is to
standardise either an incandescent lamp or an oil lamp by
comparing it with a standardized lamp such as can be obtained
from lamp manufacturers and which is known to give a cer-
tain number of candlepower when operated at a specified
voltage. A secondary standard of this kind is very much
easier to work with and cheaper to operate than either a
standard candle or amyl acetate lamp. In order to deter-
mine the candlepower of an incandescent lamp, there must
be some means of comparing the intensity of illumination
produced by the lamp with that produced by the standard.
An instrument for doing this is called a iiliotonieter.

21, Ijaw of the PJiotometer. — Suppose a candle is
placed at .^, Fig. 9, and a screen B held at a distance of,
say, 2 feet from it. The screens are here shown bent so as

INCANDESCENT LIGHTING

i32

to represent portions of spherical surfaces wtth A at the
center. Consider the portion u^cd of the screen^. The
intensity of illumination on the area abed will be a certain
amount* Now, suppose the screen to be moved back to the
position C, 4 feet from A. The total amount of hght that
fell on the area abed will now be distributed over the area
a^l/dd^. The area a^ ¥ d d^ is four times that of abcd^
because A m is twice ^/and, consequently, mh is twice /^,
or ^V is twice be. The total quantity of light falling on the
two surfaces is the samej and since the area of a^b^e^d^ is
four times that of abed, it follows that the light per unit

Pio. 9

area or the intensity of iUumination on a* ¥ d d' is only one-
quarter that on abed. Doubling the distance of the screen
from the source has cut down the intensity of illumination to
one-fourth its former value* If the distance A m were three
times as great as Af, the intensity of illumination would be
one-ninth that on abed. This law may then be stated as
follows:

The inienuty ol H luminal ion prod need by a source of light on
any objeei varies inversely as the square qI the disianee ai the
0bjee( from the sourre.

If ;r is the illumination produced, B the caodlepower of
the source of light, and d the distance, then

INCANDESCENT LIGHTING

X =

rf*

(1)

22, Klementu,!*:^* Photometer. — Suppose that the
hrightness of two sources of light, such, fur exam pie, as a
candle and an incandescent lamp, are to be compared. If
the candle A and the lamp B are placed in a dark room, so
that there will be no other light to interfere, and a screen C
is placed between them, as shown in Fig. 10, one side of
the screen will be illuminated by the candle and the other
by the lamp. If the candle and lamp are exactly of the
same brightness, the two sides of the screen will be
equally illuminated when placed midway between the sources

Pig. 10

of light; and if the screen is mounted so that it can be slid
along between the lights, a point can always be found where
the screen will be equally illuminated on both sides. In the
present case, the screen would have to be moved nearer the
candle than the lamp, because the candle is not so briEfht as
the lamp. Suppose that the screen has been adjusted so
that the illuminations are equal on each side, and that the
distances d^ and d^ have been read off by means of the
scale 5*, d^ being the distance from the screen to the stand-
ard candle and d^ the distance from the screen to the light
that is being measured.

Let Xi be the illumination produced on one side, Xm that
on the other, and B^ and B^ the candlepowers of the

INCANDESCENT LIGHTING

standard and the light being measured* respectively- Then,
from formula If JCi — ,*, and :tr, — — -*; but, since the illn-

minations on the two sides are equal, —\ = — ^,

Now, the candlepower B^ of the standard is supposed to
be known, and since the distances are also known, the
candlepower B^ of the lamp being measured can at once be
calculated. For this purpose, it is more convenient to have
the last equation in the form

J?. = 5. i^; (2)

23» The arrangement shown tn Fig. 10 is a simple form
of photometer, and formula 2 expresses the relation between
the candlepower of the standard and that of the lamp being
measured. This may be written in the form of a rule» afs
follows:

Rule* — The caftdiepmver of ike Iimtp being iisitd on a phot a-
nieier h (mmd by mi4iiipiyi7ig the candlepower of the siandard
by the giioti*mt obtained by dividing the square of the distance oi
the lamp from the screai by the square of ike distance of the
siandard frmn the screen.

ExAMPi.H.'-Stippose, m Flg» 10» that>* is a standard candle epviog
1 candlepower and that B is an Inran descent lamp. The screen is
moved until a point is found where the two stdes are equally illumi^
nated* The readiag on the scale then shows that the distance from the
standard is 20 inches. The total distance between Ihe lamps is 100
inches. What is the candlepower of ^?

SoMTTfON.— If the total lenjjth of the photometer is 100 in., the dis-
tance from the lamp to the screen mu^t be 100 — 20 — 80 In. The
candlepower of the standard is 1; hence, substituting in formula 2,

80'
^, - I X ^ - m c, p. Ans.

24* BnnBen Pliotometer.^^ — The Bimsen photometer
has been more largely used than any other. It is very simple
and is capable of giving good results if used properly. The
arrangement of the different parts Is essentially the same
as that shown in Fig, 10, but the distinguishing feature lies

132

INCANDESCENT LIGHTING

in the style of screen used. It would be a diffi-rult matter
to tell when a simple screen like that shown in Fig. 10 Is
illuminated equally on both sides» and to overcome this diflfi-
cuhy Professor Bunsen devised the screen shown in Fig. 11,
It is made by taking a piece of good quality of white paper
and making a ^rrease spot in its center, as indicated by
the star in Fig* IL If such a screen is held so that the
front side is more strongly illuminated than the back,
the grease spot will appear dark on the white ground of the

paper, as shown in (a). If, however, the screen is more
brightly illuminated on the back side, as, for example, if it
is held between the eye and a window, the grease spot
will appear light on a dark ground, as shown in {/>). If such
a screen is mounted in place of the screen C in Fig, 10,
and arranged so that both sides can be seen at once, the
grease spot will disappear almost entirely when the two
sides of the screen are equally illuminated. In order to
facilitate the observation of the screen, it is usually arranged

18 INCANDESCENT LIGHTING §32

witb two mirrors mounted at a slight angle to \U as shown
at M,M in (r), S is the screen with the grease spot, and
the observer looks at the reflection of the two sides ot the
screen in the mirrors instead of the screen itself. The
screen and the mirrors are mounted in a box^ which is open
at the ends to admit the light from the sources and which
is also provided with an opening in the front to enable the
observer to see the reflections of the screen.

25- Fig. 12 shows the arrangement of the parts of a
simple photometer of the Bunsen type designed by Elmer
G, Will young for use in connection with lighting stations.
y4f the standard^in this case an incandescent lamp of accu-
rately known candlepower — and B, the light to be measured;
D is the bar on which the carriage containing the screen
slides; the part D is usually spoken of as the photomotei*
bar- E is the carriage containing the Bunsen screen. The
motor FIe used to spin the lamp B while measurements are
being made; the reason for doing this will be explained later.
G and // are two adjustable resistances for keeping the volt*
age applied to the lamps at the proper valuer

26 1 Fig. 13 shows a Deshler-McAllister photometer— a
simple instrument that has been quite largely used in light-
ing stations for testing the light-giving qualities of the lamps
they are using* The principal difference between this
instrument and the one previously described is that an oil
lamp /4 is used as a working standard instead of an incan-
descent lamp. The bar is also provided with a scale reading
directly in candlepower, though the Will young instrnment
could also be provided with a direct-reading scale, if desired*
One objection to using an incandescent lamp as a light
standard is that its voltage must be constantly watched and
kept at the proper amount. It is largely to get around this
difficulty that the oil lamp is used- This is an ordinary
lamp provided with a double wick and an adjustable screen St
by means of which the upper and lower ragged edges of the
flame are cut off. A', A^ are standard incandescent lamps
that have been accurately calibrated at the lamp factory and

90 INCANDESCENT LIGHTING §32

of which the candlepower, at the voltage marked on them,
is known- Each of these standard lamps, in succession, is
placed at B and the pointer of the carriage set at the point
on the bar corresponding to the candlepower marked on the
lamp- The voltage at the lamp is then adjusted by means
of the rheostat G until it corresponds exactly with that
marked- When this has been done, the screen S in front of
the flame of A is adjusted until the grease spot is balanced.
The lamp A is then of the same candlepower as the standard
and may be used for the measurement of other lamps, since
after it is once adjusted it is not likely to change, though it
should be checked up now and then to make sure that it
does not do so. The object in having a number of standard
lamps A', K instead of one only is to have a check against
any errors that might be caused by changes in the lamps*
Screens L,L are provided to cut off the light from the
observer's eyes and a motor /" is used to rotate the lamp.
These station photometers are not expensive, and if prop-
erly used are of great value in detecting poor lamps,

27, After a person has become accustomed to the
photometer, good results can be obtained provided the
following conditions are fulfilled:

L The lights, both the standard and the light being
measured, should be steady,

2, The standard and the light being measured should be
of approximately the same color.

3. The brightness of the light being measured and that
of the standard should not differ to an extreme degree; for
example, good results could not be expected if an attempt
were made to compare an arc lamp with a candle.

Most ordinary photometer bars are fitted with a scale
divided into equal divisions^ as shown in Fig. 10, so that the
distances may be read off and the candlepower calculated
from these distances and the known candlepower of the
standard. If the standard used is always of the same value,
it is evident that the bar might be graduated to read directly
in candlepowerf as in the photometer shown in Fig. 13.

i32

tNCANDESCENT LIGHTING

Where many lamps are to be tested, thts can usually be
done, as the same standard can be used all the lime and
readings taken rapidly from the bar as soon as the setting
of the screen is made* Many modifications of the photometer
have been made^ but the above will give a general idea of
the principles involved and of some of the forms especially
useful in connection with electric-light stations.

]:.ieHT mSTBIBDTlOH

28* Mean Elnrlssontal Candlepower, — If an incan-
descent lamp is set on a photometer and its candlepower
measured » it will be found that different values for the
candlepower are obtained* depending on the position of the
lamp and the shape of the filament. For example, in Fig. 14
the brightness of the lamp ia the different horizontal direc-
tions It 2t 3, 4^ etc. would not be the same. The candle-
power given out in the different horizontal directions along
any line, such as those shown in Fig. 14, is known as the
horizontfLl eandlepowor for that position. The mean or

average horizontal candlepower is the average value of these
different readings and is frequently obtained by taking the
reading from the lamp while it is rapidly revolved about its
vertical axis. The photometers just described are arranged
so that the lamp can be revolved at the rale of about
180 revolutions per minute, thus giving the average, or
meani horisiontal candlepower. The horizontal candlepower
does not vary greatly in different directions with lamps as
now constructed. This is shown by the irregular curve,
Fig. 14. The distance of the points on this curve from

INCANDKSCENT LIGHTING

§32

the center represents the candlepower m the direction of the
radius from that point, and if the candlepower were the
same in all directions, the curve would become a circle,

29* Vertlcfil BlHtrlbutlon,— Fig* I'j shows the read-
ings for the candlepower obtained in a vertical plane with the
filament in the position shown. Viewed from position /,
the candlepower is practically ?.ero» because the lie:ht is
almost completely cut off by the base of the lamp* At
points 2 and i'it is a maximum, because viewed from these
points the maximum amount of the filament is seen. At
point 3 the candlepower ag^ain drops off, because here the
filament is seen end on. The curve of horizontal distribu-
;5 tion gives an idea as to

i how the lamp throws light

in a horizontal plane, and
the curve of vertical dis-
tribution shows how the
lamp behaves as to throw-
ing the light up or down-
In speaking of the candle-
power of an incandescent
lamp, the mean horizontal
candlepower is usually
meant, and this is most
readily obtained by spin-
ning the lamp as described above. In many cases, how-
ever, it is customary to measure the candlepower in one
direction only, and the error in doing so is not usually
very great, because filaments are nearly always twisted
and the candlepower does not vary greatly when the lamp
is viewed from different directions. In case the lamp is
not revolved when measurements are being taken, it should
be adjusted with the plane of its filament at such an angle
to the photometer bar as will give the mean candlepower*
For example, in Fig. lf>» suppose that AB represents the
axis of the bar and that we are lot»king dt>wn on the top of
the lamp. The line CD will indicate the relative position of

INCANDESCENT LIGHTING

the plane af the filament. The angle a at which the filament
should he iDclined will depend on the style of filament used.
For plain loop filaments it should be about Gf)*^ and for
spiral filaments 30^.

30, Meau BpherUml Caiidleijower. — If a lamp is
hung so that it can be viewed from any direction, it is clear
that if viewed from any number of diflFerent points a corre-
sponding number of different values for the candlepower
will be obtained. If several readings are taken at regular
intervals and averaged, the iiiofiii spherical eaiidlcpo^ver
of the lamp will be obtained. In other words, the mean
spherical candlepower represents that intensity of illumi-
nation to which the irregular illumination of the lamp would
be equivalent if it were aa average candlepower given

Wm. m

out miiformly in all directi&ns. The mean hemispherical
candlepower is the average of the candlepower s taken over
a hemisphere. When a lamp is provided with a shade or a
reflector, nearly all the light is thrown down and the mean
candIei>ower for the lower hemisphere is made greater than
the mean spherical candlepower for the lamp without a
reflector. In connection with commercial measurements on
incandescent lamps, the mean spherical candlepower is not
used to any great extent. It is used more in connection
with arc lamps. One arc lamp may give a widely different
spherical distribution from another, and in comparing such
lamps the mean spherical candlepower forms the fairest
basis of comparison* Incandescent lamps are made in a
variety of sizes, the most common caiidlepowers being

34 INCANDESCENT LIGHTING §32

4, 8. 10» 16, 20, 32, 50, and 100. The 16-candlepower lamp
is the one most generally used. Small lamps of a, 1, and

2 candlepower are also used for decorative and advertising
purposes.

PROPERTIES OF INCANDE8CEHT DAMPS

31- Temperature- — The temperature at which the fila-
ment of a lamp is worked may be anywhere from IpSOC^ to
1,950^ C. The hotter the filament, the greater is its light-
giving power per watt consumed. Of course, it is desirable
to operate a lamp so that it will give a large amount of light
per watt, provided this can be done without injuring the
lamp. At a temperature of about 1,900°, an ordinary lamp
will give about i candlepower per wattj a 16-candlepower
lamp would at this rate take 48 watts, or 3 watts per candle*
At a temperature of 1|800°, the same lamp might give about
i candlepower per watt and thus require 64 watts for its
operation. Although it is thus advantageous^ as far as
power consumption goes, to work the ]amp at a high
temperature, it is found that if the temperature is pushed
too high, the life of the lamp is greatly shortened. On the
other hand, if the lamp is worked at a very low temperature,
it gives a small amount of light compared with the power
consumed, and although its life may be long, it is not satis-
factory as a light- giving source.

32. EfflfU^iicy, — When the efficiency of an incandescent
lamp or arc lamp is spoken of, the power consnmption per
candlepower is meant. For example, if an incandescent
lamp required 3.5 watts for each mean horizontal candle-
power, its efficiency would be 3.5, or it would be spoken of
as a 3.5-watt lamp. This is not a very satisfactory method
of expressing efficiency, because, according to this, the larger
the power consumption per candlepower, the greater is the
efficiency; while in point of fact just the reverse is the case.
A much better way to give the efficiency would be to express
it as so many candlepower per watt, and in some cases it is
expressed this way. Evidently, the greater the number of

INCANDESCENT LIGHTING

candlepower per watt consumed, the greater is the efficiency*
At present, huwever, efficiency is nearly always expressed as
so many watts per candle. The power consumption per
candlepower varies considerably, H the filament is worked
at a high temperature, 1 candlepower may be obtained for
every 2.75 watts expended, or even less, but such lamps are
apt to have a short life and, in any event, require very
steady voltage regulation. In ordinary work, lamps give
about ,3 candlepower per watt^ i. e*, they require about
3.33 watts per candlepower* This is a fair value for the
power consumption of an ordinary lamp, A lamp may take
as low as 3 or 3.1 watts per candlepower when first installed,
but its light-giving properties fall off after it has been in
operation for a time and the power consumption may run up
as high as 3.8 or even 4 watts per candle. From 3.3 to 3.5
watts per candlepower is therefore a fair average. High-
voltage lamps {220 volt) have a somewhat lower efficiency
ranging from 4 to 4.2 watts per candlepower*

33* Connect Ions for Testtni;^.^^ — When testing lamps ,
a careful record should be kept of the length of time they
have burned, also of the voltage and current. With this
data at hand, together, of course, with the readings of
candlepower as given by the photometer, the efficiency of
the lamp at any time during the test may be at once
determined* Accurate instruments must be used, and their
scales should be so divided that the ammeter or mil-ammeter
may be read to toW ampere and the voltmeter to iV volt.
A variable resistance should also be inserted in series with
the lamp so that the voltage across the lamp terminals may
be kept nearly constant.

34. Fig. 17 shows an arrangement of connections for
lamp testing. Switch 1 short-circuits the current coil of the
wattmeter and switch 2, the ammeter. The adjustable resist-
ance allows the pressure to be maintained at the rated voltage
of the lamp under test. In Fig. 17, a wattmeter is shown in
addition to the ammeter and voltmeter, though it is not
essential because the watts can be easily calculated from the

INCANDEvSCENT LIGHTING

§32

voltage and current readings. A good ammeter and volt-
meter are to be preferred to a wattmeter for this kind of
work, as the results are more likely to be accurate. Direct
current should, if possible, be used for all testing, as alter-
nating-current instruments are more likely to lead to inac-
cm-ate results. Current supplied from a direct-current
dynamo running at constant speed may be used, but it
is more satisfactory to use a storage battery as the source
of supply, as the current from it is perfectly steady.
Readings of candlepoweri current, and voltage should be
taken as nearly simultaneously as possible. When the

AmmwUf:

Pia. 17

standard is an incandescent lamp^ it is advisable to supply
both the standard and the lamp under test from the same
drcuiL Any fluctuations in voltage will then affect both
lamps and their relative candlepower will be almost unaf-
fected. The results will* therefore, be much more accurate
than if the two lamps were run from separate sources
of current •

35 • Iiamp EBtlmates, — ^With an average power con-
sumption of 3*3 watts per candlepower^ a 16-candlepower
lamp will require Ifi X 3*3 = 52,8 watts. The current that
the lamp will require will depend on the voltage at which it

132

INCANDESCENT LIGHTING

fs operated. The current in any case can be obtained by the
following formula:

CPx IV

/ =

(3)

in which CP = candlepower;

W = watts per candlepower;

E = voltage across the lamp tenninals.

ExAMPi^B. — A 32-can die power lamp requires 3.5 watts per candle^
power and is desigued to operate at a pressure o£ 110 volts. What will
be the current taken by the lamp aad what will be Ihe resistance of
the lamp when hot?

Solution.— From formula 3,

current = — ,.;, '' =1.02 ampcresi nearly. Aha,

From Ohm*B law. /

, or J^ = yi hence,

resistance

110
1 02

1€7,8 ohms. Ana.

Note. — The value of the Tesistance of an incandescent lamp obtained
by dividing the E. M. F- by the current gtves the hot resistance.
The resistance of carbon decreases as the temperature in creases » until
a certain point is reached beyond which the resistance remains nearly
constant. Since the temperature is high in an incandescent lamp,
the cold resistance is very much higher than the hot; it may be
almost double the hot resistance. In practical work, we are not, as a
rule, concerned directly with the cold resistance of the lamp$£. and
when the resistance is spoken of, the hot resistance is meant. A
16'Candlepower, HO- volt lamp has a hot resistance in the neighbor-
hood of 220 ohms.

Small incandescent lamps require a larger number of watts
per candlepower than large ones. For example, a 4-candIe-
power lamp requires in the neighborhood of 20 watts;
6-candlepower, 25 watts; 8-candlepower. '32 watts; and
10-candlepower, 37 watts* In general, then, the substitution
of a small lamp for a larger one will result in a saving in
power, but not in direct proportion. For example, if an
8-candle power lamp were substitiUed for a 16 -candlepower.
the power consumption might be reduced from about 52.8
watts to 32 watts>

36. Allowing for toss in the line, it will probably
require about 60 watts at the dynamo terminals for every

44JB— &

38 INCANDESCENT LIGHTING §32

16-candlepower lamp operated. Hence, if the outptit of the
dynamo, in kilowatts, is known, the mimber of IB-candle-
power lamps that it is capable of operating^ may be obtamed:
approximately, by the following formula:

Number of 16-candlepower lamps = —— -~r — ^ (4)

in which If IV h the capacity of the dynamo m kilowatts.

Example. — About how many Ui-camllepgwer lamps should a
12'kilowatt dynamo be capable of operallug^

1 000 X 12
Soi*DnoN,— Number of lamps ^ * \^. — = 200, Aus.

Sometimes the output of the dynamo is given in volts and
amperes instead of in kilowatts. In such cases, the output
in watts is easily obtained by multiplying the volts by the
amperes, and the number of 16-candlepower lamps that
the dynamo can operate may then be obtained by dividing
by 60, as before.

Example.— A dynamo is capable of deUvering ats outpiit of
70 amperes at a pressure of 115 volts^ About how many 16-candle-
power lamps can it rua?

Solution, — The output m watts will be 115 X 70 = 8;050, and since
each lamp requires about 60 watts, the capacity of the machine will

be -^^ =■ 134 lamps. Ans.

Note* — When the capacity of a dynamo is jafiveu as so many lamps,
J6-candlepower lamps are always^ nieant. If '^i-candlcpowerlampsare
operated, each 32«cancllepower Lamp should be counted as the equiv-
alent of two of 16 caudle power.

37. The number of indicated horsepower required at the
steam engine to operate a given number of lamps will
depend on the amount of power lost in the dynamo and
engine* The approximate rule given above supposes that
60 watts are required at the terminals of the dynamo for
each lamp operated* There will be some loss in the dynamo
and in the engine, so that the indicated power at the cylin-
der of the engine must be more than 60 watts per lamp.
Just what this indicated power must be will depend on the
combined efficiency of the engine and dynamo, and this will*

INCANDESCENT LIGHTING

in turn, depend on the size and type of engine and dynamo.

Generally speaking^, ten 16-candlepower lamps can be
operated per indicated horsepower; this number is exceeded
somewhat with lar^e engines and dynamos, but, on the other
hand, with poor apparatus the lamps per indicated horse*
power may fall below the number given.

Example. — An isolated plant is to be tDstalled for operating 350
16-catidk power lamps: (a) What ishowld be the indicated horsepower
of the eogioe^ {6} What should be the approximate capacHy of the
dynamo In kilowatts?

SOLUTIOH,— (a) Allowing 10 lamps per indicated horsepower, th«

350
horsepower of the engine would have to be -.„- =35,

(b) Allowing 60 watts at the dynamo terminals per lamp» theotit-
put in watts would be 350 X 60 = 21,000, or 21 kilowatts. Ans.

38, Life, — The length of time that an incandescent
lamp will bum before g^iving out is very uncertain and
depends on a number of different things. Sometimes there
may be defects in the manufacture that will cause a lamp to
bum out in a very short time, though systematic testing at
the factory has resulted greatly in the reduction of the
number of such lattips that reach the consumer. Lamps are
often run at a higher voltage than they should be, and
although this makes them give a good light for the time
being, it shortens their life greatly. Raising the pressure
1 or 2 volts above the proper amount on a 110- volt lamp may
shorten its life as much as 15 to 25 per cent. On the other
hand, it does not pay the central station to run the voltage
low, because, although the lamps may last longer, they will
not ^ive a good light and will give rise to dissatisfaction on
the part of the customers. It is always best to run the
lamps as nearly as possible at the voltage for which they
are designed, and to run the plant so that the regulation will
be good, i.e., so that the voltage at the lamps will be nearly
constant, no matter how the number of lamps in use may
vary. It has been found, experimentally, that the life of a
lamp varies approximately as the fifth power of the efficiency
expressed in watts per candle* ThuSj if Lt is the life when

INCANDESCENT LIGHTING

§32

burned at an efBciency of W, and L, the life when burned at
ao efficiency of IV„

i. =

(5)

Example.— If a lamp has a life of 800 hours when burned At a
oormal efficiency of 3 J watts per candle, what will its Jile be when
burned at an efficiency of 3.4 watts per candle?

Solution.— U^t = 3.1; W^. ^ 3.4; Zi = 800; he nee » from formula 5^
800 X 3.4*

Z. =

3.r

1 ,270 hr . f approxi m ately . Aos .

The sligfht increase in the watts per candle (from 3.1
to 3.4) means that the filament is worked at a lower tem-
perature and there is consequently a large increase in the
life of the lainp^ though the light is not obtained as econom-
ically so far as the cost of power is concerned,

39* Assuming: that the voltage is kept constant, a lamp
will gradually fall off ift brilliancy after it has been burned
for some time, and after a certain point is reached it
becomes so uneconomical that it pays better to replace it by
a new one rather than attempt to run it until it burns out*
The length of time during which it pays to burn a lamp is
difficult to decide. Lamps will frequently burn over 2,000
hours before they give out, but after they have burned from
500 to 700 hours their candlepower has fallen off to such an
extent that it will probably pay to replace them. Many
large central stations make it a rule to replace lamps when
they have fallen off to SO per cent, of their original candle-
power. For example, a 16-candlepower lamp would be
discarded when it had fallen off to 12.8 candlepower.

40. The falling off in candlepower is generally attrib-
uted to a disintegration of the carbon. The filament grad-
ually increases in resistance on account of small particles of
carbon being thrown off; this increase in resistance results
in a decrease in current and* consequently, in a decrease
in candlepower. Moreover, the small particles of carbon

§32

INCANDESCENT LIGHTING

are deposited on the inside of the globe* thus producing
the well-known blackening effect and further reducing
the illuminating power of the lamp. Lamps have beeo
very much improved of late years as regards this falling
off in candlepowen The two curves, Fig, 18, given by
Mr* F, W. Willcox,"^ illustrate the improvement in this
respect, the upper curve being for a modem lamp and the
lower for an old-style lamp. Both lamps start out with the
same candlepower, and the lines show the percentage of

'^^

■^fc,

,^^

iOO

JOQ

PlQ, IS

^oa

fX^

the initial candlepower after the lamps have been burning for
di^rent intervals of time. There is a steady decline in the
candlepower of the old lamp from the time it starts burning;
and at the end of 500 hours it is only giving 70 per cent, of
the light it gave at the start. The candlepower of the other
lamp, on the contrary, increases slightly during the first
25 hours, and at the end of 75 hours has returned to its
original candlepower. It then falls off in candlepower, but

*Jouriml of Franklin Institute, VoL CXLVIIL

32 INCANDESCENT LIGHTING §32

at the end of 500 hours is still giving about 77 per cent, of
the original amount.

41. Voltages. — ^The voltage of an incandescent lamp is
the pressure that must be maintained between its terminals
in order that the resultant current shall cause the lamp to
give its rated candlepower. By far the greater number of
incandescent lamps in use are designed for voltages any-
where between*the limits of 100 and 125 volts. For example,
100, 104^ 110 are common values* When alternating current
was first introduced, it admitted the use of low voltages at
the lamps, because the current could be transmitted at high
pressure and then transformed to low pressure* At that
time, it was more diflScult to make durable and efficient
lamps for 100 or 110 volts than for lower voltages, and a
pressure of 50 or 52 volts for the lamps became common.
This pressure is no longer used on new installations, because
there is now no difficulty in making lamps for the higher volt-
ages, A pressure of 80 volts has been customary for marine
work, but in modern installations 110 to 125 volts is used*
Of late yearSi it has become possible to make lamps for
220 to 250 volts » and a nmnber of plants using lamps of this
voltage are in successful operation.

In connection with lamp voltages, it may be interesting
to note that in the process of manufacture it is impossible to
make all the lamps come out at the voltage aimed at. For
example, if a lot of 110- volt lamps were to be made up, a
great many of them would come out at 108, 109, 111, or
thereabouts. It is often a good plan, therefore, for a station
to operate at an odd voltage of, say, 107 or 111 rather than
at 110, as the chances are that if lamps are ordered for the
odd voltages they will be obtained, whereas, if ordered for
the even 110 volts, it is probable that 108-volt or 109- volt
lamps marked 110 will be supplied, because it would be
practically impossible to supply all the lamps of exactly
110 volts without especially selecting them.

42- General HeniarkB. — Incandescent lamps are made
for a wide range of voltage and candlepower. The power

i32

INCANDESCEHT LIGHTING

coiasumption per candlepower also varies through wide limits.
High-efficiency lamps, in general, will have a short life unless
the voltage regulation is very good; hence, hieh-efficiency
lamps should not be used in places where the regulation is
poor. In order to determine the current that any lamp will
take, its power consumption per candle must be known and
the current may then be calculated. When making wiring
estimates, or in any case where the approximate current
only is needed, the following values of the current required
per lamp may be used;

TABIiE I

Candle-
power

Voltage

Curretit
Amperes

Candle-
power

Voltage

Current
Amperes

110

•36

1.00

.50

2.00

J, 00

220

.30

.75

43. Heating. — A IB-candlepowerj 64'watt incandescent
lamp gives off about 220 British thermal units of heat per
hour. A British thermal unit is equivalent to the amount of
heat that is required to raise 1 pound of water from 62"^ F.
to 63^ F\ Incandescent lamps give off from 5 to 10 per cent.
of the amount of heat emitted by ordinary bat- wing: gas
burners of corresponding candlepower*

44, Ilium I nation by Iiicfindegceiit IDatnps, — In
wiring for incandescent lamps, it is necessary to locate the
lights so that the best illnniiuation will be obtained* In
factory lighting, the lamps are so placed that they will
be as near as possible to the workmen, whether at the
machine or vise.

For the interior of stores, general illumination is required.
Show windows should be lighted by reflected light onIy»
because exposed light striking the eye will cause the effect
of the general arrangement to be lost to the observer. In

mCANDESCENT LIGHTING

picture galleries, this same idea should be carried out. House
lighting is more for effect than general illumination.

In theater lighting, where the scenic effects depend entirely
on a careful adjustment of light intensities, experience is the
only guide.

Among other points to be observed in placing lights is
the color of the surrounding walls. Dull walls will reflect
only about 20 per cent, of the light thrown on them, while
a clean, white surface will reflect 80 per cent. The height
of the room also reduces the effectiveness of a given light
intensity.

The unit used for expressing the degree of illumination
produced by any source of light is the foot-candle^ or the
degree of illumination produced by 1 standard candle at a
distance of I foot from the object to be illuminated. An
illumination of 1 foot-candle is a good light to read by and
the illuminations met with in practice usually vary from
i to 2 or 3 foot-candles* Since the illumination decreases
as the square of the distance, a 16*candlepower lamp at a
distance of 1 foot from an object would produce an illumina-
tion of 16 foot-candles, at a distance of 2 feet the illumi-
nation would be 4 foot-candles, and at a distance of 4 feet,
it would be 1 foot-candle; or, i( B — candlepower of source
and D = distance in feet from object, then

illumination {foot-candles) =

(6)

The illuminating value of different lights is about as
follows;

TABIiE II

Light

Foot -Candles

Ordinary moonlight ,
Street lighted by gas
Stage of theater . .
Diffused daylight

.02S

.030

2.9 to 3,8

10.0 to 40.0

§32

INCANDESCENT LIGHTING

A clear Idea of these various intensities is easily gained
by comparison, remembering that 1 foot-candle furnishes a
good light to read by. On account of the great inflLience of
the color of walls, height of ceilings, etc., it is impossible to
give other than very approximate figures for the amount of
light required for illuminating a given room* For rooms
requiring ordinary illumination and having ceilings about
10 feet high, about .25 to .29 candlepower per square foot
should be sufficient* For rooms with hii^h ceilings Af^ to .5
candlepower per square foot should be allowed, and for very
brilliant lighting in ball rooms or similar places, the allow-
ance may be as high as 1 candlepower per square foot. Of
course, these figures are for cases where the whole room is
to be generally illuminated; when the light is used locally,
as at desks or reading tables, it may not be necessary to
have the room generally illuminated, and the allowance per
square foot might be much less than that indicated by the
above figtires,

BXAMP1.E9 FOR PBACTICE

1» Allowing for loss in the Unes, about how many 16-candIepower
lamps can a 31)0 kilowatt dynamo operate? Ans, 5/100 lamps

2, What will be the illnmination, In foot-candles^ produced by a
82- candlepower lamp placed 9 feet from the object illuminated?

Ans. ,395 foot-candle

3, How much current* approximately, would be required for the
operation of 300 22Q-%^olt lamps? Ans. 90 amperes

4, In testing" a lamp on a photometer bar having; 1,000 divisions, a
balance was obtained with the screen 300 divisions from the standard.
If the standard were 16 candlepower. what was the candlepower of the
lamp under test? Ans. S7 J candlepower

RECENT TYPES OF IKCANDESCEBTr liAMP

45. Within the last few years much experimenting has
been done in order to produce an incandescent lamp more
efficient than the ordinary lamp employ in if a carbon filament.
The investigation hat* been mainly along two lines; namely*
to produce a successful lamp employing material other than
carbon for the light-giving filament, and to produce a lamp

hfti

INCANDESCENT LIGHTING

§32

in which a gas or vapor is brought to a high state of incan-
descence. The Ncrnst lamp represents a successful type in
which the glower or lighl*giving portion is not of carbon.
So far, lighting by vacuum tubes or by means of incandes-
cent gas has not been used to any great extent, though much
experimenttng has been done* and it is possible that some
such system may ultimately prove practicable.

46, Bfflcleney of Llglit-GlTliifr SonrceSp — Any

source of light may be considered as giving out two kinds of
radiation^ — luminous radiations and obscure radiations. The
energy that is expended in the luminous source sets up
vibrations in the ether^ and those vibrations that have a
wave length lying between .000360 millimeter and .000810
millimeter are capable of affecting the eye and producing the
sensation known as light. All vibrations lying above or
below these limits are usless as far as producing light is con-
cerned. For example, all heat radiations (of long wave
length) represent so much waste energy. If we call A the
total radiation from a light-giving source, B the amount of
luminous radiation, and C the non-luminous or obscure radi-

ationi then, A - B -\- C, and the ratio — is the optical effi-

ciency of the light*giving source, because It is the ratio of

the radiation that is useful in producing light, to the total

radiation. The efficiency of ordinary light-giving sources

as measured by thrs standard is very low. For example,

the optical efficiency of an oil lamp is not more than 3 per

cent.; that of an ordinary gas burner about 4 per cent.j and

that of an incandescent lamp 5 to 6 per cent,, depending on

the temperature at which the filament is worked. The arc

lamp has a considerably higher efficiency; it may run as high

as 18 per cent, or more when measured in the direction in

which the lamp throws its maximum illumination, but the

average efficiency is not more than 10 per cent.

There is room for a great deal of improvement In the

efficiency of our light-givtng sources, and efforts to effect

such improvement have been along the lines mentioned

§32

INCANDESCENT LIGHTING

above. Contradictory as the statement may seem, it is
nevertheless true that some of the most efficient lamps are
those in which the highest temperatures are attained. In
order to get an efficient lamp, the g:reatest possible amount
of light must be produced with the smallest possible accom-
paniment of heat. In lamps operated at a high temperature,
the proportion oi light lo heat» and hence the efficiency, is
greater than in lamps where the temperature is lower, and
the effort has therefore been to produce incandescent lamps
in which the glowing material could be maintained at a
higher temperature than is possible with a carbon*fiIament
lamp. The temperature of the carbon points of an arc lamp
is over twice that of the filament of an ordinary incandescent
lamp, and the arc lamp is over twice as efficient. An incan-
descent lamp worked at high voltage gives more candlepower
per watt than when worked at normal voltage, but the fila-
ment soon burns out because it is unable to stand the high
temperature. Some of the lamps that have been brought
out and in which a higher temperature is attained than in the
carbon-filament lamp will be considered briefly.

THE NERNST LAMP

4T, Operation,— The Neriipit lamp has now been in

commercial use for some time* and has shown that it can be
depended on as a reliable and efficient source of light. The
light-giving portion or glower in this lamp consists of a
small stick or rod made of the rare oxides, such as oxides
of thorium T zirconium, yttrium, etc. This glower is a non-
conductor when cold, but when heated to a temperature of
about 700*^ C, it conducts current and is soon brought up
to a very high temperature by the passage of the current.
In order to start the lamp, therefore, some means must be
provided for 'heating the glower up to the conducting tem-
perature. This heating is necessary only during the inter-
val of starting, and after the current has been started the
beating device is cut out of service.

In order to make the operation of the lamp stabtei it is

INCANDESCENT LIGHTING

necessary to insert a resistance in series with the glower.
If the current increases by a slight amount, there is a con-
siderable reduction in the glower resistance t and this in turn
would allow a further increase in current, which would soon
lead to fusing or softening of the glower if the resistance in
series were not used to prevent it. The resistance is so
constructed that any slight increase in current causes a lar^e
increase in the temperature of the resistance wire, thus
increasing the value of the resistance. The result is that

the rise in current due to the
lowering of the resistance of the
glower is checked* and the lamp
rendered stable in its action.
The voltage of the circuit
should not vary more than
5 per cent, from normal and the
glower should be selected with
reference to the actual voltage
on which it is used. Nernst
lampSp or in fact any other incan-
descent lamp, will not give good
service on systems where the
voltage regulation is poor.

48* Description. — The
Nemst lamp, as at present con-
structed, consists of the following
essential parts: (1) the glower;
(2) the resistance J or ballast, as
it is termed by the manufac-
turers; (3) the heating device for starting the lamp; (4) the
cut-out device for cutting the heating coils out of circuit
after the lamp has been started. The lamps, as con-
structed by the Nernst Lamp Company, are made in a large
variety of sizes and styles* Some are intended for outdoor,
and others for indoor, use, but the difference between the
outdoor and indoor types lies principally in the style of
casing used to protect the parts » They are also made for a

Pio, w

§32

INCANDESCENT LIGHTING

wide range in candlepower, A 50-cati die power glower is
used as a unit, and lamps of larger candlepower are made
by increasing the number of glowers instead of using a
single glower of larger dimensions. The lamps are made
with one, two, three, four, or six glowers, giving candle-
powers of approximately 60, 110, 175, 250, and 400, and are
operated on alternating-
current circuits using
100 to 120 volts or 200
to 240 volts, A 110^
volt glower takes, ap-
proximately, .8 ampere,
while a 220-volt glower
takes ,4 ampere. Only
the smaller lamps are
made to operate on 100
to 120 volts, as more
satisfactory service is
obtained from the 220-
volt lamps.

Figs* 19 and 20 show
the general construc-
tion of a 220-volt, two-
glower lamp. As shown
in Fig. 19, the enclosing
globe surrounds the
glowers and protects
them from air*currents.
The glowers are made
of oxides, so that it is
not necessary to mount
them in a vacuum like the filament of an ordinary incandes-
cent lamp. In Fig. 20, one of the glowers is shown at a.
The heater tubes are immediately above the glowers, and
both glowers and heaters are supported in a porcelain
holder d, which can be readily detached from the main
part of the lamp whenever it is necessary to replace
glowers or heaters. The auxiliary parts of the lamp are

Piii. 20

INCANDESCENT LIGHTING

§!

Fjg. 21

protected by the removable casing* One of the armatures of
the cut-out is shown at B\ G and F are the lamp terminals.

49< The Glowers. — Fig, 21 shows a pair of glowers
and heater tubes* When mounted in the lamp the glowers
a, a are from i^tj to ti\ inch below the heater tubes d, d, and
about itV inch apart from center to center. The size of the
glowers and heaters, as shown in Fig, 21, is about the same
as used on the standard 220- volt lamp. The glower is about
>025 inch in diameter and li inches long. It is provided
with platinum terminal wires c, c attached to copper wires

that terminate in small,
tapered aluminum plugs
that allow connections
to be made or broken
easily* The platinum
terminals are attached
to small beads of plat-
inum embedded in each
end of the glower. By making the connection in this man-
ner, any shrinkage of the glower causes the connection
to become tighter and therefore does not impair the con-
tact. The life of a glower will average from 600 to 800
hours, provided the voltage regulation is such that the
increase in voltage above normal does not exceed 5 per cent.
In placing glowers in the holders, care must be taken to
allow a small amount of end play; otherwise, the expansion
and contraction may result in breakage*

50, Heatei- Tubes and Hoiaer. — Fig. 22 shows the
glower and heater tubes mounted in their porcelain holder,
The holder, together with the base on which it is moimtcd,
can be pulled away from the main part of the lamp* The
heater coil consists of a porcelain tube with fine platinum
wire wound on its surface and covered with a protecting
paste that serves to shield the wire from the intense heat of
the glower and also furnish a white surface that will reflect
the light downwards. The heater tubes ^, Fig. 22, are held
in the porcelain holder d, which is attached to the porcelain

§32

INCANDESCENT LIGHTING

base (f that holds brass pieces / to which the glowers are
connected by means of the aluminum plut^s. The terminals
of the heater tubes connect to the promts h^ f/ hy way of
the brass piece ^, which also serves as a support for the
holder d^ being attached thereto by the cotter pin a.
Prongs /, m, and n form the terminals of the glowers, at^d
when the holder is pushed up into place the prongs make
connection with contacts in the upper part of the lamp* The
parts of the holder d that face the glowers are painted with
a white paste. After the
lamp has been in oper^
ation for some time, black
oxide of platinum from
the glower terminals de-
posits on the holder, thus
blackening the surface
and interfering with the
reflection of the light.
By cleaning up the old
paste occasionally and
giving the holder a new
coat, a good reflecting
surface is maintained.
The heater coils last
about 200 hours when
used continuously, but as
they are used only for 20
to 30 seconds each time
the lamp is started, the life of a heater corresponds to a
very large number of lamp hours.

51. The steadying resistance, or ballast, Is made of
pure iron wire mounted in an inert gas such as nitrogen,
In Fig* 20, the ballasts for each glower are shown at A^A^
the fine iron wire being mounted in sealed glass ttibes. The
temperature of a wire so mounted responds quickly to
changes in current, and iron wire increases in resistance
very rapidly with increase in temperature. An increase of

¥m,n

INCANDESCENT LIGHTING

§32

10 per cent, in the current passing through one of these
ballasts will cause as much as 150 per cent* increase in

resistance. A small amount of resistance is therefore suf*
ficient to insure stable operation, and the efficiency of the
lamp as a whole is higher than if an ordinary resistance were
used. By mounting the wire as describedp all danger from

jj t^

FiQ.M

oxidation is removed, and the ballasts will last a long
time, provided the voltage regulation is good.

52, The ent-out consists of an electromagnet connected
in series with the glowers and arranged so that when current
passes through them it will attract two armatures (one of
which is shown at Bt Fig. 20) and open the circuit through

§32 INCANDESCENT LIGHTING 43

the heater coils. Each armature is suspended from its upper
end, and when the coil is energized, the armatures swing in
and open the circuit through the heater coils. There are two
armatures and sets of contacts in this lamp, so that the
heater circuit is opened in two places. The armatures are
suspended loosely from a single point of support to avoid
humming caused by the alternating current in the coil. So
far, Nernst lamps have been used mostly on alternating
current, because direct current appears to decompose the
glower and make it short lived. However, considerable
advance has been made in the production of glowers for
direct current, and doubtless such lamps will soon be avail-
able. The wire of the cut-out coil is bedded in cement
because it must stand a temperature of about 110° C. It must

Ctt-miCtif
Pig. 21

be remembered that the glower is worked at a high tempera-
ture, so that the working parts of the lamp are necessarily
subjected to considerable heat.

53. Connections. — Fig. 23 shows the connections of a
two-glower lamp, and Fig. 24 shows the same connections in
a simplified form in order to bring out the heater and glower
circuits more distinctly. The glowers a, a are connected in
parallel, and in series with each is a ballast A, B is the cut-
out coil, which operates the armatures C, C and draws the
contacts away from the contact pins Z>, Z>, thus opening
the heater circuit in two places. When the lamp is not in
use, coil B is not energized and C and D are in contact.
When, therefore, current is turned on, it takes the path
through the heaters b^ b, and the glowers a, a are heated

U INCANDESCENT LIGHTING §32

until they are able to conduct current; this usually talces
from 20 to 30 seconds* As soon as current passes tlirough
the glowers, coil B is energised and the circuit through the
heaters is broken at /?, D. Nernst lamps are installed in
practically the same manner as incandescent lamps; that is,
they are operated in parallel on constant-potential circuits.
Ballasts and glowers must be selected with reference to the
actual average voltage of the circuit; failure to do this will
result in numerous burn-outs. The lamps must be hung in
a vertical position; otherwise, the cut«out will fail to operate*
The smaller sizes of lamp are made to screw into a socket like
an ordinary incandescent lamp, but the larger sizes are con-
structed as shown in Figs. 19 and 20, and are suspended and
connected up in much the same way as arc lamps. A recent
lamp, designed to compete with the ordinary 16-candlepower
incandescent lamp, gives 25 candlepower. It consists of
the same essential parts as the lamps just described, but the
arrangement of glower and heating coil is different. The
latter is made in the shape of a comparatively large open
spiral and surrounds the glower, which is placed inside the
spiral* The glow^er and heating coi! are mounted together
as a unit, and when a glower burns out, both are renewed.
This type of holder was designed to simplify the mainte-
nance of the lamp and is intended more especially for use in
isolated localities.

54i Efficiency. — The chief advantages of the Nernst
lamp are its high efficiency, the natural color of the light, use-
ful downward distribution, steadiness, and high power factor.
The lamp takes approKimalely half the power expenditure
per candlepower required by the ordinary incandescent lamp.
The power required in the Nernst lamp is from 1,76 to
2 watts per mean hemispherical candlepower. The high effi*
ciency of the Nernst lamp is due to the fact that the glower
is worked at a high temperature, and also to the fact that the
substances of which the glower is composed possess the prop-
erties of selective radiation to a high degree, i. e., they emit
a large number of radiations that are capable of producing

§32 INCANDESCENT LIGHTING 45

the sensation of light. The color of the light approximates
closely to that of daylight, and hence is desirable for
store or art-gallery illumination, where the correct determi-
nation of color is of importance. As an offset to these
advantages, the Nernst lamp, in comparison with the incan-
descent, is somewhat complicated, and high in first cost,
though it must be remembered that the parts to be renewed
can be replaced at slight cost after the lamp is once pur-
chased, because allowance is made for the scrap platinum in
the burned-out parts. The slowness of starting is also a
disadvantage for some kinds of illumination, particularly
in theaters, or in any other place where it is desired
to switch lamps on and off frequently.

CRAWFORn-VOELKJER UkMP

55. The Crawford- Voelker lamp is another type in
which the light-giving filament is not composed of carbon.
This lamp, in its general construction, is similar to the
ordinary incandescent lamp. The filament is mounted in an
exhausted globe and no special provision need be made for
starting, because the filament is a conductor when cold.
The filament is made of carbide of titanium, formed by
combining carbon and oxide of titanium in the electric
furnace. This substance makes a tough, durable filament
that will stand a much higher temperature than the ordinary
carbon filament. So far, the lamp has not been used com-
mercially to any extent, but tests on it appear to indicate
that it has a considerably better efficiency than the ordinary
lamp. Tests have shown an efficiency of 2.53 watts per
candlepower at the start, 2.84 watts at the end of 500 hours,
and 3.35 watts at the end of 1,000 hours. Still later tests
have shown power consumptions ranging from 1.68 to
2.16 watts per candlepower. It is also claimed that this
filament does not produce blackening of the bulb found in
lamps using a carbon filament.

46 INCANDBSCBNT LIGHTING

OUaUM LAMP

56. Another type of incandescent lamp that shows a
, higher efficiency than the carbon-filament lamp is that in
which the filament is made of the rare metal osmium.
This lamp has not yet been nsed commercially, but tests
made on it show that it takes but little over half the power
for the same amount of light as the carbon-filament lamp.
Osxnium lamps maintain their candlepower well and have a
longer life than the carbon-filament lamp. The high price
of osmium prevents the commercial use of the lamp, and
another drawback is that, owing to the comparatively low
resistance of the metal, it is difficult to make lamps for
operation on the usual pressures of 110 or 220 volts.

INCANDESCENT LIGHTING

(PART 2)

STSTEMS OF DISTRIBUTION

1, In considering the different systems commonly used
for supplying: electrical energy to the lampSp the local dis-
tribution by means of the wiring In buildings will not be
described, as itiat part of the subject belongs properly to
interior wiring. Current for electric li^htin^ is distributed
from the station to the point of utilization in the same
manner as for power transmission; in fact, in the majority of
cases the electric energy transmitted is used both for light-
ing and power purposes. The following brief descriptions of
the more important distributing systems are intended to
point out how the methods already described are applied
to electric-lighting work.

In most cases, the current required for the operation of
incandescent lamps is distributed at a constant potential; i, e.,
the aim is to keep the pressure at the station such that the
pressure at the lamps will remain constant, no matter what
the load may be. If the pressure at the lamps is not main-
tained uniform within narrow limits, the service will be poor,
the life of the lamps shorty and the complaints from cus-
tomers numerous. Where the lamps are run on a constant-
potential system, the current transmitted over the lines
increases with the load, because every light turned on means
just so much more current to be supplied. The consequence
is that the drop in the line increases with the load, and in
order that the pressure at the lamps shall be maintained
constant instead of falling off on account of this drop, the
pressure at the dynamo or station must be raised slightly.

Fur noiwt ott^yrighit see pa^e wmmediaieiy foitowinz the tiiie pOft

INCANDESCENT LIGHTING

In any events no matter what means may be adopted for

distributing the current, the aim should be to provide the
lamps with a uniform pressure and to see that this pressure
is kept unifonn>no mailer how the number of lamps operated
may vary. The distribution should also be designed to accom-
plish this object with the least possible expense; u e,, the dis-
tributing lines should be laid out so as to secure the desired
results with the smallest possible amount of copper and
loss of energy.

METHODS OF CONNECTING IiAMPB

2* Ijami>8 In ParalleK — In the great majority of cases
incandescent lamps are connected in xiaral-
lel, as shown in Fig. 1. In this case, the pres-
sure between the two lines must be kept at a
constant value, otherwise the current flowing
through the lamps will vary. Since the resist-
ance of a lamp cannot change » unless the
temperature of the filament changes, the cur-
rent that will flow through any lamp depends
on but two things — the pressure between the
lines and the resistance of the lamp. The
current in each lamp is equal to the pressure
between the mains divided by the resistance
of the lamp. So long as the pressure is kept
constant, the turning off or on of any lamp
does not affect the others, but the current in
the mains will increase when lamps are turned
on and decrease when they are turned off.
Incandescent lamps are connected in this way,
because the arrangement is extremely simple;
each lamp is independent of the other s^ and
the pressure between the lines is low-

3. I^arnps lu Series. — Lamps are occa-
sionally connected in series, as shown in
Fig. 2. This arrangement is used principally
for street lighting; it is seldom used for interior work.

Pio. 1

§33 INCANDESCENT LIGHTING 3

In this case, the same current flows through all the lamps;
hence, their filaments must be of the same current-carrying
capacity. If it is desired to have some lamps of higher
candlepower than others, their filaments must be made
longer. The pressure across the terminals of any lamp
can be found by multiplying the resistance of the lamp
by the ciurent flowing. Also, since the lamps are con-
nected in series, the total pressure required to force the
current through the circuit will be the sum of the pressures
required for the separate lamps. For example, suppose that
there are ten lamps, each requiring a pressure of 20 volts
and a current of 3i amperes; also, five lamps, each requir-
ing a current of 3i amperes and a pressure of 40 volts. The
total pressure required for the circuit, neglecting the loss in

r^^ (?*L

Pio.2

the line, will be 20 X 10 + 5 X 40 = 400 volts. In this sys-
tem, the line current is small; hence, it is well adapted
for street incandescent lighting, where the area to be
covered is large. It should be noted that the current must
be maintained at the value for which the lamps are designed.
This means that the pressure between the ends of the line
must be raised as more lamps are added to the circuit,
because the resistance is increased. Also, the pressure
must be lowered when lamps are cut out, otherwise the cur-
rent will increase and bum out the remaining lamps. In the
series system, the current is constant and the pressure varies;
in the parallel system, the pressure is constant and the cur-
rent varies as the number of lamps in use is increased or
decreased. Another point to be noted is that means must be
provided for maintaining the circuit around the lamps, in

INCANDESCENT LIGHTING

§M

case they should burn out; otherwise* the break in^f of one
lamp will put out all the lights on the circuit. The method
by which this is accomplished will he described when this
system is taken up in detail* It will also be noted that if
the number of lamps operated is large, the pressure applied
to the circuit must be correspondingly high; this introduces
an element of danger and is one reason why series lighting
is not used for interior work. Lamps in series may be cut out

Fto. s

Fm. 4

of circuit by short-circuiting: them* as indicated by switch .S,
Fig. 2; whereas, in the parallel system they must be cut out
by opening the circuit through the lamp by means of a
switch in series with it. This switch may be a separate
device a^ Fig. 1, or it may be in the lamp socket and worked
by a key ^-

4# liainps in Multiple Series.— This method » some-
times called parallel series^ is a combination of the two

133

rNCANDESCENT LIGHTING

preceding and is used in a number of special cases. Perhaps
its widest use is in connection with the lighting of electric
street cars^ but it is also used In mine lighting work, where
lights are operated from the haulage system.

Suppose, for exam pie » that lamps are to be operated on
mains between which a constant pressure of 500 volts is main-
tained» as on a street raihvay. Lamps cannot be obtained
for 600 volts and a single 100* volt lamp will be burned out
instantly if it is connected across the
mains, but five 100-volt lamps may be
connected in series, as in Fig. 3, With
this arrangement, the curretit through
the series of five lamps will be about
i ampere and the pressure across each
lamp 100 volts. Any number of such
series of five lamps may be connected
across the mains. If one light goes out,
it puts out the other four in the same
circuit with it, but, if any lamp is cut out,
by short-circuiting it, the voltage on the
other four lamps becomes higher than they
can Stand, because the pressure between
the mains is constant, and cutting out the
drop through one lamp simply throws that
tnuch more pressure on the others.

Fig. 4 shows a multiple-series arrange-
ment with two lamps in series — a scheme
of connection that is sometimes used for
operating lamps on 220-volt power circuits, for example, in
mine-haulage plants. By adding the middle, or neutral, wire
to Fig, 4, the three-wire system, Fig. 5, so extensively
used for distribution in large cities, is obtained. The mul-
tiple-series system, as in Fig* 4, is not used for general
interior lighting work. It is used, however, for decorative
lighting where a number of lamps of low candlepower are
connected in series across the low-potential mains.

INCANDESCENT LIGHTING

§33

DIRECT-CURRENT, CONST AKT-FOTEI»?TLAX

SYSTEM

5. Simple Two- Wire Sy!?*tem. — This method of dis-
trfbution is very largely used fur small, isolated plants, or
any installation where the power is transmitted a short
distance only. The lamps are usually operated at 110 or
220 volts and the current is supplied by compound-wound
dynamos. Fig, 5 shows a single dynamo Cooperating lamps
on the simple two-wlr© systeni. Two main wires A, A
run from the dynamo (the various switches and measuring
instruments being here omitted for the sake of clearness)

.jjm: ..

O- C

and the lamps are either connected directly across this pair
of mains or are connected across branch mains, as shown at
B, B and C C. This arrangement answers very well for
small plants, where only a small number of lamps are oper-
ated and where they are not scattered very widely.

6. Feeders and Malus« — If the lamps are scattered over
a considerable area^ it is best to run out feeders A^B^
Fig; 7, to what are known as centers of distribution, as
at C and A and at these points attach mains E,F to the
feeders. The centers of distribution should be selected so
as to lie near the points where the bulk of the light is used.
No lights are attached to the feedersj they simply convey

tNCANDfeSCElSfT LIGHTING

current from the station to the center of distribution, which
becomes, as it were, a kind of substation. By this method,
a considerable drop can be allowed in the feeders without
causing^ any trouble at the lights. For example, suppose
that 110-volt lamps are to be operated and that a drop of
15 volts is allowable between the dynamo and the last lamp
on the line. The feeders might be calculated for, say, a drop
of 13 volts. This large drop will allow comparatively small
feeders to be used and will not be injurious to the lamps.

?WTO

//JtV.

Fio. 7

because the pressure at the point C will be maintained at 112
volts, and the variation in pressure along the lamp mains
will be but 2 volts.

7. The arrangement just described is known as the
feedor-ancl-mnln system; its advantages may be summed
up briefly as follows:

1. It allows the use of a large drop in the feeders carry-
ing the current to the point where it is distributed, thus
permitting the use of comparatively small conductors and
thereby cutting down the expense.

2. It allows this large drop without introducing large
variations in the voltage obtained at the lamps.

INCANDESCENT LIGHTING

133

3. It allows the district lighted to be divided into sec*
ttons, each supplied by its own feeder, and thus admits of
each section being controlled independently from the station.

8. Three- wire 8yfitein,^The simple two-wire system,
even if operated on the feeder-and-tnain plan, requires alto-
gether too much copper to admit of very extended use.
For moderate distances, the three-wire system. Fig. 8,
is 'used. A large amount of lighting is carried out on this
plan in New York, Philadelphia, and other large cities. It
is not confined to direct current alone, but is also largely
used with alternating current.

The two dynamos A and B are connected in series and
supply current through the feeders i, 2, 3, etc. to the differ-
ent centers of distribution, where the mains «, b, c are
attached. This arrangement effects a considerable saving
in copper over the two- wire system; the pressure com-
monly used is 110 volts on each side of the circuit, or
220 volts between the outside wires» In some recent plantSt
220-voU lamps are used, thus requiring 440 volts between the
outside wires,

9. Si>eclal Tliree*WIre Systems. — The ordinary three-
wire system has the disadvantage of requiring two dynamos.
If the load were absolutely balanced, one 220- volt dynamo
would be sufficient, but in most cases an accurate balance

INCANDESCENT LIGHTING

cannot be obtained. A number of systems have been
devised whereby a large 220-volt dynamo can be operated
on the two outside wires and the unequal distribution of
the load taken up by a balancing: arrangement of small
capacity compared with that of the dynamo*

10- Fig, 9 shows a system where the nnbalanctng in the

load is taken care of by means of a storage battery, which
is connected as shown. The middle point of the battery is
connected to the line and the 220-volt dynamo is connected
to the outside wires; if a larger current is needed on one
side of the battery than on the other, the extra current is

supplied from the battery. It is not, however, generally
advisable to use a battery for maintaining the balance con-
tinuously, because the cells become unevenly discharged.
When batteries are used on three- wire systems, they are
usually connected across the outside lines and a switch pro-
vided to connect their middle point with the neutral, so that
they can be used for balancing in case of necessity,

11. Fig* 10 shows a three-wire system fed by a 220-volt

dynamo ^^ in conjunction with a motor-dynamo aaK This
motor-dynamo is sometimes called a balanelug' set or

Fro. 10

balancer t The armatures a, a* are mounted on the same
shaft and connected in series* the ni id-point n being connected
to the neutral wire* The fields of the two machines are

INCANDESCENT LIGHTING

§33

connected across the mains, as shown at ff. When one side
of the system is more heavily loaded than the other, the
machine on the heavily loaded side runs as a dynaino and
helps to supply current to that side^ while the machine on
the lightly loaded side absorbs power and runs as a motor,
thus equalizing the load. Take, for example, the special case
shown in Fig. 10, where there are twelve lamps on one side
and six on the other, or" eighteen lamps, in all, supplied from
the 220-volt machine A. Allowing 55 watts per lamp, this

gives 55 X 18 watts and^ hence, -^^^r- ~ 4i amperes. The

current flowing out on F and back on F^ must, therefore,
be 4i amperes* The upper side requires 6 amperes and the
lower side 3, because there are twelve lamps in parallel in
the one case and six in the other. There are, then, 3 amperes
coming back through the neutral, of which H flow through a',
running it as a motor and generating li amperes in a.
This is added to the Ah in line F, thus making the six required
for the upper stde. If the lower side should become more
heavily loaded than the upper, the current in the neutral
wire would be in the opposite direction and the action of
a and a^ would be reversed; that is, a would act as the motor
and a- as the dynamo*

The motor-dynamo, or balancer, is not necessarily placed
in the station; it may be placed at a point near the center of
distribution^ thus requiring only two feeders /''and F to be
run back to the station. In this illustration, the losses in the
balancing set have been neglected. As a matter of fact,
machine A will furnish more than Ah amperes in order to
make up for the losses in a, a* and supply the lamps as welL

Fig, 11 shows the connections for a balancing set more in
detail, in) being the elementary connections and {b) the com-
plete diagram indicating the \^arious instruments* A and B
are tlie armatures of the balancer and C the armature of
the main generator; d and e are field rheostats in the shunt
fields, and / the field rheostat of the generator* In order
to start the set, it Is necessary to provide a starting rheostat
at ^, so that one of the machines can be started as a

§33

INCANDESCENT LIGHTING

I Bn

t-Aff^*

INCANDESCENT LIGHTING

§33

direct-current mo ton Voltmeters and ammeters should be
provided as shown, the former indicating the voltages of the
main machine and the pressure on the two sides of the three-
wire circuit, and the latter indicating the current output of
the main machine and the current in the neutral* The read-
ing of the neutral ammeter shows the amount of current
handled by the balancer. A trip coil k is placed in the
neutral wire leading to the balancer, so that if the current
becomes excessive, a circuit is closed through the trip coil
of the circoit-breaker k^ thus cutting off the main generator.
If an overload on the balancer were taken care of by placing
a circuit- breaker at m or w, damage would result , for if a
short circuit should occur on either side of the system, the
circuit-breaker on that side would at once fly out, and since
the main machine would still be connected, an excessive
voltage would be thrown on the lamps. In most large
stations operating on the three-wire system, the amount of
unbalancing is usually small compared with the total load
carried* so that the capacity of the balancing arrangement is,
as a rule, small compared with that of the main dynamo.
Balancing sets are now generally used in preference to
the old method employing two main dynamos connected
in series.

12. Toltafif© Regulation. — In stations where a large

number of lamps are operated, it is usually necessary to
have several distinct feeders running lo the different districts
to be lighted or supplied with power. Some of these feeders
may be long, others quite short. In order, therefore, to
keep the cross-section of the long feeders within a reasonable
size, a larger drop must be allowed in them than in the
short feeders. It is necessary, then, to have some means of
supplying the long-distance feeders with a higher pressure
than those supplying the near-by districts. Of course, the
voltage on the short feeders might be cut down by inserting
resistance in series with them, as has been done in some
cases, but this method is wasteful o£ power and is not to be
recommended.

INCANDESCENT LIGHTING

13. An excellent method, where separate dynamos are
available, is to use separate machines for supplying the long-
distance feeders, and run them at a higher voltage than those
supplying the short feeders. When only one dynamo or set
of dynamos is at hand for operating the whole system* the
best plan la to rtm the machines at the pressure suitable for
the short feeders, and use a boosier to raise the voltage on
the other feeders. Fig. 12 indicates the arrangement

astf* *

Pig. n

referred to* The plan shown is for the three-wire system,
though the same scheme may be used on a two- wire system
and is, in fact, used considerably with electric railways,
A and B arc two dynamos operating on the three- wire system
and supplying current directly to the short feeders 1,2^3, and
1\2\3'. Feeders ff, ^, r and a^&^c' run to outlying points
and I therefore, tnust be supi^lied with a higher pressure than
the other feeders. Suppose^ for example, that each dynamo

4aB— u

INCANDESCENT LIGHTING

§33

generates 125 volts and that the long-distance feeders require
140 volts between the outside and neutral wires; 15 volts
must, therefore, be added to each dynamo voltage. This is
accomplished by the boosters C D^ which are connected
as shown.

The boosters are small dynamos driven either by a
steam engine or, more frequently, by an electric motor.
The fields are separately excited from the mains and the
armatures are connected in series with each of the outside
wires. The armatures must be capable of carrying all the
current used on the long-distance feeders and be able to
generate a pressure equal to that by which the voltage is to
be raised- For example, in this case the booster armatures
would generate the extra 15 volts required and thus give
140 volts on the feeders a, b,c and a\ b\c*. By varying the
field rheostat of the boosters, the voltage on the feeders
may be adjusted.

1 4. Five- wire and Seven- Wire Systems. — The three-
wire system has been extended so as to make use of higher
potentials by employing four dynamos in series and three
neutral wires. This allows the use of 440 to 500 volts
between the outside wires and permits a still larger area to
be covered than by the three-wire system. Seven- wire
systems with six dynamos in series have also been used,
and the five-'wire system has been successfully applied on
the continent of Europe. Five-wire and seven-wire systems
have met with little favor in America, the practice being to
use alternating-current methods of distribution if pressures
higher than those given by the 110-220-volt or 220-440-volt
three-wire systems are required. The use of three- wire
systems 'with 220- volt lamps and 440 volts across the outside
wires is gradually extending, because the higher pressure
allows larger areas to be supplied and effects a saving in
copper over the 110-220-volt system.

§33

INCANDESCENT LIGHTING

DIRECT-CLTRRENT, CON STAN T-CUBRIIKT SYSTEM
15. The dlrect-eurreiit, eons tan t-curreiit fiyRtem
is very seldom used for incandescent-lighting: work. It was
employed to some extent in the early days of electric light-
in g when a few incandescent lig^hts were operated in series
with direct-current arc lampSp In such systems, the current
used was a direct one, furnished usually by a machine of the
Thomson-Houston I or Brush* type, and was maintained at a
constant value by automatically varying the E* M. F. There
were many objections to operating incandescent lamps in this
way and the system was never used to any g^reat extent.

ALTERNATIKG-CURRENT, CONSTANT- POTENTIAL

STgTEM

16. Alternating current at constant potential finds wide
application for incandescent lighting, because this method
allows lights to be operated over large areas with a com-
paratively small loss and a small expenditure for copper-
The distribution may be carried out by means of the
single-phase, two-phase, or three- phase system. If the cur-
rent were intended for operating lights only, the single-
phase scheme would be used, as it is simpler than either
the two-phase or three-phase arrangements. Most modern
lighting plants, however^ are equipped so that they can
operate motors as well as lights, and, hence, it is customary
to install polyphase systems rather than single-phase,

17* Slti|^le-Phase Systetn. — When alternating current
first came into use for electric lighting, a simple alternator
was used to supply current at a constant pressure. This
was transmitted over the line, and at the various points
where it was utilized transformers were installed to step-
down the voltage to an amount suitable for the lamps. Each
customer usually had his own transformer* If the system
were small, only a single pair of lines or feeders was run
from the station; in case the area lighted was large, a num-
ber of feeders supplying different sections was used. The

INCANDESCENT LIGHTING

§33

pressures first used were 1,000 volts on the primary mains
and 50 or 52 volts on the secondary. As the construction
of alternators, transforraers, and lamps was brought to a
higher stage of perfection, the pressures were increased to
2,000 volts primary and 100 to 110 volts secondary. The
frequency used in the early plants was usually from 125 to
133 cycles per second; in later plants, 60 cycles has become
common practice.

The great advantage of this system over the direct cur-
rent lies, of course, in the use of the high pressure for
transmitting the current. The introduction of alternating

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current rendered possible the lighting of many places that
could not afford the expense of installation that would be
necessary if direct current were used. It also rendered
water-powers available that were located at some distance
from the centers to be lighted,

18, It was formerly customary to install small trans-
formers for each customer, as shown at A,B,C^ Fig. 13,
and if a large amount of current were required at any point,
a number of transformers were connected in parallel, as

§33

INCANDESCENT LIGHTING

shown at A'. This was necessary because transformers were
not then made in large Slices- On account of the objections
to running a number of small transformers it is much better
to make use of a system of secondary mains supplying a
number of customers and to feed these secondary mains from
a few large transformers, as shown in Fig* 14. In this case^
the primary mains .1, B, running from the station, feed the
large transformers T, T, The distributing secondary mains
are usually arranged on the three-wire system, as indicated
at C thus allowing a considerable area to be supplied from

Pio,U

one pair of transformers. The current may» however, be dis-
tributed by secondary two-wire mains if the lights are close
at hand. Scattered customers must, of course, be supplied
by individual transformers, as in Fig. 13. The use of sec-
ondary mains greatly reduces the number of transformers
to be kept in repair and otherwise looked after; it also effects
$k considerable saving in power, owing to the higher effi-
ciency of the large transformers. Where branch lines E^
Fig; 13, are taken off the main feeders, main line cut-out
boxes /", /' should be installed as indicated. The secondary-
main arrangement can generally be used to advantage for

INCANDESCENT LIGHTING

i33

furnishing Ugrht to the business part of a town, while in the
residence part it is frequently necessary to use individual
transformers on account of the customers bein^ scattered.
These remarks apply also to lighting systems using two-
phase or three-phase distribution.

19, Polyphase QyBtepi^.^ — Polyphase systems of distri-
bution are used extensively for electric lighting, but, so far
as the lighting is concerned, they have little if any advantage
over the single-phase system. The chief reason for their
use is to permit the operation of alternating-current motors
from the same system as the lights. The three-phase system
also has the advantage of reducing the amount of copper
required in the lines — an advantage of considerable impor-
tance when the current has to be transmitted for a long

Flo.Ifi

distance. The regular two*phase and three-phase systems
have been described, but a few special methods of operating
lights from polyphase machines may be mentioned here.
When alternators were first installed in lighting stations,
they were of the siug-le-phase type^ because polyphase motors
had not at that time come into use and the current was
employed for lighting exclusively. When alternators are
oow installed, it is usually desirable to put in a machine

133

INCANDESCENT LIGHTING

that can operate either lights or motors, and the operatioa
of polyphajie macliines oo single-phase circuits therefore
becomes a consideration of importance.

If the various lighting circuits are arranged so that the
load on the different phases can be approximately balanced,
there is no reason why a tvvo*phase or a three*phase alternator
cannot be used to operate them, A three-phase alternator
can be operated as a single-phase machine, as shown in
Fig- 15, in case the load cannot be divided between the
different phases. When so operated* it can, if necessary, be
run in parallel with other single-phase machines. A three-
phase alternator, when run as a single-phase machine, as
shown in Fig. 15, will carry about 75 per cent, of its
rated output. For example, suppose that a three-phase
alternator has a capacity of 200 kilowatts at 2,300 volts* Its

200,000

current output will be / ^

= 60.2 amperes.

2,300 X 1.782

If the same alternator were operated single-phase, its out-
put would be about .75 X 2(X> = 150 kilowatts and the cur-
rent output would be HfM^ = 66.2 amperes; that is, with
approximately the same increase in temperature of the arma-
ture, the alternator would deliver 50.2 amperes in each of
three lines when run three-phase, or 65,2 amperes when run
single-phase. For a given output, a three-phase alternator
is somewhat smaller than a single-phase machine, because
the armature winding space is utilized to better advantage*
Consequently, a three-phase alternator, capable of giving a
single-phase output of a given number of kilowatts, costs
about the same as a single-phase machine of the same out-
put. When installing new machinery in a lighting station
that has hitherto been operated altogether by single-phase
machines, it is frequently advisable to install three-phase
alternators, even if they are operated single-phase for
the time being, because, in case occasion should arise for the
operation of motors, the three-phase current will then be
available. When three-phase aUernaiors are intended for
single-phase operation, they are usually provided with a
V-connected winding.

INCANDESCENT LIGHTING

133

30, If all three phases of the alternator are used* the out-
goiog feeders should be connected acrosis different phases,
as shown in Fi^. 16, so that the load will be, at leastp
approximately balanced. If the loads are not balanced,
there will be more or less inequality In the voltagfes on the dif-
ferent feeders, but by a judicious arrangfementof the feeders
and the loads thereon, a fairly good balance should be pos-
sible in the majority of cases. Of course, the amount of

w Aft Ufkf CiHiiit I

Lsrft
Lifhtifff I

Fio. Iff

the inequality in voltage on the different phases due to
inequality of load will depend considerably on the design of
the alternator. If the armature is of low inductance, the
falling off in voltage with increase in load wil! be compara-
tively small; in other words, the inherent regulation vvlll be
good and unbalancing of load will not cause serious unbal-
ancing of voltage* In the majority of cases, the unbalancing^

iSS

INCANDESCENT LIGHTING

His:

22 INCANDESCENT LIGHTING §a3

that may arise can be compensated for by means of feeder

potential regulators. In most stations where a number of
feeders run out to points varying in distance from the
station, these regulators are provided anyway, in order that
me voltage supplied to the lamps may be under control.

In some cases where lights are operated from a three-
phase alternator, the four-wire three-phase system is used.
This is shown in Fig* 16» The secondaries of the trans-
formers A are Y-connected and are wound to give the
voltage required by the lamps. The fourth wire is brought
from the common connection of the Y winding, and the vari-
ous single-phase circuits are connected between the fourth
wire and the other three as shown. In this case the feeder
running from the station is three-phase and the lamps are
fed from the four* wire secondary mains. The voltage
between any pair of the three mains connected to the ter-
minals of the Y winding would h^ £x V3, where M is the
lamp voltage. Since these mains are three-phase, induction
motors can be operated from them; if 126-volt lamps were
usedt standard 220-volt motors could be run from the
same mains.

Fig- 17 shows a lighting system in which the three-phase
alternator is provided with a fourth collector ring connected
to the common junction of the winding; a fourth bus-bar
is connected to this ring. This fourth wire acts as a com-
mon return, and the single-phase feeders can be connected
across any one of the three armature windings. For supply-
ing lights to distant points, long four-wire feeders may be
run out» and the lights or motors in the district supplied at
the end of the feeders can be divided so as to secure an
approximately balanced load. The action of the four- wire
three-phase system is somewhat similar to the ordinary
three-wire direct-current system,

21, Mixed System s,™Tn many large cities, extensive
installations on the Edison three-wire system have been
made in the past for the operation of both lights and
direct-current motors. These were supplied from statioDS

§33 INCANDESCENT LIGHTING 28

located as close as possible to the distribution centers. As
the area to be supplied spread, and as alternating current
became more extensively used for power-transmission work,
these companies adopted the plan of supplying the existing
direct-current systems with power from substations supplied
with alternating current from one central station, or perhaps
from a distant water-power plant.

Fig. 18 shows the scheme referred to. Alternating
current is transmitted from the central station at A^ usually
by means of the three-phase system, to the substations B
or C, where it is stepped-down by means of trans-
formers Z", Z", T, The current may then be sent through
rotary converters R^ R and fed into a three-wire system, as
shown, or it may be fed to an alternating-current motor M
that is coupled to direct-current machines O, O, Sometimes
arc lights are also supplied from these substations by coup-
ling alternating-current motors to arc-light dynamos.

A large amount of lighting is carried out, especially in
cities, by using the plan just described. Fig. 19 shows a
motor-generator set used for transforming from three-phase
alternating to three-wire direct current. The three-phase
synchronous motor A receives current from transformers
after it has been stepped-down from the high-tension line that
transmits it from the central station. The motor drives the
two direct-current dynamos B and C, which are connected in
series and supply current to the three-wire system.

For electric-lighting work, the use of a synchronous
motor driving direct-current generators gives better results
than rotary converters, because the former arrangement
maintains a steadier voltage on the direct-current side, a
feature of great importance in connection with incandescent
lighting. If the voltage supplied to the alternating-current
side of a rotary converter varies, the direct-current voltage
will also vary. Consequently, all the bad effects of drop in
the alternating-current transmission line are felt on the
direct-current side, and therefore cause fluctuations in the
lamps. If, however, synchronous motors are used to drive
separate direct-current machines, the speed of the motor will

26 INCANDESCENT LIGHTING §33

be constant so long as the speed of the distant dynamo is
constant^ no matter what may be the ftuctuations In the
voltage delivered, because the motor is bound to run in
sjmchronisni; the direct -current machines will therefore
deliver a steady voltage, because of the constant speed.
For similar reasons, synchronous motors are better than
induction motors for this work, the latter giving variable
speed and lower power facton

22 » The use of constant*potential alternating current of
the two-phase or three-phase variety allows a great flexi-
bility in the kind of apparatus operated from one station.
If it is necessary to have direct current for any purpose, the
transformation is easily effected. In general, where rotary
converters or alternating-current motors are used, it is
desirable to have a low frequency, say, about 25 or 40. On
the other hand, the frequency should not be below 30 or
40 cycles per second if the current is to be used for incan-
descent lighting- A high frequency calls for less expensive
transformers, and between all these requirements, which are
more or less conflicting, a frequency of 60 has been very
generally adopted for systems where the current is used
both for light and power.

23. Frequency Changers .^In some cases, the con-
ditions may be such that the greater part of the current on
an alternating system is utilized at low frequency for general
power purposes or for the operation of rotary converters.
However, part of the current may be required for lighting
work, for which a higher frequency is desirable. For
example » the frequency generally used might be 25 cycles
per second, whereas, the frequency required for alternating-
current arc lamps should not be below 50 cycles per second.
To change from one frequency to another, frequency
cbunijrori^ are used. Thus* a low-frequency synchronous
or induction motor can be coupled to a higher frequency
alternator. Synchronous motors are generally used in
preference to induction motors for this purpose. The
Stanley inductor alternator in slightly modified form can

§33

INCANDESCENT LIGHTING

be used as a frequency changen This machine is double,
havin^f two sets of revolvin]^ polar projections and two
armature windingfs. One side of the machine can, there-
fore» be provided with a different number of poles and
a different wiodioi: from the other. For example, one side
might have half as many poles as the other and operate
as a synchronous motor; the other side will then operate as
an alternator and the machine will constitute a frequency
changer, changing from one frequency to twice that fre-
quency* By winding the two sides of a frequency changer
for different voltages, the machine can, if necessary » be
used to transform the voltage at the same time that the fre-
quency is changed*

PROTECTION OF 8ECOin>ARY CIRCtllTS

24, Alternating current is used for lighting work
because it allows a high pressure for transmitting the cur-
rent from the station. It is necessary, however, to use a
low pressure for operating the lamps, because it is practi-
cally impossible to devise a system of house wiring that is
safe under high pressure, and, moreover * incandescent lamps
cannot be constructed for high pressure. On alternating-
current lighting systems, therefore, the pressure on the line
is much higher than that supplied to the consumer; for
e}cample, the line pressure may be 2|000 volts and the lamp
pressure 100 volts. On this account it is very important that
the secondary winding should never come in contact with the
primary, because the presence of the high voltage on the
secondary wiring is dangerous. A number of deaths from
shock can be traced to this cause; in fact, this element of
danger was at one time advanced as an argument against
the use of alternating current for lighting purposes.

In Fig. 20, let P represent the primary coil of a trans-
former connected to high-tension mains and S the secondary
coil connected to the house weiring that supplies the lamps /, L
Suppose that the insulation between the primary and secondary
coils breaks down at the point a\ also* suppose that there is a
paxtial ground on one of the primary lines e and that a person

INCANDESCENT LIGHTING

i33

standing on the ground, or in connection with anything
that can conduct current to the ground, touches one of the
wires ^» say, by touching an exposed lamp base or lamp socket.
A path through the person's body is at once established and
the high-tension current is free to flow, as indicated by the
arrows. The shock resulting' from such a current has proved
fatal in many cases. There is almost always more or less
of a ground on high-tension lines, because it is practically
1

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impossible to maintain perfect insulation where wires are
strung in the air and make contact with trees. A ground
between primary and secondary, therefore, results in a very
dangerous condition, the more so because there is noUiing
to indicate that such a condition exists until some accident
happens. The same condition will arise in case the primary
wires in any way become crossed with the secondary wires
leading from the transformer,

25. Breakdoiiv^us between primary and secondary may

be due to defective insulation, or they may be caused by a
high-potential discharge/ such as a stroke of lightning.
The insulation in the older styles of transformer was by no
means as good as that now employed; it gradually became
decomposed under the long-continued heating, in many cases
being affected so that it had very little mechanical strength
and thus provided insulation of a very poor order. Any

i33

INCANDESCENT LIGHTING

abnormal rise in voltage was almost sure to break down the
insulation of such transformers, and the breakdown was
usually followed by a burn-out. In modem transformers,
the working temperature is kept down by careful design and
efficient ventilation. Much attention has been paid to the
character of the insulation, and the use of oil, together with
the better insulation, has resulted in a great reduction in the
number of breakdowns due to lightning or other causes*
No transformer should be put into service that cannot stand
a high-potential breakdown test between its primary and
secondary. For example, an ordinary 2,000-volt li^htinf:
transformer should stand a test of at least 6,000 volts
between primary and secondary j some manufacturers give
a test of 10,000 volts. In Pig. 20, if the secondary were
permanently connected to the ground, as at /^, a person
touching either side of the secondary could never receive a
shock greater than that due to the secondary voltage.

In order to prevent accidents, a number of protective
devices have been invented to ground the secondary auto-
matically whenever a breakdown occurs, or whenever the
pressure between the secondary wiring and the ground
becomes abnormally high. These devices are not used very
extensively; yet, while they may not always be reliable in
their action, they render the system safer.

26« TlioitiBoii Protective Devices, — Fig, 21 shows a
protective device invented by
Prof. Elihu Thomson, It con-
sists of copper shields c, c placed
between the primary and sec- ^-
ondary coils in such a manner
that any connection between the
coils must take place through
the shield, which is connected
to the ground. If, therefore, a
breakdown takes place between
primary and secondary, the latter becomes grounded and
thus protects the secondary system.

Pio. 21

4«H^12

INCANDESCENT LIGHTING

§33

The ground shield is not* however, a positive protection
under all conditions and is now seldom used, A short
circuit may burn a hole through the shield, or the primary-
and secondary -coil terminals may touch each other outside

Fig. 22

the shield. Moreover, the ground shield makes the trans-
former more difficult to construct and insulate properly. If
ground shields are used, they must not form a complete cir-
cuit around the transformer core, otherwise they will act as a
. short-circuited secondary and heavy
currents will be induced in them*

^^ ■ I 27. Figs, 22 and 2^ show another

Thomson protective device. Its
operation will be understood by refer-
ring to Ftg. 23. The plate a is con-
nected to the grotmd and plates S^ b
are connected to the secondary lines.
Plates ^ and ^ are separated from
each other by pieces of thin prepared
paper c,€ that are easily able to stand
the normal secondary voltage. If,
however, the primary and secondary
become connected, or if the second-
ary voltage in any way becomes
excessive, either one or both of the
films d c break dowo^ thus grounding the secondary. If both
films break down at the same time, the secondary will be
short-circuited and will cause the primary fuses to blow.
thus cutting off the transformer. As far as the automatic

f^f^rf

^fr^

Fio.as

§33 INCANDESCENT LIGHTING 31

grounding of the secondary is concerned, it would be suf-
ficient to provide but one protective film on one side of the
secondary, but it is usual to provide two, because one may
fail to work.

28. Permanent Grounding: of Secondary. — The

most effective way of overcoming thcf danger due to
crosses between primary and secondary is to ground the
secondary permanently. It is true that there are objections
to grounding, and it is a practice that has not been generally
followed. Many station managers are not in favor of it for
the following reasons: If the secondary is permanently
grounded, another ground will establish a short circuit and
cause an interruption of the service, whereas, with an
ungrounded secondary, two grounds are necessary to give
rise to a short circuit. The grounding of one part always
makes the tendency greater for a ground to develop at
some other part and thus increases the fire-risk due to
leakage current to ground on the secondary wiring. It is
claimed by those opposed to this practice that the ground
connection invites trouble from lightning. The Fire Under-
writers at one time would not permit grounding because of
the additional fire-risk introduced, but it is now permitted, so
that there is no objection to the practice so far as fire-insur-
ance is concerned. If the secondary wiring is not good
enough to withstand the additional strain put on it because
of grounding the system, it is time that the wiring was
remodeled. It is safe to say that this objection carries little
weight if the wiring is put up in accordance with the Under-
writers' requirements. The weak point in most secondary
systems is not in the wiring proper, but at the fixtures and
outlets. There is no question but that, the permanent
grounding of the secondary renders the system safer so far
as danger to life is concerned, and if a company does not
make a practice of grounding, it should at least take the
precaution of testing the insulating properties of the trans-
formers at regular intervals as well as before they are
put into service. This does not necessarily mean that the

INCANDESCENT LIGHTING

§33

transformers must be taken down; they can be subjected to
a hig:h-potential test by means of a small portable testin£^
transformer.

In case transformers supplying: a two-wire secondary
system are grounded, the g^round connection is made from

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Pxo.21

the middle point of the secondary coil, as shown in
Fig. 24 (a). This reduces the strain on the secondary
insulation to half what it would be if either secondary line
were grounded. If the secondary system is three-wire, as in
Fig. 24 {b), the neutral or middle wire is grounded.

GROUNDING OF NEUTRAI^ ON THREE-WIRE DIRECT-
CURRENT SYSTEM

29. The grounding of the neutral wire of three-wire,
secondary, alternating-current systems protects the second-
ary from high-tension primary currents, and therefore is
desirable on the score of safety. There has been a great
deal of discussion as to the advisability of grounding the
neutral on low-pressure, direct-current, three-wire systems.
The argument as to safety from shock does not apply here
with the force that it does with alternating-current secondary
systems fed from high-tension primary lines. In direct-cur-
rent three-wire systems, the pressure between the outside
wires is seldom over 450 volts, and in most cases it does not

INCANDESCENT LIGHTING 33

exceed 250 volts, neither of which is high enough to be,
under ordinary conditions, dangerous to life. If the neutral
wire is grounded permanently, the maximum pressure that
can exist between either of the outside wires and the ground
is one-half the voltage between the outside wires; whereas,
if the neutral is riot grounded, the pressure existing between
one outside wire and the ground would be equal to the full
pressure between the outside wires in case a ground devel-
oped on the other outside wire. This fact has been advanced
as an argument in favor of grounding of the neutral, but it
is evident that it does not carry the same weight with direct-
current systems as with alternating, because with the latter
the voltage between the lines and ground may, under certain
circumstances, become as high as that on the primary, while
with the former it can i\ever be greater than the voltage
between the outside lines.

It has also been claimed that by grounding the neutral,
the earth helps the conductor to carry the current, and thus
improves the voltage regulation, particularly on unbalanced
loads when the current in the neutral is considerable. This,
however, is a doubtful advantage because, if large currents
are allowed to flow through the ground or through neighbor-
ing pipes, electrolytic action will set in wherever current
flows from the pipes or other conductors into the moist
earth, thus causing corrosion. When the neutral wire
is grounded, a ground on either of the other wires will
lead to a short circuit, whereas with an ungrounded
neutral two grounds are necessary. On small systems,
where a ground can be readily located and cleared before
another ground develops, it is not customary to ground the
neutral. It must be remembered that when the neutral is
grounded, the maximum pressure that can exist between the
outside wires and the ground is limited to one-half the volt-
age between outside wires; hence, the pressure that may be
acting on defective insulation to start a leak to groiuid can
never be as great as if the neutral were not grounded. At
the same time, a permanent ground on the neutral invites
grounds on other parts, and for a long time the Fire

M INCANDESCENT LIGHTING §33

Underwriters would not allow the neutral to be grounded?
grounding is now permitted by their rules.

If a three-wire system is carrying an unbalanced load of
lamps, and if the fuse in the neutral blows, it is evident that
the lamps on the ligrhtly loaded side will receive an excessive
voltage, and are apt to be burnt out. On tbis account, the
neutral is often not fused at all; or if it is, a heavier fuse is
used than on either of the outside wires.

If fuses are used on the neutral branches as well as on the
outside wires, the risk of blowing neutral fuses is reduced if
the neutral is grounded. Suppose* for example, that the
neutral is not permanently grounded and that a ground
occurs on the positive maia feeder; suppose, also, that a
ground occurs on a branch neutral line. The fuse on the
branch neutral will blow because it is much smaller than the
fuse protecting the main feeder, and the result will be a
burn-out of lamps* If, however^ the neutral is grounded at
the dynamo, a ground on either positive or negative will blow
one of the outside fuses and no danger to the lamps can result.

On large three-wire systems, where an extended network is
supplied through underground cables or Edison underground
tubes, the neutral is generally grounded, as the advantages
of grounding outweigh the disadvantages; for small systems
or for isolated plants it is better on the whole to keep the
neutral insulated.

AI.TERNATi:pfG-CURRENT, CONSTANT-CURRENT

SYSTEM

OBNEBAL. DESCRIPTION

30* The alternating- current , eonntant^cui^ent
system U used for series incandescent street lighting and is
well adapted for suburban districts or residence streets in
cities that are so shaded by trees as to make arc lighting
difficult* It is also an excellent system for street lighting in
small towns and villages, because it can be operated from
l^e same generating outfit used for constant -potential

i33

INCANDESCENT LIGHTING

interior lighting and the cost of the street-lighting outfit is
smaller than would be required for arc lighting. Moreover,
it requires very little work to keep the lamps in running
order, as compared with arc lamps, and street lighting can
often be carried out by this system where arc lighting would
not pay. Of course, street incandescent lamps could be
operated from constant-potential transformers in the usual
manner, but this class of lighting is usually so scattered that
parallel distribution at low pressure is out of the question.
The series arrangement uses a small current at high pressure
and hence requires but a small amount of line wire.

Series incandescent circuits are operated from the regular
constant-potential alternators. For example, in Fig. 25, A
represents a constant-potential alter-
nator supplying ordinary incandes-
cent lamps through transformer B.
A series of lamps /, / is connected
across the circuit. With this simple
arrangement, the current through the
lamps will remain constant so long

O O O

Pio.25

as no lamps burn out. If one or more lamps bum out, the
current will increase because the voltage generated by A
remains constant and the reduction in the number of lamps
lowers the resistance of the circuit. Each lamp must be
provided with a device of some kind that will automatically
maintain the circuit around a lamp in case it bums out,
otherwise the whole series of lamps will be extinguished.
The number of lamps on the circuit is fixed by the line
voltage and the voltage per lamp. Thus, if 20-volt lamps

INCANDESCENT LIGHTING

133

were used on a 1,000-volt system, there would necessarily be

fifty lamps in each series circuit, neglecttngf the volts lost in
the line. Ih order to operate series circuits successfully,
means must be provided for varying the voltage applied to
the circuits so that the current can be maintained at a constant
value within narrow limits irrespective of the number of
lamps in operation. The variation in voltage should also be
such as to admit of considerable range in the number of
lamps operated on a circuit, because in many cases the
lamps required on a given circuit might not be large
enough to take up the full voltage of the alternator.

L.AMFS

31, The lampB used for series circuits are similar to
ordinary multiple lamps except that the filament is heavier.
In the past, 3i* or 5i^-ampere lamps having an eflSciency of 3,5
or 4 watts per candlepower have been used, depending on

the length of the circuits
and the available volt-
age* In later installa-
tions, the tendency is
to use higher voltage
lamps taking a smaller
current of about U5
amperes. These lamps
are cheaper than those
designed for the larger
currents, tlius making
the cost for renewals
less and decreasing the
line loss. In the West-
inghouse system, which
is described later, ordi-
nary 60- volt or 100- volt lamps are used. The line must be
strong enough to withstand storms, hence the wire cannot
be made less than No. 0 or S B, & S., and the use of lower cur-
rent lamps does not effect any saving in the cost of the line.

PiQ. 26

%3i

INCANDESCENT LIGHTING

To maintain the continuity of the circuit firound burned-out
lamps, a film cut-out is very commonly used. This consists
of a tbin piece of paper held between springs connected to
the terminals of the lamp. As long as the lamp is burning,
the pressure to which the film is subjected is equal to the
drop through the lamp, but if the lamp burns out, the circuit
IS momentarily interrupted^ and Ihe pressure existing between
the two sides of the film rises for an instant to full line
pressure- The excessive pressure punctures the paper, thus
allowing the springs to touch and maintain the circuit around
the lamp. In the older types of lamp, the film cutout was
placed in the lamp base. In later outfits, the film cut-out is

Pto. 9T

placed in a special socket, Fig, 26, so that the lamp base is the
same as on an ordinary lamp* The lamp screws into the
socket a, the projecting part of which carries two brass con-
tact springs between which the film cut-out is placed* The
receptacle 5 is attached to the supporting bracket and the
line wires connect to terminals at /, ^ to w^hich are attached
contact springs d, f^ shown In e, which also serve to hold
the socket when it is pushed into place. When a socket is
pulled out in order to replace a film cut-out, springs d, e touch
each other before the socket is entirely removed, thus pre-
venting the circuit from being broken. Fig. 27 shows the
lamp bracket complete with its reflecton Since the pressure

38 INCANDESCENT LIGHTING §33

on these circuits is high, it is necessary to provide thorough
insulation from ^rround. A triple-petticoat, 10|000-volt insu-
lator is, therefore, inserted between the lamp receptacle and
the gooseneck, as indicated at a.

CUBRE3ST KEGULATORS

32. liaTrip-Board Hegculator. — Many different devices
have been used for maintaining: the current on series incan-
descent circuits at a constant value. The first method was
to insert a few lamps in series with each circuit in the sta-
tion and have a switch arranged so that as many of these
lamps as desired could be cut into circuit. An ammeter was
also included and whenever the current increased because of
a lamp going out on the line, the station attendant cut in a
lamp in the station to take its place and bring the current
back to normal value. This was a very inefficient method
of regulation and if the attendant were not prompt to notice
the increase in current, the lamps on the circuit might be
subjected to an excessive voltage for some time, thereby
shortening their life*

33. C R Regulator.— The C R Regulator of the Gen-
eral Electric Company consists of an auto trans former with
secondary taps brought out to a multipoint switch whereby
the pressure of the secondary of the transformer can be
added to or subtracted from the voltage of the lines. This
regulator gives a wide range of regulation and is very effi
cient, but it is not automatic and has been superseded by
other methods by which the current is automatically main-
tained at the correct value. It is very important that the
current on series incandescent circuits shall never exceed the
allowable amount, even for short intervals* This can easily
happen if the regulator does not operate automatically or if
it is not capable of maintaining constant current throughout
a very wide variation in the number of lamps on the circuit.
For example, two grounds might occur on a circuit and thus
cut out a large number of lamps throwing an excessive current
on the remaining lamps unless the regulator acted promptly.

INCANDESCENT LIGHTING

34. Beactancc-Coil Ref^ulator. — To secure automatic
regulation, a special type of reactance coil has been used in
some cases; Fig. 28 (a) illustrates the principal features of
the arrangement. The constant-potential alternator a sup-
plies current to the mains across which the lamp circuit is
connected in series with a reactance coil c. The coil is sus-
pended from a sector d and is counterbalanced by weights e.
Any tendency for the current to increase causes the coil to
be drawn down over laminated core b, thus increasing the
reactance of the coil and keeping down the current to normal
value. A properly designed coil will maintain the current

(a)

Pio. 28

constant within narrow limits, and as it operates automat-
ically, the danger of straining the lamps by the application of
an excessive voltage is reduced to a minimum. An objection
to the arrangement shown in (a) is that the series circuit is
in electrical connection with the alternator and a ground on
the circuit grounds the main distribution system.

A series circuit is usually long and grounds are quite
liable to occur, hence, it is a good plan to have it com-
pletely separated from the main system by inserting a
transformer, as in Fig. 28 {b). It should be particularly
noted that with an automatic regulator it is not necessary to
place the regulator in the station. It may be placed out on
the line and connected to the primary mains at whatever

INCANDESCENT LIGHTING

i33

point may be most convenient, thus effecting a considerable
saving in line wire and a corresponding reduction in Hne
losses. In some cases the regulators have been placed in
boxes mounted on poles.

35. Constant- Cut*rent Trmnsformer.^-The most
recent development in the line of regulating devices for
series alternating circuits is the eonstant-current trans-
former, Thrs combines, in one device, the advantages of
the automatic reactance coil and insulating transformer, and
is somewhat cheaper and more efficient than the latter com-
bination shown in Fig, 28 (d). Fig. 29 shows the main
features of the General Electric constant-current trans*
former system. The transformer has two flat coils — a pri*

— mary d that is fixed and a second-
ary c that is suspended from c

— and counterbalanced by weight /.
^^^ Coil c slides up or down over tbe

l^^llV laminated core d and when it occu-

§/ pies the position 1, where it rests

on the primary if, the secondary
furnishes its maximum E. M. F-
and operates the maximum num-
ber of lamps. The counterweight
is adjusted to balance the weight of
the movable coil less the electrical
repulsion that exists between the
^^^■^ two coils when current is flowing.

If the secondary is in position 1 and a number of lamps are
cut out, the repulsive action increases because of the momen-
tary increase in current and the secondary moves up to some
such posttton as 2; where the current is restored to normal
value by a corresponding reduction in the secondary E. M. F*
The secondary E, M, F, decreases as coil r moves up from 6^
because of the magnetic leakage that takes place between
the coils, as indicated by the dotted lines; the greater the
separation of the coils, the greater is the leakage and the
less is the secondary E. M, F. When the secondary

§33

INCANDESCENT LIGHTING

occupies position 3 (position corresponding to short circuit),
the E* M, F. applied to the series circuit is very low* This
device can be made to give very close regulationi but it is
advisable, if the transformer is operated at less than half
load, to block the coils so that, before the circuit is ploifged
in, they are about an inch farther apart than the normal

Fig. 90

operating position. This prevents an abnormal current
during the short interval required for the movable coil to
adjust itself and avoids strain on the lamps.

Fig, 30 shows an 8,S-kilowatt constant-current transformer
In which the coils, core, etc. are lettered to correspond with
Fig, 29; j^ is a dash pot provided with a by-pass and close-
fitting piston* By means of the by-pass, the steadying action

INCANDESCENT LIGHTING

S83

■MPB^WJfi^l^R"^ ■"' ^te

of the daahpot can be adjusted. The levers connected to the
connterweisht and dashpot are suspended on Jmife edged
and hf redndng the counterweight the secondary current

is increased and vice
versa,' so that the sec*
ondary current can be
adjusted within limits.
x^^^^ The priniary coil is
^2»3g22r usually wound for 1,100
■^ or 2,200 volts and the

secondary for 1.76, 3.6.
6.6, or 7.6 amperes, de*
<>iy»wy» pending on the charac-
ter of the circuit, and
fhmt^tmmr each transformer or set
of transformers is con-
nected to the Ime and
alternator through a
small switchboard.

Fig. 81 shows the
connections for a trans-
former switchboard
supplying a single cir-
cuit; it is equipped with
a recording wattmeter, potential transformer, plug switches,
ammeter, and lightning arrester. With primary pressures
less than 2,500 volts, it is not necessary to use a current
transformer with the ammeter.

Pig. 81

36. The series incandescent street-lighting devices used
by the Westinghouse Company are considerably different
from those described, in regard to the method of compen-
sating for burned-out lamps. Ordinary 50-volt or 100-volt
lamps are used; for example, on a 1,000-volt circuit, twenty
50-volt or ten 100-volt lamps would be connected in series.
The operation of the Westinghouse device will be under-
stood by referring to Fig. 32. L, Z,, L represent a series
of ten 100-volt lamps connected across the 1,000-volt

§33 INCANDESCENT LIGHTING 48

mains M. Across the terminals of each lamp» a coil c wound
on a laminated iron core d is connected so that the coil is in
shunt with the lamp under ordinary working conditions. As
long as the lamp is unbroken, only a very small current
passes through the shunt coil; just enough current will flow
to magnetize the coil sufficiently to generate a counter
E. M. F. of 100 volts. When the lamp burns out, the whole
current passes through the shunt coil, or shunt box^ as it is
often called, and as the iron in the core is worked at a point
near saturation, the counter E. M. F. rises but slightly over
100 volts, although the current through the coil is very much
greater than it was before the lamp broke. The coil, there-
fore, takes the place of the lamp and introduces into the

Pio. 83

circuit a counter E. M. F. of slightly over 100 volts to take
the place of the lamp. The current remains about the same
and the life of the remaining lamps is not endangered. If as
many as four or five lamps are out at once, the remaining
lamps become somewhat dim on account of the fact that
each shunt coil introduces a little higher counter E. M. F.
than the amount of the drop through the lamp that it
replaces. This arrangement does not, therefore, maintain
an absolutely constant current.

Like the arrangement shown in Fig. 28 {a) this system has
the disadvantage of direct electrical connection between the
series circuits and the main system, but this can be avoided
by separating the two by means of a transformer.

44 INCANDESCENT LIGHTING

lilNE CAIXJUIiATIONS

TWO-WIRE AND THREE- WIRE DIRECT-CURRaNT SYSTEMS

37. The methods for calculating the size of wire required
to transmit a given current over a given distance with a
certain allowable drop are the same as those used for the
calculation of power-transmission lines, though sometimes
the formulas are put in a slightly different form so as to
be more directly applicable to the subject of electric lighting.

The formula that is most generally applicable is the fol-
lowing:

A = il:*^ (1)

where A = required area of cross-section of wire, in circular
mils;
Z? = distance, in feet (one way), to point where cur-
rent is distributed;
/ = current, in amperes, transmitted;
e = drop, in volts.

In making line calculations in connection with electric
lighting, some judgment must be exercised in choosing the
value of the distance D, This is not the distance to the first
lamp supplied nor the distance to the farthest lamp, but the
distance to the center of distribution; in other words, the
distance to the point at which we might imagine all the lamps
to be grouped. The product of the distance D to the center
of distribution and the current / is often spoken of as the
ampere-feet of the circuit; hence, we may write the rule
as follows:

Riilo. — The area^ in circular mils, required for a tivo-wire
circuit is found by multiply ijig the ampere-feet by 21,6 and
dividing by the drop, in volts,

38. Center of Dist rihiitloii. — The distance 77 to the
center of distribution will be best understood by taking a
few cases illustrating the point. Consider a number of

1|33 INCANDESCENT LIGHTING 45

lamps /, /, Fig. 33, arranged as shown and fed by the
dynamo A. The distance from the dynamo to the first
lamp is 1,(XX) feet, and the lamps are spaced out over a dis-
tance of 100 feet. The whole of the current would have to
be transmitted through the first 1,000 feet, but from that
point it would gradually fall ofiE. We may then take the

-tOOOf^et-

— D' t050 ftft

Fig. 33

point a as the center of distribution, because the load is
about equally distributed on each side of this point, and the
distance D used in the formula would be 1,050 feet.

Take the case shown in Fig. 34, where the lamps are
spaced evenly all the way along the line. In this case, the
center of distribution a may be taken as the middle, and

Pio.84

hence the distance D is only one-half the length of the line
from A to D, The exact location of the center of distribu-
tion becomes more difficult to determine when the load is
unevenly spaced or distributed, but in most cases it can be
located close enough for practical purposes by laying out the
system and noting carefully the loads on the diflEerent circuits.

39. Current Estimation. — The current can be readily
determined when the nature of the load is known. The gen-
eral practice is to allow \ ampere for each 16-candlepower
lamp and 1 ampere for a 32-candlepower lamp on 110-volt
circuits. Some prefer to make calculations for lighting
circuits by using lamp-feet instead of ampere-feet. The
number of lamp-foot is the product of the number of
16-candlepower lamps to be supplied and the distance to
the center of distribution. When this term is used, it

4GB— 13

46 INCANDESCENT LIGHTING |8S

always implies the use of 16-Gandlepower lamps; if any
88-candlepower lamps are operated, each lamp must be
couited as two 16-caiidlepower, etc If lamp-feet are used,
tbA formola becomes

,^,m^ (2).

where A » area, in dxcnlar mils;

D » distance, in feet, one way to center of distri-

bation;
N » number of lamps (expressed in terms of 16-candle-
power lamps);
e V drop, in volts.

Bale. — To determine the area ei eroes-^ecttan tor a two-wire
ilO-volt circuit, mutUply the lamp-teet by 10.8 dnd divide by
the irep^ in volts.

40. This rule is here given because it is frequently used.
Formula 1 is, however, much to be preferred, because for-
mula 2 assumes that each lamp takes i ampere, and this
may not always be the case. Formula 1 is applicable to
any case because the current is used in it, and this current
is determined from a knowledg^e of the devices to be
operated.

EzAMPLB 1. — A dynamo A^ Pig. 33» delivers current at 110 volts to
fifty lamps distributed about a as a center. The drop must not
exceed 10 volts. Find the size of wire required.

Solution. — The distance to the center of distribution is here 1,050

feet, as already explained. The current will be 25 amperes, because

each lamp will take \ ampere. Using formula 1,

. 21.6X1,050X25 ^ .^ . ., .
A = . ~ = 56,700 cir. mils. Ans.

A No. 3 B. & S. wire would likely be used.

Example 2. — A dynamo A^ Fig. 35, supplies current through ttie
feeders b^ c to the feeding-in point a. From this point lamps are sup-
plied by means of the mains d^ e and /, g. The number of IH-candle-
power lamps and the various distances are shown in the figure. The
total drop in voltage from the dynamo to the last lamp must not
exceed 15 volts, of which 13 volts is to be in the feeders and 2 volts in
the mains; required: (a) the cross-section and gauge number if the

§33

INCANDESCENT LIGHTING

feeders *, c; (d) the cross-section and nearest f^SLU^ number of
the mains d, e; (c) the cross-section and nearest gauge number
of the mains /, ^.

Solution. — 160 lamps will require 75 amperes
60 lamps will require 26 amperes
Total current 100 amperes
(a) A drop of 13 volts is allowed in the feeders and a drop of 2 volts
in the mains. No current is taken from the feeders at any intermediate

■ 400 fief-

JOLofmy

-eoo*-

r confer ^Jfrdfufwt

/OO'-^ \

Center i^/3.
^SO'^ioma

HO at
Pig. 85

point; hence, the distance D from the dynamo to the center of distribu-
tion a will be taken the same as the actual distance, i. e., 400 feet.
Using formula 1, for the feeders,

A . 2L«.>qOO X.IOO ^ ^^^ ^^ ^.^

This would call for a No. 2 B. & S. wire. Ans.

(6) The current in the mains d, e will be 25 amperes. The distance

from a to the center of distribution will be 200 -f "4^ = 250 feet, because

the lamps are spaced evenly along the last 100 feet. The drop in the

mains is not to exceed 2 volts; hence,

. 21.6X250X25 «^ ^^ . ., .
A ^ 2 = 67,500 cir. mils. Ans.

This also wouid call for a No. 2 B. & S. wire. No. 2 B. & S. wire is
a little smaller than the cross-section called for, but it would probably
be used, as the increased drop caused by doing so would be very small.

(c) The current supplied through mains /, f^ is 75 amperes. Here
the load is uniformly distributed along the mains, and the distance to
the center of distribution is -\^ — 65 feet. The drop is 2 volts, and

A =

21.6X()5X75 ro^-^ • -1
= 52,(y.>0 cir. mils

This would call for a No. 3 B. & S. wire. Ans.

INCANDESCENT LIGHTING

§88

It will, be noticed in this example that although the*niafai8 cany a
-smaller cnnrent over a shorter distance than the feeders, they work ont
about the same siie. This is because of the large drop allowed In the
feeders compared with that in the mains.

BxAifPLB 8.— Fig. 96 shows a three-wire distributing system. The
d]rnamos A^ B supply current through feeders to the junction txn J.
Ihmn. this point mains are carried to the buildings where light is to be
supplied. The conductors marked mains are sometimes called snl>-
feeders, because' they are really branches of the main feeder and no
branches are taken off between the junction box and the end of these
lines. The total drop from the dynamo to the lamps is not to exceed
10 per cent, of the lamp voltage, and the pressure at the lamps Is to be

Pio. 86

110 volts, [a) Calculate the size of the feeders C, {b) Calculate the
size of the mains D, (r) Calculate the size of the mains E. The
calculation of the size of wires required for the house wiring will not
be taken up here, as it belongs to interior wiring, and we are only con-
cerned for the present with the outside distributing wires. The pres-
sure at the dynamo will be 110 -f (110 X .1) = 121 volts. Of the total
drop of 10 per cent., 1.5 per cent, will be allowed in the house wiring,
3.5 percent, in the mains, and the remaining 5 per cent, in the feeders,
as indicated in the figure.

INCANDESCENT LIGHTING 49

Solution. — In calculating the size of the conductors, the sjrstem
may be considered as a two-wire system, the pressure between the two
outside wires at the lamps being 2 X 110 = 220 volts and at the dynamo
2 X 121 = 242 volts. A neutral wire one-half the size of the outside
wires should be amply sufficient. The total current supplied may be
obtained as follows:

(a) Each pair of lamps on a 220-volt three-wire system requires
J ampere; hence, current in line Z^will be ^^ = 25 amperes. Current
in Zf will be^J^ = 100 amperes. Total current in the feeders Cwill be
125 amperes. The total drop between the outside wires is 242 — 220
= 22 volts. The drop in the main feeders is to be 5 per cent, of the
lamp voltage, or 220 X .05 = 11, or 5.5 volts on each side. The dis-
tance to the center of distribution is 700 feet; hence,

. 21.«X 700X125 _, -,_ . ., .
A = j^ = 1/1,818 cir. mils. Ans.

This would call for a No. 000 B. & S. wire for the outside wires from the
dynamo up to the point J. The neutral wire could be made about No. 1.

(d) The drop in mains Z> or i? will be 220 X .035 = 7.7 volts. The

area of mains D will be

. 21.6X500X25 ^c /wc • -i a
A = =r^ — ' =» 35,065 cir. mils. Ans.

This would require a No. 5 wire, and a No. 8 or 9 would be sufficient

for the neutral.

. 21.6X200X100 -^ ,^, ... , .

A = _ _ = 56,104 cir. mils, nearly. Ans.

A No. 3 B. & S. wire would probably be used for the outside wires and
a No. 6 for the neutral.

CAL<:UI.ATIONS FOR ALTERNATING-CURRENT LINES

41, A load that consi§ts wholly of lamps possesses
very little self-induction, and for ordinary lighting systems,
where the distances are short, it is usual to make the calcu-
lations for lines carrying alternating current in the same
way as was described for the direct-current system. This
assumes the power factor to be 1, which is not exactly true.
If greater accuracy is required, formulas taking into con-
sideration the power factor should be used. After the
primary current has been determined and the distance to
the center of distribution is known, the size of the primary
line wire can be worked out. The power supplied over the
line must be slightly greater than that supplied to the
lamps, on account of the loss in the transfprmers. This loss

ICANDESCENT LIGHTING

f^f course, on the efficiency of the transformerj

ui ^ older styles had a low efficiency, but very little

U wasted in transforraers of modern make. Table I

.the average efficiency at full load, as attained by good

rmers,

TABIiE I
■ EFFICIENCY OF TRANSFOHMFK9

tput

TfAttS

EHrciency
Per Cent.

Output
Watts

Efficiency

Percent.

1,000

^ 000

»0O

5,000
6,ooo

94^8

95-7
96.2
96,4
96.6
96,7

7,000 j

8,000

9,000
10,000
15,000

96.80

96.85
96,90

96.95
97-20

In order to illustrate the calcalation of primary

PlO.87

BXA.MPLB. — Current is supplied to the transformers T by means of
the primary mains A^ B, The pressure at the lamps is to be 104 volts
and one thousand 16-candlepower lamps are to be operated from the
secondaries. The pressure at the transformer is to be 2,000 volts at

§33

INCANDESCENT LIGHTING

full load and tke drop in the primary mains 200 volts, thus making the
voltage at the alternator 2,200 volts at full load. The loss in the sec-
ondary wiring at full load .nust not exceed 2 volts, and the lamps
require 3.5 watts per candlepower. The average efficiency of the
transformers may be taken at 96 per cent. Required the cross-section
of the primary wires, assuming the power factor to be 1.

Solution. — Each lamp requires 16 X 3.6 = 56 watts, and one thou-
sand lamps will require 56,000 watts in the secondary circuit at the
lamps. The total secondary current will be ^fSJ^ amperes, and since
there is a drop of 2 volts in the secondary wiring, the number of watts
lost will be *f J2^ X 2, and the total watts delivered by the secondary
must be 56,000 + M&F X 2 = 57,077. nearly. The watts delivered to

the primaries would be -—5^ = 59,455, and since the primary voltage

of the transformers is 2,000, the primary current will be V1>W = 29.73
amperes, nearly. Having determined the primary current, we can
now calculate the size of the line. The distance in this case is 2 mi.,
or 10,r)()0 ft., and the drop 200 volts. Using formula 1 and consider-
ing the problem the same as for a direct-current circuit,

21.6 X 10.560X29.73
200

33,906, approximately. Ans.

This would call for a No. 5 B. & S. wire.

43. For rough calculations of the primary current on
1,000-volt and 2,000-volt primary mains, the following allow-
ance per lamp may be used:

TABUB n
CURRENT ALLOWANCE PER IJ^lMP

Candlepower of
Lamp

1 ,000 Volts
Primary Pressure
Current per Lamp

2,000 Volts
Primary Pressure
Current per Lamp

16
32
50

.035
.050
.100
.150

.0175
.0250
.0500
.0750

For example, if eight hundred 16-candlepower lamps were
operated on a 2,000-volt circuit, the primary current would
be about 800 X .025 = 20 amperes. This, of course, does
not give the current exactly, because to obtain this the

INCANDESCENT LIGHTING

i33

efficiency of the transformers aad the lamps should be known,
but it affords a ready means of getting at the current approxi-
mately when preliminary calculations are being made, la
many cases, the more refined calculations would not change
the size of the wire in any event, because the wire selected
must be taken as one of the standard sizes, and this in most
cases is not the same as the calculated size*

44, In case the lamps are operated on two-phase or
three-phase systems, the watts to be supplied by the alter-
nator can easily be obtained when the watts per lamp and
the efficiency of the transformers are known. After the
watts have been determined, the formulas given in con-
nection with the subject of electric transmission may be
used to calculate the size of the wire.

TRAKSrORMlCR TESTING

45, In an ordinary lighting system, current is supplied

from the station to a comparatively large number of scattered
transformers, and as a general rule the greater number of
these are loaded for a few hours only. At the same time
the pressure is maintained throughout the 24 horn's, and
while the loss in each individual transformer may be small,
yet the total loss on the system may be quite large. Sup-
pose that the all-day efficiency of the transformers on a
given system is 90 per cent., the efficiency of the primary
transmission lines 95 per cent., and the efficiency of the
secondary lines also 95 per cent.; the total efficiency from the
station switchboard to the lamps will then be .90 X .95 X »95
= .812, or 81.2 per cent. Assuming that the customers pay
by meter and that all their meters register correctly, for
every 100 kilowatt-hours delivered from the station, only 8L2
kilowatt-hours would bring in returns to the company. In
many stations the percentage returned is considerably lower
than this, on account of slow-nmning meters, ineiBcient
transformers, or other causes.

The transformer constitutes an important element in the
efficiency of an alternating-current lighting system, and

§33

INCANDESCENT LIGHTING

while it is true that efficiency is not the only point to be
aimed at, there is no doubt that many systems have been
greatly improved and put on a better paying basis by a care-
ful weeding out of small and inefficient transformers. Of
course it is equally, if not more, desirable that the trans-
formers shall be reliable in operation, because immunity
from breakdowns is of even greater importance than good
efficiency. New transformers of reliable make will usually
be satisfactory as regards efficiency and insulation, but these
qualities may not be permanent. The long-continued heat-
ing of the iron core may appreciably increase the hysteresis
loss, this effect being known as aging. Also, the heating
may affect the insulation. In order to determine the condi-
tion of a transformer, certain tests are necessary; a few of
the more important tests as recommended by the General
Electric Company are here described briefly.

46. Insulation Test. — The insulation of a transformer
should be tested at three points: between primary coil and
core or case, between secondary coil and core or case, and

mmnmmm o,

-z:

u u u u

» I

Pio.88

between primary and secondary. Measurements of insula-
tion resistance by means of a Wheatstone bridge are of no
use whatever for a test on transformers. Measurements thus
made with low-potential direct current might show a high

INCANDESCENT LIGHTING

§33

insulatioo resistance, and the tnsitlatton might yet be iiiLapa-
ble of standing even the normal working pressure* Insula-
tion tests are therefore made with high-potential alternating
current.

Fig, 38 shows the general scheme of connections for a
high-potential test as applied to testing the insulation of
a transformer. The high pressure is usually obtained from
a special high -potential step-up transformer, though if this
19 not available, a number of ordinary transformers may be
used with their fine-wire coils connected in series* so as to
give the high pressure desired. The main switch A' is con-
nected to the primary coil P through an adjustable resist-
ance r that enables the high pressure generated in the
secondary S to be regulated. The ends 7, 7 of the primary
coil of the transformer under test are connected together and
to one end of S. The ends x of the secondary coils are also
connected together, grounded on the case at a, and connected
to the other terminal of S, It is important that the various
terminals of the coils be connected as indicated; otherwise,
some parts of the winding will be subjected to greater strains
than others. When the switch A' is thrown in, the high
E. M, F, generated in S tends to break down the insulation
between the primary and secondary coils ol T. The applied
pressure should be at least three times the primary pressure at
which the transformer is designed to work; i. e., a 2^000-volt
transformer should stand a pressure of at least 6,000 volts
between its primary and secondary coils.

In order to determine the applied voltage, a spark gap 9
between needle points, or a high-reading electrostatic volt-
meter Fj may be used. It has been found by experiment
that the voltage required to jump between needle points in
air increases almost in direct proportion to the length of the
gap, until about 30,000 volts is reached; 30,000 volts (alter-
nating) will jump about la inches in air between bright needle
points J 15,000 volts will jump about I inch; 10,000 volts, i inch;
and so on. A curve showing the relation between sparking
distance and voltage has been given in a previous Section,
By setting the points, say, i inch apart and then raising

INCANDESCENT LIGHTING 56

the voltage, by cutting out r, until a spark jumps across, it
is known that the pressure applied to the transformer is
about 10,000 volts. If needle points are used, they should
be renewed after every discharge; otherwise, they become
corroded and give inaccurate results.

In applying high-potential tests, care must be taken not to
strain and injure the insulation permanently. It is all well
enough to apply a test that will indicate to a certainty that
the insulation will be capable of standing the strain put on
it in service, but if the test is made unnecessarily severe,
good apparatus may be permanently injured. High-potential
tests should not, therefore, be long continued — a few seconds
is sufficient to show whether the insulation is defective or
not; a longer application will only serve to injure good insu-
lation. High-potential tests should be made when the appa-
ratus is hot, because then the insulation is weaker than when
cold, and any weak spots will be more likely to show them-
selves; besides, the transformer is warm when used imder
actual operating conditions.

47. Measurement of Core lioss. — The core losses of a
transformer are practically constant at all loads, because the
magnetic density remains nearly constant. The core losses
determine the amount of power that the transformer takes
from the line when the secondary is not loaded, and on
lighting systems it is particularly important that these
losses shall not be excessive, because there are long
intervals when the transformers are not loaded, and an
excessive core loss will have a great effect on the all-day
efficiency. The measurement of the core loss is most
conveniently made by applying a voltage to the secondary
circuit and leaving the primary open. This allows lower
voltages and larger currents to be used than if the test were
made on the primary. If the primary were connected to
the mains, as in the regular operation of the transformer,
it would be difficult to get instruments of suitable range.
The connections are shown in Fig. 39; a is an ammeter;
b^ a voltmeter; and c, a wattmeter. An adjustable resistance d

INCANDESCENT LIGHTING

133

is connected in series with the secondary, so that the applied
voltage can be varied as desired. Simultaneous readings of
the three instruments are taken, and, in addition, the speed
of the alternator should be recorded so that the frequency of
the current can be estimated. When the voltage across the
secondary has been adjusted to the nofmal voltage of
the secondary, the ammeter indicates the exciting current,
which is usually from 2 to 5 per cent, of the full-load

Fig. 39

current, and is the same percentage no matter whether the
primary or secondary is considered. In this test the exciting
current supplied to the secondary is measured; the current
that the primary will take is the secondary current divided
by the ratio cf transformation. The wattmeter c indicates
the core loss in watts, and the ratio of the wattmeter
reading to the product of the voltmeter and ammeter read-
ings gives the power factor of the transformer at no load.

48. Meivsuroiiioiit of Primary and Socoiidary lleslst-
aiioe. — In order to estimate the PR losses in a transformer
when it is fully loaded, the resistances of the primary and
secondary coils must be known. These resistances can be

§:

INCANDESCENT LIGHTING

measured by means of a Wheatstone bridge, but it is usually
more convenient and accurate to use the drop-of-potential
method if instruments of suitable range are at hand. This
method has been described in connection with the general
subject of resistance measurements, and consists in sending
a steady current of known value through the coil to be
measured and noting the drop in potential indicated by
a voltmeter connected to the coil terminals. Knowing the
values of E and /, the resistance R at once follows from
Ohm*s law.

Fig. 40 shows the connections for measuring the resistance
of a transformer primary. The current can be varied by

means of the adjustable resistance, and a number of readings
of voltage should be taken for different values of the cturent
and the resistance calculated therefrom. The average of
these results should then be taken.

In making resistance tests, the coil should be at a uniform
temperature throughout. The best way to make sure of this
is to keep the transformer in a room of uniform temperature
for several hours before the test is made. Also, care must
be taken that the current sent through the coil will not be
sufficiently great to raise its temperature appreciably during
the time the measturement is being made.

INCANDESCENT LIGHTING

§33

All resistance measurements should be reduced to a
standard room temperature of 25^ C* (77° Fj in order that
measurements made at different room temperatures may be
readily compared- The resistance R at 25° C, may be
obtained from the observed resistance H' at 7^ by means of
the formula

/?^ =. /? (1 + .004/) (8)

where

1 + .0O4/
i ^ r^ ^ 25

(4)

When the resistances are known, the copper losses in pri-
mary and secondary for any given load are easily calculated.

49. Measurement of Impedance and Copper

Ijosscs,— This test, Fig. 41, not only enables the impedance
of the transformer to be calculated, but it also gives a fairly

close idea as to the
total copper losses.
The impedance of a
transformer varies
but little with the
load, and it repre-
sents the combined
effect of the resist*
ance and reactance of
the primary and sec-
ondary coils in pre-
venting the flow of
the current. The ef-
fect of the impedance
is usually expressed
by stating the num-
ber of volts that must be impressed on the primary in order
to set up full-load current in both coils, the secondary being
short-circuited. Since the secondary is short-circuited, it
follows that the applied volts are expended in overcoming

Pio.41

^Recommendation of Committee on Standardization, American
Institute of Electrical Engineers.

§33 INCANDESCENT LIGHTING 69

the impedance, and the number of volts that must be applied
to set up full-load current with short-circuited secondary is
known as the impedance volts of the transformer. With short-
circuited secondary it requires but a small applied voltage
(from 2 to 8 per cent.) to set up full-load current; consequently,
the magnetic density in the core is very low and the core
losses are almost negligible. If, therefore, a wattmeter be
inserted, as shown \n Fig. 41, its indication may be taken as
practically equal to the full-load copper loss of the trans-
former. The variable resistance is adjusted imtil the
ammeter indicates full-load current in the primary. The
number of volts necessary to overcome the impedance is
indicated by the voltmeter, so that the value of the impe-
dance V7?'-f (2 7:nLy in ohms is obtained by dividing the
voltage by the current. With a 2,000-volt transformer,
the impedance voltage might be anywhere from 40 to 160
volts, so that a source of alternating current at fairly low
pressure is needed for this test.

50. lioacl Test. — Transformers should be given a run
under full load in order to note the heating effect. The
simplest way is to load the secondary with 'a bank of lamps
or some other convenient form of resistance and adjust
the load until the transformer supplies its rated ^secondary
current. The temperature of various parts, such as core,
case, outside of coils, etc., should be measured by means
of thermometers; if oil is used, a thermometer should be
immersed in it. The test should be continued until the ther-
mometers indicate that a constant temperature has been
attained. This method of testing is quite satisfactory where
there is plenty of power available or where the transformers
to be tested are small.

A method of making a heat test that is particularly appli-
cable where a number of transformers of the same voltage
and capacity are to be tested is shown in Fig. 42. This is
sometimes known as the motor-gctierator method^ because it
is analogous to the method of loading two generators by
coupling the machines together and running one as a motor

INCANDESCENT LIGHTING

and the other as a generator. It is possible to fully load two
transformers by taking from an outside source only sufficient
power to supply the losses. The transformers are tested in
pairs; the secondaries are connected in parallel and are
supplied from a circuit A at the normal voltage and frequency
and the current in each secondary therefore induces normal
voltage in each primary. The primary coils are connected
in series in such a way that their voltages oppose each other.

-VWWWVWVW

FiO.42

A circuit H is attached to the primary terminals, and, while
there is full voltage in each primary coil, the voltage at the
terminals of circuit /^ is zero because the two primaries are
opposed to each other. If, now, a voltap:e is impressed by
circuit B, it is evident that current will be set up in the coils
independently of the voltaj^e at the primary and secondary ter-
minals of each transformer. Each transformer is practically
short-circuited through the other, and twice the impedance

§83 INCANDESCENT LIGHTING 61

voltage applied by circuit B will cause full-load current
to flow in the coils of both transformers. Each transformer
will therefore run at full load, although the energy supplied
from the outside is equal to the losses only. Circuit A
supplies the exciting current and core loss; circuit B supplies
the copper losses. Both the supply circuits may be from
the same alternator, or two independent sources may be used,
provided that the frequency is the same for each. If both
circuits are from the same source, transformers will be
necessary to obtain the proper voltages at A and B.
Rheostats should be inserted at e and /, so that the voltages
applied to the primary and secondary may be adjusted until
ammeter g indicates full-load current in the primaries.

51. Re^iilutlon. — One of the most important features
to be considered in the selection of transformers for lighting
work is the regulation. If the voltage drops excessively
with increase of load, or on the other hand, rises by a like
amount when the load is thrown off, the service will not
only be poor, but the life of the lamps may be materially
shortened. The regulation of a transformer may be defined
as the ratio of the rise of secondary-terminal voltage from
full load to no load, to the secondary-terminal voltage at full
load. The regulation can be tested by connecting the trans-
former to a full load of lamps and then gradually removing
the load, at the same time seeing that the primary volt-
age and frequency are maintained constant. It is usually
expressed as a percentage of the full-load secondary voltage.
The regulation varies with the nature of the load; with a
given transformer the change in voltage will be greater for
an inductive load than for a non-inductive. The regulation
is therefore always given for non-inductive load unless
otherwise stated. For well-designed transformers the regu-
lation may be from 2.5 per cent, for small transformers
to 1.25 per cent, or slightly lower for large ones. If the
design of a transformer is such that there is considerable
magnetic leakage between the primary and secondary coils,
the regulation will be poor.

4tJB— 14

[INCANDESCENT LIGHTING $33

flAQE BAITTCRIES IX MGHTING STATIONS

Btopagre batteries are much used in connection
DOth two-wire and three-wire direct-current distribution
ns, being placed either in the station or near a center
ributian- When used in substations, thejr help to
tain a uniform voltage at the lamps, and also relieve
sders during intervals of heavy load* In isolated
tSi where a load oi lights and a fluctuating motor load
-J to be supplied from the same dynamo, a storage battery
jonj unction with a constant-current booster can be used
advantage to maintain a uniform load on the generating
.^ipmenti and a constant voltage at the lamps regardless
le fluctuating current supplied to the motors. Batteries
^aIso be used in connection with three- wire systems to
nsate for unbalancing, but as a general rule it is not
sable to use them in this way on account of the cells
liecoming unevenly discharged. Where a three-wire system
"^ be operated from a single dynamo, it is better to use a
T-generator balancing set to provide for inequalities in
load on the two sides of the system. The various methods
of operating storage batteries and the connections for bat-
tery boosters have been explained in a previous Section, so
that further explanation is here unnecessary.

ARC LIGHTING

(PART 1)

THE ABO

OPEN ARCS

!• General Features. — If two carbon rods attached to
the terminals of a dynamo, as shown in Fijj. 1, are first
touched together and then drawn apart a short distance, say
about i inch, current will flow between the points, the car-
bons will become heated to an exceedingly high tempera*
ture, and an electric arc will be formed between the
carbon points. The arc
is so called because the
electric flame between the

electrodes does not pass »- ^

straight across but is more 9 I^r

or less lx)w- shaped. An ~~

arc can be formed between
any pair of conducting ^B^
terminals — for example,
between two copper or
iron rods — but in this case ^®- ^

the metals are rapidly melted away. In practice, therefore,
the choice of electrode materials is limited. In nearly every
case the electrodes are in the form of carbon rods, though
many experiments have been made with other substances
and it is possible that some of these may yet prove successful.
For example, in the so-called magnetite arc lamp one elec-
trode is made of magnetic oxide of iron and the other of

Ar notiu of copyright, see paM€ immediaUly MlotnmM tki tiili i^f*
184

ARC LIGHTING

§34

copper. In some forms of arc lamp for locomotive head-
lights, an upper positive carbon with a lower negative elec-
trode of copper has been used, but we will confine our
attention for the present to the ordinary type of lamp with
both electrodes of carbon.

After the carbons have been separated for a time, they
appear as shown in Fig. 2. This represents an open arc, or
an arc formed in the open air as distinguished from one that
is formed in a confined space where very little oxygen is

present. The f!ame, or arc, con-
sists of incandescent carbon vapor
that conducts the current across
from point to point. The vapor
acts in the same way as a wire
carrying a current, and if a magnet
is brought near^ the arc will be
forced to one side- If the magnet
is strong enough, the arc will be
stretched out until it is broken*
Also, the arc itself, under ordinary
working conditions, will be sur-
rounded by a magnetic field, and it
is, no doubt, this field that causes
the arc to assume the bow shape-
The flame keeps shifting around the
points as the carbons burn away.

Fio. 2

2. Direction of Current-

The shape of the carbon points
depends on the direction in which the current flows. In
Fig, 2» the top carbon is positive and the current flows
from the top to the bottom, as is nearly always the case
with direct-current lamps. Fig. 3 shows a section of the
carbons; it will be noticed that the upper, or positive, one
becomes hollowed out slightly, as shown at a, while the
lower one becomes pointed. The hollow a is called the craitr^
and is the seat of the greater part of the light given out by
the arc. The cai'bon becomes volatilized at the crater, and

§34

ARC LIGHTING

the vapor conducts the current from one carbon to the other.
Although the temperature of the negative carbon is high, it
is not nearly so high as that of the vapor, and hence the
latter is condensed on the negative tip, form-
ing the point, or else is thrown off. Only a
portion of the vapor is so condensed; part of
it combines with the oxygen of the surround-
ing air and the burning carbon monoxide
may be seen surrounding the arc as an envel-
ope of bluish flame, similar to that which
appears over the coal in an ordinary coal
stove. With direct current, the positive car-
bon wastes away approximately twice as fast
as the negative, as it is maintained at a much
higher temperature. In the ordinary arc
lamp using carbon electrodes, the greater
part of the light is given off from the incan-
descent carbon points; the arc itself gives
comparatively little light. In some of the 'lamps recently
brought out, for example the magnetite lamp, the light is
given off almost wholly from the arc and comparatively
little is emitted from the electrodes.

Fio. 3

3. Temperature of the Arc. — The temperature of the
electric arc is the highest that has yet been produced. The
exact temperature is difficult to determine, but it is estimated
to be about 8,500° C. The carbon in the crater is vaporized;
hence, the temperature attained must be that of the boiling
point of carbon. Some idea as to what this means may be
obtained when it is known that a temperature between 1,700°
and 1,800° C. is sufficient to melt platinum, the most difficult
of all metals to fuse. This high temperature is utilized in
electric furnaces. An increase in the current does not
increase the temperature, tut it does increase the size of the
crater and hence the total amount of light given out. If
very powerful lamps are required » large carbons and heavy
currents are used to get a large crater as, for example,
in lamps used for searchlights. For ordinary commercial

ARC LIGHTING

§34

sb-eet lighting, the carbons are usually i to S inch in diam-
eter p though sometimes larger carbons are used to make the
lamps burn longer*

4. Toltnge of the Arc, — If the voltage across the

terminals of an ordinary open-arc lamp is measured, it will
be found that it usually lies between 40 and 50 volts, depend-
ing on the length of the arc; 45 volts may be taken as a fair
average. This total voltage may be considered as made up
of three parts: (a) That necessary to overcome the resist-
ance of the carbons and the parts of the lamp mechanism
through which the current has to flow; (b) that necessary to
overcome the resistance of the carbon vapor between the
electrodes; (c) that which multiplied by the current repre-
sents the energy necessary to volatilize the carbon.

The E. M, F. necessary to overcome the resistance of ^o
carbons and lamp mechanism is not very large; in most
lamps it will not be more than 5 or 6 volts, of which S to
3.5 volts may represent the drop in the carbons while the
balance is in the mechanism and various contact resistances.
The E. M. F, necessary to overcome the resistance of the
arc proper is also small^ but depends to a certain extent on
the length of the arc. In most cases it will not be more
than 5 or 6 volts. Since the voltage across the lamp is» say^
45 volts and the combined drop due to the resistance of the
carbons, lamp mechanism, and arc proper is approximately
10 volts, it follows that the balance (about 35 volts) multi-
plied by the current represents the number of watts expended
in bringing the carbon up to the boiling point and causing it
to volatilize. This voltage is often spoken of as the counter
E, M, F. of the arc, but this term is not so commonly used
as it once was. Quite a large amount of energy must be
expended to bring the carbon up to the boiling point, and tt
is now generally admitted that the large balance of voltage
required over and above that necessary to overcome the
various resistances is a consequence of the power necessary
to volatilize the carbon. The above values of the voltage
are fair average values for open-arc lamps operated with

§34 ARC LIGHTING S

direct current, but they may vary somewhat with different
makes of lamp. The actual voltage across the arc is con-
tinually varying when the lamp is in operation, but in a well-
adjusted lamp it should not vary through wide limits.

5. Current. — Ordinary direct-current, open-arc lamps
are usually operated with current ranging from 6 to
10 amperes. Very common values for the current are
6.6 amperes for lamps giving 1,200 nominal candlepower
and 9.6 amperes for those giving 2,000 nominal candle-
power. The exact value of the current is different in lamps
of various makes, but whatever it may be, it is essential
that it be maintained at a constant value if the lamps are to
work properly. If the current becomes larger than that for
which the lamps are designed, they will overheat, the
carbons will flame badly, and the service will be generally
unsatisfactory. Open-arc lamps may also be operated with
alternating current, but they are not so satisfactory as those
using direct current either as regards light-giving properties
or general performance. In the case of the alternating-
current open arc, both carbons become pointed or have very
small craters, so that the light is thrown upwards much
more than with the direct-current lamp. Also, since the
current flows alternately in opposite directions, the rate of
consumption of the two carbons is more nearly equal.

ENCLOSED ARCS
6. General Description. — Within a comparatively
recent date enclosed arcs have superseded open arcs in prac-
tically all new work, and in many old installations the open
arcs have been replaced by the enclosed type. The enclosed
arc differs from the open arc in that it is surrounded by a
small globe that practically excludes the air. Fig. 4 shows
one arrangement of carbons and enclosing globe; g is the
globe, which is from 5 to 6 inches long and about 3 inches
in diameter. Some inner globes have their lower end
closed, the bottom carbon being placed in a holder suspended
from the cap that covers the globe. The more common

ARC LIGHTING

§84

arrangement, however, is to have the globe open at both
top and bottom with the lower carbon holder supported from
below. The top and bottom edges of the globe are ground
true so as to make a tight joint*

In Fig* 4, the globe is held between a circular spring

and a thick asbestos
washer, which allow
a certain freedom of
movement under ex-
pansion and contrac-
tion and thus avoid
breakage. The lower
carbon d is clamped
by means of screw e
and the whole lower
globe can be easily
removed from the
lamp by loosening
screws d, d. The top
of the globe is cov-
ered by the £-as cap e^
which consists of an
iron casting faced off
smooth so as to form
a close fit with the
top edge of the globe*
The cap is not fast-
ened to the globe in
any way, but is free
to move about a little
and thus adjust itself
to any slight eccen-
tricity of the upper
carbon. The hole
through which the carbon slides is sh"ghtly larger than the
carbon in order to allow the latter to slide freely. Since
the top of the glass and the lower surface of the plate are
^ound plane, little air can get in between them» and the only

Fro. 4

§84 ARC LIGHTING 7

place where much air can enter the bulb is at the hole in the
center of the top plate, through the small space between
the carbon and the plate itself. In the plate shown, there is
an annular groove around the carbon where it passes through
the cap. This leaves less surface for the carbon to rub against
and affords a space in which eddies are formed by the hot air
passing up, thus further tending to keep out the cold air. The
rate at which the carbons are consumed depends considerably
on the construction or condition of the gas cap. If the cap
allows much air to enter, the consumption will be rapid.

Fig. 5 shows a style of cap used by the General Electric
Company; it consists of two parts — a cover a and a lower
casting b. In the casting is a spiral groove c that connects
with the inner part of the globe by means of holes d and
with the outer air by the opening e at the side. After the

t h ^

Fio. 3

lamp has been in operation for a short time, the spiral recess
becomes filled with gases similar to those in the globe and a
movement of the carbons, instead of drawing in fresh air,
draws in a mixture similar to that already in the globe.
Also, a slight decrease in the temperature of the arc results
in a contraction of the atmosphere in the globe; with a plain
cap, fresh air would be drawn in, but the spiral duct acts as a
gas reservoir and tends to keep the atmosphere in the globe
more uniform, thus resulting in a longer life for the carbons.
The arrangement of gas cap and methods of mounting
the enclosing globe vary considerably with different makes
of lamp.

As soon as the carbons of an enclosed-arc lamp are drawn
apart an arc is formed, as in the open lamp, but the oxygen
in the globe is soon burned out and the gases present
become rarefied, because the heat of the arc causes them to

ARC LIGHTING

§34

expand and pass out. The globe is not air-tight, so that
there is always a small amount of oxygen present, but not
enough p however p to cause the rapid combustion that takes
place in the open arc. The arc practically bums in a hot
atmosphere of nitrogen, carbon monoxide, carbon dioxide^
and a small amount of oxygen. The oxygen present is just
about sufficient to combine with what carbon is thrown off
and prevent its being deposited on the glass. If a lamp is
in good condition I it will burn from 80 to 1t50 hours, depend-
ing on the design^ without renewing the carbons* The
bulb in time becomes coated with a light-colored deposit,
sometimes mixed with a little carbon, which comes princi-
pally from impurities such as silicon; this deposit does not
cut off the light to any great extent if it is not allowed to
become too thick. If the current is excessive the globes will
become blackened or even melted* It is not usually advisable
to bum these lamps more than 120 hours^ as the deposit
becomes so thick as to cut off a considerable amount of light,

7* Consuinptloii of Carbons. — One of the most stri-
king features of the en closed-arc lamp is the slow con*
sumption of the carbons; this is, of course, due to the
absence of oxygen in the enclosing chamber* With the ordi-
nary open arc, the positive carbon is burned at the rate of
about li inches per hour, but in an enclosed-arc lamp the
consumption varies from *05 to *08 inch per hour* Enclosed-
arc lamps may, therefore, be made to burn a long time with-
out trimming; some have even been made to burn as long as
21X) hours. This is one of the features that has led to the
extensive introduction of this type of lamp. As in the open
arc, the negative carbon of the direct-current enclosed arc
burns about half as fast as the positive carbon; with alter-
nating current, the consumption is more nearly equal.

The rate at which the carbons are consumed and the
sensitiveness of the arc to slight changes in current or volt-
age depend very largely on the amount of air present in the
enclosing globe. If the voltage, current, or frequency on a
line is not steady, it is often better to work with a less

ARC LIGHTING

sensitive arc even if the life of the carbons is reduced some-
what. A gas cap that gives good results on one system may
not work so well on another, but a few trials will indicate
the best style of gas cap to use<

8» Voltagife and Current, — If the carbons of an open
arc are pulled apart a distance more than sufficient to give
from 40 to 45 volts across the arc» they will flame badly*
On the other hand, the enclosed-arc lamp is operated with a
long arc (about S inch for a voltage of 70 to 80 across the
arc) and it bums steadily without flaming. If a short arc
is used in the enclosed arc, it is found that soot or carbon is
deposited to such an extent that the lamp becomes useless;
long arcs are therefore essential in these lamps. This allows
them to be operated at a high voltage, and the best results
are usually obtained with 70 to 80 volts across the arc.
They usually operate with a smaller current than the open-
arc lamps, some of them taking as low as 2i to B amperes.
Enclosed-arc lamps have also been built to operate on 220-
volt circuits. These burn with a very long
arc and are not quite as efllicient as the
ordinary MO-volt lamps, to which the above
figtu^cs refer- A 220-volt lamp will take
from 140 to 145 volts across the arc.

9. Character of Knclosed Are,
Fig- 6 gives a general idea of the appear-
ance of a direct-current enclosed arc; this
figure should be compared with Fig. 2.
In the enclosed arc, the carbons are sepa-
rated by a wide gap, but the principal dif-
ference is that they do not take on the ^'® ®
pointed shape; the ends of the carbons remain nearly flat
and the arc keeps continually shifting around over the ends.
The flat shape of the ends is, no doubt, due largely to this
tendency of the arc to shift around* The light given out
is soft and tinged with violet rays, having much less of the
dazzling appearance so well known in connection with the
open arc. In the alternating-current enclosed arc^ the lower

ARC LIGHTING

and upper carbons are of about the same temperature and
the light is thrown np more than with the direct-current arc*
The carbons have^however^ the flat-ended appearance and the
arc shifts around even more than the direct-current enclosed
arc. In open arcs, the carbons are close together and a
shifting of the arc from one side to the other causes very
pronounced changes in the intensity of the light* In the
enclosed-arc lamp, the shifting of the arc also causes changes
in the illumination, but not to nearly so great an extent as in
the open arc. The arc is so much longer that the carbons do
not obstruct the light nearly so much when the arc shifts to
one side or the other; the illumination is therefore more
steady and uniform than that from an open arc,

10* open Versus Enclosed Ares. — -The enclosed-arc

lamp has proved superior to the open arc because of the
following advantages; (a) It gives a softer, steadier, and
more uniformly distributed light j {^) it burns very much
longer without retrimming, thus effecting a saving in the
cost of carbons and in the cost of labor for trimmings
(r) it operates with a higher arc voltage and smaller
currents thus making it more suitable for parallel operation
on ordinary constant*potential lighting circuits; (d) for
interior ilium iuati on » it involves less fire-risk when two
globes are used— the inner enclosing globe and the ordi-
nary outer globe. Against these advantages must be
placed the extra cost of the enclosing globes » breakage of
globes, and cost of keeping inner globes clean. Enclosed-
arc lamps require a higher grade of carbon than open arcs,
but allowing for this there is a saving of $8 to $10 per
lamp per year over the cost of operating the old-style,
op en -arc lamps. The open arc was never much of a success
with alternating current; it produced a loud hum and was
very unsteady* With the enclosed arc, quite satisfactory
results can be obtained with alternating current, so much
so I in fact, that alternating current is supplanting direct
current for arc lighting, particularly for street lighting or in
places where the lamps are much scattered. The mechanism

S34

ARC LIGHTING

has been designed so that little noise is possible, and the
enclosing^ of the arc prevents the humming of the arc itself
from being loud enough to be objectional. However, while
the alternating-current, enclosed-arc lamp is much superior to
the alternating-current, open-arc lamp, it can hardly be said
that it is capable of giving quite as good all-around service
as the direct-current, enclosed-arc lamp.

ARC-IilGHT CARBONS

11. Arranjjement of Carbons. — In nearly all the
lamps used for ordinary purposes, the carbons are
arranged vertically, one above the other, as shown in
Fig. 2. When so arranged, the top carbon should always
be the positive one when direct current is used, otherwise
the crater will be formed in the bottom carbon and most
of the light will be thrown up instead of down. When
lamps are first connected up, they should be allowed to
bum for a short time; if the crater makes its appearance
in the bottom carbon,
the connections to the
lamp terminals should
be reversed. Of course,
with alternating current
it makes no difference
how the lamp is con-
nected in circuit, as the
current is continually
reversing and both car-
bons burn alike. It is an easy matter to tell when a direct-
current lamp is correctly connected. Allow the lamp to bum
for a short time, then switch it off and see which carbon
remains bright the longer. The positive carbon is much
hotter than the negative, hence the negative carbon is the
one that becomes dull first.

For use in stereopticons and other projection apparatus,
the carbons are often inclined at an angle, as shown in
Fig. 7. This allows more of the light from the crater to

Pio.7

ARC LIGHTING

Fio.8

the lenses. In searchlights, a similar arrangement is
*ionly the carbons are often slanted the other way and
jht is reflected from a parabolic reflector or Mangin mir-
ror, as shown in Fig. 8,
which shows the arc
placed at the focus of
' a parabolic reflector M.

— ' ■ The rays of light on

— — strikingf the mirror are

reflected out parallel to

each other, and as they
are thus kept bunched
^ together the light may
be made to penetrate
' long distances, A small concave reflector r is usually placed
throw the rays of the arc that would ordinarily pass out-
vraMs, back toward the main reflector.

A parabolic, ground-glass, silvered mirror is used in the
United States Navy, but for ordinary commercial work the
Afangin mirror is used, as it is cheaper and easier to make.
It is a glass mirror having
two spherical surfaces A^ B
of different radii, as shown in
Fig. 9. The back surface A
is silvered and the rays are re-
flected from it. As the glass
is thicker near the edges than
in the middle, the rays are
there bent or refracted more
than they are at the center,
and by making the mirror of

the proper dimensions it can be made to reflect the rays in a
horizontal direction and give practically the same effect as
the parabolic mirror.

Fig. 10 shows another arrangement of carbons used in
searchlights. In this case the positive carbon is larger than
the negative, and both carbons are arranged horizontally.
The crater, therefore, points directly at the mirror. This is

Pio.9

§84

ARC LIGHTING

Pro. 10

the arrangement now most extensively used in America

both for naval and commercial work.

In all cases where arc lamps are used in connection with

mirrors or lenses for projection work, it is essential that the

arc be kept in the focus of

the mirror or lens. The

lamps must therefore be

arrangfed to move the car-
bons toward each other, as

they are consumed, in such

a way that the position of

the arc will not be changed;

a lamp that does this is

known as a focusing lamp. For ordinary lighting, it is not

essential that the arc be kept in one place, so the lower

carbon is nearly always fixed and the arc maintained by

allowing the upper one to move downwards as the carbon

is consumed.

Fig. 11 shows a rather peculiar arrangement that is used

for stereopticon lamps. Here the carbons are arranged at

right angles to each
other. The lamp mecha-
nism moves ^ in a hori-
zontal direction and C
upwards as they burn
away, so that the arc is
always maintained in

the same position at a. The position of C keeps it from

interfering with the lens /, and allows the greater part of the

crater in the end of B to be exposed.

12. Composition of Carbons. — Carbons used for ordi-
nary open-arc lamps in America are composed principally of
petroleum coke. This is made from the residue left from
the distillation of petroleum. It is ground up and mixed
with a binding material, such as tar, or a similar substance,
and is then molded into rods. Sometimes the rods are made
In molds under a heavy pressure, but more frequently they

Pio.ll

ARC LIGHTING

§34

are made by forcings the material through dies. The rods
are tlien gradually dried and afterwards baked or fired at a
high temperature. Gas-retort carbon has also been used for
the manufacture of arc-light carbons, the exact composition
used varying with different makers.

For enclosed-arc lamps, a very much finer quality of carbon
is required than for the open-arc lamp. If the carbons used
in these lamps are at all Impure, the impurities become vol-
atilized and are deposited on the inner globe* Enclosed-arc
carbons are therefore made principally of lampblack, which
^ is practically pure carbon, and are considerably more
expensive than the ordinary carbons made from
petroleum coke. They must be straight and of uni-
form diameter, otherwise they will not pass through
the cap of the enclosing globe properly.

Fig, 12 shows a cored carbon^ so called from the
core a running through it, A small hole in the cen-
ter of the carbon is filled with a much softer material
than the surrounding part. The soft core volatilizes
more easily than the rest of the carbon and pro-
duces a supply of vapor that increases the stability of
the arc and keeps it from shifting around so much.
Cored carbons are particularly useful for alternating-
current lamps, in which the arc is liable to be unsteady
and flickering. The cored carbon reduces the volt-
age corresponding to a given length of arc, or with a
given voltage it allows a longer arc than would be
practicable with solid carbons. Some makers use
cored carbons for both the positive and the negative elec-
trodes of alternating-current lamps, while others use them
for the positive electrode only. Cored carbons are used
more particularly with alternating-current lamps, as the plain
carbons usually give satisfactory service with direct current.
Searchlights are almost wholly operated by direct current
and the positive carbon is generally cored, as it is important
to keep the arc in one place as closely as possible,

Wbatever kind of carbon may be used^ it is essential that
it be as pure and as imiform in quality as possible* If many

Pta. 12

%94r ARC LIGHTING 16

impurities are present, they may interfere seriously with the
quality of the light. Of course, impurities are especially
bad in the case of the enclosed arc on accoimt of the deposit
caused on the inner globe, but even in the open arc they
are objectionable because they volatilize at a much lower
temperature than the carbon and thus tend to lower the
temperature and light-giving properties of the arc. Hard
spots in the carbon will cause uneven burning and carbons that
are too soft are apt to flame badly. Hard spots will also give
rise to hissing. Carbons used for open-arc lamps are usually
electroplated with a thin coating of copper. This increases
their conductivity and makes them burn more uniformly and
last longer. ^____

PHOTOMETRY OP THE ARC liAMP

LIGHT DISTRIBUTION

13. The light given out by an incandescent lamp is
fairly uniform, assuming, of course, that the lamp has
no shade on it. On the other hand, the light given out by
an arc lamp with a clear globe varies greatly in differ-
ent directions. Since the manner in which an arc lamp
distributes its light is of the greatest importance, it will be
well to examine the peculiarities of some of the more impor-
tant types. It will not be necessary here to go into the meth-
ods of measuring the light intensity, which is usually done by
means of a Bunsen or similar photometer, with the arc lamp
so arranged that its candlepower may be measured in any
direction. It is a rather difficult matter to measure the candle-
power of an arc lamp, because the arc is continually shifting.
Special photometers have been devised for the purpose, one
of which, designed by Prof. C. P. Matthews, has a number of
mirrors arranged around the lamp so that the light given out
in various directions is reflected along the photometer bar.
The setting of the screen thus gives a measure of the mean
spherical candlepower.

14, Before going into the subject of light distribution,
a few points in regard to globes may not be out of order.

4(iB— 15

ARC LIGHTING

§34

Ordinary open-arc lamps used for street lighting are gener-
ally provided with clear globes; clean globes cut off from
6 to 10 per cent* of the light, and if dirty will cut off more.
Sometimes opal globes are used» especially il the lamp is
used for interior work; these soften the light and do away
with the sharp shadows that are always present with a dear
globe* In other words, an opal globe alters the distribution
of the light considerably and avoids the deep shadows under-
neath the lamp. At the same time a globe of this kind cuts
off from 30 to 40 per cent, of the light; in fact» if the globe
is very milky it may easily cut off 50 or 60 per cent 1^ the

ifohmnfai _

case of the en closed-arc lamp, there is in addition to the
outer globe the inner globe, and hence the amount of light
cut off is somewhat increased* Reflectors are used much
more largely with the alternating -current arc lamp than with
the direct current, because the former tends to throw its light
to a greater extent above the horizontal, and by using the
reflector this light can be thrown downwards and utilized.

15, Direct-Current, Open- Arc Liamps. — The distri*
bution of light from an ordinary open-arc lamp is about as
shown in Fig. 13, This represents the variation in the

S34

ARC LIGHTING

intensity at different angles above and below the horizontal
line passing through the arc that is located at a. The
distance from a, measured along the radius at any given
angle, is proportional to the candlepower of the lamp when
viewed from that position. For example, the light reaches its
greatest intensity at a point
about 45° below the hori-
zontal and then rapidly
diminishes on both sides
of this point. Directly
above or below the arc
there is, of course, little
or no light, as the arc is
obscured by the frame of
the lamp and the carbons
themselves. The open arc
throws out comparatively
little light in the horizontal
directioji, and the quantity
of light thrown upwards is
small. It is thus seen that
the plain open-arc lamp
using a direct current, with-
out any reflector and with
simply a clear-glass globe,
gives a good distribution
of light for street lighting,
because, on account of the
formation of the crater in fig. h

the upper carbon, it throws the bulk of its light downwards at
an angle of about 45°, where it is most needed. This is one
of the reasons why the direct-current, open-arc lamp proved
so successful for street lighting. If the deep shadows directly
under the lamp are objectionable, they can be softened by
using a clear globe with the lower half ground.

16. Alternating-Current, Open-Arc Liamps. — The

<}i3tribution from an alternating-current, open-arc lamp is not

ARC LIGHTING

§34

of much practical importance because Hiese lamps are sel-
dom used. It isj however^ instructive to compare it with
Fig. 13. Fig. 14 shows the general distribution from an
alteraating-current, open-arc lamp, as determined by Uppen*
bom. A great deal of the light is thrown above the
horizontal; this is because the two carbon points are alter-
nately positive and negative, so that both become heated

to nearly an equal amount.
Such a lamp, to be effect-
ive for street lighting,
should be provided with a
reflector to throw the light
down where it is wanted.
The curves shown in
Figs. 13 and 14 represent
average distributions* It
must be remembered that
the arc always shifts around
more or less, and hence the
shape of the distribution is
constantly changing* The
curves will, however, illus-
trate the marked difference
in the light distribution
of the alternating-current,
open-arc lamp as compared
with the direct-current,
open-arc lamp.

17» DI rect* Current ♦
F"o- ^ Enclosed- Arc Xjamps.

There has been a great deal of discussion regarding the light-
giving properties and efficiency of the enclosed arc as com-
pared with the open arc. The data here given are abstracted
from a report of a committee of the National Electric Light
Association on tests made by Prof. C. P. Matthews* Fig. 15
shows the average of curves from direct-current, 110-volt,
enclosed-arc lamps used on constant-potential circuits.

§34

ARC LIGHTING

Curve A shows the distribution when the lamp is provided
with an opalescent inner globe only; there is no large outer
globe. This curve should be compared with that shown in
Fig. 13 for the open arc. With the enclosed arc, the light
is of fairly high intensity through a considerable angle
below the horizontal. In this case, the maximum value is
approximately 360 candle-
power and occurs about
30° below the horizontal.
This is considerably less
than the intensity given
by an open arc at about
40° to 45° below the hori-
zontal, but the light from
the latter falls off very
rapidly on each side of the
maximum point, whereas
in the enclosed arc it is
fairly well maintained
through a considerable
angle. Curve B shows the
distribution when the lamp
is provided with a clear
outer globe in addition
to the inner opalescent
globe. The effect is to cut
down the intensity as a
whole slightly. Curve C
shows the effect of using
an outer opalescent globe;
the effect is to make the
light approximately uniform in all directions at the expense
of cutting it down greatly.

The distribution of light from an enclosed-arc lamp is sub-
ject to considerable variation. It depends to some extent on
the shape of the enclosing globe and also on the thickness
of deposit on it. It also depends on the position of the arc
in the enclosing globe.

Fig. 16

ARC LIGHTING

§34

18» Alteriiatlngr-Current, Enclosed "Ai^ Ijaiii|)s,

The direct-current lamp ^ives a better distribution for street
lighting than the alternating-current, enc)osed-arc lamp, and»
on the whole, the latter is not quite as efficient as the direct-
current lamp. If, however, full benefit is to be obtained from
the light given by the alternating-current enclosed arc» a
reflector of some kind must be used. This is shown by the
curves in Fig. 16. Curve A represents the distribution
from an alternating-current enclosed-arc lamp that has an
opalescent inner globe and a clear outer globe. A large
quantity of light is thrown above the horizontal, as in the
alternating-current open-arc lamp. Curve C shows the dis-
tribution when the same lamp is provided with a reflector.
The curves show how the light that would ordinarily be
thrown upwards, and hence be of little or no use for street
illumination, is made available. Thus equipped with a
reflector, the alternating-current arc makes a better showing
against the direct-current arc. The alternating-current lamp
equipped with a reflector is rapidly finding favor as a street
illuminant; though it may not be quite as efficient as the
direct-current arc, its use in many cases so simplifies the
outfit required at the station that the slight difference in
the efficiency of the lamps is more than made up. This
will be more apparent later when the various systems of
supplying lamps with current are considered* In Fig. 16^
curve ff shows the distribution given by an alternating-
current » enclosed-arc lamp when used with opalescent inner
and outer globes,

CAKDLEPOWER OF ARC LAMPS

19. The can (lie power of an arc lamp is a rather
indefinite quantity. In making comparisons between dif-
ferent lamps, the only way that is at all fair is to take the
mean spherical candlepower; i. e., what their candlepower
would be equivalent to if it were equal in all directions,
instead of varying, as indicated by the curves just shown.
In comparing incandescent lamps, it is usually sufficient to
compare their mean horizontal candlepower as obtained by

§34

ARC LIGHTING

spinning the lamp; but in the case of an arc lamp, the distri-
bution is so irre^lar that the mean spherical candlepower
must be taken.

In the early daj^s of electric lighting, it was customary to
speak of the ordinary open*arc lamp as giving 2,000 or 1,200
candlepower. The candlepower of these lamps was not
nearly so high as this. It is barely possible that under
exceptional condirons the light given out in the direction of
maximum intensity might have reached these figures, but
the average candlepower was nowhere near 2,000; about
376 to 450 would be nearer the mark. This old rating gave
rise to a great deal of trouble » as customers were often told
that the lamps should give 2,QO0 candlepower and that the
lighting companies were not living up to their contracts* It
has become customary, therefore, to specify arc lamps as
taking so many watts instead of supplying a certain num-
ber of candlepower. This is generally more satisfactory,
because the watts can be measured at any time, to see if the
contract is being lived up to< The lamp formerly rated at
2,000 candlepower has thus come to mean one that is sup-
plied with 450'watts; and a 1 »200*candlepower lamp, one that
is supplied with 300 watts. The ratings, 2,000 and 1,200
candlepower, should never have been applied to these lamps
in the first place, as they have absolutely no meaning. As
has been stated » the mean spherical candlepower of an ordi-
nary direct-current open are is generally somewhere between
375 and 450 candlepower. The mean spherical candlepower
represented by curve A, Fig< 16, is about 223; curve B, 181;
curve C 166. For the alternating-current lamps, represented
by Fig. 16, the mean spherical candlepower for curve A is
about 140; for curve ^, 114.

20. PoTver Consumption per Candlepower. — ^The
number of watts that must be supplied to the terminals of
an arc lamp per mean spherical candlepower will depend
on the construction of the lamp and on the conditions under
which it is used. For example, when direct -current lamps
are operated on 110- volt circuits, it is necessary to have a

ARC LIGHTING

§34

resistance in series to take tip the voltage over and above
the 80 volts required by the arc; and even if the line voltage
were suited to that of the arc, a resistance would still be
necessary to make the lamp regulate properly, as will
be explained later. The waste in this resistance may
amount to as much as 140 or 150 watts, and this lowers
the general efficiency o£ the lamp. When lamps are oper*
ated in series, a resistance is not necessary and the waste in
the lamp is less. An ordinary series, open-arc lamp requires
about 1,2 watts per spherical candlepowen A direct-current
enclosed arc requires about 1*8 watts per spherical candle-
power, not counting the power lost in the resistance. If
a resistance is used, as in the case of a lamp operated on
110-volt direct current, the power consumption per candle-
power will be 2,3 to 2.4 watts. For example, the lamp
represented by curve .4, Fig. 15, took 4.9 amperes at 110-
volts or 539 watts, of which 147 watts were wasted in the
resistance and 392 watts taken up at the arc. The lamp
gave about 223 mean spherical candlepower; hence, the
total number of watts per candlepower was Mz = 2,4, Not
counting the loss in the resistance, the watts per candle-
power would be 1.8, nearly.

21, The alternating-current, enclosed-arc lamp requires
about 2.4 watts per spherical candlepower, not counting the
energy lost in the lamp mechanism- If an alternating-cur-
rent lamp is run from constant-potential mains, the excess
voltage can be taken up by a reactance, or choke coil, which
wastes much less energy than a resistance. The energy
wasted in the mechanism of a constant-potential, alterna-
ting-current arc lamp will not be more than half that of the
direct -current lamp using a resistance. If the power lost in
the mechanism is inchided in both cases, the alternating cur-
rent constant-potential enclosed arc will require 2.46 watts,
as against 2.3 watts required by the direct-current arc. If a
shade is used on the alternating-current arc, the power con-
sumption per candlepower delivered below the horizontal
becomes much less; but in comparing the different lamps,

§34 ARC LIGHTING 23

they should all be taken as nearly under the same conditions
as possible.

These figures are intended to give a general idea as to the
efficiency and illuminating power of the various kinds of
lamps, and represent average conditions, but lamps may be
found that will vary considerably from the above. If the
enclosed-arc lamp taking 450 watts is compared with an
open-arc lamp taking the same amount of power, it will
be found that the open-arc lamp will give a somewhat
brighter illumination on the street. Notwithstanding this
fact, the public, as a rule, does not object to the enclosed
arc being substituted for the open, because the light is
much steadier and softer and the shadows are not so
deep. The preceding figures relating to arc lamps are here
collected in Table I for convenient reference. Table II
gives data regarding the power consumption of the different
types of a well-known make of enclosed-arc lamp. By the
efficiency of the various lamps as given in this table is
meant the ratio of the watts utilized at the arc to the watts
supplied at the lamp terminals. The direct-current lamp,
run in series on constant-current circuits, has the highest
efficiency because there is very little resistance in series
with the arc. The efficiency of constant-potential lamps
is lower, because of the power lost in the resistance or
reactance that is inserted in series with the arc.

22. IlluTnlnatlon. — The number of arc lamps required
to illuminate a given space varies greatly, so that it is difficult
to give any definite figures on this subject. Enclosed-arc
lamps are now largely used for the interior illumination of
mills and factories. The light from these lamps is steady and
agreeable, and if they are provided with light opal globes or
reflectors, a very even illumination can be obtained. In textile
mills, the illumination must be very good; hence, more lamps
are needed per unit of floor area than would be required, for
example, in a foundry. Table III, given by the General
Electric Company, shows the approximate number of watts
required at lamp terminals for first-class illumination.

TABIxE I
POWBR CONSUMPTION OF AHC liAMPS

=-=s

•0

^^eIw

gfe

*^5

. e

K Type of Lamp

0 -

S(3

|c3

i
&

ill

Series open arc^ 2,000

nominal candlepower.

about 9.6 atnperes at

50 volts

460-481

450

375

1-3

1*2

Direct-curreot enclosed

arc, no volts 4.9

amperes, opalescent

inner globe, no outer

539

147

392

223

2.4

1.8

Same, with opalescent

inner and clear outer

globes . . 4 . . . .

539

147

392

181

2.9

2.T

Same, with opalescent

inner and outer

globes

539

147

392

155

2.5

Alternating-current

enclosed arc, no

volts, opalescent inner

and clear outer globes

416

342

140

2.9

2.4

Same, with opalescent

inner and outer

globes

416

342

114

3.6

3-0

S34

ARC LIGHTING

OS 0

•sf

O ^ m in O m

;g^

m
eo

•-I "♦ eo

*"2sa?i^ '

in «

O 00

CO
0)

l§

•-I in'*

*8RS.?.^

M MM

s«

O^ «

4l ■

<?^

■°?SS'«S'^

•sS

•"2<2S>?1^ *

M ^ en

M in-^r

a
o

O c

»n r

OOG

•'gRSfrsi"

^ MM

m O

— «

in CO C

M o »n O «*> r^

4rf

" 1

M •-• in en •-•

J^ O* M m O *n

•J

r^ r^oo 2 ^

i-)

— •

•^

to c

^ 3

oo C

^ V

»^ O M m O m

_ Q

oo r-» m ►- ^

3
1
1

mo Q o g o

•^ oo m 0 m
M in * i-i

in 1/

CO G

O r^oc

O «n N O m in

00 r^ cnco ^
^ en

in oo c

in r-^

en O O M^ O m
►^ oo 00 oo O
t-i en N H^

in c

oo C

■>

-1

s«

o§

•^KflSS^ ■

SB'S

T •»

00 c>

O W O O* Qv O
r-^ i>»ao O M
1- ^

O CO o

O oo M in in O

t^ r-^ «n o* ^

^ «n

en •

CO •

a: .

S .

c^,*»

CU O

a ^

•6 =^

■>

a.e c

r^ If

Sfe^fe^.«^i£

Sfe^sj^^fi 1

ue'<

:e<

.::s

CL^d:

ub^<

ei<

•CSJ

ARC LIGHTING

§34

TABI.E III
WATTS PEtt SQUARE FOOT FOR INTERIOR ABC LlGnTINQ

Balldttig

Watts per

Square Foot
Average

Conditioiis

Watts ger

Square Foot

Variatioii

Machine shops, hi^fh roofs, no belts
Machine shops* low roofs, belts, and

other obstructions .

Hardware and shoe stores , . . .
Department stores, light material,

bric-^-brac, etc .

Mill lighting, plain white goods , ,
Mill lighting, colored goods, high

looms , . , , .

General office ^ no incandescents , .
Drafting rooms .

■75

1. 00

1.00
I<10

1*30
1-50

1.75

.50 to 1. 00

•75 to 1.25
.50 to 1.00

.75 to K2S
,90 to 1*30

1,10 to 1.50

1.2$ to 1.75

1.50 to 2.00

METHODS OF DISTRIBUTION

SERIES DISTRIBUTION

23. Most of the arc lamps used for scattered street-
lighting work are connected in series. For example, in
Fig. 17, A represents a direct-current arc-light dynamo in
the station and /, /, / arc lamps situated at different points
on the street; /, /' represent the terminals of the lampSi
which are marked + and — to distinguish them from each
other. The current flows through the lamps in the direction
indicated by the arrows; the -f terminal should in each case
conpect to the upper carbon and the negative terminal to
the lower. If one of the lamps B should be connected in
the circuit backwards, as shown, the current would enter
at the lower carbon and the lamp would burn upside down;
in such a case the terminals should be changed so that the
current will enter at the top carbon, as in the other lamps.

§34

ARC LIGHTING

In a simple series circuit, the current through all the lamps
will be the same unless there is a leakage to ground and
across to the other line, as indicated, for example, by the
dotted path a-b. There will be little leakage if the line is
in proper condition, so that it may be generally assumed
that the current through each lamp is the same.

The current in the circuit must be kept constant; i. e., the
number of amperes must be kept the same no matter how
many lamps are in use. If there were ten lamps in opera-
tion, each requiring 45 volts pressure, the dynamo would
have to generate 450 volts. Suppose that three of the
lamps are cut out by short-circuiting them — lamps in a

D/namo

Pio. 17

series circuit must always be cut out by short-circuiting,
otherwise the circuit will be broken. In practice, each lamp
is provided with a switch, as indicated at 5, which is used to
cut out the lamp by allowing the current to flow past it. If
the voltage remains the same, the current will increase,
because the resistance of the circuit has been decreased; if
the current is increased, the lamps will perform badly and
perhaps be damaged. In order to keep the current the same,
the voltage should be reduced to 7 X 45 = 315 volts, when
the lights are cut out. This is done by providing the
dynamo with an automatic regulator. In case the lamps
are operated in series by means of alternating current, a

ARC LIGHTING

§34

special transformer or re^lator of some kind is used to
keep the current constant.

The series system of distribution is very widely used for
street lighting, and is, in tad, about the only system that
can be used economically where the lights are scattered-
As the same current flows through all the lamps, the system
is operated by using a small current (usually from 6 to
10 amperes) at a high pressure. This calls for a small line
wire {usually about No, 6 or No. 8 B. & S,), and thus
requires a comparatively small expenditure for copper,

24, Arrangement of Series Circuits, ^ — If a simple

series circuit is operated, as shown in Fig. 17, the voltage
generated by the dynamo or other source of current will be
the voltage per lamp multiplied by the number of lamps
plus the voltage drop in the line. If the number of lamps
operated is large, the voltage required becomes very high.
Thus, in order to operate 75 enclosed-arc lights, the machine
must generate » roughly, 6,000 volts, allowing 80 volts per
lamp so as to include the drop in the line. Up to within a
comparatively recent date, this was considered about as
tr my lamps as could be operated from one machine, because
of the difficulties of construction and operation at higher volt-
ages. The result was that a station operating a large number
of lights had to be equipped with a number of comparatively
small machines, which were, at best, not very efficient. To
overcome this, the so called mnitkircuit machines were brought
out, which are capable of operating 125 to 150 lights. The
construction of arc dynamos has also been perfected to such
an extent that machines are now built capable of operating
150 lights on a single circuit

25* Multlelrcult Series Maehtiies. — There are two

kinds of multicircuit machines; namely, those in which there
are two or more circuits in series and those in which
there are two or more circuits in parallel. The later styles
of Brush machine are examples of the first kind; the new
type of Western Electric machine is an example of the sec-
ond. The newer and larger style of Brush machine is of the

§34

ARC LIGHTING

multipolar type, but is similar in principle to the old two-pole
machine. The principal difference is in the arrangement of
the circuit connections.

Suppose that A and B represent two of the commutators
of a Brush machine which in the older machines were con-
nected in series, as shown in Fig. 18 (a), across a single
circuit. The voltage between
the terminals of the circuit 1-2
is equal to the sum of the volt-
ages generated in the sections
of the armature A and B, Sup-
pose, however, that two series
of lamps are arranged as shown
in Fig. 18 (^). Here the same
number of lamps are connected
in series as before, but they are
divided into two circuits 1-2 and
5-4, and the pressure between
points 1, 2 is one-half what it
was before, because there are
only one -half as many lamps
connected between i, 2 as there
were in the previous case.

The whole object of this
arrangement is to allow a large
number of lamps to be operated
in series without introducing
extremely high pressures on the
line and dynamo. This may,
perhaps, be more clearly under-
stood by taking the example
shown in Fig. 19. It would not
be necessary to use a multicircuit arrangement for as small
a number of lights as ten, but it will serve to illustrate the
point. If it is assumed that open-arc lamps are used and
50 volts allowed per lamp, so as to include the line drop,
500 volts will be required for operating the single circuit in
Fig. 19 (a). The fall, or drop, in pressure from the + to

X V

Fig. 18

ARC LIGHTING

§34

the — terminal of the itiachiiie can, therefore, be represented
as indicated in Fi^. 19 {a). Each section of the armature
generates 250 volts, and as these are connected directly in
series, there are 500 volts across the circuit.

Suppose, now, that the ten lamps are connected as in
Fig, 19 {^}. Take the point 1 as a starting point and assuioe
that it is at zero potential. The armature section A raises
the pressure to 2.50 volts, so that there is a difference in
pressure of 250 volts between points 3 and 1. The current

fO l^mps

Pio. 19

then passes through the circuit 3-4 containing five lamps,
and the pressure drops off as indicated. Armature B again
raises the pressure 250 volts, so as to operate the five lamps
in circuit 2-1.

It is thus seen that the multicircuit arrangement shown in
(b) operates the same number of lights as in (a), and the
maximum pressure between the terminals of the dynamo or
bet veen the terminals of either of the circuits is one-half
that in the single-circuit scheme of operation. This descrip-
tion has been given with reference to dynamos, but the same

§34 ARC LIGHTING 81

multicircuit plan can be used with transformers supplying
series alternating-current lamps. The transformer has a
secondary consisting of two or more coils connected in exactly
the same manner as described for the armature windings.

Since, in the multicircuit arrangement, as used on the Brush
machines, the several circuits are in series with each other, the
current must be the same in all and only one regulator is
necessary on the dynamo. Where two independent circuits
are operated in parallel from the same machine, the voltage
applied to each of the circuits must be capable of independent
regulation. For this reason, the Western Electric multicircuit
machines are provided with two independent regulators, one
for each circuit. Some of the larger Brush machines are
arranged so as to operate four circuits, though any of these
dynamos may be operated as ordinary single-circuit machines
if desired.

PARAIiliEli DISTRIBUTION

26. When arc lamps were first introduced, parallel
distribution was not very common, but now a large num-
ber of lamps are operated in parallel on constant-potential
circuits, both direct and alternating. The increased use of
enclosed-arc lamps for store and factory illumination is
largely responsible for this.' Such places were usually
equipped with low-pressure, constant-potential plants for
incandescent lighting, and series arc lamps for interior
work are more or less objectionable on account of the
high pressures necessary for their operation. The series
arc lamp is, however, used for interior illumination in some
large concerns where a large number of lights must be
operated. Enclosed-arc lamps are operated in parallel by
connecting them directly across the line, as indicated in
Fig. 20. Each lamp is here provided with a double-pole
switch and cut-out or branch block carrying fuses for protec-
tion in case a short circuit occurs in the lamp. Most lamps
have a switch mounted on them, and it is only necessary to
provide a separate switch, as shown, when control of the
lamp from a distant point is desired. . Of course, the switch

46B— 16

ARC LIGHTING

is arranged to open the circuit through the lamp, and not
short-circuit it, as when cutting out a series lamp. Fig< 21
shows the lamps connected to an ordinary 110-volt, direct-
current system » By using lamps with a slightly different
mechanism t they may be operated from the secondary of a
transformer, as shown in Fig, 22.

27* When arc lamps are operated from constant-potential
directK;nrrent mains, it is necessary, for two reasons, to
connect a resistance, Fig. 20^ in series with the arc* In the
first place, the lamps will not regulate well without it, and

L/fre

if^^^vitof

Fi<3. 20

in the second place, the voltages used on con slant -potential

circuits are usually considerably higher than the voltage
required by a single arc lamp, so that the eiccess voltage
must be taken up in a resistance. If an arc lamp is con-
nected directly to constant-potential mains, without the
intervention of any resistance, its action is unstable. If
the current flowing through an arc increases, the resistance
of the arc decreases, because the increased current causes
the cross-section of tlie arc to increase. On the other hand,
if the current decreases, the resistance of the arc increases.
The consequence is that if the constant voltage of the mains

S84

ARC LIGHTING

is just equal to that required by the arc and if the cturent
through the arc, for any reason, decreases a little, the
resistance offered by the arc at once increases, thus causinfi^
a further decrease of current and increase of resistance, with
the result that the arc goes out. On the other hand, an
increase of current results in a decrease of resistance, and
this causes a still further increase of current. The operation
of the lamp is therefore unstable, and the arc will not
remain constant for any length of time.

trfl

Pio.31

Now, if a line voltage somewhat higher than that required
by the lamp is used and enough resistance inserted to give a
drop through the resistance sufficient to bring the arc voltage
to the correct amount when the normal current is flowing, the
lamp will become stable in its action. For, suppose the cur-
rent decreases a little; the drop through the resistance will
decrease and, since the line voltage is constant, the voltage
across the arc will be increased, thus compensating for the

Pio. 22

alteraatingf current passes through the coil, the changing
magnetism set up generates a counter E. M. F. in the coil.
The choke coil wastes less energy than the resistance, but, of
course, it cannot be used with a direct-current lamp, as the
direct current is not capable of setting up the alternating
magnetism necessary to generate the counter E. M. F. The

§84 ARC LIGHTING 86

resistance or choke coil, as the case may be, is generally
mounted in the top of the lamp and is arranged so that it will
be ventilated, in order to insure cool running.

28. 220-Volt, Enclosed-Arc Lianips. — Enclosed-arc
lamps for operation in parallel across 220-volt mains are
built, but they are not quite as eflficient or satisfactory as
the 110- volt lamp. They operate with about 2i amperes
and take 140 volts at the arc. Another type of 220-volt
lamp consists of two 110- volt lamps combined in one;
that is, there are two sets of carbons and two arcs
connected in series. Still another plan is to use two lamps
in series across the circuit.

29, Enclosed-Arc liamps on 660-Volt Circuits.

It is very often desirable to operate enclosed-arc lamps on
550-volt railway circuits for the illumination of car bams,
street-railway parks, etc. The special types of lamp made
for this purpose are generally operated, five in series, across
the circuit so that each lamp receives, approximately,
110 volts. Each lamp is usually provided with a resistance
in conjunction with an automatic cut-out, so that in case
a lamp is cut-out of circuit the remaining lamps will not
get an excessive current and will burn uninterruptedly.

ARC LAMPS

30. The different makes and types of arc lamps in

commercial use are so numerous that it is impossible
to give a complete list of them here. This is, however,
not necessary, because many of the types differ only in
mechanical details and involve no new principles. Complete
instructions concerning the different makes are furnished by
the manufacturers, and all that is necessary is to point
out the features peculiar to lamps adapted to the various
kinds of service.

No matter what type of lamp is used, it must be arranged
so that the carbons will be kept the proper distance apart.
In a few special cases, as for example, in some searchlights

ARC LIGHTING

§34

or projectton lamps, this is accomplished by hand, but in all

commercial lighting work the lamp must be provided with a
mechanism that will feed the carbons together as they
are consumed. In most cases, the lower carbon is fixed
and the top one is fed down in such a way as to keep
the arc of the proper length. When the upper carbon is
released by the lamp mechanism i it is fed down by tlie
attraction of gravity. Gravity is therefore the propelling
force in most lamps, and the whole lamp mechanism is
essentially a device first to separate the carbons and start
the arc and then to release the carbon and allow it to
feed down at the proper time. The mechanism generally
consists of a clutch or clockwork controlled by electro-
magnets, the current in which depends on the condition
of the arc that releases the clutch or clockwork, thus
allowing the carbon to feed down whenever the arc exceeds
the length for which the mechanism is set. The mechanism
must also be arranged so that the tamp will regulate
without affecting other lamps on the circuit. This is
comparatively easy to accomplish in the case of lamps
operated in parallel, because the pressure across the mains
is constant, and each lamp is independent of the others. In
the case of the series lamp, however, the current that flows
through one lamp also flows through all the others, and
each lamp must be arranged so as to feed when necessary,
no matter what may be the condition of the others.

cqnstakt-potextiaIj lamps

31 • The regulation of constant- potential lamps is

usually brought about by an electromagnet or solenoid con-
nected directly in series with the arc, and designed to operate
either a clutch or clockwork mechanism so as to feed the
carbon when required. For example i take the simple
arrangement shown in Fig. 2J1* This is not intended to
illustrate any particular make of lamp, but simply to bring
out some of the points connected with the operation of con-
stant-potential lamps in general. By far the greater number

S34

ARC LIGHTING

of lamps in use employ a clutch rather than a clockwork
feed. In Fig. 23, /, t' are the lamp terminals connected
across a constant-potential circuit; r is the resistance inserted
to take up the surplus voltage and to make the action of the
lamp stable; 5 is a solenoid connected directly in series
with r and arranged to draw up core c when current passes;
d is the clutch, which is here shown simply as a washer with
a hole a little larger than the rod e, to which the upper car-
bon is attached; / is a stop against which d strikes when the
core c lowers a sufficient amount; g is the top (positive)

(>=p-

Pxo. 23

carbon and h is the lower (negative). The current enters
at /, passes through r and 5 to the brush k^ which makes a
sliding contact with the carbon rod e. From e^ it passes to
the top carbon g, thence to the lower ^, and out at /^ This
is supposed to be a direct-current lamp; hence, the current
should flow as shown, so as to bring the crater in the upper
carbon. With an alternating-current lamp, it would, of
course, make no difference how the lamp was connected.

When the current is off, d comes down against / and the
latter is tilted so that e slides through until g strikes h. As
soon as the current is turned on by closing switch w, the
core c is at once drawn up to the full limit for which the

ARC LIGHTING

§34

lamp is adjusted* As soon as c moves up, d tilts, as shown
in tlie figure, and grips e thus raising^ and striking or start-
ing the arc. As the carbons burn, the arc gradually becomes
longer, and consequently the resistance of the lamp as a
whole increases. One fact that must not be lost sight of is
that this lamp is connected in parallel across a constant-
potential circuit; hence, as the arc lengthens the current
through the lamp is bound to decrease, no matter what
current the other lamps on the same circuit may be taking*
The result is that as the arc gets longer, S becomes weaker
because of the smaller current and c lowers a little. When c
has moved a short distance, d comes in contact with /, and
as € drops still farther, d is tipped a little and allows rod e
to slide through. As soon as the carbons come nearer
together, the current at once increases, c is pulled up, and
the rod is held until the current becomes small enough to
allow it to feed again. In this way the carbon is fed down
a little at a time, and the feeding is brought about by the
decrease of the current due to the increase in the length of
the arc. _____^

SERIES AK€ LAMPB

32 i The regulation of series arc lamps and the

mechanism necessary for their operation present a dif-
ferent problem* In the first place, when the lamps are nm
in series, the current is always maintained at a constant
value, or it should be if the regulator on the circuit works
properly. Hence, a series magnet alone is not able to do
the regulating , because its pull remains the same no matter
what may be the condition of the arc* Again, there must
be some device in the series lamp that will preserve the con-
tinuity of the circuit in case a carbon breaks, falls out, or the
circuit through the lamp becomes broken in any way* If
such a device is not provided, an open circuit in the lamp
will result in all the lights on the circuit going out. This
device is called a cnt-mti.

Although the current through the arc remains constant in
a series system, the voltage across the arc increases as its

S34

ARC LIGHTING

lengfth increases, and this increased voltag:e is made to bringf
about the regulation. Suppose that the simple lamp shown
in Fig, 23 is modified by extending the core c downwards
and adding another coil 5', as shown in Fig. 24; the start-
ing resistance r can also be omitted, as this is to be a
series lamp, and there will be no excess voltage to be taken
up. The current is maintained at a constant value and resist-
ance is not necessary to insure stability of operation. The
second coil S^ is wound with a large number of turns of fine
wire, so that when it is connected in shunt across the arc,

Pio.2i

as shown, only a small current will flow through it. The
coils Sy 5' pull c in opposite directions, and c will always
take up a position where the two pulls are balanced. The
action of the lamp is as follows: When the current is off,
carbons ^, k are in contact. Switch m is connected across
the terminals, and in order to put out the lamp, m is closed.
When the lamp is thrown into circuit, the main current passes
between,^ and A, but since the carbons are in contact there
will be little or no drop in potential between them, and hence,
practically no current will pass through the shunt coil 5^.
Coil 5 pulls up the plunger, and in so doing lifts the upper

ARC LIGHTING

§34

carbon and starts the arc. The instant, however, that the
carbons ^ and h separate, current flows through 5^ because
there is then considerable difference of potential between
^and h. The result is that as the carbons are separated,
the downward pull of S* becomes stronger until it finally
balances the upward pull oi S^ when the arc remains sta-
tionary. As the carbons burn away, the arc becomes longer;
hence, its resistance increases and the voltage across the arc
increases. The pull of ^Sdoes not change^ because the main
current is maintained constant by the dynamo* The pull
of S keeps increasing as the carbons burn away, and c is
gradually pulled down until the lamp feeds. As soon as^
feeds down the pull of S^ decreases, because the arc shortens;
hence, the position of r becomes again balanced* and so on>
the plunger c moving back and forth through a small range
between the coils. By properly adjusting the clutch, such a
lamp may be made to keep the arc at the proper length
within very close limits,

33. The essential features of the above lamp should be
carefully noted, because most series lamps depend for their
operation on the use of two coils* One of these, the series
coil, carries the main currentj and is opposed by the shunt
coil, which carries a current depending on the length of the
arc* The current in the shunt coil depends only on the
length of the arc in each individual lamp and is independent
of the condition of the other lamps. A lamp of this kind is
known as a diikrcntinl iamp, because the position of the
core € depends on the difference in the pulls between *S'and 5^,
The simple series lamp shown in Fig, 24 is not provided with
an automatic cut-out, but the action of this device will be
explained later when some of the different types of lamp are
described. In some makes of lamp, the coarse-wire and fine-
wire coils are both wound on the same spools, and instead of
using solenoids with a core that is drawn into them, the coils
are provided with a fixed iron core and arranged so as to
attract an armature that releases the clutch or clockwork
mechanism, as the case may be.

S84 ARC LIGHTING 41

34. Some series arc lamps are of the so-called siuni
type. The series coil in these lamps is used only to strike
the arc and it does not act in opposition to the shunt coil.
The feeding is brought about by the shunt coil only, acting
against a spring. The old Thomson-Houston open-arc lamp
described later is of the shunt type, whereas the old Brush
open-arc lamp is a good example of the differential class
where the series coils and shunt coils are wotmd on the
same cores.

EXAMPIiES OF ABC liAMPS

COXSTAJNT-CURRENT, OPEN-ARC, SERIES LAMPS

35. Open-arc lamps, using carbon electrodes, are now
seldom used in America for new work and in many cases
they are being removed and replaced by lamps of the
enclosed-arc type. There are, however, quite a large num-
ber of these lamps still in use, and a short description of the
two most common types will be given here. If the opera-
tion of these lamps is thoroughly understood, the operation
of enclosed-arc lamps will be easily grasped, because the
principles involved are the same in both. •

36. BruHh Arc Lamp. — Fig. 25 shows the connections
for a Brush double-arc lamp intended for operation on a
constant-current series circuit. Two carbons are provided in
order that the lamp may burn all night without retrimming.
The lamp is of the differential type, 55 being the series
coils and S' 5' the shunt coils wound on iron cores /, m.
In the lamp these coils are wound one on top of the other,
but they are shown side by side in Fig. 25 for the sake of
clearness. P and N are the positive and negative terminals.
The poles of the regulating magnet are at /, m; o is an arma-
ture that moves up and down with the rocker R hinged at
the points />, />. The clutches are not shown in Fig. 25, but
their operation will be described later. The positive
carbons e, e are attached to the carbon rods «, v. When
no current is flowing through the lamp, the armature q

ARC LIGHTING

§34

pm. «

884 ARC LIGHTING 48

and the rocker R are in the lowest position, and the strip c
comes in contact with the terminals /, /, thus cutting out the
lamp and allowing the current to take the path P-l-2-j-i-'r-N.
C is an auxiliary cut-out provided to cut out the lamp when-
ever the pressure across the arc exceeds 70 volts. It consists
of a magnet provided with two windings a and by connected
as shown, and a pivoted armature d' that makes contact at c'
when the magnet acts. A small amount of adjustable resist-
ance r* is in shunt with the series magnet 5. By regulating
this resistance, the pull of the series magnet can be adjusted;
r is a small starting resistance connected in series with the
cut-out c.

37. First suppose that the lamp is connected in circuit but
is short-circuited by the switch blade K on top of the lamp
being placed on contact 1, Under these conditions no current
flows through the mechanism, the armature will be down, the
carbons in contact, and piece c will connect i and/. Now,
suppose switch /T to be opened; the current will then take
two paths as follows: P-r'-y-u-e-f-N im^ P'-l''2-j''i-r-N.
However, since 5, S are connected in shunt with r', a portion
of the current will flow through the series coils, taking the
path 1-2-j-S-S-yf and the armature will be lifted, thus sep-
arating the carbons and establishing the arc. As soon as
the armature is raised, contact c leaves the terminals /,/ and
the current passing through r is interrupted, with the excep-
tion of the small current that passes through the fine-wire
coils 5' S^. The clutch has now lifted the carbons and the
lamp is in operation. One end of the fine-wire coil connects
to the upper carbon, as indicated at 4, and the shunt current
takes the path d-S'-S'-b-c'-a-i-r-N', thus, the coils 5', S'
and b are in series and are connected in shunt with the arc.
Coils a and b tend to raise the armature d\ but the current
flowing under normal conditions is not sufficient to actually
raise it. It should be noticed that the current circulates
around S', S' in a direction opposite to that in S, S,

As the carbons burn away and the arc becomes longer,
the current through the shunt coil increases, thus making

ARC LIGHTING

Flo. 26

the poles of the controUmg; magnet weaker and allowing
the armature and rocker to drop gradually until the clutch
releases and allows the carbon rod to slide down a little,

38. Fig. 26 shows the clutch used in this lamp. The

piece a rises and falls with the rocker; when it is raised,
piece d is clamped against the carbon rod by means of the
small lever d^ and the movement of the armature lifts the
whole rod. When a descends, because of the magnets
becoming weaker, the whole clutch and rod move down
until the piece e strikes the plate /; £■ then
remains stationary, while a moves down a
little farther, thus moving the small lever d
and unlocking the clutch,

39. Suppose that a carbon rod sticks in
some way and fails to feed properly. The
arc gradually becomes longer and the volt-
age across it increases until the current in the
shunt circuit becomes much larger than the
normal amount; this causes the armature d^ of the auxiliary
cut-out C to be drawn up and contact made at c*. The current
then takes the path P-T-2-d^-i^-a-i-r-N; the series cot Is and
shunt coils are both cut out, but the current flowing through a
holds up d^. The cutting out of the main coils causes the
rocker to drop and c comes into contact with i and /, thus cut-
ting out the auxiliary cut-out. If the dropping of the rocker
frame makes the carbons come together, part of the current
w^ll pass through the series coils by the path B-J-S-SS-u-
e-f-N^ because in the other path there is the resistance r, and
the lamp will start up again* If starting resistance r were not
used, the path 2-j-t-i-A^ would be of low resistance com-
pared with 2-;-S-S~3'U'-€-f-N, and the lamp would not
relight. If the carbon becomes broken or falls out, a large
current will, for an instant, pass through the fine-wire coilsj
hence, d^ will at once rise and cut out the lamp. Of course,
in this case, e will come into contact with / and / and remain
there, because the carbons cannot come into contact again and
allow the lamp to relight. If no cut-out were provided^ there

§34 ARC LIGHTING 46

would not only be danger of a break in the circuit, due to the
carbons being broken or failing to feed, but in addition the
shunt coils would be burned out because the whole current
would, under these circumstances, pass through them.

40. One of the clutches is adjusted so that it will grip
the carbon rod a little before the other when the rocker is
raised. This starts the arc on that pair of carbons and they
continue to burn until the upper carbon has fed down to the
limit fixed by the adjustment of the lamp. When this occurs
the arc becomes long enough to let the rocker down sufl5-
ciently far to operate the second clutch and start the feeding
of the second carbon.

41. Tliomson-IIouston (T. II. ) Lamp. — The Thomson-
Houston lamp differs considerably from the differential lamp
just described. The series coil is used only to start the arc,
and when the lamp is in operation under normal conditions,
no current flows through the coil: The regulation is effected
by means of the shunt coil alone, and when .the lamp is not
burning the carbons are separated instead of being together,
as is the case with most lamps. Fig. 27 shows the connec-
tions and general arrangement of the essential parts.
A and B are the -h and — terminals; ££ is the carbon rod
carrying the upper carbon w; the lower carbon n is supported
by the lamp frame, not shown in the figure; ^ is a rocker
frame pivoted at x and carrying an iron armature O. This
latter has two holes in it, through which the conical pole
pieces of the magnet project when the armature is pulled
down. When the lamp is not in operation, the frame is held
at its highest position by the adjustable spring P; the
movements of the rocker are steadied by the dashpot C; s is
one of the series coils wound over the shunt coils Af of which
there are two side by side. The small coil //', called the
starting coil, is in series with the carbons and its office is to
cut the scries coil s into or out of action. It is provided
with a movable armature A', on which is mounted the insu-
lated contact / tipped with silver; e is another silver-tipped
contact connected to the point c. When no current flows

ARC LIGHTING

§34

througfh H^ e and / are in contaclj p and r are the cut*out
contacts, the action of wbich will be described later, L is
the clutch and its action is very similar to the one just
described for the Brush lamp.

42. In Figf. 27, the clutch L and frame R are up and the

carbons are drawn a short distance apart- In order that the

Fig. 27

lamp may be started, m must be lowered so as to touch n^ as
follows: At the instaat that the current Is turned on, e and/

S84 ARC LIGHTING 47

are in contact, because no current is flowing through H\
hence, as soon as the current passes, it takes the path A-b
through the series coil s-c-e-f-g-B, Practically, no current
will go from c through the shunt coil to B, because of the
high resistance of this path compared with the other. As
soon as the current passes through 5, the rocker is pulled
down and the clutch is released, bringing the carbons into
contact and allowing part of the current to take the
path A-b-H-E-m-n-B . As soon as current passes through
H, the armature K is attracted, thus separating € and / and
cutting off the current through the series coil s with the
exception of the small current through the shunt coil M,
The rocker rises and carries with it the upper carbon, thus
separating the carbons and starting the arc. As soon,
however, as the carbons are separated, there is considerable
difference of potential across the arc; hence, the shunt coil M
takes its normal current and holds the rocker at the proper
point to give the length of the arc for which the lamp is
adjusted. It is thus seen that the series coil is cut out after
the arc has been started.

The lamp is now burning, and as the arc grows longer the
pull of the shunt coil increases and the rocker is gradually
pulled down until the shoe / of the clutch comes against the
stop, and any further movement causes the rod E to slide
down a little. The pull due to the shunt coil decreases with
the shortened arc, and the rocker rises to its normal position.
The feeding is thus brought about by the action of the shunt
magnet working against the spring P,

43. If the carbons should stick and fail to feed, the arc
will gradually grow longer until the pull exerted by the
shunt magnet will be sufficient to bring the cut-out contact p
down against r. The current will then take the path A-p-
r-E-m-n-g-B in preference to passing through H\ K will
rise and bring e and / in contact. The current will then take
the path A-b-s-c-€-f-g-B\ the series coil will hold down
the armature and the lamp will be cut out unless the move-
ment of the rocker releases the rod and allows the carbon to

46B— 17

ARC LIGHTING

§34

feed, in which case the lamp will continue to hum and
rocker R will rise again, thus separating p and r. If a
carbun falls out^ the current through the shunt will suddenly
increase and the current through N will he interrupted,
J^ will be pulled down, and A^ will rise, the final result being
that the lamp is cut out*

44, When the lamp is to be switched out, switch W is
used. This takes the form of a cam I ' operated by the
lever u. When the handle is turned to one side, the cam
comes against the casting that carries the upper cut-out con-
tacti and thus establishes a short circuit from terminal to
terminal. Most series lamps of the types just described take
about 9.6 amperes for the 2,000-nominal-candlepower size
and 6.6 amperes for the 1,200-candlepower size. The pres-
sure across the arc is from 40 to 50 volts and the carbons
are generally tV inch, a inch, t\ inch, or i inch in diameter^

CONSTANT-CUKRENT, ENCLOSED-AKC, SERIES XiAMFS

45. Toltage Bequlred hy Enclosed- Arc^ Series
Liatnps. — As stated, the enclosed arc is much long^er than
the open arc; the lamps, therefore, take a rather small cur-
rent and the voltage across the arc is hi^h. This is a
decided advantag^e where lamps are operated in parallel on ,
cons tant'po ten tia! systems, where the pressure is nearly
always higher than that actually required by the lamp and
the excess voltage has to be taken np by a resistance or
choke coiL When, however^ it comes to operating lamps in
series, the high voltage across the arc becomes, to a certain
extent, a disadvantage. It means that for a given number
of lamps operated on a circuit, the pressure at the terminals
of the circuit must be higher for enclosed arcs than for open
arcs. This makes it difficult to operate a large number of
lamps from one machine, but by using the multicircuit
arrangement the pressure applied to each circuit can be kept
down. It must be remembered, however, that where these
high voltages are used the line insulation must be thoroughly
good, and attempts to use these pressures on old lines having

§34

ARC LIGHTING

poor insulation have resulted in continual trouble, to say
oothing of the danger involved,

46. Alternating-- Current, Enclosed- Arc, Series
fjampe. — Enclosed arcs are often operated in series by
constant current on alternating-current systems; i. e,, the
alternattng current through the series of lamps is maintained
at a constant value. The lamps used do not diflfer essen-
tially from those for constant direct-current circuits, except
that all magnet cores and armatures are laminated to prevent
heating due to eddy currents, and the mechanism isdesig:ned
so as to avoid -disagreeable humming. The methods for
supplying current to alternating-current series lamps and the
arrangements for maintaining the current at constant value
will be taken up when the subject of station apparatus is
considered,

47. Current. — Enclosed-arc series lamps are ordinarily
operated at about 6*6 amperes, and the voltage per lamp is
from 70 to 78 volts, depending on the length of arc for which
the lamp is adjusted. These lamps have also been built for
a current as large as 8 amperes, with a correspondingly
lower voltage, but the values given are the ones commonly
met with.

48. Enclosed- Arc Ijatnp Construction* — The mech*
antsm of an enclosed-arc lamp generally contains the same
essential features as the corresponding open-arc, but in most
cases the arrangement is simpler. The open-arc lamp must
be fed frequently, because the carbons burn at a compara-
tively rapid rate and the clutch or other feeding mechanism
must be accurately adjusted and kept in good condition if the
lamp is to burn steadily. For this reason, the upper carbon
of an open-arc lamp is attached to a carbon rod on which the
clutch operates, and which is, or should be, kept in a clean,
polished condition. The current Is generally carried to the
top carbon by means of a copper brush pressing against the
rod. In the enclosed-arc lamp, the operation of feeding
takes place at comparatively long intervals, and the feeding
mechanism does not need to be so delicately adjusted* It is,

ARC LIGHTING

§34

therefore » common practice to have the clutch operate directl7
oa the carbon and to dispense entirely with the carbon rod.
Such lamps are said to have a carban feed. The doing away
with the carbon rod raakes the construction simpler and
cheaper, besides allowing the lamp to be made shorter than
is usual where a carbon rod is used* On accoimt of the long-
arc common to enclosed-
arc lamps, their mecha-
nism must be arranged so
that it will have a long
pick-up; i. e., when the
lamp starts up the mecha-
nism must be such as to
pull the carbons a consid*
erable distance apart. In
the case of series lamps, an
automatic cut-out must, of
course, be provided. In
some of the latest types
of enclosed-arc lamps, the
series regulating coil is
made of copper strip wound
on edge and insulated with
sheet mica between the
turns. A coil so con-
structed radiates the heat
readily and is more sub-
stantial than one wound in
the usual way with cotton-
covered wire.

In takingf up the subject of enclosed-arc lamps, we will
confine our attention to two or three typical examples
that will serve to bring out the essential points relating to
their construction and operation* The number of different
makes of enclosed-arc lamp is very large, but they differ
from each other principally in details of construction* The
principles of operation are about the same in all of them,
and the following are not selected because they operate any

Pio>2a

ARC LIGHTING

§34

better than several other?, but because they will serve to
bring oot the points aimed at

49* General Electric Lamp for Constant Alter*
natlng Current. — Fig, 28 shows the general arrangement
of a General Electric lamp designed for operation on a con-
stant alternating-current circuit. There are two series coils

and two shunt coils; only
one of each shows in the
figure since the two coils
are in line* Each pair of
coils has a U-shaped, lami-
nated-iron core attached
to either end of a rocker
to which the clutch is at-
tached. Current is carried
to the upper carbon hy
means of a flexible cable
that folds up in the carbon
tube and the voltage at
which the arc operates is
adjusted by an adjustable
weight on the rocker. A
starting resistance and
cut-out are provided, the
operation of which is prac-
tically the same as described for the Brush lamp. The lamp
is of the differential type, the series coils and shunt coils
working against each other through the rocker-arm. As in
practically all enclosed-arc lamps, a dash pot is provided to
steady the movements of the mechanism.

60. Western Klectrlc I^anip. — Fig» 29 shows two
views of the Western Electric series arc lamp for constant
alternating current and Fig* 30 is a diagram of connections.
The lamp is of the differential type. The terminals are at
a and b\ c is the short-circuiting switch; d, the series coils;
and €i the shunt coils. A 0-shapedi laminated core works up
and down in each pair of coils and the arc is adjusted by

Fto. 30

%U ARC LIGHTING S8

weights attached to the rocker so that they can be screwed
in and out. In this lamp, the enclosing globe is closed at
the bottom and the lower carbon is supported from the top.
An automatic cut-out is provided at / and the starting resist-
ance is located at £'*

Enclosed*arc series lamps for constant direct current are
much the same in construction as the alternating-current
lamps. In direct-current lamps, it is not essential to have
the magnet cores laminated* All alternating-current lamps
have some inductance, hence their power factor is less than
unity (see Table II). The fact that alternating-current arc
lamps constitute an inductive load is to a certain extent a
disadvantage, but the use of alternating current for arc
lighting presents enough advantages to more than outweigh
the disadvantages of an inductive load. The arc itself is
non-inductive, but there is always a certain unavoidable
amount of inductaoce in the magnet windings.

CfONSTA^IT-POTBNTIAL, DIRECT-CUeRKNT LAMPS

51. The mechanism of the eonstant-^poteutlal^
ettclosea-ftre lamp is, as a rule, very simple* The feeding
is controlled by a magnet connected in series and there is no
need of a cut-out. The lamp should » however, be connected
to the circuit through fuses » so that it will at once be discon^
nected in case of a short circuit anywhere in the mechanism*
The series controlling magnet is usually arranged so that it
attracts a core or plunger against the action of gravity,

52. General Electric liamp. — Fig. 31 (a) shows a
General Electric constant*potential, direct-current lamp with
the casing removed. The magnets Af are in series and
arranged so as to pull up the plunger p to which the clutch
rod is attached; the movements are dampened by means of
the dashpot d. ^ is the resistance wound on a porcelain
cylinder and connected In series; by varying R, the voltage
at the arc can be adjusted. Fig. 31 (^) shows the connec-
tions which are very simple. Switch Incuts out the lamp
by opening the circuit through it, not by short-circuiting it, as

ARC LIGHTING

§34

in the case of constant-current lamps. Current enters at P
and flows through the resistance and series coils to the upper
carbon, thence to the lower carbon to N. This pulls up the
core and separates the carbons. As they bum away, the cur-
rent becomes weaker and^ gradually lowers until the clutch is

Pig. 31

released and the lamp feeds. The resistance is provided with
a sliding contact, so that the lamp can be adjusted for pres-
sures varying from 100 to 120 volts. The series coils are pro-
vided with two connections 1, V and 2, 3^ so that the lamp can
be made to operate at 4i to 5 amperes or Z\ to 4 amperes.
When the larger current is used, the connectioos are as shown

I
I

834

ARC LIGHTING

in the figure, because fewer turns are then needed to operate
the pluiigen Solid carbons i inch in diameter are generally
used, and the voltage at the arc is about 80, leaving 20 to
40 volts to be taken up in the resistance* With i~inch car-
bons, the lamp will burn 130 to 150 hours without retrimming.
Fig, 32 {a) is a view of a later type of General Electric
lamp and (d) shows the connections. Corresponding parts
in Figs^. 31 and 32 are lettered alike. The distinguishing

Pio. S2

feature of this lamp is that both the regulating and resist-
ance coils are made of bare metal strip wound on edge
with the turns separated by insulating material that is prac-
tically unaffected by heat. This construction makes very
substantial coils and the heat is conducted from the inner
part and radiated from the outside surface much more readily
than with coils wound with cotton-insulated wire.

63 • Western Electric Laiup* — Fig. 33 shows the con-
nections for a Western Electric constant-potential lamp.

ARC LIGHTING

§34

Current enters at the positive terminal and passes through

switch a, upper carbon 6, lower carbon r, coil d, adjnstable
connection e, coil /, adjustable resistance j^^ and out at the
negative temiinaL The arc voltage is adjusted by varying

the resistance ^» and the number
active turns in the regulating
coils can be changed by moving
the cross-wire e to the upper or
lower pair of coil terminals.

U-^=f -^^^^ th

•I

CONSTANT-POTEXTIAL, AT^TER-
NATlNU-CUttRENT LAMPS

Fio. 33

54, Fig. 34 shows the ar*
rangement of a constant-
potential, alternfitlng- cur-
rent lamp- The principal
distinguishing feature of the
alternating-current lamp is the
use of the reactance, or choke,
coil L in place of the resistance.
This consists of a laminated-
iron core a on which coils d are
wound. The coils are connected
in series and the ends 1, 2, St 4^
etc* left so that the wire A can be connected at different
points. This allows the lamp to be adjusted for a con-
siderable range of voltage and frequency. The reactance
coil sets up a counter E. M, F., and thus introduces an
apparent resistance into the circuit, which counterbalances
the excess voltage and makes the lamp stable in its opera-
tion. The reactance coil is more economical than a resist-
ance^ but it and the series magnets introduce seU-induction
into the circuit. The frequency should not be below 60
cycles per second for satisfactory operation. This lamp
will operate anywhere from GO to 140 cycles; it takes about
72 volts at the arc and burns from 80 to 100 hours. The
tipper carbon is cored and the lower carbon solid.

§34

AfeC LIGHTING

55. Fig. 3'^ shows a Western Electric constant-potential
lamp, five of which are operated hi series on 550-volt, direct-
current railway circuits. It is a differential lamp provided

Flo. 84

with an automatic cut-out at a. When the lamp cuts out, the
current passes through both resistances r and r,. Resistance
r is not in circuit during the reg^ular operation of the lamp,

ARC LIGHTING

§34

but when the cut-out operates this resistance takes the place

of the arc and prevents the other four lamps in the series

from an excessive flow of current* The resistance r, is in

. shunt with the series coil and

^--(/ywv^^

is used to regulate the
exerted by the coiL

puU

Fio. a5

FLAMING ARC LAMPS

56. Bretiaer IJamp.— In

the ordinary arc lamp using*
carbon electrodes, very little
light is given off from the arc
itself. The bulk of the light
comes from the highly heated
carbon points and in direct-cur-
rent lamps the crater formed
in the positive carbon is the
source of most of the light*
The large amount of light
emitted is due to the high tem-
perature attained by the carbon
points. Many attempts have
been made to produce arc lamps in which the light is
given off from the arc itself, the electrodes being worked
at a comparatively low temperature, thus securing a high
efficiency and long life* In the Bremer lamp certain
non-conducting metallic salts, as, for exaraplct calcium
fluoride, are incorporated in the positive carbon and are
given off as vapor when the lamp is in operation, thus
causing the arc to give off a large amount of light of a
reddish-yellow color. Lamps of this type have been experi-
mented with for some time but have not as yet been com-
mercially adopted to any great extent.

57, Magnetite Arc Xiainp. — The magnetite arc lamp
developed by Mr. C* P. Steinmetz is a type of direct-current
lamp where the light is given off from the arc. In this
lamp> the electrodes give no light at all but the arc is long

§84 ARC LIGHTING 59

and brilliant, emitting a light that is nearly white in color.
The electrode that is consumed consists for the most part
of magnetite or black oxide of iron. The magnetite in the
form of powder is compressed in a thin iron tube and has a
certain quantity of titanium compounds mixed with it to
increase the steadiness of the arc and improve its brilliancy.
The magnetite stick is about 8 inches in length and
i or I inch diameter. An 8-inch electrode will bum 150 to
200 hours without difficulty. The magnetite constitutes the
negative electrode of the lamp and is arranged below the
positive electrode, which consists of a copper segment that
is not burned away during the action of the lamp. The
copper block conducts the heat away so rapidly that it does
not become hot enough to melt.

When the lamp is in operation the magnetite vapor
between the electrodes is highly incandescent and the arc,
which is from I to li inch in length, emits a brilliant light.
A chimney that passes up through the lamp has its lower
opening directly above the arc so that the particles, or fine
smoke, given off from the magnetite stick can pass up
through the chimney and out at the top of the lamp. Out-
side of this chimney and the copper segment used for the
positive electrode, the construction of the lamp is very simi-
lar to that of an ordinary enclosed-arc lamp. The arc is,
however, not enclosed; the electrode material is already an
oxide, hence there is no need of providing an enclosing
globe to prevent access of air and consequent oxidation.
The lamp operates on 4 amperes at 80 volts, or takes
320 watts, and it is claimed gives a greater illumination
than an ordinary enclosed-arc lamp consuming 460 watts.
These lamps have, however, not been used commercially to
a sufficient extent to enable a fair comparison, tmder all con-
ditions of service, to be made.

ARC LIGHTING

§a4

BPECIAI> AFPtlCATIONS OF ABC liAMPS

58. Arc lamps are extensively used for stage illumina-
tion *io theaters, for photoengraving: work, blueprintingp
searchlights, or, in fact, any work where a strong light
is necessary. For most of this work, the ordinary styles of
arc lamps are not suitable, because such lamps are not of the
focusing type* For projection work, it is necessary to keep
the arc in a fixed position; in some cases this is accomplished

^:=c:e

Pio. ."MJ

by hand feeding, while in others the feeding is automatic.

Fig. 36 (a) shows an automatic focusing lamp and (i) a
hand-feed focusing lamp. The lamp (a) is usually mounted
on a stand and provided with accessories to suit it for what-
ever kind of work it is used. It is designed for 20 amperes
and is operated on direct-current circuits of 75 to 125 volts.
The hand-feed lamp shown in (i) also operates :;ormally at

§34

ARC LIGHTING

20 amperes, but by using larger carbons^ currents up to
50 amperes may be employed. The hand- feed lamp may
also be operated with alternating current, but the alter-
nating current is not very satisfactory for use in projection
work. The hum caused by the arc is often very annoying^
and moreover the arc is cotitinually shifting around. In
both lamps shown in Fig. 36, the carbons are fed together by
screws and the rate of movement is adjusted so that the arc
always remains stationary. If a lamp is to be used for short
intervals only, the hand feed will be found quite satisfactory,
because it is simple, cheap, and not li^le to get out of order.
If, however, the lamp is to be used for long runs, it is better
to have an automatic feed* The lamp in Fig. 36 (a) is fed
by the screw a, which is rotated by means of the lamp
mechanism contained in the case below* In (^), the carbons
are regulated by turning the knobs a, a,

59* When these lamps are run on a regular llO-volt
circuit, a rheostat must be inserted in series with them in
order to take up the excess voltage. The rheostat should
be capable of carrying the current required by the lamp
without undue heating, and should have enough resistance
to give a maximum drop of about 70 to 80 volts when used
on 110-volt circuits* About 20 to 30 volts of this drop
should be adjustable, so that the current taken by the are
can be kept at the proper amount. For example, a lamp
taking 20 amperes should have about 3^ ohms in the
rheostat, and at least 1 ohm of this should be split up into
10 or 15 sections and connected to a regular rheostat switch
so that a good adjustment can be obtained. A 10-ampere
lamp will require about 7 ohms in the rheostat, and
2 or 3 ohms of this should be adjustable.

SEARCHLIGHTS

60. A searchUprht is designed to concentrate the rays
emitted from the crater of the positive carbon and project
them so that they will be parallel to each other. A beam of
Ught that does not spread out will illuminate objects at great

ARC LIGHTING

§34

distances, because the intensity of such a beam does not fall
off with the square of the distance as does the light from
an ordinary source. In fact, if all the rays were exactly
parallel and the mirrors perfect and if there were no absorp-
tion of light by the atmosphere, the intensity of the beam
would not diminish at all. As a matter of fact, it does
diminish to an extent that depends very largely on the con-
dition of the atmosphere,

61, Searchlight Lamp. — Fig* 37 shows a type of lamp
used both for commerical and naval searchlights. In this
lamp the carbons are horizontal, the positive carbon being
larger than the negative and pointing directly at the mirror-
The lamp has a ratchet feed and is provided with two
magnets— a series magnet that serves to strike or start the
arc and a shunt magnet that works the ratchet feed.

Referring to Fig. 37, the shunt magnet is shown at G and
the series magnet at K. P is the positive carbon and N the
negative, j^ is a small switch for cutting off the current
from the shunt coil when it is desired to feed the lamp by
hand. The lamp may be fed by hand by slipping on a crank-
ViTench at R. Screw D feeds the negative carbon and E the
positive, the two screws being geared together at J, Cur-
rent is led into the lamp by means of two sliding contacts vf,
one of which is shown in the figure, the other being directly
behind A on the other side of the lamp, H is the armature
of the shunt magnet and /^the pawUand-ratchet mechanism
by which screw E is turned. The lamp for a 30-inch pro-
jector takes from 75 to 90 amperes, and for an IB-inch pro-
jector from 25 to 35 amperes* The working current varies
with the size of the lamp and also with the size of the car-
bons used. The voltage required at the lamp is usually
from 45 to 49 volts and the feed will frequently operate
when a pressure of 50 volts is reached.

62. The method of operating the lamp is as follows:
The carbons are adjusted by the crank- wrench to a separa-
ting distance of about i inch* The switch M is then closed.
The main switch is closed next^ and as no current can pass

'tit

ARC LIGHTING

Fto. n

46D— 18

ARC LIGHTING

§34

between the carbons, the voltage between them, and hence
the voltage across the shunt magnet Gt must be equal to the
full-line voltage; armature // is therefore attracted and the
current through the shunt circuit is broken by the contact
device ^ and the armature falls back a^fain making contact.
The armature //, therefore, vibrates rapidly and works a
pawl that shoves the ratchet /^around and feeds the carbons
together. The screws are geared together, so that screw /?
revolves one-half as fast as A. As soon as the ratchet feed
brings the carbons into contact, a heavy current flows for a
short interval and the series coils A' pull back the armature a^
and thus start the arc. As the carbons burn away, the
voltage across G increases until the ratchet feed operates
and moves the carbons a little nearer togrether. The point
of feeding can be adjusted by means of the spring c and the
length of the arc by means of nuts d. The positive carbon
holder is provided with vertical and horizontal adjustments,
so that it can be accurately lined up.

CARE AND ADJUSTMENT OF ARC IjAMPS

63 > General Remarks, — If an arc lamp is kept clean,
and if the current and voltage at which it is operated are
maintained at the values for which it is designed, it will give
little trouble. This assumes, of course, that the lamp is sub-
stantially made. The older styles of open-arc, series lamps
were usually heavily built and, as a rule, gave good service,

64. Trluinilu^. — Most open-arc » series lamps are pro-
vided with a carbon rod on which the clutch operates. If
this rod is dirty or greasy, the clutch will not work properly
and the lamp will give poor service. When trimming the
lamp, the rods should never be pushed up when they are in
a dirty condition-
Dirt on the rod is apt to cause pitting, due to the burning
action of the current where it passes into the rod from the
contact spring or bushing* If the rods are at all dirty, they
should be rubbed down with a piece of worn crocus cloth.
When trimming the lamp, care should be taken to see that

884 ARC LIGHTING 65

the carbons are of the proper length. Lack of care in this
particular is often responsible for burned carbon rods and
carbon holders. The carbons should be placed so that
they are vertically in line with each other, and the upper
carbon must have enough vertical play to allow the lamp
to pick up its arc.

65. Adjustments. — The principal points to look out
for in adjusting an arc lamp are to see that the arc bums at
the proper length and that the carbon is fed down smoothly
without any hissing or flickering. For an ordinary 1,200
nominal candlepower, open-arc lamp, the arc should be about
A inch in length; for a 2,000-candlepower, from tV inch to
A inch. The exact length will depend somewhat on the
quality of the carbons. If the arc is too short, it is liable to
hiss, or if the current is too large, hissing is apt to result.
An arc that is too long will flame badly and the lamp will
take more voltage than it should. Poor quality of carbons
will also cause flaming or hissing. The length of arc and
the feeding point can be regulated by proper adjustment of
the clutch. Directions for adjusting each particular make
of lamp are furnished by the makers, but as a rule such
adjustments are easily learned by an inspection of the lamp
itself. In some cases the clutch and rod may become so
worn that they must be replaced before a satisfactory opera-
tion can be obtained.

A good method to follow in adjusting lamps is to connect
an ammeter in series and a voltmeter across the terminals
of the lamp. First see that the dynamo is maintaining the
proper current in the circuit. If it is not doing so, the regu-
lator should be adjusted until it does. The lamp should be
hung in some place where it will not be exposed to drafts of
air, because such drafts may cause the arc to hiss or flame
even if it is properly adjusted. A rack should be provided
for supporting the lamps at such a height that the mecha-
nism may be easily inspected. By watching the fluctuations
of the voltmeter as the lamp burns, a good idea may be
formed as to the smoothness with which the lamp feeds.

ARC LIGHTING

§34

A recording^ voltmeter is very convenient for this work, as
the lamp may be left to itself for some time, and the volt-
meter will draw a chart indicating the variations in voltage
during the test.

66* Burned-Out Colls. — The controlling coils of series
arc lamps are fteqnently burned out and have to be rewound.
Burn-outs may arise from a number oi different causes*
Lightning is frequently responsible for them, as it breaks
down the insulation of the lamp or punctures the insulation
between the layers of the winding. Oiie of the most frequent
causes of burned-out shunt spools is a defective cut-out. If
the carbons stick and the cut-out fails to work, the arc grows
so long that the current in the shunt coils becomes exces-
sive, and they are sure to be burned out* The cut-out
contacts should be kept in good condition* and if burned
or oxidized J they should be carefully cleaned. Neglect to
look after the cut-out part of the lamp will surely result in
the rewinding of shunt spools, and as these are wound wirh
fine wire they are a comparatively expensive part to repair.
In some lamps, the action of the cut-out depends on the
movement of the rocker; hence, it is important to see that
the frame moves freely. If the lamp is improperly adjusted
so that it burns with an abnormally long arc, the current
through the shunt will be greater than it should be. This
will cause the coils to overheat, and while it may not result
in a burn-out at once, it is very apt to lead to it in time
by causing deterioration of the insulation and consequent
short-circuiting between layers. A similar result may be
caused by the line current being above the normal, and in this
case the series coils would also be affected. Generally, how-
ever, the series coils will stand a reasonable overload withaut
greatly overheating. Series lamps should cut out promptly,
if the upper carbon is pushed up while they are burning. If
they do not do so» there is something wrong with the cut-out
and the trouble should be remedied before the lamp is sent out,

67- Most of the above also holds true with regard to
series enclosed arcs* There is even more danger of the

§84 ARC LIGHTING 67

carbon sticking: and failing to feed properly in these lamps
than in the open arcs, because the carbon must pass through
the cap of the enclosing globe, and if the carbon has not
been gauged beforehand, a slight unevenness may cause it
to stick. It is therefore important to see that the cut-out is
kept in good condition and that there are no uneven places
on the carbons when they are put in the lamp.

68. Trlmniliifir Enclosed -Arc liamps. — Generally
speaking, it is necessary to clean the enclosing globe every
time the lamp is trimmed. If it is allowed to go longer
without cleaning, it becomes covered with such a thick
deposit that a considerable part of the light is cut off. This
cleaning can be done to much better advantage at the station
than at the point where the lamp is installed, so that the
lower globes are brought back to the station for retrimming
and are there washed by means of special appliances for the
purpose. When the trimmer goes out, he takes a clean lot
of globes, provided with lower carbons, and replaces the
old ones. Care should be taken to see that the carbons used
are of the proper length because a small length of carbon in
an enclosed-arc lamp corresponds to several hours' burning.
The upper carbons are purchased in the desired length, but
the lower carbons are very often made up of the part left
over from the top carbon. These pieces will vary in length,
and they should be cut to gauge before being placed in the
bottom holders. The upper carbons should all be gauged to
make sure that they will pass through the cap freely. For
a i-inch carbon, the maximum allowable diameter is about
.62 inch and the minimum diameter .5 inch. If the carbon
is smaller than the allowable amount, there will be too
much air admitted to the enclosing globe and the arc
will flame badly. Only the best quality of carbons should
be used in enclosed-arc lamps, otherwise the enclosing
globe will become thickly covered with deposit. Attention
should be paid to the gas caps of enclosed-arc lamps and
also to the joint between the globe and the bottom
carbon holder.

ARC LIGHTING

§34

69i Since most enclosed-arc lamps have a carbon feed, It
IS necessary to see that the carbons are smooth* because
rough spots will interfere with the operation of the clutch*
If necessary, rough spots should be smoothed down with
sandpaper. Constant-potential lamps have no cut-out to
give trouble, but they have a resistance coil that fully
counterbalances the cut-out in this respect. If the carbons
stick and fail to feed, the larap goes out; but if the lamp
does not pick up properly, the carbqns being in contact, the
resistance offered by the arc will be absent and a current
much larger than the normal will flow. If the fusible cut-out
in series with the lamp does not operate, the resistance will he
very liable to overheat and burn out. There is also danger
of the insulation on the series controlling magnet being
damaged. It is a common occurrence to find constant-
potential lamps that have been designed and adjusted for
104 to 110 volts running on circuits where the voltage is as
high as 125 or 130. Of course, under these circumstances
the lamp takes a current larger than it should » and it must
not be forgotten that the heating effect in the resistance coil
and other parts of the lamp increases as the square of the
current. A comparatively slight increase in the current willt
therefore, result in quite a large increase in the heat
developed. An abnormal current Is also liable to melt the
enclosing globe. Of course, many of the burn-outs on these
lamps may be traced to faulty design or construction, but
at the same time it is quite true that many good lamps give
trouble either because the voltage is too high or because the
lamp has not been properly adjusted to suit the voltage on
which it is to operate.

ARC LIGHTING

(PART 2)

LINE WORK FOR ARC LIGHTING

SERIES SYSTEMS

1. Size of Wire. — Since most outside lighting work
is done on the series system, and the current is usually
not greater than 9.6 amperes with open arcs or 6.8 amperes
with enclosed arcs, the line wire does not need to be large.
Generally, such lines are of No. 6 B. & S. double- or triple-
braided weather-proof wire. Triple-braid wire of this size
weighs about 585 pounds per • mile; double-braid about
510 pounds. Its resistance per mile is approximately
2.08 to 2.12 ohms. Sometimes No. 8 wire is used for
arc lines, but while it is large enough to carry the current,
it does not make as substantial a job as the No. 6. The
difference in first cost between the two sizes is not great
and, as a general rule, it will pay to put up the larger wire,
especially in localities where sleet storms are common.

Since the current is small, series arc lines may be run long
distances without giving an excessive loss. For example,
with 9.6 amperes, the drop per mile of wire is about
2.08 X 9.6 = 19.97 volts, and with smaller current it is
correspondingly less. Series arc circuits often extend
for miles, but the extension of the line simply cuts down
the pressure available for the lamps, so that a given dynamo
is not capable of operating quite as many lamps on a long
circuit as on a short one.

For notice of copyright, see Page immediately following the title pagg

ARC LIGHTING

135

2, I^ayln^^ Out Arc Circuits. — Generally, there is not
a great deal of choice as to the laying: out of an arc circuit
for street lighting, as it is determined almost altogether
by the location of the lamps. At the same time, wire and
labor can often he saved by laying out a plan of the streets
to be lighted and then an^anging the circuits so that the line
will pass through one lamp after another with as little
doubling back on itself as possible*

When laying out the line» it is a good plan, where possible,
to connect the terminals of a loop in the circuit to a switch
so that, in case of trouble, the loop can be short-circuited
and the remaining lamps on the circuit continued in operation-
Fig, 1 illustrates this; /, /, / represent arc lamps connected on

[

mm nt

r>"

-IC— '

Fio. 1

a street circuit, as shown. By putting In switches at
points A, B, the loops in the circuit may be cut out* For
example, if a break occurs at x^ switch A can be closed and the
rest of the lamps kept going while the break is being located.
A few switches arranged in this way are also of great assist-
ance in locating breaks* In Fig, 1, plain short-circuiting
switches are indicated in order to bring out the method and to
simplify the figure. In practice, a switch should be used that
will provide a path around the loop and at the same time dis*
connect the loop entirely from the remainder of the circuit, so
that it may be worked on and the fault located without danger
to the linemen. These cut-out switches are usually mounted
on a pole or at any other point where they will be accessible.

^35 ARC LIGHTING 8

3. It is preferable to have separate lines for operating
the commercial lights and street lights, because lamps used
in places of business usually have to be started earlier and
extinguished earlier than those used on the streets; more-
over, it may be necessary to run store lights for a short
period in the morning, when no street lights are needed.
Besides, the long-exposed street circuits are always subject
to breaks or other troubles that may interfere with the
regularity of the service.

No matter how carefully street arc-light circuits are laid
out in the first place with a view to economizing copper,
they soon become very irregular if the number of lights is
increased. Lights are looped in here and there, and the
result is that the general layout of the circuits assumes an
appearance very different from what was originally intended.

LINE CONSTRUCTION

4. lilne construction for arc lighting is generally
carried out by stringing the lines on poles, though in some
cities the distribution is effected by means of well-insulated,
lead-covered cables placed underground. In all construction
work connected with series arc circuits, the point must not
be lost sight of that the pressure across the terminals of
these circuits is very high and that there is always a strong
tendency for grounds to develop. A large size of deep-
groove, double-petticoat insulator should be used and the
wires kept clear of trees. Great care should be taken when
wires are run near metal awnings at the entrance to stores,
as this is a place where grounds are apt to occur and
where, in a number of cases, they have resulted in fatal
accidents. The necessity for high insulation and careful
work in connection with arc lines is even greater than it was
when about fifty lights on a circuit was a common average;
now the number of lights per circuit is often over one hun-
dred, and if the lines are not kept in good condition there is
sure to be trouble. All fittings used about the lamps them-
selves should be such as to give high insulation.

ARC LIGHTING

§35

5, Height of Tramps, — ^Arc lamps for street lighting
are nearly always placed at street intersections. When the
blocks are long, they are also placed in the middle of the
block. The older method was to use a comparatively small
number of lamps hung high above the street, but it is now
considered better practice to hang the lamps lower and to
use more of them if necessary. This is especially the case
when the streets are shaded by trees. Where the space to be
illuminated is open, the lamps may be hung fairly high, say»
30 to 40 feet above the ground; but when the streets are at
all shaded, a height of 20 to 25 feet is to be preferred.

6. Methods of Hani^Iiij^ LiampB. — There are, in gen-
eral, three methods of hanging lamps: (a) By mounting on
pole tops? (d) by suspending from mast arms or
pole fixtures projecting from a side pole; (c) by
suspending from the middle of a span wire so
that they will hang over the center of the street.
When the lamps are mounted on pole tops,
they are fixed permanently, no provision being
made for lowering them when they are trimmed.
The pole must* therefore, be provided with pole
steps, so that the trimmer can climb up to the
lamp. This method of mounting makes the
work of trimming hard» and it is therefore not
used nearly so much as other methods, which
allow the lamp to be lowered. The pole-top
mounting has a few advantages, among which
is the absence of rope and pulleys, also the
line wires when once connected up are not
moved, as they are every time a lamp is raised
or lowered. The raising and lowering of lamps
is a frequent source of breaks in the line wire
due to the slight bending and unbending that the
wire is subjected to. These advantages are,
however, more than offset by the difficuhy of trimming if the
lamps are mounted high above the street. Fig. 2 shows an
ornamental style of pole-top mounting. In this case, the lamp

Fig. 2

§35

ARC LIGHTING

is only about 20 feet above the street, and as it is used with
enclosed arcs, which are trimmed about once in a week or ten
days, the climbing up to the lamp is not as much of an objection
as with the old-style open arcs that required daily trimming.

7. Fig. 3 illustrates a typical mast-arm suspension.

The lamp is raised and lowered by means of a rope and
pulleys, and is provided with a small hood to protect the
top from the weather. The lamp is suspended from the
rope by the intervening cross-arm a and insulator b, A
cross-arm and insulator of this kind should be provided in

Fro. 8

order to secure good insulation between the lamp and the
pole fixture and also to keep the line wires spread apart.

Since the introduction of high-voltage enclosed arcs and
the operation of a large number of lamps per circuit, it
is essential that each lamp be provided with a suspension
that will give high insulation. The old-style, plain, wooden
crosspiece with a porcelain knob at each end is not sufficient.
Fig. 4 shows a Cutter pole fixture of small size used consid-
erably for street lighting with enclosed arcs. It supports
the lamp about 3 feet from the pole.

ARC LIGHTING

§35

8. The simn-wire suspension 13 illustrated in Pig. 5.

It is the best form to use when it is desired to bring the
lamp over the center of the street. A pulley is placed at
the center and another on the side pole and the poles are

usually set at diag^onaUy
opposite comers of the
street intersection. The
f^pan or suspension wire
is usually of i\*inch or
1-inch galvanized steel
and the side poles about
30 to 35 feet high with a
6-inch top. This method
of suspension, of course,
involves the use of two
poles and for this reason
the mast-arm suspen-
sion is often preferred.
The chances are that for
lighting a given town or
city a combination of the three methods may be desirable,
the style of suspension being chosen that is best adapted for
the particular location of the light.

Pre. 4

9. Arc-La fnp Pulleys. — Pulleys used for suspending
arc lamps have received a great deal of attention from those
especially interested in arc-lamp specialties. The ordinary
style of pulley is not well adapted for this kind of work. An
are^lamp pulley should always be provided with a hood to
prevent its being clogged by sleet. It is also desirable that
the pulley from which the lamp is hung be of such a design
that it will hold the lamp from dropping in case the rope
breaks or becomes unfastened in any way. In Fig. 5, a
lamp-supporting pulley is indicated at A and a swivel -pole
pulley at B. Both are of the sleet-proof kind. A number of
different I amp- sup porting pulleys are now manufactured. In
most of them either a catch or projections are arranged inside
tlie pulley casing to hold the lamp when it is raised and

i»

ARC LIGHTING

relieve the rope of all strain. When the lamp is to be low-
eredt it is ftrsst pulled up a little. This unlocks the pulley and
allows the lamp to be lowered* The use of self-locking pul-
leys also helps to make the operation of trimming more rapid.

10. Rope. — ^The rope used for raising and lowering the
lamps is an important item on a large system and should be
carefully selected. Practice varies greatly as to the kind of
rope used. Formerly, manila rope was used almost exclu-
sively, but the tendency is now toward a solid braided cDtton
rope or a flexible wire rope. When cotton is used for this
purpose, it is provided with a wax finish that keeps the rain
from soaking into and rotting it. The rope is usually Sinch
in diameter » though i-inch is sometimes used with heavy

FtO.6

lamps* If wire rope is used, it is nsually the so-called
tinned sash card, which is a rope made up of a hemp center
smrounded by tinned steel wire* It was formerly the practice
to coil up enough surplus rope on the pole at each lamp to
allow the lamp to be lowered to the ground* It is now cus-
tomary to end the rope in such a w^ay that another rope may
be hooked on to it and the lamp lowered* This extra rope,
known as a trl miner ^s rope^ is from 20 to 30 feet long and
is provided with a snap hook at one end and a number of
rings near the other, the latter being spaced so as to suit the
varying heights at which the lamps may be hung. The end
of the rope on the pole may be fastened by means of special
pole padlocks, made for the purpose.

ARC LIGHTING

}35

11. Cut-Out 8wlteIies,~The rules of the Fire Under-
writers require that wherever constaiit-currenr arc wires
enter a buildings an approved double-contact service switch
shall be installed, so that the current can be cut off at any
time. These switches must be substantially made, must be
mounted on incombustible bases, and must be placed where
they may be easily reached by policemen and firemen. They
must have good contacts, be quick in action, and show
clearly whether the current is on or off.

Fig. 6 shows the Wood arc cut-out, a style that has been
extensively used and which will serve to illustrate the opera-

Fio.A

tion of cut-out switches in general. The parts here shown
are mounted in a waterproof cast-iron box with an open-
ing past which an indicator moves to show when the current
is on or off.

Two blades a^ b^ Figf. 6 (^)i are attached to the line termi-
nals c^ d^ as shown. The house terminals are connected Co
the posts <f, /. When the handle is pushed up, the porcelain
rollers r, r press the blades into the clips on terminals r, /
and thus connect the line with the lamps. When the lever
is pulled down, the rollers bear on the lower part of the
blades, causing^ them to leave the clips on the posts e^ f and
swing over so as to rest on the casting k, thus cutting out
the lamps and allowing the current to flow directly across

§S5

ARC LIGHTING

from one blade to the other and disconnecting the house
wires entirely from the line* The springs shown in the
figure make the action quick and positive.

12, Cut-Oiits on Are Lamps.— Nearly all arc lamps
are prov^ided with a simple short-circuiting switch by means
of which the lamp can be cut out. This switch does not,
however, disconnect the lamp entirely from the circuit, and
it is always dangerous to work on a lamp under such circum-
stances when standing on the ground, because there is liable
to be a ground, on some part of the line, that provides a
path for the current through the person working on the
lamp. Since the introduction of con-
stant-current circuits operating a large
number of lights, the danger from
shock has materially increased, and
lamps are now h'equently equipped

Pio,7

Fio. 8

with absolute cut-out switches that are separate from the
lamp and that will cut out the lamp and disconnect it
entirely from the circuit. Fig. 7 shows a series arc lamp
equipped with a separate cut-out switch of this kind,

13# Ijooplniir In Tmnips on Series Circuits* — When
a lamp is looped in on a series circuit out of doors, it is not
necessary to provide a cut-out switch at the point where it
is cut into the line, though switches are sometimes placed at
the lamp itself. Fig* 8 shows one method of looping in on
a series circuit. An arm ^, provided with insulators c,d^ is

ARC LIGHTING

§35

mounted as shown* The loop a runs to the lamp or, in case
the circuit is carried into a building, runs to the cut-out*
When a circuit is to be looped in between poles, the break

Pio. g

may be made by usinif a single porcelain insulator, as shown
in Fi^, 9, or if higher insulation is required between the
terminals of the break* two insulators connected by a short

Fio. 10

length of wire may be used. Fig, 10 shows another method
of accomplishing the same result by using a special porce*
lain insulator,

TESTIKO ARC-LIGHT LIKES

14* Since street arc-lighting circuits are generally long,
considerably exposed, and of comparatively small wire, they
always give more or less trouble on account of grounds,
breaks, and crosses. Breaks are of quite frequent occur-
rence, especially during heavy wind or sleet storms, and
very often cannot be detected by a mere inspection of the
line* The wire may be broken though the insulation holds
the ends together^ so that, to all appearances, the line is
intact* Breaks are especially liable to occur at the point
where the line loops from the pole to the lamps.

Grounds are most likely to occur around the fronts of
Stores where the wires are run in proximity to iron awnings

§36 ARC LIGHTING 11

or fittinsfs. Also, where the lines run throug^h trees, there
will always be more or less of a gjound, especially in wet
weather. In this case, however, the trouble would be more
correctly termed a leak, as it is due to defective insulation
and does not constitute a direct connection to ground, as
would happen, for example, if one of the lines came into
contact with an iron pole or a gas or water pipe.

Crosses are caused by one line coming into contact with
another, and, under ordinary conditions, should not occur
frequently if the line is well constructed. Of course, heavy
storms, especially sleet storms, may cause a great deal of
trouble on arc lines, but we are now speaking of the troubles
that are liable to occur under ordinary working conditions.

All arc lines should be tested at intervals during the day
to see if any faults have developed, so that they can be
looked up and remedied, if possible, before it comes time to
start up in the evening. This may be done in various ways,
but in many cases grounds and breaks are located by the use
of an ordinary magneto-bell. This bell requires no battery
for its operation and is able to ring through a long length of
line; moreover, it is easily carried around from place to place.

15. liocatin^ Breaks. — Series arc circuits should be
frequently tested for breaks by connecting a magneto to the
terminals of the circuit, at the station, and ringing it up. If
the bell fails to ring, it shows that the circuit is broken
somewhere and the break should be looked up at once. If
the circuit is arranged in loops that can be cut out by means
of switches on the poles, the first thing to be done is to cut
out the loops in succession until a ring is obtained. This
will show in which loop the break is, and the fault can then
be further located, as described later; or, in many cases, it
may be found by a simple inspection. In general, however,
the problem will be to locate a break on a simple series cir-
cuit, such as that shown in Fig. 11. The irregular outline
represents a circuit, or portion of a circuit, of which
c, b are the terminals; /, /, etc. represent the lamps. It is
found by ringing up between a, b that there is a break on

46B— 19

ARC LIGHTING

§35

the circuit indicated at the point jr, though its location is not
known as yet. First connect a and b together and ground
them, as shown by the dotted hnes. Then go to point r,
as near the middle of the circuit as possible, and open
the circuit by lowering a lamp and removing the wires, or in
any other way that may be convenient. Attach one terminal
of the testing magneto to ground, by connecting it with a
hydrant or other ground connection that may be at hand* and
the other terminal to one end of the circuit d; ring up, and if
the bell rings, it shows that the portion of the circuit from d
around to the station \% all right and that the break is in
the other half. Close the circuit at € and move on to a

Fio. 11

placQ /, about half way between c and the station. The
circuit is here opened and the magneto-bell connected as
before. If a ring is obtained when the bell is connected to
the left-hand end of the line, it shows that the stretch of
circuit f-g-b is intact; while, if the bell does not ring when
connected to the right-hand side, it shows that the break
is between / and c, because the previous test showed that
the part d-l-l-a was all right. In this way, by making a
few tests, the stretch of circuit in which the break occurs can
be located within narrow limits, and the break itself can then
usually be found by a careful inspection.

16. Liocatin^ Grounds. — When a line becomes grounded
at any point x, as indicated in Fig. 12, the ground may be
located by using a magneto, in which case the ends of the
line a,b at the station are left open, instead of being

§35

ARC LIGHTING

grounded, as when testing for breaks. The line is then
opened about the middle point c and each side rung up,
one terminal of the magneto being connected to the
ground. The side on which a ring is obtained is the one

on which the ground exists. The half on which the ground
is located is then opened at its middle point, and in this
way the part of the line that is grounded is soon located
within narrow limits.

17. liocatiiig Grounds by Means of Voltmeter. — If

a high-reading voltmeter is available, it can be used for
locating grounds on an arc circuit, as indicated in Fig. 13.

-X6S0

Pio. 13

The dynamo is here omitted, but it is supposed to be opera-
ting the circuit connected to its terminals a, b.

In this case, there are, say, fifteen lamps operated on the

ARC LIGHTING

[35

circuit. The total pressure generated by the dynamo is,
say, 15 X »50 = 750 volts, allowing: 50 volts per lamp* The
difference of potential between the negative side of lamp 1
and a+ is 50 volts, between the negative side of 2 and
^H-j 100 volts, and so on, as shown in the figure. If one
terminal of the voltmeter is connected to «+ and the other
to ground, a reading will be obtained whenever there is a
ground on the Hoe* Suppose, for example, that there is
a ground at (7'; the voltmeter will then be connected across
four lamps and will give a reading of about 200 volts. The
voltmeter reading, there fore ♦ indicates how far the ground
is out on the line. If, for example, a reading of about
100 volts is obtained, it is known that the ground is some-
where between the second and third lamps.

18. Differential Metliotl of Lioeatltifir Grounds.
This method consists in balancing the drop through an
artificial line against the drop through the portion of the
circuit from the station to the point where the ground exists;
it will be understood by referring to Fig, 14.

The terminals of the circuit are indicated at a, t^ and, for
the sake of illustration, ten lamps are shown. The total
pressure generated by the dynamo will be about *500 volts,
and the drop in pressure between a+ and different points
on the circuit will increase as the lamps are passed, as
shown by the numbers 50, 100^ etc. The testing apparatus
consists of a number of equal resistances 1^2,3^1, etc. con-
nected in series, with terminals brought out to a switch, as
indicated. These resistances should be fairly high, say
about 50 ohms each. Ordinary 52- volt incandescent lamps
will answer. A detector galvanometer C is connected to
the switch blade and to the groimd. One end x of the
resistance is connected to a-h. The other end of the cir-
cuit — ^ is connected at the point jsr, so that the number of
resistances will correspond to the number of lamps on the
circuit to be tested. The switch arm is then moved to the
right until the galvanometer deflection comes to zero. In
this case, the deflection will be zero when the arm is at the

ARC LIGHTING

point y between resistances G and 7. The fall of pressure
from tf-f through the artificial circuit corresponds to the
fall in pressure from a+ around the arc circuit; hence, when
a point is reached where the drop in pressure from «+
around to the s:round is equal to the drop in the artificial

PlO. 14

line, the two pressures counterbalance each other, as indi-
cated by the arrows, and no current flows through the gal-
vanometer. As soon as the point corresponding to that
where the j^round exists is passed on the switch, the galva-
nometer will reverse its deflection.

ARC LIGHTING

§35

lilGHTNING PROTECTION FOR ARC CIKCITITS

19, Series arc-light circuits are very likely to bring in
iightning discharges to a station, because they cover such
large areas and are usually much exposed. They should*
therefore, be well protected by lightning arresters. The
arresters used on arc circuits differ little, if any, from those
used on other circuits. Care must, of course, be taken in

selecting an arrester to see
that it is adapted to the volt-
age of the circuit and also
to the kind of current; i. e.»
direct or alternating. Many
of the older types, which
were quite satisfactory on
circuits operating as high as
60 to 75 lamps, are not suit-
able for high-voltage circuits
operating 125 to 150 lamps*
If the older types of arrester
are to be operated on such
circuits, two of them should
be connected in series.
Each side of every arc-light
circuit should be equipped
with an arrester at or
near the point where the
wires enter the station. The
arresters may be mounted back of the arc-light switchboard
or on a special rack placed near the point where the wires
enter the building,

20, Llgbtiiiiig Arrester for Arc I^inp^. — Although
lightning may not get into the station, it sometimes punc-
tures the insulation of the lamps out on the line and is
responsible for many burned-out colls. In order to prevent
this, small arresters, or spark gaps, may be connected across
the terminals of the lamp. Fig, 15 shows a simple arrester

Fia.15

§36 ARC LIGHTING 17

for this purpose. It consists of two brass cylinders with a
small gap between them, and when a discharge comes
along the line, it jumps between the cylinders and thus
passes along to the regular lightning arresters, which carry
it to ground. The lightning will jump the gap in pref-
erence to passing through the lamp because of the reactance
of the regulating coils in the lamp.

ARC-LIGHT DYNAMOS

DIRECT-CURRENT MACHINES

MACHINES FOR CONSTANT-CURRENT DISTRIBUTION

21. In the early days of arc lig^hting;, the lamps were
nearly always operated in series by direct current supplied
from constant-current dynamos designed specially for this
class of work. In later years, the use of constant-potential
lamps has become so great that constant-current, arc-light
dynamos do not occupy nearly so prominent a place in light-
ing stations as they did. Constant alternating-current gen-
erators are now seldom installed; if constant alternating
current is required for the operation of series lamps, it is
obtained from regular constant-potential alternators by the
use of constant-current transformers or automatic reactance
coils, in the same way as in series incandescent lighting.

Constant direct-current arc macbincs are always
series-wound and may have armatures of the open-circuit or
closed-circuit type. These machines generate a small cur-
rent at high voltage; hence, a shunt winding for the field is
out of the question because of the exceedingly large amount
of fine wire that would be required for it.

22. Constant-current, arc-light dynamos are, in many
respects, a decided contrast to the constant-potential, direct-
current machines used for low-pressure lighting or street-
railway work. In the first place, arc machines must generate

ARC LIGHTING

%BB

a comparatively small current (from 6 to 10 amperes), but
the maximum pressure that they are called on to deliver
at full load is very high. Moreover, they must be con-
structed so as to keep the current at the required amount
through a wide range in the number of lamps operated.
Constant-potential dynamos do just the opposite* They
maintain the pressure (usually from 110 to 600 volts) at a
constant or nearly constant value and the current varies with
the load, A constant-potential machine can be made self-
regulating by providing it with a compound field winding,
la order, however, to make a direct-current machine regulate
for constant current, it is necessary to provide it with an elec-
tromechanical regulator of some kind that will adjust the volt-
age with changes in load, so as to keep the current constant.

23. For convenience, constant-current arc machines may

be divided into two general classes: (a) those with open-coil
armatures and (^) those with closed-coil armatures^ Of
machines with open-coil armatures, the most prominent
examples are the Thorn son -Houston (T, Hj and the Brush,
Large numbers of these machines have been installed in the
past and their principles of operation have already been
described. The Thomson-Houston machine is not now
regularly manufactured; neither is the old two-pole type of
Brush machine. The Brush multipolar machine ^ which is
illustrated later, may be taken as typical of the modem con-
stanti direct-current, arc-light dynamo with open -circuit type
of armature. Machines having closed-circuit armatures are
represented by the Wood (Fort Wayne) and Western Elec-
tric makes. Both of these machines have armatures of the
ring type* On constant direct-current machines, it is neces-
sary to have an automatic regulator that will change the
voltage with change in load so as to keep the current con-
stant. In some cases» the regulation is accomplished by
shifting the brushes; in others, the brushes are shifted and
at the same time the ampere-tums on the field are varied,
either by cutting some of the field trirns in or out or by varying
an adjustable resistance shunted across the field winding.

[36

ARC LIGHTING

24. BruBh Arc Dyimmo. — The later style of Brush
arc dynamo is shown in Fig* 16* These machines are much
larger than the old bipolar type and have a higher efficiency.
The armature M is of the ring, open*circuit type, and its
general construction is the same as that of the older-style
armature with a number of improvements in the mechanical

details and method of insulation. The connections are also
slightly different in order to adapt the armature to a four-
pole field. Instead of connecting diametrically opposite coils
in series » as in a two-pole machine, four coils situated one-
quarter of a circumference from one another are connected

ARC LIGHTING

in series and the terminals brought out to the commutator

segments*

The field is the same, in some respects » as that on the old
machinet but there are four poles on each side of the arma-
ture instead of two. On each side» the poles are alternately
north and souths but poles directly opposite each other are
of the same polarity* For example » in Fig< 16, poles A^ A
are alike and of one polarity, while B, B are also alike but of
polarity opposite to ^, ^:

The other chief point of difference between the new-style
and old-style Brush machines lies in the regfulaton The old
regulator was entirely separate from the dynamo, but m the
later machines the regulator is mounted on the dynamo. It
varies the amount of the resistance shunted across the field p
and also shifts the brushes around the commutator. The
regulator, Fig, 16, is in the box C; rheostat D is connected
in shunt across the terminals of the field by means of the
wires a, fl^ and is divided into a number of steps, connec-
tions to w^hich are made by an arm moving over the con-
tacts i. This arm is shifted by the regulator and at the
same time the brushes are tipped by means of the rocker-
arm € attached to the brush-holder yoke d.

25. The Regulator. — Two types of regulator have
been brought out for multipolar Brush machines. The first
type used magnetic clutches to move the rheostat arm. The
one now made is shown in Fig. 17. It is thrown into or out
of action by an encased magnet m connected in series with
the lamps. Magnet m does not move the rheostat arm <2, but
simply controls a valve that admits oil, under pressure, to
either side of a vane or piston that swings around in the
closed chamber h. The oil pressure necessary to operate
the piston is maintained by means of a small rotary pump c
driven by a belt from the dynamo shaft running on pulley d.
The lower case is filled with oil to a point a little below the
rheostat-arm shaft. Oil is drawn from the lower part of the
box and discharged through the valve, which moves up and
down in a small valve chamber. When the current is at its

§85

ARC LIGHTING

normal value, the valve occupies a central position and the
ports are arranged so that oil circulates through the valve
chamber without moving the rotary piston or vane attached

Pio.17

to the rheostat arm. One end of the lever, pivoted at k,
Fig. 17, is attached to the valve, and the other end to the
armature of magnet m. If the current becomes weaker

ARC LIGHTING

§35

than normal, m rises and the valve lowers, thus admitting
oil to one side of the rotary piston in casing b. li the
current becomes stronger than normal the armature lowers,
raises the valvej and turns the rheostat arm in the opposite
direction,

26, In addition to moving the rheostat, the regtdator

tips the brushes by means of an arm extending from the
rocker and carrying a toothed arc that engages with a small
spur wheel on the shaft carrying the rheostat arm* By this
movement the brushes are adjusted %vith the changes in load
so as to keep the spark at the brushes about I inch long on
short circuit and i inch long on full load. This controller
will hold the current at its correct value with very little
variation either way.

CL08ED-C0IL MACnmES

27. The Wood are dynamo, Fig, 18^ has a simple,
closed-coil ring armature and a commutator divided into a
large number of segments so as to keep the voltage between
segments low and prevent undue sparking. The controlling
magnet m of the regulator is connected in series with the
line and operates the lever n. The brushes are moved by
means of a small, double friction clutch that is contained in
the casing shown at er. When the lever is pulled up beyond
the normal position , the clutch moves the brushes forwards
by means of the gears b^e^d^ thus lowering the current, li
the current becomes too weak, the lever moves down and
the clutch moves the brushes back, thus increasing the cur*
rent. These dynamos operate on a single circuit and are
made as large as l-W-lights capacity*

28» The Western Electric machines also have closed-
coil armatures; the larger sizes are of the four-pole type and
have two pairs of brushes. They are provided with two
regulators and supply two circuits in paralle!; each of the
regulators controls one pair of brushes. This is a some*
what different multiple-circuit arrangement from that of the
Brush machine, in which the two loops or circuits are in series

§35

ARC LIGHTING

and the current is bound to be the same in each. When the
circuits are Ln parallel, each must have a regulator of its own,
but under no circumstances can the pressure obtained

Fto, IS

exceed that which is ordinarily applied to one circuit: I- e*,
half the pressure that the machine would have to generate if
all the lamps were connected in series.

tC£V£RSAl* OF POLABtTT

29, Sometimes the polarity of arc machines becomes
reversed. This is usually due either to lightning^, wrong
plugging at the switchboard, or the circuit from the machine
coming into contact with some other circuit* When the
polarity is reversed i the lamps operated by the machine
will burn **upside down"j i. e,, the lower, or short, carbons
will be positive and will bum twice as fast as the upper.

ARC LIGHTING

§35

If the current h allowed to flow in the wrong direction for
any great length of time, the bottom carbon holders will be
destroyed. It is important, therefore, to see that trouble of
this kind is remedied as soon as possible. As far as the
lamps are concerned » the trouble can be overcome by simply
reversing the ping connections at the switchboard, but the
polarity of the dynamo should be righted at the first oppor-
tunity. This may be done as follows: Connect the brushes
together by a piece of wire so that the armatures will be
short-circuited and hence will allow current to pass through
the fields without running the machine as a motor. Then
connect the positive pole of another machine to the negative
pole of the machine to be fixed and allow the current to
flow for a few moments. If another machine is not avail*
able, a number of cells of battery may be used. This will
reverse the polarity and bring the machine back to its former
condition. After this is done, the short-circuiting loop may
be removed from the brushes. Do not attempt to reverse
the polarity while the machine is running.

KUNNINQ ARC MACHINES IN SERIES

30. Sometimes conditions may arise where it is neces*
sary to i*un two arc machines in series in order to supply
the lamps on a given circuit, because the number of lights
to be operated may exceed the capacity of any one of the
available machines. The two machines are connected in
series by connecting the positive terminal of one to the
negative terminal of the other, in just the same way as cells
are connected together when their E< M. F.'s are to be
added. When arc machines are nm In this way there is
often trouble due to the current seesawing or hunting. The
current, instead of remaining steady, surges up and down*
This is caused by the unstable action of the regulators on
the two machines; both try to do the regulating at once and
the result is an unstable condition of affairs. Under such
circumstances it is best to throw one regulator out of
action and make the machine generate its full-load voltage

§85 ARC LIGHTING 25

by blocking the regulator or setting the brushes at their
position of maximum E. M. F. This machine will then
generate a constant E. M. F., and whatever changes are
necessary will be taken care of by the regulator on the
other machine.

AliTERNATING-CURRENT, ARC-LIGnT DYNAMOS

31. Constant-Current Alternators. — The operation
of arc lights in series from constant-current alternators
is not common, for though such alternators have been built
they are used to but a limited extent. Unless used with
step-up transformers, they have the same disadvantage as
direct constant-current machines; i. e., in order to operate
a large number of lamps they mu3t generate a very high
pressure.

32. Although it is quite possible to operate alternating-
current arc lamps in series from constant-current alterna-
tors, the present practice is to generate the current by
constant-potential alternators and then to supply it to the
series circuits either directly, by means of special constant-
current transformers, or through a regulator of some kind
that will vary the E. M. F. applied to the circuit as the load
varies. The advantage of this plan is that it allows series
arc lamps to be operated from the same alternators that are
used to operate incandescent lamps, thus simplifying the
station equipment. Also, one large alternator operating at
a moderate pressure can be made to operate a large number
of series lamps by running a number of circuits all fed in
parallel from the same dynamo and each circuit provided with
an independent regulator or transformer to keep the current
in that circuit constant.

OPERATION OF SERIES ARC LAMPS FROM CONSTANT-
POTENTIAL. ALTERNATORS

33. Operation Directly From Machine. — Suppose
that alternator Ay Fig. 19, generates current at a constant
pressure of 2,000 volts. If enclosed-arc lamps are used,
each lamp will take about 80 volts and about twenty-five

ARC LIGHTING

gS5

lamps can be connected in series across the line, as indi*
cated. This is similar to the method described for operating
incandescent street lamps in series* With this scheme of
connection it is necessary to provide each lamp with a cut-
out of some kind that will insert a resistance or reactance in

;

Fio. 19

the circuit whenever a lamp is extin^ruished; otherwise^ the
current will increase, for it must be remembered that the

pressure applied to the circuit is constant no matter how
many lamps may be in operation.

34. Use of Adjiist^blo Trail sroriner» — The operation
of lamps direct from the machine is only possible when the
number of lights on the circuit is suited to the voltage of the
dynamo* This is generally not the case, and the above
arrangement is therefore of limited application and has
been used in comparatively few cases. Instead of supplying
the lamps directly from the machine, a considerable range
of applied E. M. F. can be obtained by using a constant-
potential transformer with its secondary coil split into a
number of sections. Each lamp is provided with a reactance
coil, as be fore ^ but the use of the transformer admits of a
considerable range in the number of lamps that may be
operated on a circuit; that is, the combined voltage necessary
for the lamps may be considerably different from that
generated by the alternator. This arrangement does not,
however, provide automatic regulation and is therefore
undesirable.

§36

ARC LIGHTING

35. Operation From Couetant-Current Transform-
ers*— A method now largely used for the operation of
series altematingKiurrent lamps from constant-potential
alternators is that in which a special transformer is used
to transform from constant potential to constant current.
This system is practically the same as that described for
the operation of series incandescent lamps by means of a
constaQt-ciirrent transformer.

Fic> a>

Pig. 20 shows one of the larger sizes of General Electric
constant*current transformer with the case removed. There
are two fixed primary coils P P and P* P^ and two mov-
able secondaries S S and S* S\ The two secondaries are

46B— 20

ARC LIGHTING

§35

counterbalanced against each other by nieans of the levers,
sectors, aad chains shown in the fi^re. bo that when the load
is light both coils occupy a position near the center, and when
it is heavy they both move toward the end coils* The
weight w required to counterbalance the repulsion effect is
carried by a small auxiliary lever / that projects through the
top of the case. The two secondary coils can be connected
in series to feed a single circuit, or they can be connected to
two circuits^ as in the multicircuit Brush dynamo.

36- Const an t'Current transformers can be placed either
in the station or in a substation at a convenient point near
where the lamps are to be supplied* In some instances
they have been placed in substations and equipped with
automatic time switches that cut them out io the morning
as soon as the lights are no longer needed* At light loads,
a system of this kind has a poor power factor; but if worked
at nearly full load, the power factor is about .8, or about as
good as the power factor of a load of induction motors.
The low power factor has been urged as an objection
against systems of this kind; and while it undoubtedly is
an objection, it must not be forgotten that the doing away
with arc-light dynamos and running all the lights, both arc

836

ARC LIGHTING

and incandescent, from the same machine is an advantage
that goes far to outweigh the disadvantages of a low
power factor.

37. Rosrnlatlon by Means of Variable Reactance.

Balanced reactance coils are also used for the operation of
series arc lamps from constant-potential mains in the same
manner as described for series incandescent circuits. Fig. 21
shows a regulating coil made by the Western Electric
Company. The coil a, which is partially counterbalanced by

weight c, is so suspended from a sector b as to slide up or
down over the central part of the m-shaped laminated core.
Any increase in current causes the coil to be drawn up, thus
increasing the reactance of the circuit and maintaining the
current at constant value.

Fig. 22 shows different methods of supplying the arc
circuit from constant-potential mainSt The most desirable

ARC LIGHTING

§35

arrangement is shown in (a), where the arc circuit is supplied
from the secondary of a main transformer that is provided

with a number of taps so that the transformer voltage can be
adjusted to suit approximately the number of lamps to be
operated. This requires but little voltage to be taken up in
the reactance coil under normal full-load conditions and
therefore secures a better power factor than if the lamps
were operated as in (^). In this case the secondary of the
transformer is not adjustable, and if the voltage required by
the lamps is much less than that furnished by the transformer
considerable voltage must be taken up in the reactance coiL
The voltage across the terminals of the reactance coil is out
of phase with the main secondary voltage; hence, the greater
the voltage taken up by the regulator, the lower will be the
power factor. In (c), the arc circuit, with its regulator in
series, is attached directly to the mains. This is not as
desirable an arrangement as {a) or (^), because a ground on
the arc circuit grounds the main circuit also, as pointed out
in connection with the operation of series incandescent lamps,

38. Econonxy Cotls. — Sometimes it is desired to

operate alternating-current axe lamps from 220- volt or 440-
volt circuits. Lamps have been built to operate directly on
220 volts but they are not as satisfactory or as efficient as
low-voltage (100-1 20- volt) lamps. A satisfactory method

-e^ie-

'44aiK-

^^^ Lamps fb) laifyjs

Pig. 2S

of operating low^- voltage lamps on these moderately high-
voltage circuits is by means of economy coits^ or auto-
trans formers, shown in Fig. 2^'^, The economy coil is
wound on a laminated iron cor^ in the same way as the coil

§35

ARC LIGHTING

of an autotransformer, and a tap is brought out at the
middle point, as in (a), if the coil is used to transform
from 220 to 110 volts; if used on 440 volts, the secondary
is connected so as to include one-quarter of the total
number of turns on the coil.

39. Balancini; Coils. — Sometimes these coils are used
as shown in Fig. 24, where they split up the voltage as
indicated. Thus, in (a), a 220-volt, two-wire system is
changed to a three-wire system with 110 volts on each side.
If one side becomes more heavily loaded than the other, the
current on the heavily loaded side flows through the neutral
to the coil on that side. The transformer action between
the coils maintains an approximately constant voltage on the
two sides no matter whether the load is balanced or not.
An autotransformer used in this manner is often called a
balaiiclniBr coll. In (d), the same principle is followed out

- ^^c^^< -

KsmmKmm^

-f/OV-
X—

-//ov:-
— X —

-^40V-

K^mmmmj

•^2201/.-

•^tlOV-

440^-

-eeov:-

-novr-

Fig. 24

except that a five-wire system is supplied from the coil.
The middle wire is usually grounded so that the pressure
that may exist between any wire and the ground can never
exceed half the voltage between the outside lines. An
arrangement similar to that shown in diagram (^) is often very
useful in installations where alternating current is distributed
at 400 to 500 volts for power purposes, as for example in
large manufactories, and where it is desired to have several
lower voltages for the operation of arc and incandescent
lamps or for use in starting motors. The balancing coil has
to be large enough to handle the unbalanced current only, and

ARC LIGHTING

i35

hence is much smaller than a regular transformer capable of
transforming the whole of the power supplied to the second-
ary circuit. Balancing colls» or autotransformers, should
not be used where there is a very great difference between
the primary and secondary pressures. Under ordinary con-
ditions, if the primary pressure is over 500 volts it is safer
and better to use a regular two^coil transformer*

AKC-L-IGHT SWITCHBOARDS

GKNKRAIj CONSIDEFEATION8
40- Arc-llirht swltcliboarcls bear little resemblance to
those used for constant-potential incandescent lig:htin^. In
most stations of any size, there are several arc machines, or
if alternating current is used, several arc-light transformers
and several circuits. It is desirable to have the switchboard
arranged so that any machine or transformer can be con-
nected to any circuit and so that a circuit can be transferred
from one source of supply to another while in operation, or,
if necessary, so that circuits can be operated in series. An
arrangement of switches to accomplish this would be
exceedingly complicated, and arc-light boards are there-
fore of the plug variety. The various connections are
made by inserting plugs into receptacles, the circuit being
completed on older boards by flexible cables and on later
types by the plug itself.

41. Operating Cipcults In Series, — ^Qulte frequently,
when the number of lamps on one circuit is insufficient to
load up a dynamo or transformer, two or more circuits are
connected in series at the switchboard. With direct-current
boards, the terminals of the circuits should be marked +
and — on the switchboard, the + side being that at which
the current leaves the station and the — side that at which
it returns. In connecting direct-current circuits in series,
the — end of one circuit should be connected to the -f end
of the other^ as indicated in Fig. 25. If two — ends are

§85

ARC LIGHTING

connected, the current will flow through the second circuit in
the wrong direction and the lamps will bum **upside down."
The switchboard is usually equipped with an ammeter,
which will indicate when the current is flowing in the proper
direction. Some of these ammeters, for example, the Weston,
will not give a deflection over the scale unless the current

A+

■^

Ca6/e

B- [i-

I 1

*- X X

OrcuttB

^y^

3 Swifchdoanf

OrcwfA

Pio. 25

flows in at the + terminal. Others have an indicating attach-
ment that shows whether or not the current is flowing the
wrong way. It goes almost without saying that series arc cir-
cuits are never connected in parallel. If this were done, the
current would split between the circuits and the lamps would
not operate properly.

CONSTRUCTION AND OPERATION OP ARC
SWITCHBOARDS
42. simple Board With Cables.— Fig. 26 illustrates
about the simplest possible type of board equipped with an
ammeter and terminals for two machines and four circuits.
These terminals take the form of sockets or spring jacks
mounted on the board, and connections are made between

ARC LIGHTING

§36

the various receptacles by means of heavily insulated, flex*
ible cables provided with a plug at each end. Each terminall
is double, and those for the dynamos are arranged in the
lower row and marked -h-^, —A, -\-B, —B, each dynamo
being disting^uished by its letter A or B. The terminals
of the four line circuits are arranged in two rows in the
upper part of the board and are marked +i, —1, +2, —2,
+S, —J, +4, — 'i, each circuit being distinguished by its
number 1, 2, 3, or 4. The ammeter AM is mounted in the
center of the board and is provided with terminals + and — *
The board itself is usually made of a ^ood quality of marble.

Jff

*■

X 1

<&■©

#•

@i@

-' k

. A

\ Ak.

"\/r ^

i::^

>7\r

^ /p

f<&x^

— 1

V-

Fio.as

Slate is not a good tnaterfal for arc boardsi as it is liable to
contain metallic veins. It must be remembered that the
pressure between the terminals of an arc machine at full load
is very high* hence the switchboard terminals must be well
insulated. On most boards » the terminals are not even
allowed to come in contact with the marble, but are insulated
from it by means of hard-rubber bushings, the marble serving
merely as a support and not depended on for insulation.

The operation of plugging in circuits or dynamos always
appears confusing when explained on paper. It is, howevert

§35

ARC LIGHTING

comparatively easy to follow out oa the board itself, where
one can handle the cables or plugs and make the required
connections for himself* A little practice during the day*
time, when the circuits are not in use, will soon enable one
to become so familiar with the method of operation that all
necessary changes can be made quickly and with certainty.

In making changes on an arc board, it must be distinctly
borne in mind that a circuit carrying current should not be
broken in order to cut in or out line circuits containingf lamps.
If the circuit is opened, the effect is to increase the resist-
ance of the circuit by a large amoixnt, and the voltage will
rise greatly. Besides causing a long, vicious arc at the
switchboard and perhaps injuring the attendant, it is very
hard on the insulation of the dynamo or transformer* If a
dynamo or circuit is to be cut out» it should first be short-
circuited* Arc machines and constant-current transformers
are not injured by short-circuiting as constant-potential
apparatus would be, because as soon as they are short-
circuited the voltage generated drops to a very small amount.
In Fig. 26 each terminal is made double, so that transfers
can be made without opening the circuit.

In Fig. 26 circuit 1 is *'dead/' because its terminals are
not connected to anything. Circuit 2 is on dynamo A, the

path of the current being H-j^- +^ 2 ^L Circuits

3 and i are in series with each other on dynamo St and the
ammeter is also in series in this circuit. The path of the cur-
rent is +B\ through the ammeter to -\~3 3- +4- —4-^B.

43, Suppose it is desired to connect the ammeter in
circuit 2. To disconnect it from circuits 3 and ^, it is
first short-circuited by plugging in a cable across the termi-
nals ~\-B and +5, The two plugs on the cables leading to
the ammeter may then be withdrawn from H-^ and H-^, and
the circuit will not be opened. The plugs removed from
+^ and -hi3 may then be inserted at -k-A and +2, respect-
ively, thus shunting the ammeter across the cable ^A ~^2-
The cable -(-^ +2 is then removed and the curreut supplied
to circuit 2 passes through the ammeter*

ARC LIGHTING

§35

44. Again, with the connections as shown in Fig:* 26,
suppose that it is desired to connect circuit 1 in series with
circuit 2 without shutting down either the dynamo or cir-
cuit 2* The first step will be to connect terminal —1 with
terminal +2, then terminal -\-A with terminal +i. The
cable directly connecting terminal -k-A and +2 may now be
removed without opening the circuit at any point and at the
same time throwing the two circuits 1 and 2 in aeries.

45, Brush Plujr and Spring^ Jack, — In case cables are
used for making the connections, it is necessary to have the
plugs thoroughly insulated so that there will be no chance
for the switchboard attendant to make accidental contact
with any of the terminals on the board during: the process
of plugging. No live metal work of any kind should be
allowed on the face of the board. Moreover, the plugs
should be constructed so that in case a circuit is opened by
their withdrawal, the consequent arcing will not cause damage.

Fig, 27 illustrates the style of plug used on boards for
large Brush machines. A is the marble panel and b the

metal plug, or contact, attached to the cable as shown. Cis
a cup-shaped casting to which the line is connected and into
which b slides and is held by the spring clip j, so as to make
a good contact. C screws on to the end of the hard -rubber
bushing D and is separated from the marble by the insula-
ting washer E, F is a hard- rubber sleeve, or tube, and G
a mat3le handle; A is a spiral spring that causes the steeve F
to slide over the contact piece b when the plug is pulled out,
so that by the time the plug is pulled entirely out of the board,
the contact b is completely covered and there is no danger of

§35

ARC LIGHTING

the attendant comine into contact with it. When a plug is
Inserted, the nose of the sleeve /^ comes against casting C
and as the plug is pushed on in, contact b passes through
the hole in Cand is held by the spring s. These jacks are
usually mounted in pairs connected together, so that transfers
can be made without opening the circuit,

46, Weetern Electric PIuk and Jack, — Fig. 28 shows
a jack and plug used by the Western Electric Company, It
consists of a main jack A and two smaller jacks B, B, which
are used in making transfers* The springs a, b^ t hold the

Pro. 38

plugs in place by engaging the groove on the end of the

plug. This plug also has a hard- rubber sleeve c that slides
over the metallic terminal d as soon as the plug is pulled
out* The general arrangement of the plug and jack will be
apparent without further explanation,

47. Board Without Cables. — Fig. 29 illustrates the
principle of one of the earlier types of board made by the

General Electric Company, in which cables are almost wholly
dispensed with. This is accomplished by means of two
groups of contacts arranged in two parallel planes a little

ARC LIGHTING

r35

distance apart. The contacts in the front group are divided
into pairs of boriasontal rows, each pair being connected to
the terminals of one of the d^rnamos. The contacts on the
back group are divided into pairs of vertical rows, each pair
being connected to one of the circuits* The contacts, which
are in the form of bushings, are directly opposite each other
and the connection between any dynamo and any circuit is
made by a long brass plug that is pushed through the out-
side contact to the inside. In Fig. 29, the dynamo terminals
are lettered A+^^^t etc.j and the circuit terminals 1+^1^^

as in the preceding case. The back, or ciraiii^ board is
provided with an extra row of contacts at the bottom, by
means of which circuits may be connected in series, using
for the purpose cables having suitable terminals, similar to
those used for connections in the form of board first described.
For the arrangement of plugs shown in Fig, 29, the path

of the current is as follows: ^-h-2+-2^ JS^ S-A — .

Circuits 2 and 3 are in series on dynamo A. Also circuit 4 is
on B because B-^ and B— are plugged through to 4-^ and
i~. Circuit I is dead« By using a cable with short plugs

(

§35

ARC LIGHTING

that only reach throug^h the front bushings, dynamos may be
connected in series, if necessary.

In Fig. 29 the sets of bushings are shown separated much
farther than they are on the actual board, in order to make
the figure clear. On the actual board the back contacts are
carried on vertical copper straps that are attached to the
front board. Fig. 30 shows the general appearance of one
of these boards and indicates the location of the positive and
negative terminals of the dynamos and circuits. Fig. 31

Pio. 80

gives an idea as to the method of mounting the bushings
and is self-explanatory. Bushings b are used for connecting
circuits in series.

48. Carrier-Bus Board. — This is a later type of board
made by the General Electric Company; it is somewhat similar
to the one last described, but is constructed in the form of
panels and arranged so that more dynamos or circuits can be
added at any time by adding more panels to the existing
board. Transfers of circuits from one dynamo to another

ARC LIGHTING

§35

are effected by means o£ bus-bars mnnin^ across the back
of the board, and no cables are required. The general
arrangement of the board will be understood by referring to
Fig. 32. In view U)y the lower terminals bnC^d,e,itg are
connected to the machines A, B, and C The terminals at
the top connect to the circuits 1\ 2',
and 5^ The crosspieces B^ 4, 5, 7, 8,
f :r/jr:::il| l and *J run across the back of the board

and can be connected to similar cross-
pieces on the next panel by means
of the connection strips 5'', A^\ 5",
etc. and plugs inserted in the side
sockets m^ m. An ammeter jack is
connected in each side of each cir-
cuit, the ammeter being connected
by inserting a plug at any one of the
upper row of jacks b, c^ d^ etc, in
view {a). It is desirable to have the
ammeter arranged so that it can be
cut in on either side of a circuit
because it facilitates testing for
grounds. A leakage of current from
the dynamo to ground and thence back
to the other side of the machine through a ground somewhere
out on the circuit will cause a reading of the ammeter, when
connected in one side of the circuit, different from that
obtained in the other side.

-u..

Pio, m

t=)

49. Figs. 33 and 34 show the style of plug switch and
plug used. All condncting parts are insulated from the sup-
porting panel by means of porcelain insulators; the back
contacts are held out from the board by porcelain pillars;
and the whole constniction is such as to give a high degree
of insulation. When the plug is inserted, connection is
made between the front and rear contact bushings or
thimbles, and when a plug is withdrawn, the arcing takes
place within the fiber tube, Fig. 33; a long break in a confined
space is thus secured and the arc suppressed,

8S5

ARC LIGHTING

50. The ammeter Jack for connecting the ammeter in
circuit is shown in Fig, !W; Fig. 36 shows the special plug
used with the jack. In Fig. 35, a and b are two small bus*

bars, Insulated from each other and connected to the termi-
nals of the ammeter, that run across the back of the board

■ACTW^ffj

f^tftf/mr^ihr

P^v^i^Offt i/mjfrtr V

/7p^rv^

Tifr/nfnB^^

"' -"l

. 1 v^^fMteff

Fio. 3^

and have contact bushings in line with the plug recep-
tacles ^, €t dt etc, Fig, 32 (a). Mounted directly back of each

ARC LIGHTING

§35

receptacle and in line with it is the jack, consisting of a con-
tact bushing r, Fig, 35, contact spring d, and terminal e. When
the plug is not in place, spring d makes contact with bush-
ing c and the current passes from / to f and thence to the

Fio.M

circuit. The plug, Fig. 36, has three contacts a^ i, c\ b and €
are parts of the same brass rod, but sleeve a is insulated.
When the plug is -inserted, point c pushes spring d out
from the contact bushing c. Fig, 35> and at the same time

/fc*r*i*-v

FiQ. 35

part h of the plug makes contact with the sleeve in bus-bar b*
Sleeve a on the plug connects bushing Cx Fig, 35, with bus-
bar u. Thus, when the plug is inserted, current entering
at / takes the path /-bushing ^--sleeve a on plug-bus*bar

-^i¥3id^Wt» -

Fto. M

a-ammetef'-bus-bar ^-contact b on plug-tip c on plug-spring
(/-terminal ^-circuit. When the plug is withdrawn, spring d
makes contact with € before the circuit through the ammeter
is broken, thus preserving the continuity of the circuit.

ARC LIGHTING

51* The method of using the board will be understood by
referring to Figs. 32 (c) , 37» and 38. There are three breaks
/, i\i'\ Fig. 32 (r), in each vertical strip between a dynamo
terminal and a corresponding circuit terminal When, there-
fore, these breaks are plugged across, as indicated by the
three rows of plugs in Fig* 3*2 (iz), dynamo A is operating
circuit 1'; dynamo /?, circuit 2^; dynamo C circuit 3\ This will
be apparent by referring to Fig, 37* The vertical lines here
represent the vertical bars^ in which the breaks are indicated
by open spaces. The black dots represent the plugs, and

+i^ +»- +5'^

J- +1- ^s-

Ifdi**-*/^ •ff*

!:i_^^^-_^^

£!_JiL

b^^^^n^^dL^^^-^d

^€*-^dl^^^iL

^»* B^10 **^m**^i9 •/l«*^J#

^-_^^2

fr « -i e 1/ L

i^4

\i z^ z*'* *p# • /• w

M pT M3fT_IZ3-Jj^

<?,

*ii4

^^^i3^^&_^Cs_^s^&

iwfiL-.^

+ A-

Flo. S7

+ €-

+ ^-

FlO.38

/i. '^i*

are supposed to connect the two terminals between which
they are inserted. Fig* 32 represents the ordinary condition
of running, where the cross-bars are not in use.

52. Suppose it is desired to shut down machine B and
run circuits 1' and 2' in series on machine A. Insert plugs
at f», dt, Ctr and if, and remove plugs if. and </»* This leaves
two circuits and two machines in series, Short*circuit
machine B by inserting a plug at €r and cut out machine B
by removing plugs d^^ and Ao. Then take out plug d^^ and
the board will be as indicated in Fig. 38. The path of the
current will now be ^+ -i&.<,-*.~^t-J'+ through circuit 1^-1^—
'€^-€tr-dg-d^-2' -\- through circuit 2*-2' eg-e^-^t'-c^-c^^-A —;

4613^21

ARC LIGHTING §35

I i' and 2* are m series on dynamo A. Atthotigh

uations on these boards are not so easy to follow

±1. A diagram, the manipulation of even a large board

thing that is soon learned when one has the board

111V before him. In order to distinguish between the

Z. switches and thns reduce the liability of making

\\\ open-circuiting, bus'disconnecting, and ammeter-

X acles are provided with brown porcelain bushings.

bus-iransfer receptacles have blue porcelain bushing

are indicated by the black rings in Fig. S2(a).

fa toart^

Toli/if

PIO.S9

53. Transfer Boards. — It is highly important that all
arc-line wires brought into the station should be run as
straight and free from crossings as possible. A number of
fires have resulted from the numerous crossings and the
general maze of wires to be found in some of the older
stations, especially at the point or in the tower where the
wires enter the building. These crossings were generally
made in order to bring the wires to the switchboard in the

835

ARC LIGHTING

correct order for connecting up. In some stations, in addi-
tion to the switchboard, a transfer board is provided to
enable the lines running to the switchboard to be connected
to any of the lines running out of the station. By using a
transfer board, the wires coming into the station may be
brought in in any order that may be most convenient, and
they may be run straight to the board without crossings.
They may then be sorted out and connected to any desired
circuit terminals on the
switchboard by using the
transfer board. The trans-
fer board is also very useful
for changing the terminals
of a circuit from one part
of the board to another,
as it enables it to be done
without disturbing the con-
nections at the switchboard
terminals themselves.

The general arrange-
ment of the transfer board
will be understood by re-
ferring to Fig. 39. A num-
ber of bare No. 4 or 6
B. & S. wires a b are
stretched vertically, 5 or
6 inches apart, on a sub-
stantial framework. In
Fig. 39 (a) they have been
shown a little to one side
of each other in order not
to confuse the connections. Between these, a corresponding
number of horizontal wires c are stretched. One set of ver-
tical wires a runs directly to the circuit terminals on the
switchboard and the other set b connects to the line wires.

The horizontal wires are used for connecting across from
any line to any switchboard lead. For example, suppose
1 and 1' are the circuit terminals that are to be connected

f Force/a/rt or^/s39
/nsa/iftor

Pio.40

ARC LIGHTING

135

to switcbboard leads o, p. By connecting to the cross-wire^
as shown at'^, /, line 1 is connected to q^ and by connect-
ing as shown at m.ii^ line V Is connected to p^ By this
arrangement, therefore, the line and switchboard connec-
tions can be transferred in any way desired. The actual
number of wires used in any case will, of course, depend
on the number of circuits to be accommodated. The con-
nections between vertical and horizontal wires are usually
made by means of a clamp connector^ somewhat similar to
that shown in Fig. 40 {a). Different methods are used for
stretching the wires on the frame, but they should always
be moimted so that they will be thoroughly insulated. On
this account the wire should be passed through porcelain or
glass insulators at each end, as indicated in Fig* 40 (jJ).
The wires are stretched tightly by screwing up on the nut n
and the line wire attaches to terminal /*

SWITCH BOAKnS FOK ALTERNATING-CCRRENT
SKRIES SYSTEMS*

64. General Electric Switchboard. — When series
alternating-current arc lamps are operated from constant-
potential alternators, either through constant-current trans-
formers or otherwise, it is usual to provide a small
switchboard for each transformer or regulator; that is,
the various devices necessary for the control or protection
of the transformer or regulator and the circuits supplied
from it, are grouped together and the board is frequently
placed near the transformer that it controls.

Fig, 41 shows front and rear views of a General Electric
board of this kind designed for a 35-1 ight transformer sup-
plying current to a single series arc circuit* The board is
equipped with an ammeter a^ plugs b^ b for breaking each
side of the arc circuit, a plug receptacle € for short-circuiting
the arc circuit or secondary of the constant-current trans-
former, two plugs d, d for disconnecting the primary of the
transformer from the alternator, and a Thomson recording
wattmeter e for measuring the total watt-hours supplied.
The ammeter a is supplied with current from a current

ARC LIGHTING

transformer / mounted on the back of the board so that the
uistmment is thoroughly insulated from the high-pressure
arc circuit. The potential transformer j^ steps down the
primary pressure for the potential coil of the wnttmeten and
the case k contains the non-inductive protective resistance

Pm. «

in series with the potential circuit of the wattmeter. The
plug switches dt d are connected to the primary of the
transformer through high-tension enclosed fuses that pro-
tect the transformer from overload. Plug switches b^ b

ARC LIGHTING

§35

are thoroughly insulated by beiog: mounted on porcelain
Insulators as shown. Fig- 42 shows the connections for
this switchboard. The corresponding parts in Figs. 41
and 42 are lettered alike so that further explanation is
unnecessary.

55. Fig. 43 shows the connections for a similar board]
used with a transformer of 100-lights capacity supplying
two circuits on the multicircuit plan. The transformer is

r. Lmps

Lifff^tftf

^fjiSiiiiKe

C/Ztf#

Feq.42

Fig. 13

provided with two secondary coils, which are connected
in series through the two lighting circuits. The primary is
also provided with two windings so that they can be
connected in parallel for 1,100 volts or in series for
2,2(K) volts. The plugs for each circuit are arranged as
in Fig. 42, but only one ammeter is provided^ the primary
of the con slant -current transformer being connected to an
ammeter plug that can be inserted in suitable jacks, without

§36

ARC LIGHTING

opeotng the lamp circuit, and thereby made to indicate the
current in either circuit.

56* The ammeter jack used on this board is shown
in Fig. 44* The ammeter is connected to the plug by
means of a twin cable, one end of which is connected to
sleeve i> and the other to contact r; b and € are, of course.

>i*jr J *\-jr.' J V%^.f*i0r

45*^^

Fto, 41

insulated from each other, Wlien the plug is loserted,
^ is in contact with a, and f with d and e, thus cutting
the ammeter into circuit. When the plug is withdrawn,
spring d makes contact with the bushing to which a is
connected* thus maintaining the circuit*

Fig. 46 shows the construction of the plug switches. The
plug is a straight brass rod with a well-insulated handle and.

FJ0.4&

when inserted, makes connection between the front and rear
bushings. When the plug is withdrawn, the arcing takes
place within the fiber tube and is smothered out.

57. Westorn Elect i*Ie Swltchbciarrt* — Fig. 46 shows
a switch used by the Western Electric Company on
altematiag-cUTxent arc switchboards. It is of the plunger

ARC LIGHTING

§86

type^ each side of the circuit being broken when the handle
is pushed in. The arc is broken within the porcelain
cylinders so that there is little chance for it to hold over and
burn the contacts.

Fio.4fl

Fig. 47 shows front and rear views of the small switch^
board panel used with each of the transformers supplying
series circuits. It is equipped with a tubular switch a^
operated by handle 5^ and fuses r, d enclosed in porcelain

Pio. 47

handles so that they can be easily removed for renewaL
The ammeter e is connected directly in the circuit, but for
very high pressure circuits it would be advisable to operate
the ammeter from the secondary of a series transformer.

§35

ARC LIGHTING

Fig. 48 shows one arrangement of an arc switchboard
together with the transformers and regulators through
which the alternating current is supplied from the machines
to the circuits. The switchboard is motmted in a gallery and

Pio.48

the transformers and regulators are placed underneath, as
shown. This plan of mounting the board in a gallery is used
quite largely in large city stations or in other places where
space is limited.

r
I

INTERIOR WIRING

(PART 1)

PRELIMINARY CONSIDERATIONS

1. The subject of interior wiring involves a study of the
various methods for supplying electric current to devices,
such as lamps, motors, etc., used in buildings; also, the
methods for operating bells, burglar alarms, and other
minor appliances operated by electricity.

In electric wiring, the ultimate object is the conveying
of the electricity to the lamp, bell, motor, or other device
that is to be operated. But this must be done in a proper
manner; otherwise danger, unsatisfactory operation, and
waste • are sure to result.

2. Four things should be considered in every electric
installation: {a) safety, {d) satisfactory operation, (c) con-
venience and neatness, and {d) economy. The first is by far
the most important. Therefore, the electrical worker should
understand, first of all, what are the sources of danger in the
use of electric currents and then what precautions are neces-
sary and what conditions must be complied with to avoid
these dangers. When he thoroughly understands these
things, he should learn how to make his work satisfactory in
other respects and profitable to himself.

The same causes that, under certain conditions, make
electricity dangerous to life also make it a source of fire
hazard. There are also conditions under which an electric
current may cause fire, although it may not be directly

For notice of copyright, see Page immediately Mlowin£ ike itiU page
248

INTERIOR WIRING

dangferous to life. In discussing the precautions necessary
to avoid any chance of fire from an electrical cause, the
student will learn how to avoid danger to life as well, so
that it is unnecessary to discuss that subject by itself*

FIRES CAUSED BY ELECTRIC WIRING

3, The so-called * 'electrical fires/' or fires that are caused
by the presence of electric wires or apparatus within a
building, can be divided into three classes, as follows;

1. Fires catised by poor work or improper materials,

2, Fires caused by overloading the apparatus or wire
with a higher voltage or with more current than it was
designed to carry,

Bu Fires caused by lightning striking the outside lines or
by the crossing of circuits that should never come into
contact with one another.

A good Job of interior wiring overcomes all danger due
to the first two of these sources of hazard and most of the
danger due to the third, but not all, for accidents sometimes
occur outside of the buildings, against the results of which
the present accepted devices for the protection of inside
circuits are not sufficient. The failure of a lighting company
to use proper lightning arresters and transformers* or to
insulate the outside wires thoroughly may cause trouble
within a building in which the wiring is properly done.

THE NATIONAI^ IGLECTRICAL COBB

4. When electric lights first came into general use, the
insurance companies discovered that there were many fires
of electrical origin, because the wiring was of very inferior
workmanship. The various associations of underwriters,
therefore, formulated rules in accordance with which they
required (hat all wiring be done or they would not insure
buildings containing it. In the course of time, these various
rules of local associations were reduced to a uniform code»
and finally, in 1898, they became known as the National
ElectrLcal Code and received the indorsement of practically

-a^

§43 INTERIOR WIRING S

all the inspection bureaus throughout the United States^
besides that of the following organizations: the American

Institute of Architects, the American Institute of Electrical
En^ineerSp the American Society of Mechanical Engineers,
the American Street Railway Association, the Factory Mutual
Fire Insurance Companies, the National Association of
Fire Engineers ^ the National Board of Fire Underwriters,
the National Electric Light Associationg the Underwriters'
National Electric Association,

A few cities have rules of their own that differ slightly
from this code, but the differences are not vitaL Any per-
son doing work in any city where there is municipal legisla-
tion governing his work should investigate the laws of that
particular place before undertaking to lay out work for him-
self. Every wireman should be supplied with a copy of the
latest edition of the National Electrical Code and do work in
compliance with those rules » whether additional laws exist
or not. Copies of the code and of all other information
published by the Underwriters* Association for the sake of
reducing the fire hazard can be obtained by writing to the
laboratories of the National Board of Fire Underwriters at
Chicago or by applying at the nearest Underwriters' Inspec-
tion Bureau, The rules are revised by conventions as often
as changes in the electrical art make such revision necessary.

5. Fittings That May Be Used. — In addition to this
code of rules, the National Board of Underwriters publishes
twice each year a list of approved fttttngs for use in con-
nection with the code. This list contains the names of articles
that have been found entirely satisfactory, together with the
names of the manufacturers. It does not contain a list of ali
fittings that will pass inspectioui and many good articles are
not listed in its pages.

fKXAMPI^BS OF ELECTRICAL FIRES

6. That the student may properly understand the nature
of the fire hazard due to the presence of electric circuits, before
studying the various preventives, the following typical exam-
ples of electrical fires are briefly described. These are reports

INTERIOR WIRING

1 43

of actual fires and burn-outs taken from the Quarterly Fire
Reports of the National Board of Fire Underwriters*

L Loose connection on series incandescent circuit in
show window* Arc ignited insulating covering of wire and
fire spread to surrounding infiammable materiaL Four
sprinkler heads opened and extinguished the fire. Contents
of window destroyed*

2. Socket*shelI burn-out in show window of millinery
store* Short circuit caused by metallic shell of socket on
window fixture establishing connection between projecting
strands of flexible fixture wire,

3* Paraffin-covered wire used for pendants for drop
lights. Wiring installed on a motor circuit, after inspection^
by occupant of building who wished to secure light* Short
circuit ignited paraffin covering and whole place burned up*

4* Short circuit or ground on constant-potential lighting
circuit, where mains ran unprotected through damp wood-
work in a brewery. The arc thus formed ignited insulating
covering of the wire and fire comniunicated to woodwork of
frame building.

5, Short circuit in flexible cord in show window burned
out the window*

6. Heating effect of incandescent lamp. A 16-candIe*
power incandescent lamp on a 52-volt circuit was left lying
on a coat in a newspaper office* About 4 hours after the
lights were turned on the coat was discovered smouldering,
and on being moved burst into flame*

7* Revolving wheel of incandescent lamps in show win-
dow covered with handkerchiefs burned out the window
either by sparking at the commutator or from heating effect
of the lamps,

8* Sparks from an arc lamp dropped on a table under-
neath that was covered with open boxes of shirt waists.
The table and contents destroyed, otherwise no considerable
damage.

9, Flexible lamp cord wound around a gas fixture having
a soft-rubber insulating joint. The current grounded through
the joint and the arc ignited the escaping gas.

§48 INTERIOR WIRING 5

10. Overheating: of No. 14 B. & S. wires due to partial
short circuit, caused by moisture, through porous crockery
knobs on which wires were mounted. The fuses, which
were too large, did not melt for some time and the burning
insulation of the wires set fire to combustible material near,
causing a loss of $15,000.

11. A fuse block, improperly constructed and placed in
close proximity to woodwork, held an arc after a short circuit
long enough to set fire to the woodwork.

12. Main feed-wires placed in an elevator shaft were
short-circuited by a breakdown of their insulation. A heavy
arc was established that set fire to building.

13. Overheating of resistance coil of arc lamp that was
improperly insulated and too near adjacent woodwork set
fire to building.

14. Short circuit of No. 14 wires installed, contrary to
rules, in molding in a place exposed to moistiu-e. The fire
was stubborn and burned fitfully between floors and was
not extinguished before a loss of $2,000 had been sustained.

15. Fire in public institution. Building wired through-
out with weather-proof wire run through joists without
bushings, both wires of the circuit being brought through
one hole at lamp outlet without separation. Short circuit
occurred in attic that quickly set fire to dry timbers.

16. An Edison plug cut-out was improperly used to pro-
tect a 5-horsepower motor operating at a difference of
potential of 220 volts. Fuse in blowing failed to open
circuit, thus maintaining an arc that set fire to building.

17. Circuit controlling an electric flat iron was left turned
on, becoming overheated and sefting fire to the table. Cir-
cuit had no signal lamp or other indicating device recom-
mended for such equipment.

18. Overheating of mechanism in a 2,000-candlepower
series arc lamp, the metal casing of which did not fit, set
fire to the ceiling. The store was closed, but the lamp had
been left burning until the circuit was shut off. This fire
illustrates the advisability of cutting all current out of build-
ings when the same are imoccupied.

INTERIOR WIRING

§43

19. A fire occurred in Bhow window, caused by a bath
towel falling from support on to a lighted incandescent

lamp in bottom of window; the towel becoming ignited set
fire to the contents of window and damaged some of the
stock in store,

20. Lightning entered building over badly installed watch-
man circuit. No protective devices at entrance to building.
Wires badly insulated; fastened by staples. Heat of wires set
fire to joists of building,

21* Ground of 110- volt circuit on gas pipe in attic. Arc
burned i-inch hole in pipe and set fire to escaping gas.

22. Fire in basement of building caused by accumulation
of sodium salt on back of three-wire molding run on brick
wall. Trouble occurred at a point where a nail had been
driven through molding into wall.

23. Short circuit in fixture canopy ignited ceiling above
fixture. Fire also occurred at same moment in cabinet at
center of distribution. It was found on inspection that the
branch cut-out contained copper wire.

24. An ignorant workman installed a lighting circuit in
lead -covered cable, fastening same to iron ceiling with
staples. Breakdown of insulation of cable set fire to ceiling,
when it was found that no main switch had been installed
and current could not, therefore, be cut ofiE*

25. Switch on electric4ight circuit was mounted in dry-
goods store at a point where draperies came in contact
with it. Flash from same ignited draperies and fire spread
rapidly to millinery and other inflammable material.

20. Breakdown of insulation on wires of lighting circuit in
a fine residence set fire to woodwork inside partitions. Fire
occurred at night» and owing to delay in sending in alarm and
the distance from fire-department headquarters, fire was not
extinguished until a heavy loss had been sustained,

27* Electric -light wire sagged and made contact with
telephone wire running to cable box. Box and cable con-
nections completely destroyed.

28. Burglar-alarm, electric-bell, and electric-light wires
came together inside the partitions of a residencep The

§43 INTERIOR WIRING 7

insulation on the wires was ignited and fire followed up the
partitions. Owing probably to lack of oxygen, fire did not
break out of partitions, but spread so generally over the
house inside that much damage had to be done before it
could be extinguished.

29. Circuits were run in circular loom tubing immediately
over a steel ceiling. Where the tubing came through the
ceiling for a loop, the sharp edges of the ceiling cut through
the same, short-circuiting the wires. Arc ignited the insu-
lation of the wires, fire following same up under the ceiling.

30. Fire in livery stable due to blowing of fuse in
uncovered cut-out into straw. Fire spread so rapidly that
it was impossible for the department to control it.

31. Fire in basement of hotel caused by water leaking
and running down the blades of a switch on 500-volt circuit.

32. Serious burn-out of a fire-alarm system by cross on
500-volt feed-wires of an electric railroad. Nine fire-alarm
boxes, a tapper, and an indicator were burned out, the
repeater also being partially destroyed. Fire was also
started in the residence of the chief of the fire department,
but was promptly extinguished. It was found on inspec-
tion that the instruments were protected by fuses that were
much too short.

7. Figs. 1 to 6 illustrate some characteristic bum-outs;
they have been drawn from photographs of burn-outs that
have actually occurred.

Fig. 1 shows a gas pipe that was melted by an arc caused
by a heavy current-carrying circuit crossing a signal circuit
that was connected to the pipe. The connection to the pipe
was poor and unsoldered.

Fig. 2 shows joints made with No. 10 wire on a circuit
designed to carry 200 amperes. The use of such a poor
joint gave rise to heating: that resulted in the burning out of
the wire.

Fig. 3 shows a fixture canopy with a hole melted through
it, caused by a fixture cut-out inside the canopy becoming
short-circuited.

40B— 22

§43

INTERIOR WIRING

Fig. 4 shows a bym-out caused by a short circuit between
weather-proof wires used in molding. Wire with weather-
proof iiisiilation only should never be used in molding, and
lis use in molding is prohibited by the Underwriters.

Figs. 5 and 6 show burn-outs caused by short circuits in cut-
outs. The burn-out in Fig* 5 was due to defective design,

Fio,S

the two sides of the circuit being brought so close together
that when a fuse melted the arc held over and destroyed
the cut-out.

In Fig. 6 the cut-out was placed horizontally. When the
fuse melted, the metal ran down and established connection
between the lines, thus resulting in a short circuit.

INTERIOR WIRING

§43

GENERAL RULES

8, Iti wiring for electric lights and power, there are certain
rules that apply equally to all systems and voltages! these
will be our first study. In what foilows, rules and explana*
lory notes taken from the National Electrical Code are
indented in order that they may be distinguished from the
explanations and other matter. In most localities these
rules have the force of laws* Many of the National Code
rules deal with the construction oi the various fittings used
for interior wiring; these concern the manufacturers of the
fittings rather than the workmen who install them. Most of
the rules here given relate to the installation of appliances.
Fittings given in the lists issued by the National Board of
Fire Underwriters comply with their rules*

GENERAL RULES— ALL SYSTEMS AND VOLTAGES

Wires —

a. Must not be of smaller size than No.
B. & S., except in fixtures and fiexible cords.

This is because wires of smaller size are likely to
break or become loose* so that the work does not remain
mechanically secure, and because a small wire is much more
likely to be overloaded by connecting a few additional lamps
to it than is a larger wire.

^, Tie- wires must have an insulation equal to
that of the conductors they confine.

c. Must be so spliced or joined as to be both
mechanically and electrically secure without solder,*
they must then be soldered to insure preservation,
and the joint covered with an insulation equal to
that on the eonditctors.

Stranded wires must be soldered before being
fastened under clamps or binding screws» and

§43 INTERIOR WIRING 11

whether stranded or solid, whfen they have a eondtic-

tivity greater than No. 8 B. & S. gau^e, they must
be soldered into lugs for all terminal connections.

All joints must be soldered * even if raade with some form
of patent spiking device^ This mling applies to joints and
splices in all classes of wiring covered by the?;e rnles»

9, Whenever it is possible to avoid making joints, it is
advisable to do so; but
where joints are necea-
sary, great care must be
taken to do the solder* ^^^^

ing welK and to leave no corrosive acid on the wire. There
are several soldering compounds now on the market that

will tin the wire weU

MMi^a^^QSh^ll^l^^ enough to make a good

^^^^^^^^^^^^^^^ joint and yet leave no

Pio,i acid on it. Soldering

fluK in the form of sticks

is more convenient than liquid soldering fluid.

Soiaerlng Fluid. —

The following formula for soldering fluid is sug-
gested:

Saturated solution of Kinc chloride ...,>.,. 5 parts

Alcohol 4 parts

Glycerine .,**...* . 1 part

10* Joints. — Figs. 7» 8, and 9 illustrate joints in com-
mon use. In removing
the insulation from the
wires where joints or
connections are neces-
sary, and in scraping the
wire to clean it before
making the joint* great
care must be exercised
not to cut into the wire
and lessen its cross-sec-
tion and consequently, ^9*^
its carrying capacity. Especial care must be taken in handling

INTERIOR WIRING

§43

fixture wires, which are small and easily cut or broken,
A comparatively small nick in a copper wire will make it
break easily.

In recovering the wire with insulating tape, a sufficient
amount of tape must be used to afford ample protection*
When rubber-covered wires are spliced or joined, two kinds
of tape must be used, the first of pure rubber softened by a
volatile oil, and the second of cloth saturated with a
moisture-proof adhesive materiaL

11. Kules Bel a tl Tig to Wires (Conttnued),^ —

d. Must be separated from contact with walls,
floors, timbers, or partitions through which they
may pass by non-combustible, non-absorptive insu-
lating tubes, such as glass or porcelain.

BushiDi^ tntist tie long enough to bush the entire length
of the hole ia one coatinuous piece, or else the hole must
firnt be bushed by a continuous waterproof tube. This tube
may be a conductor, such as iron pipe, but lu that case
an fas^latiag btij^hing must he pushed into each end of it
far enough to keep the wire absolutely out of contact with
Ihe pipe.

e. Must be kept free from contact with gas,
water, of other metallic piping, or any other con-
ductors or conducting material that they may cross,
by some continuous and iirnily fixed non-conductor,
creating a separation of at least 1 inch. Deviations
from this rule may sometimes be allowed by special
permission*

When one wire crosses another wire, the best anfl usual
means of separating them is by means of a porcelain tube
on one of them* The tube should be prevented from mov-
ing out of place, either by a cleat at each end or by taping
it securely to the wire.

The same method may be adopted where wires pass dose
to iron pipes, beams^ etc, or, where the wires are above
the pipeSt as is generally the case, ample protection can
frequently be secured by supporting the wires with a porce-
lain cleat placed as nearly above Ihe pipe as possible >

/. Must be so placed in wet places that an air
space will be left between conductors and pipes in
crossing* and the former must be run in such a way
that they cannot come In contact with the pipe
accidentally. Wires should be run over, rather

S48 INTERIOR WIRING 13

than under, pipes on which moisture is tifeely to
gather or which, by leaking, might cause trouble
on a circuit.

g. The installation of electrical conductors in
wooden molding or when supported on insulators
in elevator shafts will not be approved* but conduct-
ors may he installed in such shafts if incased in
approved metal conduits.

Un d ergrr o ii n d Co u ^ u ctors —

a. Must be protected, when brought into a build-
ing, against moisture and mechanical injury, and all
combustible material must be kept removed from
the immediate vicinity,

b. Must not be so arranged as to shunt the cur-
rent through a building around any catch box.

This refers to catch boxes in the street, from which the
wires should run to the buildings, and not from street to build-
ings building to building, and back again into the street,
around one or more catch boxes, thus shunting whatever
protective devices there may be in the catch boxes-

f. Where underground service enters building
through tubes, the tubes shall be tightly closed at
outlets with asphaltum or other non-conductor, to
prevent gases from entering the building through
such" channels.

d. No underground service from a subway to a
building shall supply more than one building except
by written permission from the Inspection Depart-
ment having junsdiction*

12, Carrying Capacities of Wlros. — As every wire
carrying an electric current is somewhat heated, it is neces-
sary to know how much current can safely be carried by a
wire of a given size. Table I supplies this information.

Table of Carrying Capacity of Wires. ^ —

The accompanying table (Table I), showing the
allowable carrying capacity of wires and cables of
98 per cent, conductivity, according to the standard
adopted by the American Institute of Electrical

INTERIOR WIRING

§43

TABIiE t
CARRTING CAPACITY OF INS0LATED ^riBES

Rtibber*Cov-

Weather* Proof

Circular Mils

B. & S, Gauge

ered Wires
Amperes

Wires
Aniijeres

V-H .1 L !_■ LB 1 ^ f. -J-Til. 1 |.£^

(Approxiniiite)

1,634

2,583

4,107

6.530

IO13S0

16,510

26,250

33iioo

41,740

52,630

131

66,370

10?

r56

83,690

127

l8s

105,500

150

220

133*100

ooo

177

262

167,800

OOO0

2iO

312

211,600

|i 200

300

200,000

270

400

300,000

330

500

400,000

390

590

500,600

450

680

600,000

500

760

700,000

550

840

800,000

600

920

900,000

650

1,000

1,000,000

690

ijOSo

1,100,000

730

1,150

r, 200, 000

770

1,220

1,300,000

810

1,290

1,400,000

850

1,360

1,500,000

Ego

1,430

1,600,000

930

1,490

r,7oOsO00

970

1.550

i.8oOjOoo

IfOIO

1,610

1,900,000

m .

1 ,050

1,670

2,000,000

143

INTERIOR WIRING

Engineers, must be followed in placing interior
conductors.

For insulated aluminum wire the safe carrying capacity is
84 per cent, of that given in the table for copper wire with
the same kind of insulation.

The lower limit is specified for rubber-covered wires to
prevent gradual deterioration of the high insulation 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
above table.

The carrying capacity of Nos. 16 and 18 B. & S. gauge

' wire is given, but no wire smaller than No. 14 is to be

used, except as allowed for fixture work and flexible cord.

13. Wire Gaufires. — It sometimes happens that wires of
scant size are sold to the unwary. A workman constantly
using wires of various-
sizes soon learns to
gauge the size of wires
by his eye, but it is bet-
ter to use a wire gauge
frequently to avoid mis-
takes. A wire of given
size should just enter
the slot intended for
that size in the style of
gauge shown in Fig. 10.
Gauges in the form of ^
vernier caliper, meas-
uring the diameter of
the wire in thousandths
of an inch, or mils,* are usually more accurate. Table II,
giving the diameter in mils and cross-sectional area in

Fio. 10

^Diameters of wires are usually expressed in mils or thousandths
of an inch and cross-sectional areas in circular mils. 1 mil = ttArt
inch = .(K)l inch. 1 circular mil is equal to the area of a circle of
which the diameter is 1 mil and cross-sectional areas of wires are des-
ignated by the number of circular mils contained in their area. The
circular mil is a more convenient unit than the square inch in which
to express the areas of round wires since the number of circular mils
bears a simple relation to the diameter in mils. If the diameter d is
expressed in mils, then the number of circular mils cross-section is cT,
Thus, a No. ()00() wire. Table II, has a diameter of 460 mils, or .460 inch,
and its area in circular mils is 460* = 211,600. Isquareinch = 1,273,240
circular mils.

INTERIOR WIRING

§43

circular mils for the B, ^ S, sixes coTnmonly used in interior*
wiring work, is here inserted for convenient reference* The
number of circular mils cross-seetion as gfiven in this table
is more accurate than in Table I^ but the areas as given in
Table I are close enoug^h for all practical calculations,

TABL-E 11

lilMXNSIONd OF BARE COFPEB WIRE B. A S. GAUGE

Gattge

Diameter

Area

Gaujje

Diameter

Area

lumber

MUs

MUa

Number

Mib !

Circular

MUa

00 oo

460.0

2tif6oo.o

12S.5

16,509.0

OOO

4og.6

167,805.0

114-4

13*094,0

364.8

133.079.4

101*9

io,38ko

324*9

I05.S34-S

90,7

8,234.0

289,3

83.694. 2

80,8

6p529.9

257*6 1

66,373.0

72,0

5,178.4

229.4

52,634.0

64.1

4.106.8

204.3

41,742^0

57^1

3*256.7

181.9 '

33,T02.0

50. S

2,582*9

162,0

26,250,5

45.3

2,048*2

M4-3

20.8i6<o

40.3

1.624.3

WIRING FOR liOW-POTENTIAIi SYSTEMS
14. Definition of Liow-Potentlal System. —
LOW-POTENTIAL SYSTEMS

550 Volts or Ijess

Any circuit attached to any machine or combination
of machijies that develops a difference of potential
between any tzvo wires of over 10 volts and less than
550 volts shall be co7isidered as a low-potential circuit
and as coming tinder this class, unless an approved
transformi77g device is used that cuts the difference of
Potential down to 10 volts or less. The primary cir-
cuit not to exceed a potential of 3,500 volts.

§43

INTERIOR WIRING

Before pressure Is raised above 300 volts
on any prevl€ju»ly existing Bystem of wiring:,
the whole iiiuet bo etrlctly brong:ht tip to all
of the reqiif rementB of the rules at date.

Until recently, low-potential systems were limited to 300
volts or under» but the limit has been raised to 550. However,
560 volts cannot be applied to old systems unless the above
rule is complied with. Low-potential systems are usually
constant-potential systems also; that is, the potential or
pressure between the terminals of the machine or at some
definite points on the line is almost uniform. Only constant-
potential systems will be considered under this heading*

A few general rules apply to the various kinds of work
under these systems. They are as follows;

15. General Roles. —

Wlree —

a. Must be so arsttJisetl that tinder no eir-
cuniBtaneeB shall tliei^ be a difference of
potential of over 3O0 volts between any bare
metal In any dlittrlbutlnijr s^wltcb, cut*out
eabtnetf or etiulviilent center of distribution.

d. Must not be laid In plaster, cement^ or simi*
lar finish and mast never be fastened with staples,

c> Must not be fished for any great distance^
and only in places where the inspector can satisfy
himself that the rules have been complied with.

d. Twin wires must never be used, except in
conduits or where flexible conductors are necessary,

e. Must be protected on side walls from mechan-
ical injury. When crossingf floor timbers in cellars
or in rooms where they might be exposed to injury p .
wires must be attached by their insulating supports
to the under side of a wooden strip not less than
i inch in thickness and not less than 3 inches in
width. Instead of the running boards, guard strips
on each side of and close to the wires will be
accepted* These strips to be not less than I: inch
in thickness, and at least as high as the insulators,

Suitahle protection oa side walls may be secured by a sub-
stantial boxiagj retaioiag an air space of 1 inch around the

INTERIOR WIRING

§43

coDductors, closed at the top (the wires passinjf throttgh
bushed holes), and extendinjaj not less than 5 feet from the
floor; or by an iron-armored or metal sheathed insulating
conduit stiffideatly strong to withstand the strain to which
it will be subjected, and with the ends protected by the
lining or by special insulated bushings, so as to prevent the
possibility of cutting the wire insulation; or by plain metal
pipe, lined with approved flexible tubing, which must
extend from the insnlator next below the pipe to the one
next above it.

If metal conduits or iron pipes are used to protect wires
carrying alternating currents, the two or more wires of each
circuit musf be placed in the same conduit as troublesome
indoction effects and heating of the pipe migbt otherwise
result. And the insulation of each wire must be reenforced
by approved flexible tubing extending from the insulator
next below the pipe to the one next above it. This should
also be done in direct -current wiring if there is any possi*
bility of alternating current ever being used oa the system*

For high*voltage work, or in damp places, the wooden
boxing may be preferable, because of the precautions that
would be necessary to secure proper insulation if the pipe
were used. With these exceptions, however, iron pipe is
considered preferable to the wooden boxings and its use
is strongly urged. It is especially suitable for the protection
o£ wires near belts, pulleys, etc.

/- When run in unfinished attics, or in proximity
to water tanks or pipes, will be considered as exposed
to moisture,

16# The reason for the first part of {6) is that plaster

and cement are likely to corrode the insulation on the wire
and cause it finally to break, If the plaster is damp, leakage
takes place J the wire is gradually dissolved by electrolysis,
and finally it becomes so thin it cannot carry its current
without excessive heating and, perhaps, not without meltingf.
While there are many places where wires embedded in plaster
have been used for years without serious trouble, because ot
the dryness of the buildings where they are in use, trouble
may develop at any time and the practice is always a danger-
ous one.

The second part of (^) is Inserted as a direct prohibition
against running electric-light wires as bell wires are usually
put up* Staples not only do not insulate the wire, but are likely
to cut into the insulating covering already on it. Rule (f)
is to prevent the location of wires where it is impossible to
know that they are properly supported and insulated.

§43

INTERIOR WIRING

17. The suggestions regarding the protection of wires
on side walls or other places where they are liable to be
damaged, should be carefully noted. In interior wiring,
one of the chief sources of risk is the currents that may
flow from the wiring to ground if the insulation becomes
defective. The danger from leakage currents either from
wire to wire or from wires to ground is fully as great
if not greater than that from overloaded wires or from
actual short circuits between wires.

SYSTEMS OF DISTRIBUTION FOR INTERIOR WIRING

18. The voltages in common use on low-potential sys-
tems are: For direct currents. 110 and 220; for alternating
currents, 104 to 110. These are used on both two-wire
and three-wire systems. Many lighting companies allow
for various amounts of drop at different points on their
lines and install lamps of different voltages, as, for
instance, 108-volt lamps near the generator and 100-volt
lamps at the extreme end of the line, with lamps of inter-
mediate voltages at intermediate points. But the lamps
used in any one building are usually all of the same voltage.

19. The Two- Wire System. — This is the simplest plan
of wiring and the one in most general use. Fig. 11 shows
in diagram its essential features. The diagram of connec-
tions is the same for all voltages and for alternating or

. Wires.

Pig. 11

Tynr

Lamp^

direct currents; but the fittings, such as lamps, sockets,
cut-outs, and switches, and the sizes of wire used will be
very different. The fittings and the proper sizes of wire to
be used will be discussed later.

INTERIOR WIRING

S48

20. The Edison Three-Wire System. — This system
comes next m importance and extent of use; it also is used

with various voltages and with direct or alternating currents.
Usually the pressures are 110 volts between either outer
wire and the middle or neutral wire and 220 volts between
the outer wires. Fi^^. 12 shows the diagram of connections.
This system is also sometimes installed with 220 volts
between the neutral and outer wires and 440 volts between
the outside wires-
Referring to the dtagjam, Fig, 12, observe the following:
When the currents in the two outside wires are equal in
amount, no current passes over the neutral wirej but when

Fig, 12

the currents are not equal, that is, when more lamps or
motors are on one side of the neutral wire than on the
other, the *' difference current*' flows on the middle wire,

21. The advantage of this system is that with lamps of
any given voltage it is possible to save in the amount of

wire required* In the outside lines of the lighting company
is where the greatest saving is effected, because the neptral
wire is there much smaller than the outer ones, and three
wires are used instead of four^ which would have to be run
if the generatoris were operated ijidependently* In interior
wiring, the saving is not so great, because the neutral wire
must be large enough to carry the current in case all the
load is turned off one side of the circuit, as would be the case
if the fuse on one side should blow and that on the other
side did not, and because in small installations* where unbal-
ancing is likely to occur, three- wire mains must be large to
reduce this trouble to a minimum.

§43

INTERIOR WIRING

22. The three-wire system also has some disadyantafi:es.
Its most objectionable feature is that if any one line is
opened, as by the blowing of a fuse on one line only, the
system is unbalanced and a voltage different from that
intended for the apparatus is thrown on the lines, unless the
line loss is very small indeed. If it is the middle wire that
opens, the whole 220 volts
may be thrown on 110- volt
apparatus, if the system
is much unbalanced. For
this reason, some Edison
companies refuse to place
cut-outs on the neutral
wire; but the main switch
should in all cases open
all three lines. Another
weakness of the three-wire
system is the fact that
there is m6re danger in
220 volts than in 110, and
a shock received from a
220-volt circuit may be
very severe. The wiring
is somewhat more com-
plicated, but owing to the
saving in line materials,
the Edison three-wire system has been introduced to a very
great extent and still meets with much favor in new installa-
tions, besides extending the network of its wires from
existing stations. Lately it has had a new competitor in the
220-volt two-wire system, which has grown in popularity
with the perfecting of the 220-volt incandescent lamp.

Pio.18

23. It is the usual practice to run the three wires no
farther within the building than to the centers of distribu-
tion, and from these centers to use the two-wire system,
dividing the circuits as equally as possible on the two sides
of the three-wire circuit, as shown in Fig. 13. By this

INTERIOR WIRING

1 43

means» the branch lines are fused on both sides and amply
protected against excessive currents » though not against
high voltage. If the neutral wire within the building is
protected by a fuse as large as that in either of the main
wires, the danger of that line opening is very small.

34, A method of running wires on the two-wire plan
that is sometimes confused with the three-wire system is
illustrated in Fig. 14. In this method the middle wire carries
the whole current, while each outside wire carries the current
necessary for the lights on its side. This method effects no
saving of copper; in fact, it often requires more than the
two- wire system would, because the three wires must gen-
erally be of the same size, as explained under the subject of
cut-out protection. The object of the arrangement is solely
to make it possible to turn off a number of the lights with-
out running four wires. The Underwriters will not permit
it with more than 660 watts on a side,

25, House wiring should consist of two distinct portions:
the distribution circuits, w^hich ran from the lamps to a
center of distribution and which should always be two-
wire circuits, and the mains, which run from the outside
lines to the distribution center and which must conform to
the requirements of the particular system to be used. I£

TITTTTT

rrmr

mains must be installed before it is known what system Is

to supply current, it will be sufficient to rtm four wires of
the size required were the lamps to be divided equally
between two separate two-wire systems* This will make it
possible to connect to any system operating at the voltage
for which the wiring calculations are made.

INTERIOR WIRING 28

SWITCHES AND CUT-OUTS

26. There are certain devices for the protection of con-
stant-potential systems that are necessary no matter what
voltag^e is used. Should anything: happen to damage the
wiring, it is necessary that the wires be disconnected from
the source of supply of current with the least possible delay.
The devices for this purpose that are operated by hand are
called switches. Those that work automatically are called
automatic cut-outs. These latter are of two kinds —
fuses and circuit-breakers.

Both a switch and an automatic cut-out must be placed at
or near the place where wires enter a building. They must
also be placed at various other points on the wiring.

27. The object of the cut-out is to protect the wires and
the devices connected to them from damage due to the
presence of too much current from any cause whatever.
The ordinary cut-out consists of a porcelain base that carries
suitable terminals for holding a piece of fusible wire, or fuse,
which melts and opens the circuit whenever the current
becomes excessive. Not only must the cut-out protect the
lines when there is trouble, but it must be so placed that it
can be reached to replace the fuse or reset the circuit-
breaker when the trouble is remedied. It must also be
arranged so that the blowing of a fuse or the opening of a
circuit-breaker cannot do any damage.

28. Switches are designed to disconnect the lines from
the source of electricity, not only when there is trouble, but
when convenience requires, as in turning off lights, starting
and stopping motors.

Circuit-breakers are not as commonly used in interior-
wiring: work as are fusible cut-outs. They are automatic
switches controlled by an electromagnet and are made in a
number of different styles. Whenever the current exceeds

4GB— 23

INTERIOR WIRING

§43

that for which the circuit-breaker is adjusted, the electro-
magtiet attracts its armature and releases the switch^ thus
opening the circuit,

The following rules regarding these devices must be
observed in all cases:

S^vltclies, Cut-Outs, Circuit-Breakers, Etd—

a. Must, whenever called for, unless otherwise
provided, be so arranged that the cut-outs will pro-
tect» and the opening of the switch or circuit-
breaker will disconnect, all the wires; that is, in
a two-wire system the two wires, and in a three-wire
system the three wires, must be protected by the
cut-out and disconnected by' the operaUon of the
switch or circuit-breaken

h. Must not be placed in the immediate vicinity
of easily ignitible stuff or where exposed to inflam-
mable gases or dust or to flyings of combustible
material-

In starch and candy factories, gram elevators, flouring
tnills^ and buildings used for woodworking^ or other purposes
that would cause the fittings to be exposed to dust and flyings
of inflammable matermU the cnt-outs and switches should
be placed in approved cabinets outside of the dust rooms.
If, nowevert it is necessary to locate them in the dust rooms ,
the cabinets must be dust-proof and must be provided with
aeU-closing- doors>

€. Must, when exposed to dampness, either be
enclosed in a waterproof box or mounted on porce-
lain knobs.

d. Time switches must be enclosed in an iron
box, or cabinet lined with fire-resisting materiaL

If an iron box is used, the minimum thickness of the iron
must be J2»inch (No. 8 B, * S. gauge).

If cabinet is used, it must be lined with marble or slate at
least i inch thick ^ or %vith iron not less than .128 inch thick.
Box or cabinet must be so constructed that when switch
operates, blade shall clear the door by at least 1 inch.

Automatic Cut-Outs {Fuses and Circuit-Breakers)

Excepting- on main switchboards, or where otherwise
subject to expert supervision! circuit- breakers will not bo
accepted unless fuses are also provided.

a. Must be placed on all service wires, either
overhead or undergjound, as near as possible to the

§48 INTERIOR WIRING 25

point where they enter the building and inside the
walls, and arranged to cut oflE the entire current
from the building.

Where the required switch is inside the building, the cut-
out required by this section must be placed so as to pro-
tect it.

In risks having private plants, the yard wires running
from building to building are not generally considered as
service wires, so that cut-outs would not be required where
the wires enter buildings, provided that the next fuse back
is small enough to properly protect the wires inside the
building in question.

b. Must be placed at every point where a change
IS made in the size of wire (unless the cut-out in
the larger wire will protect the smaller).

29. The object of a fusible cut-out is to protect the
wire; therefore, it must be placed so that all the current
that flows through the wire to be protected will also pass
through the cut-out. The fuse is proportioned so that its
carrying capacity will not exceed the carrying capacity of
the wire, as given in Table I; hence, if an excessive cur-
rent flows, the fuse will melt and open the circuit before
the wire becomes overheated. If a branch wire, say No. 14,
were connected to a main, say No. 10, and if no cut-out
were placed at the junction, it is plain that, since the
fuse in the No. 10 wire has a carrying capacity in excess
of that allowed for No. 14, a short circuit or overload
on the branch line might cause overheating of the No. 14
wire. Very often, however, the fuse in the larger wire is of
such size that it protects the smaller wire, in which case it is
not necessary to place a fuse at the junction point. For
example, take the case where No. 14 wire at a fixture outlet
is attached to the fixture wiring. The wire in the fixture is
usually No. 16 or No. 18 in order that it may pass between the
gas pipe and the outer shell, but the fuse in the cut-out or on
the panel board at the distributing center is proportioned in
accordance with the carrying capacity of the fixture wire
instead of the No. 14 wire running from the panel board
or cut-out to the fixture; hence, in this case the fuse in
the larger wire protects the smaller wire and a cut-out in the

INTERIOR WIRING

§43

fixture canopy where the fixture wire attaches to the No, 14
lines is unnecessary; in fact, fixture cut-outs are prohibited
by rale (c) given below.

c. Must be in plain sig^ht or enclosed in an
approved cabinet and readily accessible. They
must not be placed in the canopies or shells of
fixtures*

Tti« ordinary porcelain link- fuse cut-out vlll not be
approved. Link fuses may be tised only when mounted
on approved slate or marble bases and must be enclosed
in dust- tight, fireproof cabinets^ except on switchboards
located well away from combustible material, as in the
ordinary engine aud dynamo room where these conditions
will be maintained.

30, Rule (f) is important. It prohibits the use of the
small cut-outs that were formerly placed in the canopies of
fixtures in order to protect the fixture wiring. These cut-
outs gave a great deal of trouble and introduced a fire risk
that more than offset any advantage they might have had.
It has been found safer and more satisfactory, therefore, to
omit them and let the fuse in the cut-out on the branch main
leading to the fixture afford the protection, as explained
under rule (^),

It should also be noted that this rule prohibits the use of
the ordinary porcelain link- fuse cut-outs that were, until
recently, very largely used for the protection of circuits*
The link fuse consists of a piece of fuse wire or strip pro-
vided with copper terminals, the fuse wire or strip being
exposed to the air. These fuses were held between suitable
terminals mounted on a porcelain base. The use of link
fuses is still permitted when they are mounted on slate or
marble distributing boards and placed in fireproof cabinets,
but the link-fuse porcelain cut-out is no longer permitted
and it is now necessary to use enclosed fuses instead.
Enclosed fuses and link fuses will be described in detail
when fittings are taken up.

d. Must be so placed that no set of incandes-
cent lamps requiring more than 660 watts, whether
grouped on one fixture or on several fixtures , or

§43

INTERIOR WIRING

pendants, will be dependent on one cut-out. Spe-
cial permission may be given in writing by the
Inspection Department havin^f jurisdiction for
departure from this rule in the case of large chan-
deliers, stage borders, and illuminated signs*

The above rule shall also apply to motors when more
than one is dependent on a single cut-out.

The idea Is to have a small fus« to protect the lamp
socket and the small wire used for fixtures^ pendants, etc.
It also lesseDS the chances of extinguishing a large number
of lights tf a short circuit occurs.

On open work in large mills, approved link' fused rosettes
may be used at a voltage of not o%»er 125, and approved
enclosed 'fused rosettes at a voltage of not over 250, the (use
in the rosettes not to exceed 3 amperes, and a fuse of over
25 amperes must not be used in the branch circuit.

AH branches^ or taps, from a three- wire Edison system
must be run as two-wire circuits,

31, Rule {(i) is very important because it liniits the
number of lamps that may be operated on any one circuit-
On 110-volt circuits, 660 watts is equivalent to not more
than twelve 16-candlepower lamps; on 220'Volt circuits not
more than ten 16-candlepower lamps. It is best not to
exceed ten lamps to a circuit except in the special cases
mentioned in the rule. The fused rosettes referred to under
rule id) are small porcelain cut-outs from which the lamps
are suspended* It should be particularly noted that these
rosettes are not allowed on pressures higher than 125 volts
unless they are provided with enclosed fuses.

Rule (d) also applies to motors when more than one
motor is dependent on a single cut-out. This refers partic-
ularly to fan motors, as most motors for power purposes will
be over 660 watts capacity and each motor will therefore
require a branch circuit and cut-out of its own.

f* The rated capacity of fuses must not exceed
the allowable carrying capacity of the wire. Circuit-
breakers must not be set more than 30 per cent.
above the allowable carrying capacity of the wire,
unless a fusible cut-out is also installed in the circuit*

This is very important* A fuse block not properly fused
is of no use whatever* Irresponsible parties sometimes
place fuses much too large to protect the wire and which

INTERIOR WIRING

i43

would destroy the cut-out if they should ever blow, besides
doing other damage. SometimeSj also, fuse blocks are found
having copper wire where the fuses should be; of course,
they are of no use with such connections. The common
custom of fusing with wire much larger than that allowable
is one of the reasons for the prohibition of link-fuse porce-
lain-base cut-outs* The bases used with enclosed fuses are
not easily fused with any wire that may be convenient
because the terminals are not suited to a wire fuse. Note
that rule (e) fixes the maximum size of fuse to be used on
any circuit by the carrying capacity of the wire protected
and not by the current required for operating the devices
used on the circuit. For example, the carrying capacity of
a No. 14 rubber-covered wire is 12 amperes and the rated
capacity of the fuse used on a No. 14 circuit could be as
high as 12 amperes without breaking the rule, though there
might only be ten 110- volt lamps on the circuit requiring a
current of about 5 amperes for their operation.

Cut-outs should always be installed in a location where
they can be easily reached for the replacement of fuses.
This is a point too often neglected in the laying out of
interior wiring, particularly for small houses where regular
distributing panel boards are not used.

When arc lamps are operated on constant-potential circuits,
each lamp must be pro\nded with a cut-out and the branch
conductors leading from the mains to the lamps should have
a carrying capacity about 50 per cent, in excess of the
normal current in order to allow for the increased current
required when the lamp is started or when the carbons
become stuck. If each lamp is not fed by a separate branch
circuit running from a panel board or fuse cabinet, it is
necessary to locate an end osed-fuse cut*out at the point
where the wires leave the mains for a lamp.

32. Circuit-breakers may be set so as to work with
greater accuracy than fuses; they respond more quickly to
sudden overloads, for fuses require a little time to get
hot enough to melt. For this reason^ circuit-breakers may

§48 INTERIOR WIRING 29

be set for higher currents than fuses. If they are not so set,
they will give trouble by opening the circuit on momentary
overloads that would not be sufficient to melt the fuses.
Circuit-breakers are usually installed to protect machines,
such as motors and dynamos; they are not used for the pro-
tection of the branch distribution circuits in buildings because
the rules require that they shall only be used in such places
where they will at all times be under expert supervision.

33. Rules Relating: to STvltohes. —
Bwltclies —

a. Must be placed on all service wires, either
overhead or underground, in a readily accessible
place, as near as possible to the point where the
wires enter the building, and arranged to cut off
the entire current.

Service cut-out and switch must be arranged to cut off
current from all devices, including meters.

In risks having private plants, the yard wires running
from building to building are not generally considered as
service wires, so that switches would not be required in each
building if there are other switches conveniently located on
the mains or if the generators are near at hand.

b. Must always be placed in dry, accessible
places and be grouped as far as possible. Knife
switches must be so placed that gravity will tend
to open rather than close them.

When possible, switches should be so wired that blades
will be *'dead" when switch is open.

If knife switches are used in rooms where combustible
flyings would be likely to accumulate around them, they
should be enclosed in dust-tight cabinets. Even in rooms
where there is no combustible material it is better to put all
knife switches in cabinets, in order to lessen the danger of
accidental short circuits being made across their exposed
metal parts by careless workmen.

Up to 2»50 volts and 30 amperes, approved indicating snap
switches are advised in preference to knife switches on light-
ing circuits about the workrooms.

c. Must not be single-pole when the circuits that
they control supply devices that require over 660
watts of energy or when the difference of potential
is over 300 volts.

INTERIOR WIRING

§43

This rule U) is important, because it restricts so severely
the number of lamps that tnay be controlled by a single-
pole switch,

d. Where flush switches are used, whether with
conduit systems or not, the switches must be
enclosed in boxes constructed of or lined with fire-
resisting material. No push buttons for bells» gas-
lighting circuits, or the like shall be placed in the
same wall plate with switches controlling electric-
light or power wiring.

This requires an approved box in addition to the porcelain
enclosure of the switch.

e. Where possible, at all switch or fixture out-
letSt a 1-inch block must be fastened between studs
or floor timbers, iiush with the back of lathing, to
hold tubes and to support switches or flKtures.
When this cannot be done, wooden base blocks not
less than f inch in thickness, securely screwed to
the lathing, must be provided for switches and also
for fixtures that are not attached to gas pipes or
conduit tubing.

34* Construetfon of Cut- Outs, Circuit-Breakers,
Etc. — The rules that have just been given relate to the loca-
tion and installation of cut-outs » circuit-breakers, switches,
etc* In addition to these rules there are a large number of
Underwriters' rules that relate to the construction of these
devices, but for the most part these concern the manufac-
turer rather than the wire man. A few only of the more
important of these rules will be given here as a genera]
guide to the wireman,

Cu1>Outs and Circuit-Breakers —

a. Must be supported on bases of non-combus-
tible, non-absorptive, insulating materiaL

L Cut-outs must be of plug or cartridge type,

when not arranged in approved cabinets, so as to
obviate any danger of the melted fuse metal com-
ing in contact with any substance that might be
ignited thereby.

§43 INTERIOR WIRING 31

r. Cut-outs must operate successfully on short
circuits, under the most severe conditions with
which they are liable to meet in practice, at 25 per
cent, above their rated voltage, and with fuses
rated at 50 per cent, above the current for which
the cut-out is designed.

d. Circuit-breakers must operate successfully on
short circuits, under the most severe conditions
with which they are liable to meet in practice, when
set at 50 per cent, above the current, and with a
voltage 25 per cent, above that for which they are
designed.

e. Must be plainly marked, where it will always
be visible, with the name of the maker and the cur-
rent and voltage for which the device is designed.

Snap Switches. —

a. Current-carrying parts must be mounted on
non-combustible, non-absorptive, insulating bases,
such as slate or porcelain, and the holes for support-
ing screws should be countersunk not less than
i inch; in no case must there be less than -^ inch
space between supporting screws and current-
carrying parts.

Subbases, of non-combustible, non-absorptive
insulating material, that will separate the wires
at least i inch from the surface wired over should
be furnished for all snap switches used in exposed
knob or cleat work.

b. Covers made of conducting material, except
face plates for flush switches, must be lined on
their sides and top with insulating, tough, and
tenacious material at least iV inch in thickness,
firmly secured, so that it will not fall out with
ordinary handling. Side lining should extend
slightly beyond the lower edge of the cover.

c. The handle, button, or any exposed plart must
not be in electrical connection with the circuit.

Switches that indicate, upon inspection, whether
the current be '*on'* or **off** are recommended.

Some of the common styles of switches and cut-outs will
be described later when the methods of wiring are taken up.

INTERIOR WIRING

§43

OPEN WORK IN DRY PLACES

35, Open work is generally used in factories, ware-
houses, mills, and other places where there '-s no objection
to having the wires in plain sights or in old buildings, where
the expense of concealed work overbalances the objection-
able appearance in the mind of the owner. It is the
cheapest kind of construction and very often the safest*
This method of wiring will be explained by means of simple
examples. ^

SIMPLE EXAMPLE OF PACTORT WIRING

36* Consider a factory, such as a long machine shop,
where there is but one floor to be wired for 110-volt
enclgsed-arc lamps and incandescent lamps on the so-called
tree system; that is. with but one set of mains or feeder
wires leaving the dynamo and with other lines branching
from these mains to the points where lamps are required*

^£7'

n H M *i W N H H W K H H 11 1* II f N

^ ^

J|£

M~m -^ M »4 *4 H >f H W M M H — -*- ** t^C

3htd

cH-l

Pig. 15

Let Fig, 15 represent the outlines of such a factory, in
which incandescent lamps are to be hung on lamp cord at
the points marked X and enclosed-arc lamps are to be placed
where the marks O are shown. After finding the cheapest
way in which this factory can be wired in order to satisfy

843

INTERIOR WIRING

the Underwriters, we will see what modifications can be
made to better the light, improve the system, and make it
more convenient and economical in operation.

37. Assume that each 16-candlepower incandescent lamp
requires 55 watts; some good lamps take less power, but it
is not safe to count on less. Also assume that each enclosed
arc is to take 5 amperes while burning and 12 amperes to
start on. There are 40 incandescent lamps and 6 arc lamps
to be wired.

55 (watts) H- 110 (volts) = .5 (ampere per lamp)
40 X .5 = 20 (amperes for incandescent lamps)
6x5 =30 (amperes for arc lamps)

Total amperes = 50

which must be carried on the mains for a short distance
at least.

Referring to Table I, we see that the smallest wire that
will carry 50 amperes with safety is No, 6 weather-proof.

38. Rules Relatingr to Wires for Open Work. — For

open work in dry places we have in addition to the general
rules relating to wires, the following special rules regarding
wires used in open work:

Wires —

a. Must have an approved rubber or **slow-bum-
ing*' weather-proof insulation.

b. Must be rigidly supported on non-combusti-
ble, non-absorptive insulators that will separate the
wires from each other and from the surface wired
over in accordance with the following table:

Voltage

Distance From

Surface

Inch

Distance

Between Wires

Inches

0 to 300
300 to 500

84 INTERIOR WIRING §43

Rigid supporting^ requires under ordinary coadltiofls^
wherfi wiring along lliit surfaces, supports at least every
4i feet. If the wires are liable to be disturbed, the distance
between supports shouH be shortened. In btiildings of mill
construction, mains of No. 8 B. & S. wire or over, where not
liable to be disturbed, may be separated about 4 inches and
run from timber to timber, not breaking around ^ and may
be supported at each timber only*

This mle will not be interpreted to forbid the placing of
the neutral of a three- wire system in the center of a three-
wire cleat, provided ihe outside wires are separated 24 inches.

39» Rubber-covered wire used for in tenor- wiring^ work
consists of a tinned copper wire with a covering^ of rubber
with an outer braiding of cotton soaked in preservative com-
pound. For voltages up to 600 and for sizes of wire from
No* 15 to No, 0000 the thickness of insulation varies from
A inch to /r inch, being thinner on the smaller sizes of wire.

40. Slow-burning weather-proor wire is less expen-
sive than rubber-covered and is good enough for open work
in dry places where the wire is in contact with insulating^
supports only, as in the case with the example of factory
wiring now under consideration. This wire is provided
with two coatings, one of which is fireproof in character and
the other w^eather-proof. Most of this wire was formerly
made with weather-proof braid on the outside, but the
Underwriters now require the fireproof braid to be placed on
the outside, and the compound with which it is treated
slicked down so that the wire wiU have a hardi dense finish.
The Underwriters lay down specifications to which the
various kinds of wire must conform » Wire obtained from
almost any reputable manufacturer meets the requirements,
so it will not be necessary to give the specifications here.

Owing to the fact that ordinary weather-proof wire and
fireproof and weather-proof are much cheaper than rubber-
covered, there is a tendency on the part of the unsctnipulous
contractors to use these wires in places where rubber-covered
wire only should be used. They are not allowable for
concealed work or for open work where dampness is present.
Fireproof and weather-proof wire is not so liable to burn as
the old weather-proof, which had but one or more braidings

INTERIOR WIRING 85

soaked in weather-proof compound, and it is able to repel
the ordinary amount of moisture found indoors. It is
not suitable for outside line work. In general, fireproof and
weather-proof wire can be used only in those cases where
the insulating supports on which the wire is mounted are
depended on for insulation, the covering being regarded
simply as a precaution against accidental contact with other
wires or any other objects. With rubber-insulated wire,
the covering may in some cases be depended on altogether
for the requisite insulation, as, for example, where the wires
constituting the two sides of a circuit are drawn through a
system of pipes or conduits.

41. Deternil nation of Sizes of Wire According to
Current Capacity. — Observing the location of the lamps
as shown in the diagram. Fig. 15, it is seen that on each
side of the building and down the center they are arranged
in straight lines. Therefore, it will be easier to run the
wires along these lines and to fasten the rosettes (small
porcelain fittings from which the lamps are suspended)
directly to them, rather than put in short branch lines
and nm the principal wires in any other way. The wires
will therefore be run as shown in the sketch, where each
line is supposed to represent a pair of wires put up on
knobs or cleats.

Eighteen incandescent lamps are on one line, twenty-one
on another, five arc lamps on a third, and one arc lamp and
one incandescent lamp on a fourth. Referring again to
Table I, we find that these lines will require wires of the fol-
lowing sizes: Twenty-one incandescent lamps( 10.5 amperes),
No. 14 wire; eighteen incandescent lamps (9 amperes),
No. 14 wire; five arc lamps (25 amperes), No. 10 wire; one arc
lamp and one incandescent lamp (5.5 amperes), No. 14 wire.

42. lioeatlon of Cut-Outs. — Since not more than
660 watts can be dependent on one cut-out, if. we lay out
the wiring as stated thus far it will be necessary to have
fuses in all the rosettes and also a separate cut-out c at each
arc lamp. There must also be a cut-out at the point where

INTERIOR WIRING

§43

each branch line joins the mains. The small wires running
from the cut-outs to the arc lamps may be No. 14, which is
larg'e enough to carry the star tin g^ current of
12 amperes continually, if necessary. The main
switch and cut-out should be located near the
dynamo in the engine room. The wiring^ as now
laid out, if put up properly, will comply with all
the Underwriters* rules> but it will not neces-
sarily give satisfaction; it will merely be safe.
But before entering on the matter of how to
improve the plan of the wiring, we will consider
some of the fittings and methods of work that
should be used on an installation of this kind.

FITTIHeS U8KI> FOR EXPOSED WIRING

43, Open work must always be put up as
though there were no insulation whatever on
the wires themselves^ ^ The
wires must be supported on
insulators so as not to come

Fio.U

PiQ.17

Pio. IS

into contact with any woodwork, pipes, or any
other thing except insulating supports-

143

INTERIOR WIRING

44. Fftttngs for Supporting Wire. — ^Some varieties

of porcelain fittiugs suitable for this kind of work are shown
in Figs. 16 to 25. inclusive. Fittings quite different in desigrn
may be used if they comply with the rules*

Fig* 16 shows an ordinary porcelain knob, in section;
these are made in various sizes, and the size used will
depend somewhat on the size of wire to be accommodated.

Fig, 17 shows the common, 4-inch, porcelain ttilie used
where wires are run through joists. Fig. 18 is the style of
tube used where wires are brought
through window frames from the
outside* The end is curved down-
wards to prevent water running in,
and the drip loop a is formed to
allow the water to drip off- A
similar tube, only longer, is used
for bringing wires in through brick
or stone walls. Fig. 19 is a long,
straight, porcelain tube used for
passing through walls or 0oors.
Note that the head a is some distance from the end, so that
when the tube is used for carrying wires through floors the
exposed part of the wire will be above the floor*

Fig. 20 is a single-wire cleat* used mostly for supporting
fairly large wires* Fig. 21 shows a two-wire cleat designed to

Pio. so

Fig. 21

Fio. 22

support the wires 2\ inches apart, in order to conform with
the Underwriters* requirements. Many other cleats are made,
but they are much the same in general construction* It is
always best to put up cleats and knobs with screws, as a

INTERIOR WIRING

§43

better job is done than when nails are used; nails are, how-
ever, sometimes used, a leather washer being placed between
the nail head and the porcelain, to prevent the latter from
being cracked* Fig^- 22 is a kuob cleat used for supporting

Pig. aa

single wires where something neater than the ordinary knob
is desired. It does away with the necessity of a tie-wire
and is provided with four different sized grooves so that it

will accommodate wires
of various thicknesses.
Fig. 23 shows a double-
headed tube used when
wires cross each other.
Porcelain tubes should
always be used where
crossings of this kiod
occur. The tube shown
in Fig. 17 is frequently
used for this purpose;
but If this is done* the
end without a head
should be taped to the
wire to prevent the tube
sliding along.

Fig, 24 shows a fused
rosette or ceiling cut-
out made in two parts*
a and b. Part a is screwed to the ceiling and the lamp is
hung from the cap b. The lines are attached to the ter-
minals fj c* and the lamp cord to d, d^i /, /' are the small
fuses. When the cover b is attached to a by a twisting
movementi terminals g, ^' lock with //, /i' and make the

Fio. 24

%4Z

INTERIOR WIRING

connection from the mains to the lamp. The cord should be
knotted at i so that the pull will not come on the connec-
dons ci, ti\ Rosettes with link fuses* as shown in Fig: 24,
must not be used on pressures ovrer 125 volts or for more
than 3 amperes. They must not be located where inflam-
mable flyingfs or dust will accumulate on them and the next
fuses back of them must not be ot over 25 amperes capacity,
as the rosettes cannot safely break large currents. Fused
rosettes are not advised where drop cords can be properly
protected by line cut-outs* With the layout shown in Fig, 15,
it will be necessary to use fused rosettes for the incandescent
lamps- Cut-outs of the plug or cartridge type would be
necessary for the arc lamps because the current for each
lamp exceeds the maximum of 3 amperes allowed for
the rosettes.

45, For such work as is now being considered, the prin-
cipal porcelain articles required are the cleat, the rosette, and
the cut-out, all of which
are made in several forms.
The selection of such fit-
tings must be made with
reference to the work in
hand.

If the wires are placed
high out of reach and
the distance between the
points of support is con-
siderable, they should be
separated a foot or more
and fastened to knobs. Where passing through walls or par-
titions, the wires should be protected by porcelain bushings.

If a lamp is needed not more than 3 feet from the direct
line of the wires, it can be hung where required by means of
aeelUu^ button. Fig, 25? but lamp cord must not be used to
run lamps in this way more than 2 or 3 feet from the rosette.

46* Flexible t^amp Cord.— In selecting lamp cord for
this kind of work and in securing good sockets, too much

Pl«. 25

40B— 24

INTERIOR WIRING

care cannot be taken, for trouble occurs more frequently in
lamp cord and sockets than in any other part of the wiring,
i£ these articles are not of the highest grade. There is much
temptation to use lamp cord for purposes other than those
for which it is designed. The rales regarding it are given
here, and special attention is directed to them:

Flexible CorU^

a. Must have an approved insulation and cov-
en ng»

S. Must not be used where the difference of
potential between the two wires is over 300 volts.

c* Must not be used as a support for clusters^

d* Must not be used except for pendants, wiring
of fixtures, and portable lamps or motors, and port-
able heating apparatus*

The practice of making the pendants lan necessarily long
and then looping: them up with cord adjusters is strongly
advised against. It offers a temptation to carry about lamps
that are intended to hang freely in the air, and the cord
adjusters wear off thp miiiilation very rapidly.

For all portable work, includinj^ those pendants that are
liable to be moved about sufficiently to come in contact with
surrounding objects* fiescible wires and cables especially
designed to withstand this severe service are on the market
aad should be used.

The standard socket is threaded for i-inch pipe, and if it
IB properly bushed* the ree a forced flexible cord will not go
into it; but this style of cord may be used with sockets
threaded for i-inch pipe and provided with substantial bush-
ings. The cable is to be supported, independent of the
overhead circuit, by a single cleat, and the two conductors
then separated and soldered to the overhead wires.

The bulb of an incandespent lamp frequently becomes
hot enough to ignite paper, cotton, and similar readily
ignitible materials, and in order to prevent U from coming
in contact with such materials, as well as to protect it from
breakage, every portable lamp shouid be surrounded with a
substantial wire guard.

r. Must not be used in show windows,
/. Must be protected by insulating bushings
where the cord enters the socket.

j^. Must be so suspended that the entire weight
of the socket and lamp will be borne by knots under
the bushing in the socket, and above the point
where the cord comes through the ceiling block or
rosette* in order that the strain may be taken from
the joints and binding screws.

§43

INTERIOR WIRING

47» In selecting flexible cord for any given job of wiring:,
the class of work for which the cord is to be used most be
kept in view*

The following rule specifies the kind of insulated cord
that must be used with portable apparatus.

Far portable lamps ^ small motars^ etc.:

a* Flexible cord for portable use must meet all
the requirements for flexible cord for pendant lamps
both as to construction and thickness of insulation,
and in addition must have a tough braided cover
over the whole. There must also be an extra layer
of rubber between the outer cover and the flexible
cord, and in most places the outer cover must be
saturated with a moisture-proof compound thor-
oughly slicked down. In offices, dwel lings » or in
similar places where appearance is an essential
feature, a silk braid may be substituted for the
weather-proof braid.

48» Tjamp Bases. — The style of lamp socket used in a
given job of wiring will depend on the kind of lamp t>as©
used on the system* A large number of different styles of
lamp bases have been brought out^ but the number has
gradually been cut down until the three types shown in

Fig, 26 cover practically all the lamps in use in the United
States; these are the Edison (^),the Thomson-Houston {b),
and the Sawyer-Man* or Westinghonse (r). Of these three,
the Edison base is the most popular and is rapidly super-
seding the other two, la each case, the terminals of the

INTERIOR WIRING

§43

socket are marked ij*. When the lamp is placed in the
socket, these make connection with corresponding terminals,
thus connecting the circuit with the lamp.

49, Liamp Sockets and Receptacles, — A large variety

of lamp sockets are manufactured, but they are all much the
same in general design. Some of these are provided with

Fig. 27

Fi6. m

keys for turning the light oflE or on; others are keyless— the
light being controlled by a separate switch. The main
thing to look out for in selecting sockets is to see that they
are substantial; one of the most common sources of trouble
on incandescent-lighting circuits is flimsy sockets that are
continually getting out of drder. Fig. 27 shows a typica]

Fm. ^

Fio.ao

key socket for an Edison base lamp. Sockets should be so
constructed that the shell a will be insulated from the wires.
The rubber or composition bushing shown in Fig* 28 must
be used to protect the cord where it passes through the
shell. Ordinary key sockets are suitable for work with
incandescent lamps not exceeding S2 caudlepower.

§43

INTERIOR WIRING

Fig. 29 shows a waterproof, keyless socket for an Edison
base. The shell a is of porcelain and the wires b,b are
attached directly to the mains. Sockets of this type are
required by the Underwriters whenever wiring is done in
damp places, such as breweries, dye houses, etc.

Fig. 30 (a) and (b) shows two styles of keyless recepta-
cles. That shown in Fig. 30 (a) is almost entirely of porce-
lain and is designed for a lamp having a Thomson-Houston
(T. H.) base. That shown in Fig. 30 (b) is provided with
a porcelain base and a brass shell, the terminals being
designed to take a Sawyer-Man, or Westinghouse, base.

CURRENT REQUIRED FOB LAMPS

50. In making wiring calculations, it is necessary to
know the current taken by the lamps. This varies some-
what with different makes and can be calculated exactly if
the watts per candlepower are known. For ordinary calcu-
lations, it will be found convenient to use the current given

TABIjB III
POWER CONSUMPTION OP INCANDESCENT LAMPS

Candlepower

Voltage

Current
Amperes

Watts

.27

.32

.50

1. 00

220

.30

1. 00

in Table III. The current taken by enclosed arc lamps
varies with the make and size of lamp. About 5 amperes is
a fair average for constant-potential enclosed arcs, though in
some cases lamps may be designed for 6 amperes, while in
others where a long arc is used, the current may be as low
as 4 amperes.

INTERIOR WIRING

§43

FUSES

51, litiik Puses* — Fi£, 31 shows an ordinary link fuse

consisting of a fusible wire or stripy- (generally made of a
mixture of ]ead and tin) provided with copper terminals a,b.
The terminals are necessary in order to provide good con-
tact between the fuse and the fuse-block terminals; and, also^
to prevent damage to the soft fuse wire from the clamping

screws- Link fuses are
gradually going out of use;
they are not as reliable as
enclosed fuses of the plug
or cartridge types and are no longer allowed except in
rosettes where the current must not exceed B amperes^or on
panel boards that are mounted in fireproof cabinets. Even
on panel boards, the best practice is to use enclosed fuses
in preference to those of the link type even though the

^^P

Pig, SI

Fro. 32

latter are not prohibited. For all fuses mounted on porcelain
bases and used outside of cabinets, the enclosed type must
now be used,

52. Enclosed Fuse®, — The oldest type of enclosed fuse
is the Edison pliiir, Fig. 32. They are used on 125- volt cir-
cuits and are made for currents from 3 amperes to 30 amperes.
They are also allowable on three- wire circuits with grounded
neutral where the pressure between the outside wires does

INTERIOR WIRING

Dot exceed 250 volts. The fuse /, Fig, 32, ia mounted In a
procelain holder and attached to the screw terminal s and the
contact p; the holder is provided with a brass cap with an
openiog covered with mica or with a plain cap without mica.

Af€f//tS

Fuse P/idf

I V J i I i

Pig. 33

These plugs screw into the receptacles on the fuse block,
and whenever a fuse blows, a new plug is inserted*

Fi^. 33 (rt) shows a ihree-wire nxalti block and (*) a three-
wire brancli block; {c) shows three two-wire double

INTERIOR WIRING

§43

branch blocks £rouped together to form a distributing
center. The advantages of this type of fuse are that it is
enclosed and that it gives good contact between the fuse and

the fuse-block terminals*

53- Most enclosed fuses are of the so-called cartridfre

type, shown in Fig, 34. The enclosed fuse consists
essentially of an insulating tube provided with metal ends b, S
that fit into clips c,c when the tube is placed in position.
The fuse wire {which is often made of zinc or aluminum)
passes through this tube and is surrounded with a non-con-
ducting material that will flux with the molten metal and
effectually suppress the arc. One objection that has been

urged against enclosed fuses* outside of their higher cost as
compared with link fuses, is the difficulty in telling whether
a fuse has blown or not since it is enclosed and cannot be
seen. In the type of fuse shown in Fig. 34 this difficulty is
overcome by shunting the main fuse by a small wire that
runs under a label on the cartridge. When the main fuse
blows, the small wire at once melts and makes a mark on
the label.

Fig, 35 shows an adaptation of the cartridge type of fuse
to the Edison plug. Cut-outs already installed for use with
Edison plug fuses can thus be made to serve for cartridge
fuses and can be used for pressures as high as 250 volts.
The small cartridge fuse a is pushed through the hole in the
bottom of the plug and is held by the clip 5 so that when the
plug is screwed in place the current passes through the fuse
by way of the contacts c, d^ e. When a fuse blows, it is

843 INTERIOR WIRING 47

necessary to replace the cartridge only and not the whole
plug as with the Edison plug fuse.

54. The chief advantages of enclosed fuses are that they
are more reliable than link fuses and prevent arcing. The
fuse wire is not exposed to air-currents and it is impossible
for it to come in contact with substances other than those
for which the fuse was originally designed and adjusted.
Manufacturers of enclosed fuses make arrangements for
refilling the cartridges, so that the expense of using these
fuses is not as great as their first cost would indicate.

55. Ratluiir of Fuses. — Every fuse must be marked
with the rated current that it is designed to carry and also
the voltage of the circuit for which it is intended. The rated
current is not the current at which the fuse will open the
circuit. According to the National Code, fuses must be
constructed so that with the surrounding air at a temperature
of 75° F. they will carry indefinitely a current 10 per cent,
greater than that at which they are rated, and at a current
15 per cent, greater than the rating, they will open the circuit
without reaching a temperature that will injure the fuse
tube or terminals of the fuse block.

WIRING FOR A UNIFORM DROP

56. In the method of wiring illustrated in Fig. 15, the
lamp on the extreme end of the line in the office is mu9h
farther from the dynamo than the first lamp on that line.
Owing to the resistance of the wire, the distant lamp will
not bum as brilliantly as the nearer one; therefore, it is
desirable to have a system of wiring on which the lamps will
all glow with equal brightness. Also, it is not desirable, in
many cases, to have a rosette with a fuse at each lamp, as
this means many small fuses, and many very small fuses,
besides causing more trouble, are not as reliable as a few
larger ones. Fig. 36 represents the factory wired so as to
avoid these two undesirable conditions. Where joints are
made without changing the size of the wire, no cut-outs are

INTERIOR WIRING

§43

required. In these wirme: diagrams but one line is drawn to
represent the two wires that must be installed.

Id the wiring diagram shown in Fig. 36, there being less
than 660 watts on any branch circuit, fuses may be omitted
from the rosettes (or fuseless rosettes installed). Fuses o£
a proper mze to protect the lamp cord must be placed in the
cut-outs, that is, 6-ampere fuses if No. 16 cord is used. In

./-KT-

M M H-

^OM

-K a W rtn f44 H* H H K »■

JTfiiL

hr-

-MEL

-«— • )< m M *i H w

Fto,38

such an installation, No. 18 lamp cord cannot be used without
fused rosettes, unless not more than six lamps are placed on
a branch circuit, because a 3 -ampere fuse is required to pro-
tect No. 18 wire, and if placed in a cut-out, it will not allow
current to pass for more than six 110- volt lamps. The sizes
of wires permitted by the insurance rules will be the same
as in the first case studied*

67 < We will now take up the subject of line calculations
with reference to loss of power » or drop in potentiah
Table IV gives the resistance of pure copper wire at 75*^ F.
(24^ C), which is the temperature at which wiring calcula-
tions are usually made. The conductivity of commercial
copper wire is from 98 to 99.5 per cent, of that of pure
copper.

In ordinary interior wiring, the variations in resistance
due to changes in temperature are usually disregarded,
although they must be taken into account in the design of
most kinds of electrical apparatus where they affect the
regulation very much, as, for instance » in the field coils on

§43

INTERIOR WIRING

TABIiB IV

RESISTANCE OF PURE COPPER WIRK

Number
B.A8.

Resistance at 75^ P*

Ohms

Feet

per 1,000 Feet

perMUe

per Ohm

oooo

.04893

.25835

20,440.

ooo

.06170

.32577

16,210.

.07780

.41079

12,850.

.09811

.51802

10,190.

.1237

.65314

8,083.

.1560

.82368

6,410.

.1967

1.0386

5.084.

.2480

1.3094.

4,031.

.3128

I. 6516

3.197.

.3944

2.0825

2,535.

.4973

2.6258

2,011.

.6271

3.3111

1,595.

.7908

4.1753

1,265.

.9972

52657

1,003.

1.257

6.6369

795-3

1.586

8.3741

630.7

1.999

10.555

500.1

2.526

13.311

396.6

3.179

16.785

314.5

4.009

21.168

249.4

5.055 .

26.691

197.8

6.374

33.655

156.9

8.038

42.441

124.4

10.14

53.539

98.66

12.78

67.479

78.24

16.12

85.114

62.05

20.32

107.29

49.21

25.63

135.53

39.0a

32.31

170.59

30.95

40.75

215.16

24.54

51.38

271.29

19.46

64.79

242.09

15.43

81.70

431.37

12.24

103.0

543.84

9.707

129.9

685.87

7.698

163.8

864.87

6.105

2066

1,090.8

4.841

260.5

1,375.5

3.839

328.4

1.734.0

3.045

414.2

2,187.0

2.414

522.2

2,757.3

1.915

658.5

3,476.8

1.519

830.4

4,384.5

i.ao4

1,047.

5,528.2

.955

INTERIOR WIRING

§43

a generator. The greatest variation in temperatnie at all
likely to occur, and that will occur but rarely and only in
open work, is about 100° F* This will correspond to a
change in resistance of about 21 per cent*

The resistances of wires smaller than No. 18 are of no
use in practical wiring, hut are given for reference, as small
wires are used in many pieces of mechanism, such as fan
motors, resistance boxes, etc*, with which wiremen have to
deal» and also in bell and annunciator work*

58* The efficiency of a system of electric wiring is low
if the percentage of power that is consumed in heating the
wires instead of being conveyed to the lamps or other trans-
forming devices is large* This loss of power {in waits) is
equal to the volts drop in the line multiplied by the current
in amperes. Wiring specifications usually call for so many
volts drop or not more than a certain percentage of drop
on the line between the lamps and the center of distribution
and between the center of distribution and the point where
the wires enter the building or where the dynamo is located.

CALCUUiTrON OF JANB l«OSBE8 »UB TO RESTSTAJ?JCJK

59. We will now calculate the drop on the wires in the
factory shown in Fig. 36, using the smallest wires permitted
by the Underwriters. The distance from the dynamo D
to point A, which is the average distance that the current
travels on the No. 6 wire, is 150 feet (allowing for risers to
a ceiling 15 feet high). As there must be two wires, the
total length of wire is 300 feet or ,3 thousand feet.

The resistance of 1^000 feet of No. 6 wire (Table IV) is
,3944 ohm; therefore, the resistance of 300 feet of No. 6 wire
is .3 X .3944 = .11832 ohm. This line carries 50 amperes.
By Ohm*s law, the drop is given by the following relation:
Drop in line (volts) = current in line X resistance of line;
hence, drop = 50 X 418 ^ 5.9 volts.

The line from A to B carries current for nine lamps, or
4.5 amperes. Its distance is 140 feet and the resistance
of the No. 14 wire is 2.526 ohms per 1,000 feet; hencei

848 INTERIOR WIRING 61

drop = 4,5 X ^ ?i^^ X 2.526 = 3.18 volts drop on the

J.|UUU

branch line of No. 14 wire.

The total drop from D to B will then be 5.9 + 3.18
= 9.08 volts. This is 8.25 per cent, of 110 volts, altogether
too much for such a plant as we have been considering.

The reason why such a large loss must not be permitted,
in addition to the simple matter of economy of power, is
that such a large falling oflE in voltage will greatly reduce
the brightness of the lamps and poor service will result.
The cost of power alone, however, is usually a sufficient
reason to prohibit such great losses in the wiring.

60. The plant we are considering requires 50 amperes
at 110 volts, or 5,500 watts. This, if furnished by a light-
ing company, will cost between 10 and 20 cents a kilowatt-
hour, at the rates ordinarily charged. That will be from
$.55 to $1.10 an hour for light. 8.3 per cent, of this is
4.565 cents to 9.13 cents an hour. If the lights are used
an average of 2 hours a day 300 days a year, this will
amount to from $27.39 to $54.78 a year. Even if the loss
were only one-fourth as great, the saving in tl^e cost of
light in a year would more than pay for the additional cost
of wire.

It is usual to specify a 2-per-cent. drop for such installa-
tions as this when the current is to be purchased at fairly
high prices, and a 3-per-cent. to 5-per-cent. drop where
the current is produced cheaply, as by a dynamo on the
premises. Not more than a 5-per-cent. drop should be per-
mitted on short distances, even where very cheap work is
desired. This would be accomplished in this case by using
No. 4 wire for the feeders and No. 12 for the branch lines.
The student may calculate the loss exactly by the use of
Table IV.

61. Drop In Apc-Iilght Wlrlngr. — ^The loss on the arc
lines using No. 10 wire from the point A is found as
follows. The resistance of No. 10 wire is about 1 ohm
per 1,000 feet.

INTERIOR WIRING

143

Drop iTomA to lamp No. J = 15 {amperea) X ^^^^/^^^^^ ^ -^ ^^*

2 V SO V 1
Drop from lamp No. 2 to lamp No, 3 = ^^^ ^qcS^ " ^ ^**

.5 volt

2 X 50 X 1
Drop from lamp No. I to lamp No, f = 5 x - , QQ|y"~

Drop from lamp No. i to lamp No. 5 ^^ .5 volt

Drop from A to lamp No, 4 = 10 X^-^^^ = .8

Total drop to lamp No. i = .3 + 1 + .5 = 1.8 volts

Total drop to lamp No. 2 ^ .3-J-l = 1.3 volts

Total drop to lamp No, 5 = *3 volt

Total drop to lamp No, d = 3 volt

Tola! drop to lamp No. £ = .8-|-.& = 1.3 volta

These slight variations can be permitted on the arc lamps
without inconvenience.

62, size or Wire for Arc Ijlghts,— It should be noted
that No, 10 wire is the smallest permitted on this line if the
line is protected by but one ctit-out. But if the line is
divided into two parts, one for lamps Nos. 1, 2, and 3 and
one for lamps Nos. 4 and 5, with separate cut*outs for each
of these lines, smaller wires may be used, so far as the
Underwriters' rules are concerned, Figf, 37 shows the sizes
permitted (a) with a single branch block and C^) with a
double branch block.

The wires that have their sizes designated by odd num-
bers from No. 7 up are not usually manufactured and cannot
be purchased except on special order* Therefore, work must
be done without using Nos. 7, 9, 11, and 13 » The resist-
ances of these sizes, however, are given in the table, as these
wires are extensively used in the manufacture of electrical
machinery. In tables given later, the above sizes are not
given, aUhough in a number of cases they would come
nearer the calculated size* In interior wiring it does not» as
a rule, pay to be too saving in regard to the sizes of wire^
and the nuisance of carrying a large number of sizes of wire
in stock more than counterbalauces any slight gain there

§43

INTERIOR WIRING

might be in the copper used on a given job. For this reason,
the above odd sizes are not generally used. Moreover, the

mtm/r

2S4mfia9fys€.

MkJt KV/w

=S:^-<^

PiO. 37

tendency is always to add more lights to a system, and it is
best to be liberal when installing the wire.

CALCULATION OF THE PROPER SIZE OF WIRE FOR A

GIVEN LOSS

63. WlrlnpT for 110 Volts, 2 Per Cent. Drop.— We

will now calculate the sizes of wires required in the building
wired according to Fig. 36 for a loss of 2 per cent. (2 per
cent, of 110 = 2.2 volts).

This calculation will be made with a view to making the
drop uniform along all the lines; that is, we will make the

INTERIOR WIRING

§43

volts drop per foot of line as nearly equal as possible in
feeders and branches. The proper value of volts drop
per foot is found by alio win ij the desired drop to the most
distant group of lamps in the system and distributing this
drop imiformly along the lines to the generator.

The average distance from the dynamo to the most distant
group of lamps ^ is 150 + 140 = 290 feet. This requires
580 lineal feet of wire, or .58 thousand feet, there being two

lines. ^f^^fM = 3,8 volts per 1,000 feet. 3,8 (volts)

-7- 50 (amperes) =s .076 ohm per 1,000 feet for mains* The

nearest wire to this is No, 00, with *078 ohm per 1,000 feet.
Using this, the loss on the mains will be .3 X .078 X 50
= 1,17 volts, leaving 2.2 - 1.17 = 1,03 volts to be lost in
the branch line. The length of the branch is 140 feet (280
or ,28 thousand feet double distance) and the drop per

1,000 feet is ^ = 3.68 volts.

The current in the branch

is 4.5 amperes; hence^ the allowable resistance per 1,000 feet

IS --

3.68
4.5

= .82 ohm. This would call for a No. 9 wire. In

Art* 59 the sizes were No. 6 for the mains and No, 14 for
the branch under consideration; consequently, to redoce the
drop from 9.08 volts to 2.2 volts these sizes must be increased
to No. 00 and No. 9, respectively.

64* Wiring for 220 TaltB, 3 Per Cent. Brop. — As a

hirther exercise in calculating the required sif.es of wires in
terms of resistances per 1,000 feet, let us ascertain the proper
sizes of wire to equip the factory with 220- volt lamps, allow-
ing 3 per cent. loss.

As 220-volt lamps are not as efficient as 110-volt lamps,
allow 60 watts per Ifi-candlepower lamp and 3 amperes per
enclosed-arc lamp. The circuits for incandescent lamps
carry approximately equal loads and are of about the same
length, so that it will be sufficient to calculate the size of
wire for one circuit only. 10 (lamps) X 60 (watts per lamp)
+ 220 (volts) = 2.73 amperes.

S43 INTERIOR WIRING 65

4 X 2.73 = 10.92 amperes for incandescent lamps
6 X 8.00 = 15.00 amperes for arc lamps
25.92 amperes total current

3 per cent, of 220 volts is 6.6 volts. ~ = 11.38 volts lost

.58

11 OQ

per 1,000 feet; ^^^ == .44 ohm per 1,000 feet for the mains.

The wire with resistance nearest this is No. 6, with .394 ohm
per 1,000 feet. Using this size, we have a loss on the mains
of .3 X .394 X 25.9 = 3.07 volts, leaving 3.53 volts to be
lost on branch lines.

The size of these branch lines will, therefore, be found as

O CO

follows: -^ = volts drop per 1,000 feet in branch lines and

.28

~ H- 2.73 = 4.62 ohms per 1,000 feet.

.28

Table IV gives 4.009 ohms per 1,000 feet for No. 16 wire,

which is smaller than the Underwriters will permit. No. 14

must be used, even though it is larger than necessary as far

as the drop is concerned. The loss on the branch line will

then be .28 X 2.526 X 2.73 = 1.93 volts, leaving 6.60 - 1.93

= 4.67 volts to be lost in the mains, instead of 3.07, as pre-

4 fi7
viously calculated. — "- -r 25.9 = .6 ohm per 1,000 feet in
.3 ,

feeders. No. 8 wire has .627 ohm per 1,000 feet and is

nearest the required size.

In 220-volt wiring, where the distances within the building

are short, the wireman will usually find that the minimum

sizes of wires specified by the Underwriters are large enough

to carry the current with less than 2 pei* cent. loss. In small

dwellings wired on the closet system of distribution with

220-volt circuits, it will not be necessary to pay any attention

whatever to the drop on inside lines.

65. Center of Distribution. — In making calculations
relating to wiring, the distance to be taken is the average
distance through which the current supplied can be con-
sidered as flowing. For example, take a case like that

463—25

INTERIOR WIRING

§43

shown in Fig, SS, where a circuit is run from a distributing
point ^ to a number of lamps B. For the first 100 feet no
lamps are connected; we then have, say twelve lamps spread
out over 50 feet at the end. In calculating^ the drop on such
a circuity it is evident that the full length should not be taken,
because the whole of the current does not flow through all the
line. The current keeps decreasing as each lamp is passed.
The canter of distribution for the lamps will, therefore, be
at C and the average length of wire through which the
6 amperes is carried is 2 X 125 = 2*50 feet. If the lights were
bunched at the end of the line, the distance to the center

. f2Sp ^

Fio.38

of distribution would be the same as the length of the
line I and the length of wire through which the 6 amperes
would flow would be 2 X 150 - 300 feet. If the lights were
spaced uniformly throughout the whole length of the line> the
average distance would be -^-|^ = 75 feet and the average
length of wire used in making calculations for drop would be
150 feeti By laying out a plan of the wiring, the average
distance over which the current Is transmitted can usually
be determined without much trouble and close enough for
practical purposes.

§43

INTERIOR WIRING

66. Selection of FlttlofiTB for 220- Volt Wiring.— In
220*volt wiring, great care must be taken in the selection
of fittings* Cut-outs, sockets, and switches desigtied for
110-volt working and not improved during recent years so as
to comply with the more severe reqiurements of the present
day must not be used on higher voliages* Keyless sockets
should be used for 220-volt work
and the lamps controlled by
switches; no rosettes with link
fuses should be installed, fuses
being placed in approved cut-outs,
one of which should be provided
for each ten lamps or less. If
proper precautions are taken to
procure good cut-outs, sockets,
and switches* there is no especial
difficulty to be encountered in
220-volt work, though the lamps
are not as efficient as can be pro-
cured for lower voltages.

Fig. 39 (a) and (^) shows two
cut-outs designed especially for
220-volt work. The construction
is such as to secure higher insula-
tion and less liability to arcing
than with the ordinary 110-volt
fittings. Fig* 39 (a) is a three-
wire branch block shown without
the fuses in place. Fig, 39 (^) is
a three-wire main block with the
fuses / in their proper position.
These fuses are of the enclosed
type and are held by clips ^,^, (a).

Plug fuses of the cartridge type, Fig. 35, can be used on
220-volt circuits with the cut-outs mounted open. Cut-outs
should be provided with barriers or porcelain partitions
between the fuses. Fig. ?^9, so as to prevent arcing between
the terminals and accidental short circuits in case any

INTERIOR WIRING

§43

conductor happens to fall across the cut-out. Open link fuses
on 220-volt circuits are only allowable when used on enclosed
slate or marble tablet boards,

67. Size of Wire for Three- Wire System-— If it is
desired to wire the shop that we have been considering for
110- volt lartips on the Edison three-wire system, the sizes of
the main wires required will be the same as for the 220- volt
two- wire system, and a thirds or neutral, wire must be
installed. This is usually placed between the other two; if
the wires are put on cleats, three-wire cleats may be used.
The neutral wire must not be smaller than will be required
for the safe carrying capacity for the current of all the lamps
on one side of the circuit. In this case, that current is
25 amperes and the wire must not be smaller than No< 10; it
should be larger to prevent unbalancing when lamps are
turned off-

68- Unbalauclug of Tliree-Wire System, — The

unbalancing of a three-wire system with the three wires of
equal size is illustrated in Pig. 40 (a) and (d). When the
system is balanced, as in (a), there are 3 amperes in the

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outside wires and no current in the neutraL Taking the pres- h
sure between A and C or C and £" as 112 voltSt and between |
B and D qx D and /^as 110 volts, there is a drop of 2 volts

§43 INTERIOR WIRING 59

in AB and one of 2 volts in EF. The resistance A B^ CD^
and EF must, therefore, be f ohm, in order to gfive a drop
of 2 volts with a current of 3 amperes. If the load becomes
unbalanced, as in (^), there will be a current of 3 amperes
in ^^, as before, 2 amperes in CD^ and 1 ampere in EF.
The drop in ^ i9 will be i X 3 = 2 volts; in CD, i X 2
= li volts; in EF, I X 1 = i volt. The total drop in the
two outside wires will now be 2 + f = 2f volts, and hence
the pressure between the outside wires at the end of the line
must be 224 — 2f = 221i volts. Taking the upper side of
the circuit, we have 3 amperes flowing out through A B and
2 amperes flowing back through C D\ the drop on this side
must, therefore, be 2 + Is = 3i volts and the pressure
between B and D must be 112 - 3i = 108f volts. The
pressure between B and /^is 22li volts; hence, the pressure
between D and /'must be 221i - 108f = 112|. The result
of the uneven load is, therefore, that the voltage rises in the
lightly loaded side and falls on the side having a heavy load.
If the neutral wire were smaller, this unbalancing would
be greater.

The branch lines of a three-wire system being simple two-
wire circuits, they must be calculated for the proper current
and drop in the same way as ordinary two-wire circuits*

INTERIOR WIRING

(PART 2)

UNIFORM DROP IN FEEDER LINES

CAIiCUIiATING SIZES OP WIRE REQUIRED

1. In installations where there are many sets of feeders
running to various departments, it is usual to allow a certain
loss in the feeders and a certain other loss in the distribu-
tion wires. The drops in all feeders are made equal, and
the dynamo is operated at a higher voltage than the lamps
will stand, with the intention of losing a definite amount
before the lamps are reached. It is important that the
voltage at the lamps should never exceed that for which
they are intended.

2. Fig. 1 represents a plant, such as a wagon works or
furniture factory; only the outlines of the buildings are
indicated. The dynamo and switchboard are located at Z? in
the engine room. The various centers of distribution are to
be at or near the centers of the various floors, and a separate
pair of feeders is to be run to each distribution center.
Where elevator shafts are convenient, they are used to run
risers to the upper floors. In the case illustrated there are
fourteen pairs of feeder wires, each pair being represented
by one line in the figure.

A 115-volt dynamo and 110-volt lamps are to be used. A
loss of 2 volts is to be allowed in the distribution wires and

For notiu of copyrizht^ see Page immediate^ (ollowtn£ ike title pag$
144

INTERIOR WIRFNG

§44

a loss of 3 volts in the feeders, irrespective of their length.
The figure shows the plan of the feeders on one floor only;
the small round dots indicate risers.

^BtfOfy^

J^£fiOfyC

m km

ra€ii»y8

Dfftfw /jhem

e,3d'4^)tff m^ ¥¥6ttt»s

PVh^9 /yf floor

G^/st

Fio. 1

We will calculate the feeders on one floor only.

Lamps

Amperes

Distance
Feet

Length of Wire
Feet

Shop A,

130

260 (.26 thousand)

Shop B,

150 (.15 thousand)

Shop C,

170 (.17 thousand)

Shop Dt

175

350 (.35 thousand)

§44 INTERIOR WIRING S

The resistance per 1.000 feet of these feeders required to
give a drop of 3 volts and the nearest sizes of wires obtain-
able, are calculated as follows:

^^^ ^' ^ = -461, No. 6 has .395 ohm per 1,000 feet
25 X '^u

Shop B, -ir^rz = 1.000, No. 10 has .999 ohm per 1,000 feet
20 X -15 I

Shop C, ^ - = .882, No. 10 has .999 ohm per 1,000 feet

IKj X . 1 *

^^°P ^' ^ = -429, No. 6 has .395 ohm per 1,000 feet
ISj X •«>5

This method of calculating required sizes of wires can be
applied to any kind of wiring for any practical purpose; but
to avoid the necessity of figuring out each case, wiring
tables have been prepared by which the proper size can
be determined without calculation.

CAIiCUL.ATION OF WIRE SIZES IN TERMS OF RESISTANCE
PER l.OOO FEET

3. Calculations based on resistance per 1,000 feet may
be put in the shape of a formula, as follows:

__ 1,000 <? /-iv

in which r« = resistance of 1,000 feet of wire to be used;
e = drop, in volts;
D = distance, in feet;
/ = current, in amperes.

For example, to carry 10 amperes 600 feet (600 X 2
= 1,200 feet of wire) with 3 volts drop, the resistance per

1,000 feet will be r« = ^'^^ ^— = .25 ohm per 1,000

feet. No, 4 wire has about this resistance, as may be seen
by consulting a wire table.

4, Wiring Table Giving: Distances for Drop of
1 Volt. — In Table I, distances in feet are given in the top

INTERIOR WIRING

§U

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^ M M O O 00 4Q » dO O O m m tft ^ m fit M

^n M O O OoD^fiaOOOOO ^A^rnv^Ci M

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^-fti « « O O OeowouOOOsD^O viiA*ft"r*

flj

ti9Cm}

§44

INTERIOR WIRING

horizontal line. Beneath these distances are columns con-
taining numbers that designate the proper size of wire to
use to obtain a drop of 1 volt when the wire carries the cur-
rent given in the corresponding line in the left-hand column.
If it is desired, for example, to find the size of wire neces^
saiy to get a loss of not more than 1 volt with 20 amperes,
and a distance of 140 feet (i, e., two wires, 140 feet long),
we look under 140 and to the right of 20 and find the fig-
ure 2. No. 2 wire will be required. If it is desired to
find the wire required for a loss of 2 volts with 20 amperes
and a distance of 140 feet, we may divide the distance by
the loss in volts and use the table as before; i. e., under
70 and to the right of 20 is found 5> No, 6 is the proper
wire. Or, we may use the distance given and divide the
current by the number of volts; i.e., under 140 and to the
right of 10 is found 5. The table is sufficiently accu-
rate for all practical purposes, but where very great exact-
ness is desired ^ it is better to calculate the lines. For the
smaller sizes in this table, the nearest even sizes of
wire above No, 6 are given because the odd sizes are not
ordinarily used.

CAIiCtJLATION OF WIRBB IN TBBM8 OF CIRCITLAR^ M1I3

5- In the Underwriters' table of safe carrying capacities^
the wires are listed both by number (B. & S. gauge) and by
circular mils. Cables having^ no B. & S. gauge number
are listed by circular mils only. Large cables of any desired
cross-section in circular mils are made by all the leading
manufacturers of insulated wires.

It is often more convenient to calculate the size of wires
or cables in terms of circular mils than in terms of resistance
per 1,000 feet; and calculations in terms of circular mils are
applicable to wires or cables of any size or shape.

A round wire 1 mil in diameter has a cross-section of
1 circular mlK A copper wire 1 mil (nht inch) in
diameter and 1 foot long (1 mn-foot) has a resistance of
10.8 ohms; or, t mii*ioat oi capper has 10 S ahms rtsisiame
ai 75^ K

INTERIOR WIRING

§44

A wire 2 mils in diameter has a section of 4 circular mils
(sometimes abbreviated C, M. or cir. mils); 3 roils in diam-
eter, 9 circular mHs; 4 mils, 16 circular mils; 5 mils, 25
circular mils; x mils» x' circular mils, Th€ circular mils
crasS'Secliofi ni any round wift is equal to the square of tls
dianider in mils. The circular mils of anjr conductor of
other shape is equal to its area in square mils multiplied by
1.273 or divided by .7854. For instance, the circular mils
of No. 0000 wire (diam. = 460 mils) = 460' = 211,600 cir^
cular mils, white a bar of copper i inch by \ inch (250 mils
by 500 mils) has a section of 250 X ^500 =^ 125,000 square
mils, or 250 X 500 X 1.273 ^ 159,125 circular mils.

6. If the length, in feet* of a wire is known and also its
area, in circular mils* the resistance may at once be deter-
mined by the formula

10.8 Z.

R =

cir. mils

(2)

In this formula, L mnat be the total length of wire in feet.

Also, since the drop ^ in a circuit is equal to the current

/ X resistance R^ we have

10<8 LI

drop e =

cir, mils

or if the drop is given and we are required to find the size of
wire to give this dropj we may put formula 3 in the form

10.8 Z/

circular mils =

(4)

In these formulas, L is the total leng^th of the circuit, i* e.^
the distance to the lamps and back again. If the distance to
the lamps, one way, is called D, we may put formula 4 in the
form

21.6/?/

circular mils =

(5)

This last formula will generally be found as tiseful as
imy that can be given for interior-wiring calculations. It
will be well to commit it to memory, because one does not
always have a wiring table at hand when calculations are to

§44 INTERIOR WIRING 7

be made and, besides, calculations have often to be made
that are beyond the rang^e of the tables. It can be applied to
any two-wire system or to the three-wire system, as illustrated
by the following examples:

Example 1. — By means of formula 5, calculate the size of wire
necessary to supply eighty 16-candlepower lamps situated at a distance
of 200 feet from the center of distribution. The allowable drop is to be
3 volts.

Solution.— We have D = 200 and ^ = 3. Each 16-c. p. lamp will
take about 1 ampere; hence, / = 40.

. ., 21.6 X 200 X 40 --.^
cir. mils « « = 67,600

or between No. 2 and No. 3 B. & S. No. 2 wire would likely be
used. Ans.

Example 2. — Calculate the size of wire necessary to supply one
hundred lamps on a llQ-220-volt three-wire system. The distance
from the center of distribution to the lamps is 250 feet and the drop on
each side of the system is not to exceed 3 volts. The lights are sup-
posed to be balanced, fifty lamps on each side.

Solution. — The simplest method of solving this problem is to treat
it as if it were a two- wire system and use formula 6. Each pair of
lamps will take \ ampere; hence, the current in the outside wires,
when all the lamps are burning, will be ^ = 26 amperes instead of
H* = 60 amperes, as it would have been if a two-wire system had been
used. The allowable drop on each side of the circuit is 3 volts; hence,
the total drop in the outside wires will be 6 volts. We have, then,

., 21.6 X 250 X 25 „„ -^

cir. mils = 2» " 22,500

A No. 6 wire will be large enough and also would likely be installed
for the neutral. Ans.

The same method may be used for a 22Q-440-volt three-
wire system, except that in estimating the current, allow
about .3 ampere for each pair of lamps instead of .5 ampere,
as in the previous case.

7. Estimation of Current Required by IJainps. — ^As

mentioned, it is customary in estimating the current taken by
lamps to allow about a ampere for each 110- volt 16-candle-
power lamp, and others according to the values given. The
most acciurate way, however, is to figure the current from

INTERIOR WIRING

§44

the total watts supplied and the known voltage- For a two-
wire system the current is as follows:

« _ number of lamps X watts per lamp /g\

voltage at lamps
For a balanced three-wire system

Ctirrent =s number of lamps X^ watts per lamp /wy

voltage between autside wires at lamps
These formulas are general and apply to lamps of any
eflSciency.

CALCULATIONS FOB ALTEHNATIITG CtTHRKNT

8, For ordinary two* or three-wire work with alternating
current, calculations may be made in the same way as for
direct current* When wiring is done io conduit, the two
wires must be run in the same conduit » otherwise inductive
effects will greatly reduce the voltage at the lamps. With
ordinary open wiring, the induced counter E. M. F. is not
usually large enough to produce any noticeable effects,
especially when the load consists wholly of lamps. When
lamps are operated on two-phase or three-phase alternating-
current systems, the different circuits are connected to dif*
ferent phases so as to balance the load, and as far as interior
wiring is concerned, the lighting circuits are single- phase and
are calculated in the same way as ordinary two-wire circuits.

OTHEH FORMS DF ^WIRINO TABLES

9, Before leaving the subject of wire calculations, atten-
tion is called to the fact that there are methods of arranging
wiring tables other than that given in Table I, for it is easy
to produce several arrangements of the same matter. The
table that one is most accustomed to use seems the simplest.
Tables calculated for incandescent lamps, instead of for
amperes, are useless for general work and should not be
used for calculating wiring for lamps, unless it is known
that the efficiency of the lamps on which the table is based
is the same as that of the lamps to he used.

Table II is very convenient because it gives the distance
exactly corresponding to the required drop. To use it^ divide

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INTERIOR WIRING

§44

the number of amperes transmitted by the number of volts
drop desired. Find the nearest number to this result in the line
of amperes; below this find the distance, in feett most nearly
corresponding to the given distance; to the left of this, in the
column of wiie sizes, is given the number of the required wire.
For example, to find the size of wire to transmit 15 amperes
140 feet with 3 volts loss, divide 15 by S and find the quo-
tient 5 in the line of amperes. In the column below, we find
the nearest distance 153, and to the left of this the size of
wire required, No. 8.

10* Probably the most convenient of aD methods of

calculation, after one is accustomed to using: it, is the
graphic method, in which amperes and distances are laid off
at right angles to one another, and the wires corresponding
to different values of these quantities, for a loss of 1 volt,
are represented by curved lines. Figs, 2 and 3 are diagrams
of this kind. Notice that every wire curve is dotted for a
short distance for currents larger than the maximum allowed
by the Underwriters' rules for that size of wire* In deter-
mining the size of wire from these diagrams, do not use the
dotted portions of the curves. If a point should come near
one of the dotted sections, use the next larger size of wire.

To use such a diagram » find the point where the lines
representing amperes and given distance intersect, and
take the wire indicated by the wire line nearest this point.
Unless the wire line is very close, take the larger wire of
the two lines oo each side of the intersection point.

For example, to find the wire required for 7 volts loss in a
distance of 125 feet, with 21 amperes, divide 21 by 7, which
gives 3 J the line of 3 amperes intersects the line of 125 feet
about midway between the lines representing No. 10 and No* 12
wire; hence, the larger size of wire, No. lO, would be used.

11* In calculating the sizes of wires for 52-, 104-, 220-,
or 250- volt work, or for any intermediate voltage, it must

be borne in mind that lamps burning on lower voltages than
110 take more current, and those burning on higher voltages
take less current. An ampere per lamp for 52- volt lampSi

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INTERIOR WIRING

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§44

INTERIOR WIRING

i ampere per lamp for 104- or 110-volt lamps, and .3 ampere
per lamp for 220-volt lamps is a safe basis for calculations
where good lamps are used. Also, it must be remembered
that **per cent, drop" and **volts drop" are very difEerent
things, as set down in Table III.

The figures given in the table represent the actual drop, in
volts, for the line voltage at the top of each column, with the per-
centages of drop given in the left-hand column. For example,
a drop of 5 per cent, on a voltage of 150 would give 7.5 volts.

TABIiE III

Line Voltages

cj2

104

150

220

250

.52

1,04

I.I

1.5

2.2

2.5

1.04

2.08

2.2

3.0

4.4

5.0

1.56

3.12

3.3

4.5

6.6

7.5

2.60

5.20

5.5

7.5

II.O

12.5

3.64

7.28

7-7

10.5

15.4

17.5

5.20

10.40

II.O

15.0

22.0

25.0

7.80

15.60

16.5

22.5

33.0

37.5

FUSE PROTECTION FOR CONDUCTORS IN PARAIiliEL

12, It is sometimes desirable to run two or more small
wires in parallel, instead of one large wire or cable, for
convenience in handling the wires, to obtain a certain carry-
ing capacity with the use of less copper, to use material
that happens to be at hand, or for other reasons. When
two or more wires are run thus and are connected together
at their ends, separate fuses must be placed in series with
each wire, and not one fuse for all the wires in parallel.

Fig, 4 (a) and (d) illustrates the correct and the incorrect
methods of connecting such cables. Multiple conductors of
this kind may sometimes be used to advantage in over-
hauling or remodeling old work, where the wires originally
installed are too small, and in wiring an old building by the

INTERIOR WIRING

§44

use of molding, where large wires cannot be handled with-
out defacing ihe walls.

For convenience in comparing the conductivities of wires,
Table IV is jjiven. As an illustration, it is seen from the
table that instead of a single No. 2 wire we might use a No. 4
and a No. 6; two No. 5; four No, 8; etc. Of course, nothing
smaller than No. 14 can be used for interior wiring.

The conductivity is directly proportional to the total
cross-section of all the conductors in parallel, and the total
resistance is inversely proportional to the total cross-sectioo.

/^m W^rcs ^4 Amperes ^a^/t or/^^

^OArtw^re fuses f&

6SAm^isf^/as€ &f

f£^ ^ f€ss t^prfiU^

I^^H

F^G. I

13. Cfrcutts of several wires in parallel are sometimes
run where a large drop in voltage is not objectionable, but
where a single wire small enough to produce that drop will
not carry the current safely. Two or more small wires will
safely carry more current than one large wire of equivalent
cross-section, because two small wires have a greater surface
area from which the heat can escape than has one wire of
twice the cross -section* For instance, suppose that it is
desired to run wires in molding to secure a drop of 4 volts
with 65 amperes over a distance of 100 feet* Calculating^
the required size of wire by means of Table II» we see that
No. 5 will give the required drop. But No. 6 rubber-covered

§44

INTERIOR WIRING

H
O

O
u

H
H

++++++++++

►"• M roTfinNO t^oo ONO

128—18
128 — 19
128 20

C/3

»n NO t^ 00 Ov 0

T T T T T T

TT TT '^ '»t- '^ Tf

NO VO NO NO NO NO

M POTTinvO t^OO OvO

T T T T T T T T T

a
o

OvO •I M POTTinNO t^oo 0
vONOvONOvONONivONOvOvO

■♦-»

NO t^OO OvO •-• M POrrmt^OvO

00000000000000000000000600

3
cr

fOTfinvo r^oo OvO ►"• m ttnooo 0

lliitiitlilttT

0 •-• N r^ yr m \o r^oo 0^ ^ fo»nts.ON

1 1 1 1 1 1 1 1 1 1 T T T T T

^ M rOTTinNO t^OO OvO M TfNOOO O

+ + + + + + + + + + + + + + +

OO»-«NtOTfmvOt^00OM^NO00

0 I-, M IH 1^ l-l

Number of
Wire,
B. & S.
Gauge

||go«c.oTr«>vo(»22?'2

INTERIOR WIRING

§44

wire will safely carry only 54 amperes, while 65 amperes
is to be transmitted. By using two No. 8 wires, which are
equivalent in cross-section to one No. 5, we can safely cany
the current with the specified drop. If the current were
still g:reater, we could use one No* 8 and two No. 10 wires
with about the same results. However, such arrangements to
secure a drop are only used in emergencies or under special
conditions, and are usually only temporary expedients,

14- Calculation of Wires In Parallel- — If a number
of wires are to be used in parallel to do the work of a single
large wire, i. e., to carry a certain current a given distance
with a specified drop, the combined cross-section of the
smaller wires must equal the cross-section that the large
wire would have. Suppose, for example, that a wireman at
a distance from a supply house has on hand a large amoimt
of No* 12 wire, but no larger wire, and that he desires to
carry a current of 40 amperes, 150 feet (one way) with
3 volts loss. How many No. 12 wires should be connected
in parallel to secure the result? Using formula 5^ / = 40,

D — 150, and e — ^\ hence, circular mils = — — — -—-

= 43,200,

The cross-section of No* Vt wire is 6,5-30 circular mils,
approximately; hence, to make up a cross-section of 43,200 cir-

cular mils, -^ '^_ „ =^ 6.6 No. 12 wires in parallel would be
o,5<yO

required. In this case^ therefore, it would be necessary to use

seven No. 12 wires, as this is the whole number nearest to 6.6.

Take another example. In an old building, wired with
too much drop, it is desired to reen force the mains so as to
reduce the drop to 2 volts. A circuit of No, 8 wire carrying
20 amperes a distance of 150 feet is to be reenforccd* What
size of wire should be used?

The cross-section necessary to carry 20 amperes, 150 feet
with a drop of 2 volts is, from formula 5,

21.6X150X20

circular mils =

= 32,400

§44 INTERIOR WIRING 17

No. 8 wire has a cross-section of 16,510 circular mils;
hence, the crosj-section to be added is 32,400 — 16,510
= 15,890. Another No. 8 wire (16,510 circular mils) con-
nected in parallel with the No. 8 wire already installed, will
give slightly more than the required cross-section and would
therefore be used.

EXAMPL.E8 FOR PRACTICE

1. Determine, by means of formula 6, the size of wire required to
carry 30 amperes a distance of 150 feet (one way) with a drop of
3 volts. Ans. No. 6 B. & S.

2. If a circuit 200 feet long (single distance) carries 25 amperes and is
of No. 6 B. & S. wire, what will be the drop in volts? Ans. 4.1 volts

3. If a circuit of No. 10 B. & S. wire carries 20 amperes a distance of
200 feet (single distance) what size of wire must be connected in parallel
with the existing wire to limit the drop to 2 volts? Ans. No. 5 B. & S.

4. A current of 40 amperes is to be carried 300 feet (single
distance) with a drop of 3 volts. Assuming that No. 10 B. & S. is the
only size of wire available, how many wires must be connected in
parallel to carry the current with the specified drop? Ans. 8 wirea

WIRING IN DAMP PIjACKS

16« Where wiring is done in damp places, special pre-
cautions must be taken and special rules observed. The
following Underwriters* rules apply to this work:

Wires —

In damp places^ or buildings especially liable to mois-
ture^ or acid, or other fumes liable to injure the wires
or their insulation:

a. Must have an approved insulating covering.

For protection against water, rubber insulation must be
used. For protection against corrosive vapors, either
weather-proof or rubber insulation must be used.

b. Must be rigidly supported on non-combustible,
non-absorptive insulators that separate the wire at
least 1 inch from the surface wired over, and wires
must be kept apart at least 2a inches for voltages up
to 300 and 4 inches for higher voltages.

Rigid supporting requires under ordinary conditions,
where wiring over flat surfaces, supports at least every
\\ feet. If the wires are liable to be disturbed, the distance

INTERIOR WIRING

§44

between supports should be shortened. In buildings of mill
construction, mains of No. 8 B. & S, gauge wire or oveT»
where cot liable to be disturbed, may be separated about
6 Inches, and run from timber to timber, not breaking
around, and may be supported at each timber only.

BocketB^ —

a. In rooms where inflammable gases may exist,
the incandescent lamp and socket must be enclosed
in a vapor- tigrht globe and supported on a pipe
hanger, wired with approved rubber-covered wire
soldered directly to the circuit,

d. In damp or wet places or over specially
inflammable stuff, waterproof sockets must be used*

Waterproof sockets should be hung by separate stranded ^
rubber-covered wires, not smaller than No. 14 B. & S*
gauge, which should preferably be twisted together when
the pendant is over 3 feet long. These wires should be
soldered direct to the circuit wires, but supported inde-
pendently of them.

Fig, 5 shows a waterproof globe for use where infiatn-
mable gases may exist. In wiring

damp cellars, it is especially desirable
to have the lamps divided among sev-
eral small circuits, so that the blowing
of a fuse will not put out many lamps.
In such work, rosettes should never
be used, but the drop wires should be
soldered to, but not supported by, the
line wires» and the joints should be
thoroughly wrapped with insulating
tape. The cut*outs should be placed
outside the cellars, in a dry place^ if
possible, otherwise they should be
placed in waterproof boxes* It should
be noted that, in damp places, par-
ticular attention must be paid to the
character of the insulation. There
must be a clear air space around
the wires so that there will be no
^**' * chance for moisture to accumulate

and cause short circuits.

§44 INTERIOR WIRING 19

CONCEALED WIRING

16. Concealed >vlrliis is usually installed according
to one or more of the following methods: concealed knob and
iubcy cofiduit, and molding. Concealed knob-and-tube work
has been used in the past more than either of the other
methods; it is the cheapest of the three and is quite safe if
properly installed. The local rules governing wiring in
some of the larger cities have recently prohibited this
class of work, but it is allowed by the Underwriters' rules.
Conduit work is expensive and the knob-and-tube plan
affords a means of concealing wires at comparatively small
cost and, while it is unquestionably not as safe or as perma-
nent as the conduit method, there is no reason why it
should not be safe and satisfactory if the work is done as
it should be. It is much used for dwelling houses or simi-
lar places where the cost must be kept down. Conduit
wiring involves the installation of a complete piping system
in addition to the wiring system so that the cost becomes
very great. It represents the best method of wiring and
is now used on all important work where the highest degree
of safety and permanence is required. It is the only class of
wiring to be considered for fireproof office buildings, hotels,
or similar structures. The use of molding work is confined
almost entirely to old buildings where the wires cannot be
concealed and where it is necessary to run them in wood-
work to match the woodwork in the rooms. Very often
concealed knob-and-tube work can be combined with conduit
work to advantage, flexible condnits being very useful where
wires must be fished for short distances or where they have
to be run in places where there is not room enough for
supporting them on porcelain insulators. The concealed
knob-and-tube method does not afford the wiring mechanical
protection, and consequently is not suited to places where
the conductors are liable to be disturbed or come in contact

^^0

INTERIOR WIRFNG

with other objects. However, in non-fireproof buildings
where the wires can be run between the joists there is little
danger of their being disturbed, and wires well supported on
knobs have amply high insulation. The class of work to be
used in any given case will depend on the character of the
building to be wired, the allowable cost^ and on the local
regulations, if any, governing the wiring of buildings.

coxceali:t> knob-a^"d-titbk work

17* The most common way of concealing wires in non-
fireproof buildings is to run them through the joists between

the floors and ceilings
and through studding
partitions, and to in-
sulate them by means
of porcelain knobs and
tubes, as shown in
Fig, G. The holes
should not be closer to-
gether than is allowed
by the Underwriters'
rules, and the tubes
should fit tightly in the
holes. When the holes
are not horizontal^ but
are bored from above

or below obliquely, ihe tubes should be put in with their

heads on the high side, so that they cannot fall or slide out;

and when tubes are placed so

that there is any strain on them,

their heads must be so placed

that the tubes cannot slip.

Holes should be bored of such

a size that the tubes can be

inserted by driving lightly. Do

not make the holes too small or

there will be danger of breaking

the tubes. Holes must be bored sufficiently far away from

Fia. 6

§44

INTERIOR WIRING

the floors and ceilings to be out of reach of nails that may
be driven into the joists after the work is coocealed. Bush*

ings must be long enough to reach all the way through the
joists, with i-inch projection,

18. Where wires come through the plaster to outlets or
cut-outs, they must be protected by flexible insulating tubes

I 1 '•

r^>-.--

that will preclude all possibility of contact between the wires
and other objects. Careless work is often done at outlets »
with the result that a job that is otherwise well put up will
show poor insulation. The same outlets are very often used

INTERIOR WIRING

§44

both for gas and electricity , and if the wires are not well
protected where brought out, a ground on the gas-pipe

may result.

Fig* 7 shows the method of bringing out a ceiling outlet
with knob-and-tube work. The flexible conduit used to pro-
tect the wires projects as far as, or slightly beyond » the end
of the pipe and runs back as far as the porcelain support
next to the outlet. Fig, 8 {^) and (d) shows two methods
of bringing out side-wall outlets, (a) being a combination
gas and electric outlet and (^) a plain electric outlet. The
latter shows a board nailed across between the studs to sup-
port the fixture. In both cases the flexible conduit extends
back to the insulators, as required by rule {^)>

19. For running wires parallel to joists, knobs are
generally used because they make it possible to keep the
wires well separated. The following rules apply to this
kind of work:

Wires—

Far cmuealed knab-and-iube work.*

a. Must have an approved rubber insulating
covering.

b. Must be rigidly supported on non-combus-
tible, non-absorptive insulators that separate the
wire at least 1 inch from the surface wired over,
and must be kept at least 10 inches apart, and,
when possible, should be run singly on separate
timbers or studding. Must be separated from con-
tact with the walls, floor timbersi and partitions
through which they may pass by non -combustible,
non-absorptive insulating tubes, such as glass or
porcelain*

Rigid supporting requires under ordinary condltfons,
where wiring along flat surfaces, supports at least every
4i feet. If Ihe wires are liable to ba disturbed, the distance
between supports sfaoutd be shortened,

c* When, in a concealed knob-and-tube system^
it is impracticable to place any circuit on non-
combustible supports of glass or porcelain, approved
metal conduit, or approved armored cable must be
used except that if the difierence of potential

§44 INTERIOR WIRING 23

between the wires is not over 300 volts, and if the
wires are not exposed to moisture, they may be
fished on the loop system if separately incased
throughout in continuous lengths of approved
flexible tubing.

In general, when conduit of any kind is used in connection
with concealed knob-and-tube work, it must be installed in
accordance with the rules governing the use of conduit as
given later. In most interior wiring for lighting work, the
pressure between any pair of wires will not exceed 300 volts^
so that in cases where it is necessary to pass wires through
spaces where porcelain supports cannot be used on account
of lack of space or because they must be run through some
place that is inaccessible, it is allowable to fish the wires
through provided they are separately incased in flexible
tubing. The loop system referred to in rule (r) is explained
in connection with conduit wiring. It should be particularly

Fm. 9

noted that wires must not be run through flexible tubing
in cases where dampness is present. The armored cable
referred to in rule (e) would seldom be required in connec-
tion with knob-and4ube work in a new building where every-
thing is accessible; but in an old building where there are
objections to tearing up floors to insert wires, it may often
be used to advantage* particularly if the wires are liable to
be exposed to mechanical injury.

Fig, 9 shows an armored iivhi cable; the wire is rubber-
covered and over the heavy insulation is wound a steel strip
that interlocks so as to form a continuous protection. It is
possible to use armored cable for the complete wiring of a
building, in which case outlet boxes, etc, are provided as in
conduit wiring, described later. The conduit system is, how-
ever, preferable because the wires can be withdrawn, WTiere
armored cable is used in damp places it must have a lead

INTERIOR WIRING

§44

sheath between the Insulation and the armor* Protected

flexible cord, of the same style, is a very convenient article
to "Use in wiring- offices, banks, etc., where small conductors
must be rarried behind desks or fastened to iron or cabinet
work, and in many other places where ordinary cords will
not do and will not be permitted.

The following rule governs the arrangement of the wire at
outlets when it is run on the concealed knot>-and-tube plan:

d. Must at all outlets, except where conduit is

used, be protected by approved flexible insulating
tubing, extending in continuous lengths from the
last porcelain support to at least 1 inch beyond the
outlet* In case of combination fixtures, the tubes
must extend at least flush wHh the outer end of the
gas cap.

It should be particularly noted that in concealed knob-and-
tube work, or in fact in any kind of concealed wiring, the
wire must be rubber-covered. Weather-proof or fireproof
and weather-proof wires are prohibited for concealed work.
The calculations for concealed wiring are the same as for
open work; but it must be remembered that rubber-covered
wires are not allowed to carry as much current as weather-
proof wires, as shown by the Underwriters' table of carry-
ing capacities,

20. Use of Cabinets and Panel Boards. — For con-
cealed work* the closet, or cabinet, system of distribution

is now universally used. In it the mains are run to cahinets
or panel boards set in the wall, and the lines running to the
lamps are distributed from these. Many styles of these
panel boards are manufactured, and the kind used will
depend largely on the size and allowable cost of the instal-
lation. For the cheaper class of work» the cut-outs may be
grouped together and placed in a cabinet formed in the walh
This cabinet should be neatly lined with e-inch asbestos
secured in place by tacks and sheUaced, Where the wires
pass into and out of the sides or bottom, they should be
bushed with porcelain tubes. A neat glass or asbestos-lined
door should be provided, A cabinet made in this way is

§44

INTERIOR WIRING

iBexpensive and safe, though slale- or marble-lined cabioets
are much better and their use is strongly recommended,
Skte- or marble-lined cabinets should alwa]^3 be provided
with a job of conduit wiring.

Fig. 10 will give an idea as to the essential parts of a
panel board. In this case, the wires are run in conduits.
The bo]t is mounted in the wall and consists of two com-
partments j the inner compartment containing the panel
board, and the outer one, or gutter^ as it is sometimes called.
All boxes are not provided with this gutter, but the best
ones are, as It gives a
convenient space in
which to arrange the
wires in case they
should not come to the
box in the best order
for connecting up- The
box is made of slate
or marble slabs. The
trim around the door
covers the gutter; it
should be put up with
screws so that it may be
removed if necessary.

The mains usually
pass through the panels
vertically and are con- ^^ ^^

nected to bars from which the various lamp circuits branch
out side wise. Fuses are inserted in each side of each
circuit, and switches are also provided in some cases.
Chough sometimes the panel board carries fuses only in
case the switches are iocated near the lamps rather than at
the center of distribution represented by the fuse cabinet.

Fig, 11 shows a panel board equipped with double-pole
knife switches a and enclosed fuses b. Eighteen branch
circuits are accommodated and the three-wire vertical mains
are attached to the copper bars c.c^t'i the mains enter at the
bottom, being conducted to the board through the large

INTERIOR WIRING

§44

144

INTERIOR WIRING

conduit d that projects a short distance into the i^i^tter, or

distribution compartment. The casing and door are removed
in order to show the method of bringing the wires around to
the various switches. The outgoing circuits are carried
through the conduits c that enter at the top, each conduit
containing a twin w^ire. The panel board constitutes the
back of the cabinet and the sides and ends are of i-inch
slate. The main fuses are of the enclosed type and are

Pio.12

shown at /. The lining^ of the gutter is of iVinch enameled
iron or i-inch slate or marble. With knob-and-tube work the
gutter may be lined with i-inch asbestos firmly tacked in
place, though it is always better to use slate or marble lining*

21. Instead of building a box of slate or marble pieces,
iron or steel boxes lined with slate or marble are much
used. Fig. 12 shows a cabinet of this kind ready to be set

46B— 27

INTERIOR WIRING

§44

into the wall and connected up. It is made of a sheet-steel
box a, whose sides and top are lined inside with i-inch slate
slabs *. The panel board c constitutes the back of the box*
In the fig:ure the opeoiDgs t/ for the branch circuits are
arranged to take conduits. The two-wire vertical mains
are connected to terminals ^,^ and, through the main fuses,
to the bars /, /. Each branch circuit is provided with fuse
tenninals and a knife switch h*

Fig* IZ (a) shows a style of panel board that uses a speciftll
kind of fuse holder which serves the purpose of a switch when
it is desired to disconnect any circuit* Panel boards using
combination fuse holders have been adopted quite largely,
for they have one advantage in that the holder may be
entirely removed from the board w^hen the fuse is being
replaced, or a reserve holder may be put in instead of the one

§44

INTERIOR WIRING

removed. Fig. 13 (d) shows one of these holders. It is
held in place by the clips d,y, shown in (a), that receive
the blades a, a'. Link fuses are here used; they are allow-
able because the fuse holder is used in a fireproof cabinet
and not in an open cut-out. Fig. 14 shows a plain two-wire
board for four branch circuits; it is equipped with Edison fuse
plugs and has no switches. The foregoing will give a general
idea as to the construction of these boards. They are made in
all sorts of combinations and, in fact, are usually made to order
for any given job. In large wiring systems, the design of the

Fio. 14

cut-out closets, or cabinets, is a matter of great importance, and
the location of these closets is equally important; they should
be placed in a position where they can be readily reached.

Cabinets must be provided with a substantial door; if glass
is used it must not be less than A inch thick nor more than
1 foot wide. At least 2 inches clear space must be allowed
between the fuses and the glass. The door must close against
a rabbet, so as to be dust-tight, and bushings through which
the wire enters must fit the box tightly. Wires should com-
pletely fill the holes in the bushings; if necessary, the wire
should be built up with tape so as to keep out dust*

WIRING A DWEIililNG HOUSE

22. In laying: out the wiring for a dwelling house, the
first thing: to do is to locate the cut-out cabinets. In
many dwelling: houses, only one cabinet may be neces-
sary, but in houses designed to be occupied by more than
one tenant, a cut-out cabinet should be installed for each

INTERIOR WIRING

§44

tenant. In large houses, it is often convenient to have a
cut-out cabinet on each floor^ with vertical xriains running
through them from the top to the bottom of the house. If
only one distributing: point is used, it should be either in the
cellar or attic and risers should run to the different floors.
If it is known that the wires are to enter the building in the
cellar, the distributing center should be located there; if the
wires enter in the attic, the distributing point should be
located there. This assumes that vertical risers are run from
the distributing center to feed the various floors. In case a
single pair of vertical mains is used with the circuits branch-
ing off on each floor, the mains may be run from the top to
the bottom of the house and the current supplied from
either end*

No matter what arrangement is adopted for distributing
the current, the distributing centers, or cut-out cabinets,
should be in or near a partition that is located so as to make
the running of risers easy. They should also be as near the
center of the building as possible and on an inside wall^ so
as to guard against dampness,

23« Figs* 15 and 16 show two floors of a typical dwell-
ing* The distributing points are located in the hallway near
the center of the house, because such location is central and
easy to get at. The various branch circuits on the plans are
indicated by single lines, although each line represents two
wires. The wiring is supposed to be done on the ordinary
concealed knob-and-tube system and no circuit carries more
than ten lights. Switches are placed on the side w*alls, as
shown at s. The switch for controlling the hall lights should
be placed at some convenient point near the door, so that the
lights may be turned on when entering the building. It is
sometimes convenient to have another switch at the head of
the stairs for controlling the hall light, so that the light may
be turned on or off from either above or below. This
requires the use of three-point switches, the necessary con-
nections for which will be explained later* In the plans,
double-pole switches are indicated; single-pole switches*

§44

INTERIOR WIRING

Fio. IB

INTERIOR WIRING

§44

which are cheaper to install, may, however, be used when
not over 660 watts are controlled,

24, LayloK Out circuits. — In layingf out the various

branch circuits, the first thing to do is to locate the lights on
the plan and then group these lights for the different cir-
cuits, so that there will not be more than ten or twelve lights
on each one* After this is done the lines may be marked;
in doing this, due regard should be given to the direction in
which the joists run, so that the wire may be put in with as
little boring and cutting as possible. Run parallel to the
beams wherever it can be done, even if it does take a little
more wire- The best time to wire the building is after the
floorbeams and studding are in place, but before any lathing
or plastering has been done* In Fig. 15, four circuits are
provided, all terminating in the cut-out cabinet in the hall,
where they are attached to the vertical mains. For the
second floor, Fig, 16, three circuits are sufficient. No. 14
wire is, used for all these circuits. It will be found that
No. 14 wire (the smallest that the Underwriters allow) is
large enough for any of the branch circuits met with in
ordinary house-wiring work. The number of lights per cir-
cuit is small and the distances short, so that No. 14 will
carry the current with but a small drop in voltage.

25. The MafQS^ — If vertical mains are used, the cur-
rent that they will carry will be less at one end than at the
other» because current is taken oil at the different floors. It
is usually advisable, however, to make the mains the same
size all through an ordinary house, because it costs but
little more and enables the current to be supplied from
either end. In large buildings, where it would not pay to
do this, it is customary to install a number of risers feeding
different sections of the building and running to a common
distributing point, usually located in the basement* The
mains must, of course » be designed to carry the current in
accordance with the Underwriters' requirements or to limit
the drop to the allowable amount if the wire required by the
Underwriters will give too much drop* Suppose that the

§44

INTERIOR WIRING

FIS.U

INTERIOR WIRING

§44

house under consideration has a total of 60 lamps. The
current in the mains will then be SO amperes, and at least
a No, 8 wire will be required to satisfy the Underwriters*
requirements*

By referring to Table 11^ it is found that No, 8 wire will
carry 30 amperes a distance of 25.5 feet with a drop of
1 volt* For a building of this kind, the drop from the point
where the current enters the building to the lamps should
not exceed 2 to 2.5 volts. The drop in the branch circuits
is very small, but it would be advisable to put in No. 6
mains, as the difference in first cost will be but little. It is
the usual practice to make the mains of liberal cross-section.
For a house of this size No. 4 would often be used, although
it does not need to be as large as this so far as drop is
concerned.

26- Mat 11 Switch J Cut-Ont, and MetePp^ — At a con-
venient point near the place where the wires enter the build-
log, a main cut-out and switch must be placed, as required
by the Underwriters, The cut*out should be placed nearest
the point of entry, the switch next to it, and the meter last.
Never permit the meter to be installed between the switch
and the cut-out, as in that case it may register a small
amount each day, even if the switch is open. If a knife-
blade switch is used at the entrance to the building, it should
be placed so that when opened it will not tend to fall closed
of its own accord. It is also advisable to place it in an
asbestos -lined box provided with a lined doon

The best arrangement of the wires for the meter will
depend to some extent on the type of meter used. In a
great many cases, however, the wires enter the left-hand
side of the meter and pass out at the right. Fig, 17 repre-
sents a typical arrangement of main fuses, switch, and meter.

Most recording electric meters consist of a small electric
motor, the revolving part of which turns on jew^eled bear-
ings and is connected to a train of gears and dials. The
motor is governed by means of retarding devices » so that it
runs at a speed accurately proportional to the load. Some

§44

INTERIOR WIRING

meters read in ampere-hours, but most of those now installed
read in watt-hours and are provided with two coils, one
of which is connected in series with the circuit, like an
ammeter, and the other across the circuit, like a voltmeter.
The current in the first is, therefore, equal to the current
supplied, and the current in the second is proportional to the
voltage. The force tending to drive the motor is, therefore,
proportional to the product of the amperes and volts, i. e.,
to the watts. The small third wire running into the meter,
Fig. 17, is to supply current to the potential coil. With
ampere-hour meters, a series coil only is used, and the speed
of the meter is proportional to the current and not to
the watts.

The voltage of a lighting system is, however, practically
constant, so that the watt-hours may be obtained by multi-
plying the ampere-hours by the voltage without serious

RfCore//na

Watt
/^e.ter

Afa/rt raseS/ocA

f^fenfta/Wfre^ To House Wiring

Pio. 17

error. Reliable meters are made for all voltages and sys-
tems and for alternating . or direct currents. They are
accurate to within 98 per cent, on ordinary loads, but are
liable to be out as much as 5 per cent, on small loads, and
most meters will take a very small load without turning at all.
However, they are seldom operated under such conditions.

27. In new buildings, it is often not known what system
of electric lighting: will be used when the wiring is finished.
Owners also desire quite frequently to be able to avail them-
selves of any advantage in price that may be brought about
by competition between different systems. It is therefore
desirable that each new house shall be wired in such a
manner that light may be secured from any system in use;
that is, from 110- or 220- volt two- or three-wire systems.

INTERIOR WIRING

§44

The following typical specifications cover all the maia
points necessary for such a piece of work in an ordinary
dwelling house*

Other details, such as the location of additional switches^
the use of particular kinds of cut-outs, etc., may be added to
these specifications if desired. The specifications cover only
the concealed work.

Specifications for Concealed ElectriC'Light Wiring

For 110- or fiSIKVolt 9y sterna

DlBtdbutfon
Cabinet

CIrculti

Ftii«ft

Wina

A distribution cabinet is to be located on
some inside wall, In a readily accessible place,
on the second floor or the attic, as near the
center of the building as possible*

The cabinet must be lined with slate i inch
thick and fitted with a door covered on the
inside with slate i inch thick.

From this cabinet separate circuits must be
run to the outlets in such a manner that not
more than ten 16-candlepower incandescent
lamps shall be placed on any circuit. Wher^
ever the number of lamps is not marked on-
the plans or otherwise specified as greater than
here required, pendants shall be considered as
intended to carry four lamps each and brackets
one lamp each.

All fuses must be located on a panel board
placed in the distribution cabinet. The panel
boards must be of slate at least i inch thick
and be provided with terminals designed for
enclosed fuses. Both sides of all lines must
be fused and the fuses must be of a type suit*
able for use on 220 volts and capable of inter-
rupting the arc due to a 220- volt short circuit.

All circuits running from the distribution
center must be of No. 14 B. & S., or largefp

§44

INTERIOR WIRING

Mains

Extra Wire

Manner of
Pastenlnar
Wires

Space
Between
Wires

OuUets

rubber-covered copper wire of a make accepted
by the National Board of Fire Underwriters.

From the distribution cabinet to the attic,
and also to the basement, a pair of mains must
be run, the size of which will depend on the
total number of lights in the house, as follows:

17 lamps, or less
18 to 24 lamps, or less
25 to 33 lamps, or less
34 to 46 lamps, or less
47 to 65 lamps, or less

No. 14 or larger
No. 12 or larger
No. 10 or larger
No. 8 or larger
No. 6 or larger

If the house contains more than sixty-five
lamps, it is advisable to have more than one
distribution center and pair of mains.

A third wire, two sizes smaller than these
mains, must also be run from the attic to the
basement, through the distribution cabinet, to
make possible the use of the three-wire system.

Wires running parallel to joists must be
fastened on porcelain knobs, placed on different
timbers, and kept as far apart as possible. In
passing through joists, floors, and other wood-
work, the holes must be bushed with porcelain
tubes, which must extend at least i inch through
the wood and be so arranged that their weight
will tend to keep them in place rather than to
cause them to slip out.

All wires must be kept at least 10 inches
away from one another, from gas or water pipes,
iron beams, bell or annunciator wires, speaking
tubes, furnace pipes, and other conducting
materials, except at the distribution cabinet and
fixture outlets. Where wires cannot be kept
this far apart they must be run in conduits.

Flexible insulating conduits must be used at
outlets. Special care must be taken to insulate
from the gas pipe at outlets.

INTERIOR WIRING

S44

Runnier
Alone Brfck
or Stone

Ctir-Oat «t)d

laipecHon.
Certificate,
and
ParcaeoC

Brick and stone walls must be avoided wher-
ever possible. Wherever wires pass along them*
they must be incased in approved coiidnits.

There must be supplied and installed by the
contractor a raain-line cut-out and a quick -break
switch, both double- pole, to be located in the
attic at the end of the feeder lines. These
devices must be approved by the Underwriters
as capable of breaking the current for the
total number of lamps wired, at either 110 or
220 volts. Knife switches, if used, must be
so connected that they open downwards and
the blades must be "dead" when the switch is
open, and must be mounted in an asbestos
or slate-lined box provided with a similarly
lined doon

The contractor most notify the Underwriters'
Association of the progress of his work in time
to have a thorough inspection made {2 days
before work is concealed at least). He must
secure a certificate from that Association stating
that the work is suitable for use on 110- or
220-volt service, two- or three-wire systems*
before any payments shall be made to him.

SWITCHES

28. Switches located at various points on the walls of

rooms are a great convenience and should be installed on
all first-class jobs of any magnitude. The single-pole snap
switch (for not more than 660 watts) is the simplest and
cheapest. It opens one side of the circuit only. Next in
frequency of its use is the double-pole snap switch for larger
chandeliers or groups of lights. In addition to these, there
are a number of special uses of switches to allow lamps to
be controlled from two or more points,

29, Control of liamps From Tvro Poitits.— -Fijj. 18
(a) and (^) shows a switching arrangement for controlling

§44

INTERIOR WIRING

the light or group of lights L from two points A and B.
This scheme is used principally in halls where it is desired
to control the light from either up or down stairs. It
requires two three-point switches 5, S, which are here
shown as simple lever switches. There are a number of
different makes of switches for this purpose, but the prin-
ciple of all is the same, though the mechanical details may
differ. By comparing the diagrams with whatever make of
switch he may have to install, the wireman should have no

Pio.18

difficulty in getting the connections correct. By examining
the connections, it is seen that the lamps L may be lighted
or extinguished from either point. Either method of con-
nection (a) or (3) may be used, and the one that will be
most convenient in any given case will depend to some
extent on the general layout of the wiring.

A modification of this arrangement is shown in Fig. 19 (a)
and {b). In this case, one of the three-way switches is

INTERIOR WIRING

§44

f-tam

_ M&m_

replaced by a three-way socket. By using a three-way
socket on the fixture in connection with a three-way switch

oa the side wall, a
lamp may be turned
on or off either at the
socket or at the switch.
Both schemes of con*
nection {i^) and {b)
accomplish the same
resulti and the one that
is most convenient in
any case will depend
considerably on the lo-
cation of the supply
mains.

5o^sf Switch

Mmn

<pi

PiO. 19

30. Control of
Ijl^htB From Three
or More Points. — ^To

control lights from
three stations, as indi-

cated in Fig^* 20, it is necessary to use two three-point

switches A^ C for the end stations and a four-point switch B
for the middle station. When B is in the position shown,

Mfffj

45^

FI0.2D

points 1 and 2 and points S and 4 are connected togfether-
When the switch is turned, these connections are broken and

§44

TNTERTOR WIRING

points 1 and 3, 2 and 4 are connected* By tracing out the

path of ihe current, the student will see that the lights may
be turned on and off from any iitation independently of the
position of the switches at the other stations. By cutting in
a four-point switch for each additional station this scheme
can be extended to any number of stations desired, and !s
often used for stairways in apartment houses,

31* Electrolier Switches, — These switches usually
have three or four points and are used in connection with
electroliers to enable a part or the whole of the lights to be
operated as desired; sometimes they are mounted in the
electrolier itself. They are made in a variety of forms and
the connections necessary are, as a rule, easily understood
by an examination of the switch that it is proposed to use*

32. Snap Switches. — Fig. 21 shows a typical single-
pole snap switch; the same type of switch is made double-
pole; also, three-point and four-point for the control of lamps
from two or more stations. The wires come through the
porcelain base of the switch and are held in posts a ^, which

Fio.31

also carry the switch contacts. When the switch is closed, the

rotary cross-piece c makes connection between posts a b, thus
closing the circuit. A double-pole switch has two pieces c
and four contact posts. It is desirable to have snap switches
provided with an indicating dial, as shown in Fig, 21 (a),

INTERIOR WIRING

§44

unkss the position of tlje switch handle shows clearly
whether the switch is **on" or *'uff/* Indicators are specially
useful when a number of switches are mounted together*
Snap switches are comparatively inexpensive but they pro-
ject from the wall and do not make as neat a job as flush
switches, which set into boxes placed in the walk With
conduit wiring, flush switches are nearly always used and,
even with concealed kno1>and-tuhe wiring they are used on
jobs where a neat appear^ice is desired.

Fig, 22 (a) shows the jjeneral appearance of a flush
switch of the push-button type. The mechanism (d) is
double pole and when the light button is pushed in, cross-
piece cc swings around and niakes contact between clips a
and ^* In order to prevent arcing at the contacts, all
switches are constructed so that they will open or close with
a quick positive motion.

When switches arc mounted flush, an iron box must be
provided in which to place them. This box may be either
of cast iron or stamped steel and must completely enclose

§44

INTERIOR WIRING

the switchi thus providing a protection in addition to the
usual porcelain base that carries the switch mechanism-
Fig. 23 shows a stamped-steel switch box* The cover,
which carries the switch, is attached to the box by means
of screws passing through slotted holes.
This allows the switch to be placed squat ^.'
even though the box may have been
mounted slightly crooked or displaced
sJightly during the installation of the
wires. Steel boxes can be obtained with
any combination of inlet holes so that
they can be suited to wires coming in
Irom any direction. In many cases the
boxes are made so that pieces of metal
can be knocked out, thus making holes wherever desired.
There should be no holes in the boxes other than those
used for bringing in the conduits.

Fio. 38

F1XTUKE8

33 p The selection of suitable fixtures and the proper
wiring of them are important matters. The wireman should
not be satisfied to put up any fixtures that may be furnished*
He should examine them and test them himself* The fol*
lowing rules should be observed;

Flxtures^ —

a. Must» when supported from the gas piping or
any grounded metal work of a building, be insu-
lated from swch piping or metal work by means
of approved insulating joints placed as closely as
possible to the ceiling.

Das outlet pipes must be protected above the insulating
joint by approved Insulating tubing* and where outlet tubes
are ujied they must be of sufficient length to extend below
the insulating joints and must be so secured that they will
not be pushed back when the canopy is put in place-

Where canopies are placed against plaster walls or ceilings
in fireproof huildings or against metal walls or ceilings or
plaster walls or ceiiinjcs on metallic lathing in any class of
build ings, they must tie thoroughly and permanently insu-
lated from such walls or ceilings.

46B— 2a

INTERIOR WIRING

§44

b. Must have all burrs, or fins, removed before

the conductors are drawn into the fixture,

c. Must be tei^ted for contac:ts between conduct-
ors and fixture, for short circuits, and for ground
connections before it is connected to its supply
conductors.

34* Rule (c) is important. In wiring up fixtures, it is
an easy matter for the fixture wire to become grounded on
the shell and all fixtures should be thoroughly tested with a
mag^neto before they are connected to the circuit. It is much
easier to locate the faultsi before the fixtures are put up than
it is after. In connecting fixtures to the line wires, all joints
should be soldered and thoroughly taped so that there will
be no danger of groimding or short-circuiting when the
canopy is pushed up in place. Particular attention should be
given to the connecting of the lamp sockets j this is a part of
the fixture wiring that is often slighted and causes many
short circuits and grounds. Great care should be taken to
see that the sockets are good, and also that they are strong
enough to bear the weight of shades. Faulty sockets are
more likely to cause trouble on fixtures than on drop cords,
for the socket itself is always grounded on the fixture, and if
either wire becomes grounded on the socket shell, it is in
consequence grounded on the fixture.

mSlTQATING JOINTS

35. The Insnlatloj? Joint is the most important elec-
trical fitting used in fixture work; joints are made for all pos-
sible combinations. Fig. 24 shows a very good stylej piece a

screws on to the gas
pipe and d to the fix-
ture* The parts are
separated by insu-
lating material rf. and
the outside of the
joint is covered with
molded insulation d. The gas pipe above the joint must
be covered by an insulating tube» as required by rule (a),

PiO. 24

§44

INTERIOR WIRING

Art, 33, and after the outlet wires have been soldered to the
fixture wires the joints should be carefully taped and the wire
bunched in below the insulatini^ joint so as not to interfere
with the canopy. In connecting insulating joints to the gas
pipe* red lead or white lead should not be used; asphaltum or
some similar insulating compound is preferable. Insulating
joints should be tested before being used
and canopy insulators should be installed
as required by rule {a}. In ordinary
dwelling houses, where the ceilings are
plastered on wood lath, or in other non-
fireproof buildings where there Is no metal
work about the ceilings or walls, it is not
necessary to use canopy insulators. The F10.25

canopy is the brass cup-shaped piece used at the top of fix-
tures to cover the joint. It is in contact with the fixture;
hence* it is important that it be insulated from metal ceil-
ings, or else all the benefits derived from an insulating joint
will be lost. Fig. 25 shows a canopy insulator, which is simply
an insulating ring placed between the canopy and the ceiling.

36. The E. M, F. between the wires used on electric
fixtures must never exceed 300 volts and the wires must not
be smaller than No. 18 B, & S, gauge. If wires are secured
to the outside of fixtures, as is sometimes the case when old
gas fixtures are fitted with electric light, they must be
fastened so that there will be no danger of the insulation
being damaged by the pressure of the fastenings or by the
motion of the fixture. The wire used for fixtures must be
rubber-covered » and may be solid or stranded. Special wire
is made for this purpose*

Fixtures should be firmly fastened in place.* Combination
fixtures are supported by the gas pipe but plain electric
fixtures are generally fastened by screwing them into a wall
or ceiling plate, or crowfoot. This method is satisfactory if
a solid wood backing is provided and the fixture is not very
heavy. In the case of heavy electroliers, the pipe should
extend through the ceiling and be firmly fastened to the

INTERIOR WIRING

§44

joists or other secure support* In cas^e outlet boxes are
used, as with conduit work, the gas pipe extends through the
box and carries the fixture if a combination fixture is used.
For plain electric fixtures, the outlet boxes are provided

With a threaded projection, which holds the fixture, the out-
let box serving as a base or crowfoot. Pig- 26 (a) shows

the arrangement of a plain electric fixture and a combination

fixture connected to outlets
wired on the concealed knol>
and-tube plan. The flexible
tubing projects through the ceil-
ings as shown, and is connected
to the fixture wires* In the
combination fixture (*), the fix-
ture wires are run between the
outer shells and the gas pipe^.
When old fixtures are to be
wired, they must be taken down

and supplied with insulating joints. Sockets may be attached

to old gas fixtures by means of spars Fig* 27, that fasten to

the fixtures at the gas burners.

§44 INTERIOR WIRING 47

liOCATION AND DISTRIBUTION OF liAMPS

37. The character of the lamps to be used and their
location is a matter that must be determined in each case by
the purpose for which the lamps are installed. For signs and
decorative work, they are used solely to attract attention or
to produce ornamentation. In interior lighting, their purpose
is to illuminate other objects either close at hand, as with
desk lamps, or at a somewhat greater distance. Where
illumination is the sole requirement, the lamps should be
placed where they cannot be seen, but where they will throw
their light on the object to be illuminated, as on the stage
of a theater. In general work, however, it is not possible
to place the lamps in this manner, but they should be placed
where they will not be too conspicuous. When they must
be in view, the lamps should be surrounded by shades that
will diffuse the light and take away the glare. Frosted
globes are of assistance in many places, but it is better to
have the light diffused by a shade. Shadows should be
avoided as much as possible.

38. Chandeliers are usually relied on for general illumi-
nation. They should be hung high to get the best effects,
and should never be as low as the level of the eye of a
person standing. Borders or rows of lights placed on the
ceiling near the walls give very good illumination without
hurting the eyes. To get the best illumination with the
smallest number of lamps, the walls and ceilings should be
finished in light colors or in white and should be kept clean.
It is cheaper to retint ceilings than to burn many lamps;
this is especially true of stores, where much illumination is a
necessity. Walls papered in dark colors and woodwork of
dark, rich wood make it almost impossible to light a
room brilliantly.

On account of the great influence of the color of walls,
height of ceilings, etc. it is impossible to give other than
very approximate figures for the amount of light required
for illuminating a given room. For rooms requiring ordinary

INTERIOR WIRING

§44

illuminatian and having ceilings about 10 feet high, about
*25 to .29 candlepower per square foot should be sufRcient.
For roomB with high ceilings ,45 to .5 candlepower per square
foot should be allowed, and for very brilliant lighting in ball-
rooms or similar places, the allowance may be as high as
1 candlepower per square foot Of course » these figures
are for cases where the whole room is to be generally illu-
minated; when the light is used locally, as at desks or read-
ing tables, it may not be necessary to have the room generally
illuminated and the allowance per square foot might be much
less than that indicated by ihe above figures.

CONDUIT WIRING

EARLT COI!«3BUlT SYSTEMS

39- A number of years ago, before there were uniform
rules governing the installation of wires to make them safe,
it was a common practice to use, for electric lighting, wires
wound with cotton thread saturated with paraffin* These
wires were fastened with wooden cleats nailed against the
walls and ceilings. Signal and bell wires are still some-
times put up iu this way* The first step in the direction of
improvement was limiting the number of incandescent lamps
allowed on a given size of wire. The next was the substi-
tution of ** weather-proof** or "Underwriters' " wire for the
paraffin-covered "office wire/* Later came the porcelain
cleat, which was not in general use before 1892,

The manner of installing wire in concealed work has
undergone a similar evolution* At first wires were pulled
through holes in the joists and installed without any pro-
tection other than their insulating covering; sometimes even
two wires were pulled through the same hole, but this was
not long tolerated* EVogress came along two distinctly dif-
ferent lines: one that of insulating the wire by the use of knobs
and tubes, as previously described; the other that of providing
a continuous racewayj or conduit, for the conductors*

INTERIOR WIRING

One of the first conduit systems and one that came into
very extensive use» though it is not now allowed by the
Underwriters, was that of the Interior Conduit and Insula-
ting Company* It was made of paper wound in an ingenious
manner, so as to form a tube, and coated with tar inside
and out. These tubes were installed as a continuous race-
w^ay from outlet to outlet, and one or two wires, as happened
to be most convenient, were pulled into each conduit.

These paper tubes were very brittle, and the system was
improved by covering them with a thin shell of sheet brass.
Then came the requirement that the conduit should never
contain more than one wire. At one time, "brass-covered
interior conduit work" was considered the best possible kind
of construction,

An excellent tube that may be used in some places, though
not approved as a conduit proper, is the flexible Clrciilar-
Ijoom tube. This is a woven tube treated with insulating
material that makes it hold its shape. It has no metal
covering, but is stronger than the brass-covered interior
conduit and more convenient to use* It will be permitted
under the present rules only in special cases, as it is not
waterproof or nail*proof* It is very useful for fished work in
connection with knob-and-tube wiring and also for protecting
wires at outlets. This tube must not be used in places
exposed to moisture.

APPRO YED COMDiriT SYSTEMS

40* The conduits now approved by the Underwriters are
iron pipes with or without insulating lining, and flexible
armored conduit made of interlocked steel tape. They are
divided into two classes — llntd and uniimd. When unlined
conduits are used, an additiona! braided covering must be
placed on the wire, the idea being that the extra braiding
on the wire takes the place of the lining in the pipe.

Formerly, most conduits were lined, but it is now customary
to use unlined conduit with wire having extra heavy braiding.
Twin wire is generally used, the two wires being covered
with a common outer braiding.

INTERIOR WIRING

§44

Fig. 28 shows a piece of iron-armored, lined condtiit; a is
the armor about i inch thick, which is the same as ordinary

gas pipe; b is the insulating lining, not less than A inch

thick and adhering to the outer pipe. Conduit, whether

lined or unlinedt is put up in the same manner as a good job

^^m o£ gas- fitting. In fact, unlined conduit is practically

the same as gas pipe except that the interior surface

is galvanized, enameled, or otherwise treated to make

it smooth and to keep it from rusting. Great care

should be taken at the joints to see that the pipe

is reamed and that the ends come together, so as to

form a smooth runway (free from burrs) for the

wire. In many places the conduit may be bent and

the use of an elbow, with its threaded joints, avoided.

There are several devices on the market for bending

conduit » but about as good a way as any to bend

*#^ conduit is to get a good stout piece of spruce or hard

\iffr pine and bore a hole in it a little larger than the

FI0.2S conduit* The pipe is then passed through the hole

and the bend easily worked in. Another improvised form

of bender is made by securing a short piece of li-inoh

pipe into a 1 J-incb T and clamping the piece of pipe in a vise.

The conduit can then be passed through the T and bent to

any desired shape. For iron-conduit wiring, the wireman

should be provided with a regular outfit of pipe*fitter's tools*

41, Most conduit wiring is now carried out on the single-
tube system, i. e,, both wires or a twin wire are run in the
same conduit. This plan requires less conduit and labor
than the double-tube system and :s, in faet> the only allowable
arrangement when alternating currents are used. In the
case of a large church » supposedly wired for 52 volts, 2 per
cent. loss, the contractor ran the wires in separate pipes^
with the result that when the current was turned on only
13 volts were obtained at the lamps. It is cheaper, as well
as better, to use twin or concentric conductors in a single
conduit, except for very large cables that are to carry direct
currents.

INTERIOR WIRING

42. Use of Outlet and Junction Boxes. — Since in any
conduit system the primary object is to have the wires
arranged so that they can be withdrawn, it is necessary,
whenever a branch is taken off, to provide a Junction box
of some kind, because splices cannot be made at intervening
points without interfering with the withdrawal of the wires.
Conduit wiring is, therefore, done on the so-called loop

Offcut

Cut§ltT

fa)

CiffdMtr

r»^

Pio. 29

system. This will be understood by referring to Fig. 29
(a) and {b)\ L, L, L, etc. are lamps on one circuit that is to
be supplied from a panel board or distributing center located
at A, In (a), the wiring is indicated as it might be done
with the ordinary knob-and-tube system, using branches
whenever they will reduce the labor and the amount of wire
necessary; {b) shows the same lamps wired on the loop
system, using outlet boxes b and looping out the twin wire
at each lamp. No branches are taken off between outlet

INTERIOR WIRING

S44

boxes ^ and by disconnectmg the wires mnmng to the lamps,
the main wires can be withdrawn.

The loop system using iron conduits is, of course^ very
much more expensive than the knob- and- tube system* It
is, however, much more permanent in character and is the
only style now used in the best class of buildings* The
best method of running the conduit, so as to save bends and
make the conduit as short as possible, must be left to the
judgment of the wireman. In laying ont such wiring, he
must remember that the two wires are run together and
that he cannot make short cuts with single wires, as in
knob-and-tube work,

43 » Conduits less than I inch inside diameter are not
allowable, and an outlet box must be provided at each outlet*
When branch lines are taken off* a junction box must be
provided* Junction boxes and outlet boxes are manufactured
in a large variety of forms to accommodate conduits comingf
into them from different directions. Fig. 30 (a) shows a
round cast-iron junction box. These boxes should be

mo.m

mounted firmly in the wall and be placed so that the surface
will come flush with the plastering* The split nuts a, a hold
the conduit in place.

Fig* 30 U) shows an outlet plate. The conduit is
clamped in openings a and the gas pipe is clamped in ^-
Outlet plates must not be used unless it is impossible to
install a regular outlet box. Outlet boxes used with lined
conduit must also be lined and all boxes, whether lined or

§44

INTERIOR WIRING

iinlined, must be enameled, galvanised, or atberwise treated
inside and outside so as to prevent rust. Very convenient
junction and outlet boxes are now made of stamped steel and
are arranged so that one or more openings may be made in
the side by taking out a small disk. Fig, 31 shows a box of
this kind. The conduit enters the box and, projecting
through it about i inch^ is held in place by an insulating
cap a that screws over the end
on the inner side, A check-nut b
screws up against the outside of
the box- Fig. 32 shows these
fittings more in detail. Boxes of
this type may be suited to different
locations by simply knocking out
or removing the disks whenever
openings are needed. This avoids
the necessity of carrying a large number of different boxes
in stock. Outlet boxes may be obtained that are pro-
vided with special covers to accommodate almost any make
of flush switch.

When a change in the size of wire is made in a junction
box, it is necessary to protect the smaller wire by a cut-out.
Special cut-outs are made for mounting in junction boxes,

Fio. 31

!n^ut&tt&n

Fio. 82

but in most cases the wiring is laid out so that all fuses will
be grouped on panel boards arranged in cut-out cabinets,
each branch circuit running directly from the panel board to
the lamps.

44* Fig. 33 shows one method of arranging a ceiling
outlet tor a combination fixture in a fireproof building

INTERIOR WIRING

§44

wired with iron-armored conduit* The floors are made of
hollow tile placed between I beams. On top of the I beams
wooden stringers are laid and the rough flooring is laid
diagonally on these stringers. The finished floor is laid
on top of the rough flooring. The gas pipes and electric
conduit are laid in the space between the under side of the
rough flooring and the top of the hollow tile. After the
pipes and conduit have been laid, this space is filled with
concrete. The conduit elbows and the gas pipe are brought
down through the tile to the steel outlet box a. The ends
of the conduit are provided with insulating nipples *, b^ and
the gas pipe c, where it passes through the box, is provided

Pjq. 33

with an insulating sleeve d. The wiring is on the loop
system, the twin loop e being brought down from the conduit
and the wires in it attached to the fixture wires as shown.
The canopy is separated from the ceiling by the canopy
insulator /, Of course the arrangement of outlets will differ
cons>iderably as to details, depending on the style of the
outlet box used and the method of bringing down the conduit
to the box. In general, the conduit should tie brought down
so as to necessitate as little cutting of the arch as possible;
the outlet box should be well secured to the conduit, and the
fixture must be firmly supported.

§44

INTERIOR WIRING

Fig* 34 shows an outlet far a fixture or bracket where the
outlet box is mounted against a brick walL In ibis case the
outlet is ioT electric light only^ and the fixture is supported
by screwing it on to a threaded stud fastened to the back of
the box. The outlet is wired on the loop system; hence, two
conduits are necessary, one to bring the twin wire down and
the other for the return. A double*po1e wait switch would be
wred in the same way» so far as the arrangement of outlet
box and conduit is concerned, but the loops would, of course,
be cut and the terminals attached to the switch. In some
cases where outlet boxes are mounted
on brick walls it may be necessary to
cut out the brick so as to bring the
outer edge of the box flush with the
plaster, but generally the wooden
strips, or furring, nailed on brick walls
to take the lath will make sufficient
depth between the surface of the
plaster and the brick wall to take the
outlet box. Outlet boxes should be
secured in place by first drilling and
plugg^ing the brick and then fastening
the box with screws or nails.

When laying out a job of conduit
wiring, the first thin^ to do is to
locate the distribution cabinets and
then the various outlets for lamps,
switches^ etc., as specified on the
architect's plans* Too much care cannot be taken in properly
locating these boxes; when a building is in rough condition
with nothing in place other than rough walls or partitions, it is
an easy matter to make mistakes in locating outlets, with the
result that when the rooms are finished the outlets are found
to be out of place and can only be fixed by doing some of the
work over again or possibly by having to install molding.
All outlet boxes should be put in place before any conduit is
run; the vvireman can then see just where the outlets are
located and can plan the work so as to use the minimum

INTERIOR WIRING

§44

amount of conduit and labor. Switch outlets should be

placed about 4 feet 3 inches from the floor and side-bracket
outlets about 6 feet. Firm supports should be provided for
outlet boxes in all cases; oo ordinary walls or ceilings boards
should be nailed across between the joists or studding.

45* wire Used in €onauIt@. — Single wire used in
lined conduit is the same as rubber-covered wire used for
other low- voltage work. If twin wire is used, each conductor
must comply with the requirements for other low- voltage,
rubber- cove red w^ire, except that each wire may be taped
instead of braided, and there must be a braided covering over
the whole. For unUned conduits, the same requirements
hold, and in addition the wire must be provided with an extra
braiding at least ^^ inch thick.

46, The following are some of the more important rules
relating to the installation of conduits:

• Interior Conilults —

The object of a tube or conduit Is to facilitate the insertion
or extraction of the conductors, and to protect them from
niechanical injury. Tubes or conduits are to be considered
merely as raceways, and are not to be relied oo for insulation
between wire and wire or between the wire and the ground.

d. No conduit tube having an internal diameter
of less than ^ inch shall be used; measurement to
be taken inside of metal conduits.

b. Must be continuous from one junction box to
another or to fixtures » and the conduit tube must
properly enter all fittings.

In case of underground service connections and main
runs, this irvc^lves ruaning each conduit continuously into
^ a mam cut-out cabinet or gfntter surrounding the panel
board, as the case may be.

€. Must be first installed as a complete conduit
system, without the conductors.

d. Must 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 bos:es.

In btiildinp^s already constructed where the conditions ate
such that neither outlet bos nor plate can be installed ^ theso

§44

INTERIOR WIRING

appliance roay be oraitterl by permis.sion of the Inspection
Depart lue tit having jurisdiction^ provided that the conduit
ends are bushed and secured,

£, Metal conduits, where they enter junction
boxes and at all other outlets, etc., must bo pro-
vided with approved bushings 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.

A Must have the metal of the conduit perma-
nently and effectually grounded.

It IS essential that the metal of conduit systems be joined
so as to afford electrical conductivity sufficient to allow the
largest fuse or cSrcuit-breaker in the circuit to operate before
a dangerous rise in temperature in the conduit system can
occur. Conduits and gas pipes must be securely fastened in
metal outlet boxes so as to secure good electrical connection.
Where boxes us^ed for centers of distribution do not afford
good electrical connection, the conduits must be joined
around them by suitable bond wire«* Where sections of
metal conduit are installed without being fastened to the
metal structure of buildings or grounded metal pipings they
must be bonded together and joined to a permanent and effi-
cient ground connection*

g. Junction boxes mtist always be installed in
such a manner as to be accessible,

h^ 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
not to be less than 3i inches- Must have not more
than the equivalent of four quarter bends from out-
let to outlet, the bends at the outlets not being
counted,

47, While a conduit system is considered merely as a
system of raceways for the wires, if it is properly installed,
all joints firmly made, and an efficient ground provided, it
serves the purpose also of an additional protection. No
ground can then occur anywhere in the concealed wiring in
the building except on the conduit, and if that is grounded
to the earth, it cannot do any damage. If two grounds
should occur on opposite sides of the line, a "dead" short
circuit would be formed through the walls of the iron pipe.
Tbis will blow the fuses on the lines affected, disconnecting
themj but doing no other damage* In a job of conduit wiringi

INTERIOR WIRING

§44

the conduit is, of course » installed during the construction
of the building before lathing and plastering are done. The
wires are, however, not drawn in until all rough work on the
building is completed [note rule (c)].

There has been much discussion as to what constitutes a
permanent and effectual ground in such work. In small
installations the ground should be of as great carrying capac-
ity as the conductors within the conduit* In large plants
this is not practicable* Where conduits pass from junction
box to junction box, they should be well connected, electric-
ally as well as mechanically, to the metal of the boxes, so
that no part of the conduit system will be insulated from or
in poor contact with the rest of the system* If good contact
cannot be made between the pipe and box, the pipe should
be carefully cleaned on each side and a copper- wire jumper
connected around the box.

Screw joints between varioits lengths of pipe and between
pipes and junction boxes and cut-out cabinet frames are to be
preferred to all other kinds of joints, because they are more
secure and afford better electrical contact. To secure them
in an entire system, it is necessary to use a few right-hand
and left -hand couplings or a few unions. Where unions are
used, they should preferably be of brass, because brass gives

better contact at the sliding
joints than iron. In most
cases, however, instead of
a union or right-hand and
left-hand coupling, the
thread is cut well back on
one piece, the coupling
screwed on and afterwards screwed back over the other piece.
But owing to the difficulty of installing screw joints in all
places, and because other joints are easier to make and
require less expensive fittings (though not so good), many
systems have been designed in which other kinds of joints
are relied on. Whatever system is used» the workman must
not shirk the duty of making good pipe connections, which
are as importaDt as soidered joints on the wires.

F(0. s&

§44

INTERIOR WIRING

48. Flexible ArmorGd Contluit. — In order to avoid
joints and make the conduit cheaper and easier to install,
flexible nrmorecl oonclults have been brought forward.
Fig* 35 shows a piece of the Greenfield conduit and the

Fio. 36

tnethod of connecting it to a junction box. This conduit is

made oi interlocked steel ribbon wound spirally. It affords
a good protection to the wire against mechanical injury and

46B— 29

INTERIOR WIRING

§44

is easily installed^ but it is not waterproof. It is, therefore,
inferior to the iron conduit for damp places or where the
conduit has to be laid in concrete.

49. Drawing Wires In Condiilts.^ — When the wires
are to be drawn into conduits, soapstone should be blown
through first, as it makes the wire sHde through more easily
and take the ells better. A * 'snake" is first run through,
the tube and the wire pulled through by means of it. The
snake usually consists of a steel ribbon about 1 inch wnde
with a ball about \ inch diameter on the end. If the conduit
has many turns, it is advisable to use a coiled spiral spring
about 4 inch diameter and 6 or 8 inches long with a ball on
one end and the other end fastened securely to the steel
ribbon. The end with the piece of spring is pushed in first
and the spring passes around the turns easily.

Fig. 36 shows one floor of a dwelling house wired .with
conduit. 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.

50» Wooden rn old lugs are used for running wires over
woodwork, on walls, door and window frames, and other
places where they cannot otherwise be well concealed*
Moldings put up on ceilings or walls should be arranged
symmetrically, so as to disguise their purpose, even though
it may be necessary to put up blank molding for this
purpose. Work of this kind is confined almost exclusively
to old buildings, and molding should not be used where it
can be avoided. The following rules relate to moldings:

Wooden Moldln^B —

a. Must have both outside and inside at least
two coats of waterproof paint or be impregnated
with a moisture repellent.

§44 INTERIOR WIRING 61

b. Must be made of two pieces, a backing and
capping and must afford suitable protection from
abrasion. Must be so constructed as to thoroughly
incase the wire and provide a i-inch tongue between
the conductors and a solid backing that, under the
grooves, shall not be less than J inch in thickness*

It iB recommeaded tbat only hardwood molding be used.

Wires—

For maiding- work:

Must have approved rubber-insulating covering.

Must never be placed in molding in concealed or
damp places or where the difference of potential
between any two wires in the same molding is over
StX) volts.

51. Irresponsible parties sometimes run w^eather-proof
wire in moldings. This practice is dangerous, for there is
practically no insulation except that on the wire, if the mold*
ing becomes damp; in cleat and tube work there is an air
space, and in conduit work an iron pipe, as an additional
protection. Moreover, a wire with an air space or an iron
jacket around it cannot do much damage even if it does
become very hot; but a wire embedded in wood if overloaded
excessively will char and possibly set fire to the wood.

Fig, 87

because the heat cannot easily be dissipated. For these
reasons molding work is now prohibited in some of the larger
cities. Dampness is the greatest enemy of molding work.

However, where hardwood moldings and rubber-covered
wires of sufficient size are used in places always dry, this
kind of work is quite safe. Moldings are especially conve-
nient in running border lights around the walls of rooms,
and in wiring for temporary displays, and other work of a

INTERIOR WIRING

§44

semipermanent nature. They should not be run on brick
walls where there is liability of moisture working through
from the back. They are made in a variety of styles i some
of which are ornamental and nicely finished to match the
trimmings of the rooms in which they are used* Fig. 37
shows a typical two-wire molding that conforms to the
Underwriters' requirements, since it has the backing a and
capping d.

TESTS

52. After a job of wiring has been completed, tests should
be made to see that all connections are correct and also that
there are no groimds or crosses between the wires. All
circuits should be tested before fixtures of any kind are put
up, and each fixture should be tested carefully before it is

PiO.38

put in place. Fixtures when received from the factory are
not usually wired ^ and connecting the sockets, etc. must be
done before they are put in place. If this is not carefully
done, the fixture wire is apt to become grounded; hence, the
necessity of testing out fixtures before they are put into

§44 INTERIOR WIRING 63

position. For most of this testing a masrneto-bell is used.
This is a small hand-power electric generator connected with
a bell similar to the call bell on a telephone. In Fig. 38, /, /'
are the terminals to which wires are attached in order to test
any circuit; when a circuit is established between them the
bell rings. These instruments are designed to ring the bell
through resistances of 5,000 to 10,000 ohms, or more,

53. Each branch circuit should be tested by connecting
its terminals at the panel board or cut-out with the magneto.
The wires at all the outlets should be separated and the cir-
cuit rung up. If no ring is obtained, it shows that there is
no cross between the wires. The wires coming out of each
outlet should then be touched together in turn and also their
corresponding switch outlets, if there are any, to see if the
connections to the outlets are all right. After each outlet is
rung up, its wires should be left separated. Each side of
the circuit should then be tested for grounds. If it is a con-
duit system, one terminal of the magneto should be connected
to the sheathing and the other to each side of the circuit in
turn. If no ring is obtained on either side, it shows that
the wire is clear of grounds. If a ring is obtained, the ends
should be carefully examined, and if necessary the wire
must be drawn out and examined. In knob-and-tube work
the method of testing is practically the same, only in test-
ing for grounds one side of the magneto may be connected
to a gas or water pipe. Each fixture should be subjected
to similar tests, and after all the fixtures are in place, the
system as a whole should be tested.

54, Unden?vTlteps' Tests. — An insurance inspector
usually tests each branch line with a magneto for con-
tinuity, short circuits, and grounds. He then usually
counts up the number of lamps on each circuit and notes
the sizes of wire used to see that no wire is overloaded when
all the lamps are on. Concealed work must be inspected
before the lath and plaster are put on, otherwise it will not
be passed without special investigation; this means tearing
up floors and walls, which is expensive to say the least.

INTERIOR WIRING

§44

In most Installations, where the inspector has no reason
to sUvSpect that any fatiUy material has been used, he is
able to satisfy htm self by these tests and by examining^ the
work with his eye; in fact, in niany case^^ an ocular inspec-
tion is the only inspection made by the authorities, if they
are satisfied that the contractor is honest and has made the
other necessary tests.

55. Where more partictilar attention is given to a piece
of work or where it is desired to learn whether an old

installation or one not properly inspected at the time the
work was done is up to the standard of safety, the insulation
resistance is measured*

Insulatton Heslstance —

The wiring in any building must test free from
grounds; i. e., the complete installation must have
an insulation between conductors and between all
conductors and the ground (not including attach-
ments, sockets, receptacles, etc.) of not less than
the following:

Up to
Up to
Up to
Up to
Up to
Up to
Up to
Up to
Up to

5 amperes

10 amperes

25 amperes

50 amperes

100 amperes

200 amperes

400 amperes

800 amperes

1,600 amperes

4,000,000

2,000,000

800,000

400,000

200,000

100,000

25,000

12,500

ohms

ohms
ohms
ohms

ohms
ohms
ohms
ohms
ohms

All cut-outs and safety devices should be in place
when the above test is made.

Where lamp sockets, receptacles, and electroliers,
etc* are connected, one-half of the above will be
required.

Where lamps or other devices are suspected of taking
more current than they should or where the load on any
line is, for any reason, in doubt, the current should be
measured with an ammeter.

§44 INTERIOR WIRING 66

MEASUREMENT OF DROP, IN VOIiT8

56. If the current can be turned on in order to make a
test of the drop in voltage, the best way is to use a volt-
meter and determine the actual drop on each line at full
load. With an ordinary voltmeter, the best method is to
have two pairs of test cords and plugs connected to a double-
pole double-throw switch. One pair of test cords should
run to the distribution center; the other should run to the
fixture to which the drop is to be determined., The switch
should be so connected to the voltmeter that a reading of
the voltage at the end of one pair of cords can be taken one
instant and that at the end of the other pair of cords the
next. The difference is the drop, in volts, on that line. All
of the lamps should be turned on while the measurements
are being taken, and several sets of readings should be made,
because currents supplied from central stations suffer varia-
tions in voltage.

MARINE WORK

57. Wiring on board ships is subjected to some special
conditions and therefore requires special treatment. The
first important condition not usually met with on land is the
motion of the ship, which makes it necessary to avoid all
forms of construction where chafing or breaking might take
place. The second important peculiarity is the, constant
dampness of the atmosphere. For these and other reasons
a separate code has been prepared for marine work, from
which the following rules are selected. They embody the
Aief points in which marine work differs from other work.

Wires —

a. Must be supported in approved molding or
conduit except at switchboards and for portables.

Special permission may be given for deviation from this
rule in dynamo rooms.

b. Must have no single wire larger than No. 12
B. & S. Wires to be stranded when greater carry-
ing capacity is required. No single solid wire

INTERIOR WIRING

§44

smaller thao No. 14 B* & S, except in fixture wir-
ing to be used.

StraDded wires must be soldered before being fastened
under clamps or binding screws, and when they have a con-
ductivity greater than No. ID B. & S, copper wire, they raust
be soldered into lugs.

€^ Splices or taps in conductors must be avoided
as far as possible. Where it is necessary to make
them, they must be so spliced or joined as to be both
mechanically and electrically secure without solder.
They must then be soldered, to insure preservation,
covered with an insulating compound equal to the
insulation of the wire, and further protected by a
waterproof tape. The joint must then be coated or
painted with a waterproof compoundp

Wlifes for Molding^ Worlc —

a. Must have an approved insulating covering.

The insulation for conductors, to be approved, must be at
least A inch in thickness and covered witb a substantial
waterproof and fi a me- proof braid.

The physical characteristics sball not be affected by any
change in temperature up to 2(X)^ F. After 2 week?^' sub-
mersion in salt water at 70^ F*, it must show an insulation
resistance of 100 megohms per mile after 3 minutes' electrifi-
cation with 550 volts.

b. Must have, when passing through water-tight
bulkheads and through all decks, a metallic stuffinif
tube lined with hard rubber. In case of deck tubes,
they shall be boxed near deck to prevent mechan-
ical injury*

€* Must be bushed with hard -rubber tubing
i inch in thickness when passing through beams
and non-water-ti^ht bulkheads.

Wires for Conduit Work —

a. Must have an approved insulating coveringf.

The insulation for conductors for use in lined conduitSi lo
be approved, must be at least i^ inch in thickness and be
covered with a substantial waterproof and flame-proof braid*
The physical characteristics shall not be affected by any
change in temperature up to 200° F.

After 2 weeks' submersion in salt water at 70° F., it must
show an insulation resistance of 100 megohms per mile after
3 minutesi' electrification with 55() volts*

For unlined metal conduits, conductors must con-
form to the specifications given for Lined conduitai

S44

INTERIOR WIRING

and in addition have a second outer fibrous cover-
ing at least iV inch in thickness and sufficiently
tenacious to withstand the abrasion of being drawn
through the metal conduit.

b. Must not be drawn in until the mechanical work
on the conduit is completed and the same is in place.

c. When nm through coal bunkers, boiler rooms,
and where they are exposed to severe mechanical
injury, must be incased in approved conduit.

TABIiB V
TABI^ OF CAPACITY OF WIRES FOR MARINE WORK

B. & S. G.

Area. Actual
Circular Mils

Number of
Strands

Size of

Strands

B. & S. G.

Amperei

. 19

1.288

1,624

2,048

2.583

3.257

4.107

6,530

9,016

11,368

14.336

18,081

• 35

22,799

30,856

38,912

49.077

60,088

75,776

100

99,064

120

124,928

145

157,563

170

198,677

200

250,527

235

296,387

270

373.737

320

413,639

127

340

Portable Conductors —

Must be made of two stranded conductors, each
having a carrying capacity equivalent to not less
than No. 14 B. & S. wire, and each covered with an
approved insulation and covering.

Where not exposed to moisture or severe mechanical
injury, each stranded conductor must have a solid insulation

68 INTERIOR WIRING §44

at least A inch in thicknejis txntl rausi show an insulation
resistance h«iween conductors and between either conductor
and the ground of at least 50 meguhms per mile after 2 weeks'
submersion in water at 70° F., and b« protected by a slow-
burning* tough-braided t outer covering.

Where exposed \o moisture and mechanical Injury — as for
use on decks, holds, and fireroomft — each stranded conductor
shall have a solid insulation, to be approved, of at least
Vi inch in thickness and be protected by a tough braid. The
two conductors shall then be stranded together, using a jute
filling. The whole shall then be covered with a layer of
flax, either woven or braided, at least ^^ inch in thickness,
and treated with a non-infiaramahle, waterproof compotind.
After I week's submersion in water at 70*^ F,, it must show
an insulation between the two conductors? or between either
conductor and the ground of 5C* megohms per mile.

Wooden moldings must be constructed according: to the
requirements for ordinary interior-wiring work and in addi-
tion must conform to the following rules:

a. Where molding is run over rivets, beams, etc.,
a backing strip mu^t first be put up and the molding
secured to this.

5. Capping must be secured by brass screws,

Cut-Outs —

a. Must be placed at every point where a change
is made in the size of the wire (unless the cut-out
in the larger wire will protect the smaller)*

6. In places such as upper decks, holds» cargo
spaces, and firerooms, a w^ater-ti^ht and fireproof
cut-out may be used, connecting directly to mains
when such cut-out supplies circuits requiring not
more than 660 watts energy.

f , When placed anywhere except on switchboards
and certain places, as cargo spaces, holds, firerooms»
etc., where it is impossible to run from center of
distribution, they shall be in a cabinet lined with
fire-resisting material,

d. Except for motors, searchlights, and diving
lamps, shall be so placed that no group of lamps
requiring more than 660 watts shall ultimately be
dependent on one cut-out.

Fixtures —

a. Shall be moitnted on blocks made frotn well-
seasoned lumber treated with two coats of white
lead or shellac.

§44 INTERIOR WIRING 69

b. Where exposed to dampness, the lamp must
be surrounded by a vapor-proof globe.

c. Where exposed to mechanical injury, the lamp
must be surrounded by a globe protected by a stout
wire guard.

d. Shall be wired with same grade of insulation
as portable conductors that are not exposed to
moisture or mechanical injury.

e. Ceiling fixtures over 2 feet in length must
be provided with stay-chains.

WIRING ESTIMATES

58. It is difficult to lay down any reliable rules to be
used in estimating the cost of a proposed wiring job. As
when estimating in other lines of work, experience must
largely be relied on. The prices of labor and material vary
so widely in different sections of the country that any general
rules might lead to very inaccurate results. Moreover, these
prices are always fluctuating. One frequently sees state-
ments to the effect that certain kinds of wiring can be done
for so much per lamp or so much per outlet, but it is evident
that while such figures might be fairly correct so far as the
average of a large number of installations is concerned, they
might be far from correct when applied to individual cases.

59. The only way in which to obtain a fairly close esti-
mate of the cost of a given installation is to prepare plans
and lay out the circuits, marking the size of the wire and
the capacity of the various switches and cut-outs required.
By laying out these plans, the amount of wire, conduit, and
other material required may be arrived at quite closely.
The number of switches, cut-outs, etc. can be counted up
and their cost estimated. In measuring the length of the cir-
cuits, do not forget to take into account the wire and material
necessary for running up and down walls to switches or
outlets. Margin should be allowed for such material as
tape, solder, etc. The labor item will depend largely on
whether the building to be wired is an old one or one in the
process of construction, also on the style of wiring used, so

INTERIOR WIRING

that the labor item can only be determined from a careful
inspection of the premises to be wired and experience on

work of a similar class. An ordinary two-story dwelling
house wired on the concealed knob-and-tube system will
require about 6 days' labor of a man and helper. Some
small houses will require less than this. Old houses require
a much larg^er expenditure of labor^ because there is liable to
be considerable molding work to be done*

It is unsafe to assume a certain cost per outlet in fig-urinir
on a job of wiring unless one has been doing considerable
work of a certain class. As a rough guide, however, it may
be stated that ordinary dwellings wired on the concealed
knob-and-tube plan will cost from $2 to $3 per outlet,
This, of course, does dot include the fixtures » but should
cover the cost of snap switches and porcelain cut-outs.
Ordinary exposed wiring can usually be run for $1 to $1,75^
per drop, including rosettes, cord, and sockets, though,
of course, very much depends on how closely the lights are
grouped. It is evident that if the lamps are scattered very
much, the cost of wire, porcelain fittings, and labor will be
comparatively high, and this wnll increase the cost per drop.
Wiring with iron-armored conduit is expensive, but it is
substantiah For small installations, it will probably cost
from $5 to $6 per outlet; in large installations, the
cost will be somewhat less. It must be remembered that
these figures are only approximate. The cost in different
localities might vary widely from the above, and the only
way to make a fairly close estimate is to lay out the circuits,
make a list of the material needed, and estimate their cost
and the probable labor required. :

INTERIOR WIRING

(PART 3)

COMBINING SEVERAL WIRING SYSTEMS

STORE lilGHTINO

1. A large electric-light installation generally requires
many kinds of wiring, and there are usually special condi-
tions that determine what kind of work is to be done in each
locality. As an example, we will take the wiring system of
a certain department store as it was actually put in.

After a careful study of the conditions existing, the man-
agers of the store concluded that enclosed-arc lamps were
best suited for the general illumination of their stores, and
that incandescent lamps should be installed at desks, in
closets and warerooms, and occasionally in show windows.
Accordingly, the premises were wired for 250 enclosed-arc
lamps and 500 incandescent lamps at 110 volts.

Separate feeder wires were run to the ten departments.
Two dynamos were installed in the engine room in the sub-
basement, one of which was capable of supplying current for
one-third of the lamps and would be used when the load was
light, while the other was capable of operating two-thirds of
the lamps and some sm*all motors. When the entire load
was on, the two generators operated in parallel.

2. In order that light could be secured in case of a
breakdown of the plant, service wires from the Edison three-
wire system were brought into the basement and connected
to the switchboard in such a manner that this current could

For notice of copyright, see Page immediately followinM the title pag§
145

INTERIOR WIRING

[45

be used. The double-throw switches and connections nec-
essary to change over from Uie two-wire to the three- wire
system, where arc lamps dre used, are shown in dia^am in
Fig. 1 («)* A special four*pole double-throw switch was
installed* If there had been no arc lamps requiring the direc-
tion of the current to be constant, one three-pole double-throw

+ - + -
' — ^— I — 4—

-i-^

-g

-t-f?

^^=W

-?f

faj

+ - +- ±A nn

+/»_

Jl^

^^nr

(b)
Pio. 1

switch, connected as in Fig. 1 {b)y would have been sufficient.
The use of the three-wire system in this case involved no
saving in the lines, as that system extended only to the main
switchboard, beyond which the two-wire system was used.

3. The large feeder cables were run from the engine
room to the centers of distribution in each of the various

§45

INTERIOR WIRING

departments, in iron-armored conduits, one cable to a con-
daiL Cables and not wires were used, because heavy solid
conductori) cannot be drawn into conduits with bends in them.
These conduits were put together with screw couplings and
corner boxes of special design at each elbow^ as the cables
were very heavy. In the basement* the conduits were con-
nected together by locknuts and a bus-bar, which was g^rounded
to the water main back of the main valve on the automatic-
sprinkler system by an iron rod^ which was inserted in the
water pipe like a tap* This afforded an excellent ground.

4. Cut-out cabinets were installed in each department-
When in conspicuous places, they contained marble tablets
on which were mounted lugs to receive fuses. Enclosed
fuses were used and a switch was provided on the tablet for
each circuit. The tablets were mounted in hardwood cabi-
nets with plate*£lass doors that opened by sliding down-
wards like a window sash. In less conspicuous places, the
cabinets were provided with hinged wooden doors, were lined
with asbestos, and provided with porcelain cut-outs of the
enclosed-fuse type. For each enclosed-arc lamp, a separate
branch line was run from the nearest cut-out cabinet. Large
departments were provided with several cut-out cabinets con-
nected to the same pair of feeders.

5* The branch lines were run in various ways; some of

them were run in pipes* some in molding, and some were
run open. Where placed in pipes, twin conductors were
used and the lamps were hung from the pipe ends by means
of an insulating joint. All branch pipes were connected
together and to the feeder pipes at the cut-out cabinet in the
same way as the feeder pipes were connected together in
the basement

6. A drop of 2 volts was allowed in the mains and a drop
of 1 volt in the distributing wires for incandescent lamps.
All distributing wires for the arc lamps were No. 14, and
the resistances at the lamps were adjusted so as to secure
80 volts at the arc. From a distribution closet in one of the
busiest departments, twin conductors of No* 14 wire were

INTERIOR WIRING

§45

run to the grenerator switchboard, in an iron pipe, and con*
nected to a voltmeter on the switchboard. The terminals of
these pressure wires in the closet were connected, with proper
cut-out protection, to the terminals of the feeders* The
dynamo tender was, therefore, able from the indications of
the voltmeter to regfulate his machines so as to maintain a
constant potential of UO volts at the cabinets.

7» The show windows were lighted by enclosed-arc lamps
hnnif in the space above the goods displayed, but out of sight
from the street* Only the outer globes projected below the
dust-proof casing surrounding the window space. Thus*
brilliant illumination was secured with very little glare and
with great economy. The lamps were so arranged that they
could be lifted out of the globes whenever it was necessary
to trim them; but the globes were never removed, being
cleaned while in place. This arrangement proved very
effective and convenient. Additional circuits were run
to various points for connecting incandescent lamps and
special apparatus for holiday displays.

THEATER WIRING

8» The wiring of, theaters and entertainment halls pre-
sents some peculiar features. All the lamps must be con-
trolled from one pointy usually on the right wing of the stage.
Most of the lights on the stage are arranged in borders, or
long rows, that contain several circuits of lamps of various
colors, and are also usually provided with dimmers. There-
fore, the stage switchboard of a large theater is quite a com-
plicated affair compared with the distribution closets used in
ordinary work.

In cases where there are a large number of borders of
incandescent lamps, it is inconvenient to divide them into
circuits of only 660 watts* and permission can usually be
obtained from the Underwriters to place more lamps on such
circuits if special care is taken.

9. 8taK© dlmmera are of two kinds — resistance dexes

and rcaciive coils. The latter are more economical, but can be

§45 INTERIOR WIRING 6

used with alternating currents only. Resistance boxes can
be used with either direct or alternating current. Care must
be taken to locate them where they can be kept cool by the
circulation of fresh air. Reactive coils cut down the E. M. F.
applied to the lamps by inserting a counter E. M. F. in the
circuit. All kinds of stage dimmers must be thoroughly
fireproof in construction and must be mounted on fireproof
frames so that there will be no possibility of their setting fire
to adjacent objects. Old-style resistance boxes were fre-
quently provided with wooden casings, but this is no longer
permitted. There are many reliable types of fireproof dim-
mers and they can be obtained for almost any desired
range of current and voltage. In selecting dimmers of the
resistance type, care should be taken to see that all sliding
contacts are of ample capacity and substantially constructed.
Most of the dimmers in common use consist of a resist-
ance split into a number of sections, so that the amount of
resistance in series with the lamps may be varied. They
are made in a number of diflEerent forms, some of them being
arranged so that their operating handles interlock, allowing
them to be operated singly or together in any desired com-
bination. Dimmers are, of course, connected in series with
the circuits that they are intended to control.

WIRING FOR SPECIAIi PURPOSES

10, While in most work of a permanent character the
closet or cabinet system of distribution, with very slight drop
in the branch lines, is the proper system to adopt, there are
special conditions that sometimes make it desirable to install
wires for a very low price, for temporary or occasional use.
In such installations, the efficiency is of comparatively little
importance, but the proper regulation and uniform voltage
at the lamps are as important as in permanent work.

!!• Let us take a case, such as the installation of a thou-
sand 8-candlepower lamps for decorative purposes around
the cornices of a building at a fair, where the wires will be
up for a few days or weeks only. All the lamps are to be

46B— 30

INTERIOR WIRING

§45

burned at the same time. In such a case* it may be eco-
nomical to allow as much as 12.5 per cent, drop on the lines
and use lOO-volt lamps on 112,f5-volt service. One pair of
feeder lines will be run around the building, a distance of
1,000 feet. It is desired to have the drop such that there
will be 100 volts at any point between the lines when 112*5
volts is applied at the terminals; this can only be accom-
plished by running the lines in opposite directions and hav-
ing them change in size often enough to secure practically
uniform drop per foot, Figf. 2 (a) illustrates such an arrange- 1

fa^

^doafwef

Pin. 1

■>«»» ' fes

V — zsp — A

ment, and {0) shows the same thing drawn In a straight line
instead of a square. This is sometimes called the unit'
paraiiei method of feeding*

12. There will be a lamp for every foot, and there will
be required forty branches of No, 14 wire, with 25 lamps
on each branch, as shown in Fig. 2 {b}. Weatherproof
wall receptacles will be used. The total length of wire
in the mains is 2,000 feet. The length of wire to any
given branch is 1,000 feet; hence, the rate of drop must be
12,5. volts per 1^000 feet* On account of the method of
feeding from each end, it is easily seen in Fig* 2 {^) that

§46

INTERIOR WIRING

the length of wire through which the current flows to any
point (i must be 1,000 feet. The currents that various wires
will carry with a drop of 12,5 volts are as follows:

Size of

Volts

Rbsistancr phr

A «j"nD<'D t

Wins

Drop

1.000 Fkkt

XlMFtfKl

No. 14

12.5 -

- 2.521

4.96

No. J 2

12.5 -

- 1.586

7.88

No. 10

12.5 -

.997

12.5

No. 8

12.5 -

.627

19.9

No. 6

12.5 -

.394

31.7

No. 6

12,6 -

.313

39.9

No. 4

12.6 -

.248

50.4

The amperes for larger wires can be found by consulting

the tables in fniertar Wirings Part 2*

Since the lamps are to be 8 candlepower, there will be
about 1 ampere for every four lamps, and consequently for
every 4 feet of line (two wires). In making up a conductor
to have nearly uniform drop, it will be necessary to com-
promise for all points that do not exactly correspond with
the above -calculated current values. For instance » if No. 12
wire is joined to No. 14, it must be at a point where there is
between 4,96 and 7.88 amperes. If lengths of wire are
selected so that this joint will come half way between the
points where the wires exactly correspond, it will be near
enough. The results will then be as tabulated on the
following page*

In this table the second column is obtained by dividing
the volts drop (12,5) by the resistance per 1,000 feet of the
various sizes of wire. The third column is found by taking
the approximate value of the current multiplied by 4 because
there is 1 ampere for every 4 feet of cornice. The fourth
column is obtained hy taking one-half the difEerence between
the succeeding quantities in the third column and adding this
difference to the quantity in the third column. For example,
at a point 20 feet from the end, the current is 4,96 amperes
and at a point 32 feet from the end it is 7,8B amperes.
As stated above, lengths of wire will be selected so as to

INTERIOR WIRING

§4fi

bring the joints between the different skes of wire mid-
way between the points where the wires correspond. Hence,
in the first case, if there is a current of 7.88 amperes
32 feet from the f-nd and a current of 4.96 amperes 20 feet

from the end, the joint will be 20 -f

32-20

= 26 feet from

the end and 26 feet of No. 14 wire will be required. Also, in
the case of the No. 8 and No. 6 wires, there is a current of
19,9 amperes 80 feet from the end and 31,7 amperes 127 feet

SizPDf
Wire

Ainperes

Giving

12. s Volts

p«r i»ooo Feet

Corresponding

Dtstunee

From End of

Line

Distance of

End of Wire

From End of

Line

Length of
Wire to
Be Used

4^96

7.88

12. S

19-9

104

\ ^

31-7

127

144

^ S

39-9

160

181 '

50,4

202

228

63^5

254

287

80.1

320

362

loo.S

403

4S7

127.5

Sio

576

iig

160.3

641

7^4

143

000

201.6

S06

189

0000

25S-I

1,020

1,000

from the end; hence, the joint between the two sizes will be

80 +

127 - 80

= 103.5 feet from the end. In the table, the

nearest even number of feet is given, so that this is taken
as 104. In the case of the 0000 wire, the distance from the
end of the line corresponding to a drop of 12.5 volts works
out 1,020 feet, though, of course, there will not be quite as
)arge a current as 255.1 amperes because the line cannot be

§45 INTERIOR WIRING 0

longer than 1,000 feet. This quantity is, however, used in
determining the distance (913 feet) of the end of the 000 wire
from the end of the line. The distance of the end of the
0000 wire must, of course, be 1,000 feet because the cornice
is 1,000 feet long. The lengths in the fifth column are
obtained by subtracting the successive values of the fourth
column, for example, 65-41 = 24, 104 - 65 = 39, etc.

13. Cut-outs of the following amperes capacity will have
to be installed:

15 amperes, to protect Nos. 14, 12, and 10
65 amperes, to protect Nos. 8, 6, 5, 4, and 3
130 amperes, to protect Nos. 2, 1, and 0
160 amperes, to protect No. 00
250 amperes, to .protect Nos. 000 and 0000

This statement assumes that weather-proof wire is to be
used. Fig. 3 is a diagram of a portion of the wiring' in
place, showing the connections of cut-outs.

To 0r^o//inf ^f3ft. i ^ 833 ff to Maifi Cutout '

A/^3

^(^. /3 lamps J

{) n 0 {|) o CM) ov

^Cutout 63/4 ni/>erfs. /f^J.
r- *- eSJ/f fo en^ of //>•€.

roMair* ^ ^ eSJ/f fo €fUfo/ft>

Cufouf^/pyf.\

/Z lamps. ^ N»f4 ty/>»

) {> ^ ;) \) c; c> u o u 0 o u u.o.o

-23'

\\ {> Vi y \) c; c> u o u c) o

^d C.P.LamffS J

Pio. 8

14. Another method of wiring for temporary work is to
put up wires on the feeder system just large enough to
carry the current, and then calculate the drop and install
lamps of the required voltage. This is a simple and very
cheap method. In the case of the border lamps just con-
sidered, there would be eight pairs of feeders of No. 10 wire,
with 125 lamps per feeder. If they are arranged as shown
in Fig. 4, the lengths of these feeders and the drop on each
may be, roughly, as follows, if each lamp required \ ampere.
Current in each feeder is "4^ amperes, and No. 10 wire has a

INTERIOR WIRING

gl5

resistance of about 1 ohm per 1,000 feet. The approximate

lengths of the feeders will be as given below:

Two lines 42-5 feet (two wires) long, 26.6 volts drop
Two liaes 300 feet (two wires) long, 18,8 volts drop
Two lines 175 feet (two wires) long, 10.9 volts drop
Two lines 50 feet (two wires) long, 3.1 volts drop

The resistance of 425 feet (,425 thousand feet) of No. 10
wire is, approximately > ,425 ohm and the drop in the first
case = H^ X *425 X 2 = 26,6. The others are found in a
similar manner. In the distribution, about 1 volt would
be lost. Consequently, if 125 volts is supplied, the lamps
should have voltages of 97, 105, 113, and 121 if each lamp
requires i ampere*

-/^s/l-^

-fOOO/t,'

Ezr

M&*ns catrt^mf /^SS £ am^

^m/^t^^f^

£^isff/As^fft^
Cmnfer

Fio. 4

15. There are many other methods or plans by which
such a building could be wired for a large drop and still be
furnished with uniform and steady Ifght. These suggestions
merely show how material may be saved. By making every
installation a matter of special study, until he has thoroughly
mastered every detail of the business, the wn reman will dis-
cover niany ways of economizing labor and material. that can-
not be brought to his attention in any other manner. Before
using any unusual method, however, he should make certain
that there is no objection on the part of the Underwriters or
of the Fire Department to what he proposes to do.

§46

INTERIOR WIRING

HIGH-POTENTIAL SYSTEMS

16. The Underwriters* rules so far given apply to systems
usingf 550 volts or less; for pressures over 550 volts, the
followm^ rules apply*

HIGH-POTENTIAL SYSTEMS

55D to a,500 VoltB

Any circuit attach ed to any mackine or camSina-
tirni of machines which deveiops a difference of poteri-
iiai between any two wires of ot^er 550 volts and less
than S^BOO voUs skaii be cmisidered as a higk-polential
circuii and as coming^ und^r that class ^ unless an
approved transhrming^ device is used which cuts the
difference of patential down to 550 votls or less.

Wires—

ff. Must have an approved rubber insula tin if
covering.

6. Must be always in plain sight and never
incased except where required by the Inspection
Department having jurisdiction.

c. Must be rigidly supported on glass or porce-
lain insulators, which raise the wire at least 1 inch
from the surface wired over, and must be kept
about 8 inches apart*

</, Must be protected on side walls from mechan-
ical injury by a substantial boxing, retaining an air
space of 1 inch around the conductors, closed at the
top (the wires passing through bushed holes) and
extending not less than 7 feet from the floor. When
crossing floor timbers in cellars or in rooms where
they might be exposed to injury ^ wires must be
attached by their insulating supports to the under side
of a wooden strip not less than i inch in thickness.

17» It is never advisable to bring high-potential wires
into a building when it can be avoided. The danger to life,
due to their presence, is greater than the 6re hazard. An
arc on a high-potential circuit carrying much current, onc^

INTERIOR WIRING

§45

started, will continue to bum even when the points between
which it plays are separated several inches; and a lightning
discharge can easily start such an arc. High-potential
systems of over 650 volts are usually alternating. Series arc-
lighting circuits are the only important direct*current high*
potential circuits much used in the United Stales* With the
exception of arc lamps, it is seldom necessary to bring any
high-potential wires inside of buildings. Where alternating
current is used, the line pressure is lowered by means of trans-
formers, and it is never necessary to bring the high -pressure
wires farther than the substations or transformer rooms.

18. Ti'aiisforniers. — The ordinary alternating-current
transformer consists of two coils of wire wound on an iron
core built up of thin sheets of iron. One of these coils, the
primary^ has a comparatively large number of turns and Is
connected to the high-pressure line. The other coil, the
secandary, has a small number of turns and is connected to
the lamps or other devices to be supplied with current. The
high -pressure current flows through the primary and sets up
an alternating magnetism through the secondary and induces
an E* M. F, that is proportional to the ratio of the number
of turns in the secondary coil to the number of turns in the
primary. For example, if the primary had ^five hundred
turns and the secondary fifty, the secondary voltage would
be ifiH>, or iV the primary voltage, and if the primary were
supplied at 1,000 volts, the secondary would deliver 100 volts.
Special attention should be given to the following rules gov-
erning the installation of transformers. Cut-outs on primary
circuits must be of some pattern especially designed and
approved for the purpose; ordinary fuse blocks must not
be used for high voltages.

19* HulcB Relatingr to TFansformep Installation.

Tran s form e r s —

a. Must not he placed inside of any building,
excepting centra! stations, unless by special per-
mission of the Inspection Department having juris-
diction.

845 INTERIOR WIRING 18

b. Must not be attached to the outside walls of
buildings, unless separated therefrom by substantial
supports.

( When permitted inside buildings)

a. Must be located at a point as near as pos-
sible to that at which the primary wires enter the
building.

b. Must be placed in an enclosure constructed of
or lined with fire-resisting material; the enclosure
to be used only for this purpose, and to be kept
securely locked and access to the same allowed only
to responsible persons.

c. Must be effectually insulated from the ground
and the enclosure in which they are placed must be
practically air-tight, except that it shall be thor-
oughly ventilated to the outdoor air, if possible,
through a chimney or flue. There should be at least
6 inches of air space on all sides of the transformer.

20. The greatest danger to be feared in the use of trans-
formers is the grounding of the primary on the secondary
wires. This may occur either on account of a breakdown of
the insulation under working conditions or because of light-
ning striking the primary wires. Efficient protection against
lightning is an essential part of the out-of-door and central-
station equipment.

WIRING FOR ARC liAMPS

21. Constant-Potential Arc I^amps. — The use of arc

lamps in parallel on low-potential circuits has already been
considered. Wiring for these lamps is done in practically
the same way as for incandescent lamps, so that no special
comment is necessary. The following special rules relate to
arc lamps operated on low-pressure circuits:
Arc Tjipflits on ILiow-Potentlal Circuits —

a. Must have a cut-out for each lamp or each
series of lamps.

The branch conductors should have a carrying capacity
about 50 per cent, in excess of the normal current required
by the lamp to provide for heavy current, required when
lamp is started or when carbons become stuck, without
overfusing the wires.

INTERIOR WIRING

§46

L Must only be furnished with such resistances
or regulators as are enclosed in non-combustible
material, such resistances bein^ treated as sources
of heat. Incandescent lamps must not be used for
resistance devices.

r. Must be supplied with globes and protected
by spark arresters and wire netting aronnd globe,
as in the case of series arc lights.

Outside are lamps musl be suspended at least 8 feet above
sidewalks. Inside ara lamps must be placed out of reach or
suitably protected.

22. Constant-Current Arc Lamps. — Arc lamps used
for street lighting are nearly always run in series. With
this arrangement the same current flows through all the
lamps and must be maintained at a constant value by tlie
generator, no matter how many lights may be in operation*
The voltage generated by the dynamo therefore varies with
the load and the current remains constant. This is just the
reverse of the constant-potential system. It is easily seen
that if the number of lamps is at all large, the pressure
applied to the circuit has to be very high; hence, arc lamps
connected to such a circuit must be treated as being on
a high-pressure system and wired accordingly. Series arc
lamps are also used lor indoor tlluminatton» though not as
extensively as formerly.

23, In all constant-potential installations, protective
devices are installed to open the circuit whenever the lines
are overloaded or the apparatus does not operate properly.
In constant-current working, the circuit must never be opened
while the dynamo is running. The protective devices used
on constant-potential working must* therefore, never be
installed on constant-current circuits.

All series-arc apparatus is thrown out of circuit by shunt-
ing or short-circuiting the main circuit before opening the
lines on which the apparatus is connected. The switch
should be constructed so that the lamp will be disconnected
from the line after it has been shunted and the switch should
indicate clearly whether it is on or off. It should also be
semi-automatic in its action; i. e., when the handle has been

§45

INTERIOR WIRING

thrown the blades should be so actuated by springs that they
will move quickly and not stop between points and thus draw
an arc* The constant-potential arc lamp has -proved such a
success that it has largely replaced the series lamp for inte-
rior lighting, thus doing away with the high-tension wiring,
which at best was always a necessary eviL

24, The general method of installing series arc4ighting
wires is similar to that used in other high-tension interior work.
They must be very thoroughly protected against accidental
contact with anything not intended to connect with them,

Rubber^covered wire mounted in plain sight on porcelain
insulators must be used and an approved service switch
must be placed where the wires enter the building so that
the high-tension current can be completely cut off by firemen
or policemen in case of fire in the building- The wires must
be kept at least 8 inches apart. It must be remembered that
there is always a strong tendency for grounds to develop on
series arc-light circuits on account of the high pressure used.
For this reason the Underwriters* rules are particularly exact-
ing regarding the insulation of interior wiring for this class
of workj and all fittings used must be carefully selected; for
example, ordinary snap switches are not allowed. In case it
is necessary to run the wires up side walls, they must be
protected by a boxing that will leave a clear air space of
1 inch around the wires. This boxing must be closed at the
top in order to keep ont dirt and rubbish and the wires must
be bushed with porcelain tubes where they pass through the
top of the casing.

The current supplied to constant-current arc lamps seldom
exceeds 9 or 10 amperes and often it is as low as 6,H
amperes. As far as mere carrying capacity is concerned,
No, 14 wire will be large enough to satisfy the Underwriters'
requirements; but the wife is frequently of the same size as
that used by the lighting company for the outside lines,
which must be as large as No, 6 or No, 8 B, & S, in order
to secure sufficient mechanical strength and also in order to
reduce the drop in the line<

INTERIOR WIRING

§4€

25. The tendency is to connect more and more arc
lamps on a series circuit* In the early days of electric
lighting, arc machines were made to operate 1, 2, or 3
lamps* The number was increased to 30 or 50, and finally
to 60, where the limit remained for a few years. But
machines are now built to operate as many as 125 lamps
on a single circuit, and are in quite general use, although the
Underwriters prohibit the bringing of circuits of more than
3,-500 volts (70 series arc lamps) within buildings. With
45 volts at the arc and 5 volts lost on the line for each lamp,
we have on a 125-lamp machine a total potential difference of
6,250 volts, A shock received through the human body from
such a circuit is almost sure to be fatal. Too much care
cannot be taken not only to insulate the wires and locate
them out of reach, but also to insulate the lamps. They
should be hung from an approved form of hanger board or
insulated supports, and not from hooks screwed into the
ceiling.

26* Incandescent liamps on Series Circuits, — The

use of incandescent lamps connected in series for street
lighting is quite extensive, but such lamps are rarely brought
inside of buildings* When they are, the rules for other
classes of high-potential work apply. Each lamp must be
provided with an automatic cut-out and must be suspended
from a hanger board by means of a rigid tube. Lamps
must not be connected in series^parallel or parallel-series
and under no circumstances should they be attached to gas
fixtures.

Incandescent lamps used on series circuits must be pro-
vided with fittings designed for that purpose. The rule
against series-parallel connections means that a connection
such as twenty 110-volt lamps in parallel must not be placed
in series with a 10-ampere arc-lighting system. The burning
out of one or two incandescent lamps on such a system
would throw too much current on the others, burn them out.
and destroy the sockets* Many other reasons forbid such
connections.

§45 INTERIOR WIRING 17

WIRING FOR BliECTRIC MOTORS

27. The wireman is frequently called on to connect up
motors; these are nearly always operated at constant poten-
tial, and the wires are installed as for other wiring of this
kind. They are usually operated on 110, 220, or 500 volts
direct current or on similar voltages alternating current.
Alternating-current motors are usually run on either the two-
or three-phase system. Care should be taken to see that
the interior wiring has sufficient capacity; to determine which,
the current taken by the motor at full load should be known.

It is well to allow a liberal amount of current for small
motors, because of their low efficiency. The efficiency of a
large motor can be learned from the manufacturer; and high-
grade high-priced machines are more efficient than cheap
ones; this is a most important consideration to the pur-
chaser. For the purposes of wiring, however, it is safe to
figure 90 per cent, efficiency for motors over 10 horsepower
in capacity, 85 per cent, for motors between 5 and 10 horse-
power, 80 per cent, for motors between 2 and 5 horsepower,
75 per cent, for motors of 1 horsepower, and lower efficien-
cies for motors of smaller sizes. Alternating-current motors
take somewhat more current for the same output than those
operated on direct current. Table I gives the approximate
value of the current in the lines for motors of various sizes
and voltages. These figures will vary somewhat in indi-
vidual cases, because the efficiency and other characteristics
of motors vary considerably. The current taken by a motor
at full load is usually given by the makers on the name plate
of the machine. If it is not given, the table will serve as a
guide in determining the size of wire to be used.

28. Motors should, whenever possible, be insulated from
the ground by means of wooden base frames. This, how-
ever, can seldom be done when motors are mounted on
machine tools or for similar work. The wiring must be
carried out in the same way as required for lights. Where
motors are mounted near or on machinery, special precautions

INTERIOR WIRING

$45

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§46 INTERIOR WIRING 19

must be taken to protect the wires by running them in
pipe or flexible conduit. The branch circuits running from
the mains to a motor should be designed to carry at least
25 per cent, more current than that for which the motor is
rated, in order to allow for the large current at starting and for
occasional overloads. A main switch must be provided that
wiU open all wires leading from the mains to the motor
unless the motor is less than i horsepower and is operated
on less than 300 volts, in which case a single-pole switch
may be used. Each motor must also be provided with a cut-
out, but if an automatic circuit-breaker that opens all the
wires leading to the motor is used, the main switch and cut-
out may be dispensed with and the automatic circuit-breaker
made to serve both as switch and cut-out. A single-pole
circuit-breaker cannot be used instead of the switch and cut-
out; in any event it is advisable to equip motors with circuit-
breakers, particularly if they are used to drive machinery
likely to cause temporary overloads.

29. The switch and starting box should be located within
sight of the motor and the starting box should be equipped
with an automatic release attachment that will allow the
rheostat arm to fly back to the oflE-position in case the power
fails. Motors must not be run in series-parallel or parallel-
series except on constant-potential systems, and then only by
special permission.

The Underwriters' rules prohibit the operation of motors
or lights from street-railway circuits, except in street cars,
car bams, or railway power houses. The reason for this is
that one side of a railway system is grounded to the rails,
and the installation of motors or lights would always intro-
duce more or less fire risk.

INTERIOR WIRING

§45

BELL WIRING

30. Electric bells, burglar alarms, and electric gas-
lightitig appliances bring in another class of wiring with
whfch the wireman has to deaL If these appliances are put
in properly, they may be a great convenience; if not, they
are continually getting out of order and may prove to be a
regular nuisance. This class of work is often slighted and
put up in a cheap manner, but it will pay in the end to have
it put up carefully. The bells and annunciators that show
from what point the bell was rung are operated by primary
batteries , which are of low voltage, and no fire hazard is
introduced if the bell wires are kept well separated and
insulated from electric light and power wires.

THE EtECTKiC BELL
31- The electric bell is a very simple piece of appa-
ratus. Fig. 5 shows a skeleton belK in which all the parts are
visible. With the battery wires connected at the termi-
nals /, i\ the course of the current is: From the terminal / to
the adjustment screw j, which is tipped with platinum in
order to prevent oxidation of the contact surface, through
the spring / and the end ^ of the armature to the coils of the
magnets m, m\ and out at the terminal /', When no current
is passing, the armature is held from the poles of the
eleclromagnetSi as in the position shown^ but as soon as a
battery circuit is closed and a current sent through the coils,
the magnets become energized and attract the armature m^
which swings about the pivot p, causing the hammer // to
strike the belL This movement breaks the circuit between
s and /, and the iron cores being thereby demagnetized, the
spring € draws the armature away, when the spring / again
touches the screw x» completing the circuit. As long,
theOi as the battery current is free to flow, this vibration of

§45

INTERIOR WIRING

the armature and hammer will continue. The tension of
the release springy c may be changed to suit the strength of the
battery by means of the regulating screw r, which Is pro*
vided with nuts on each side of the supporting pillar. The
bell mechanism is usually enclosed to prevent entrance of
dust or insects, which may interfere with the working of the
bell by lodging on the contact points » thereby preventing
the current from passing through the magnets*

32, The bell just described is of the common vibrating
Glass. When a bell is required to give a single stroke each
time the circuit is closed, that is, for each momeotary flow of
current, a slight difference in the
connection of the ordinary bell is
necessary. A wire is connected be-
tween the end of the magnet coil m
and the terminal /, so that the circuit
is simply from one terminal to the
other through the coils. Hence,
when a current passes through the
coils, the armature is attracted and
held, a single stroke being given to
the bell; on interrupting the current,
the armature is drawn hack to its
normal position by the spring c.

33 p The buazer, shown in Fig. 6,
is used in places where an electric
bell would be uadesirable, as in small,
quiet rooms or on desks, and is constructed on the same
principle as the bell except that the armature does not carry
a hammer. In the ilUistration, the cover c is removed,
showing the magnet coils m, m' and the armature a. An
adjusting screw s is provided to regulate the stroke of
the armature and the consequent intensity of sound. The
wires from the push button and battery are secured at d
and e, and on closing the circuit, the rapid vibration of the
armature causes a humming or buzzing sound, whence
the name.

Fio> 5

40B— 31

INTERIOR WIRING

§45

Bu2zers are generally used for signaling in places where
a bell would make too much noise, as^ for exampte, between
the dining room and kitchen of a residence.

34, The circuit-closing devices used on bellwork usually
take the form of a push button. These are made in all
sorts of styles. The very cheap wooden ones are seldom

sMisfactory and bronze push but-
tons should be used where ex-
posed to the weather. Fig, 7
shows the ordinary round push
button- The wires enter through
holes in the base and attach to
springs b and €\ the cover d
screws on. When e is pushed,
b and c come together^ and com-*
plete the circuit.

One cell of any efficient type
will ring a good bell over a
short length of wire, but it is
never advisable to rely on less
than two cells^ even in the smallest installations. When sev-
eral cells are connected together to form a battery, the zinc
qI one must be joined to the carbon of the next and the free

Fro. 7

§45

INTERIOR WIRING

terminals at the ends of the row of cells connected to the
line wires,

36, Electric bells can be had of all sizes, Verjr cheap
bells should not be used, as they require much battery power
and soon get out of order. Trouble is usually found first at
the contact points or the armature pivot. Contact points
should be tipped with platinum or silver* platinum being
much the better material for this purpose, as it never cor-
rodes or tarnishes, but it is more expensive than silver,
which is much used on cheap bells.

In an ordinary dwelling there are frequently three electric
bellsi one located at a convenient point in the rear hall
with a push button at the front door; one in the kitchen
with a push at the back door, and one, a bu22er, located in
the kitchen with a push in the dining-room floor. These
bells may all be operated by the same battery. The battery
should be located in a cool place, but where it never is cold
enough to freeze; preferably in the cellar, where the air is not
so dry that the water in the cells evaporates rapidly. Cells
should not be allowed to become dry. Water should be
added from time to time so as to keep the level of the solu-
tion up to the proper height, which is usually marked on the
glass jar.

66. Many different types of cell are manufactured that
are suitable for bell work. Most of them are of the open*
circuit type, which are intended to furnish current for short
intervals only and will run down if used continuously.
Crosses between the wires or grounds will often cause the
cells to run down rapidly. Most of these cells will recover
to a certain extent if allowed to stand for a while on open
circuit, but they should never be allowed to become short-
circuited if it is possible to avoid it.

The cells in ordinary use on bellwork have electrodes of
zinc and carbon and contain a solution of sal ammoniac
(ammoiuum chloride), Sometimea they also contain a

INTERIOR WIRING

§45

"depolkri^ing*' agent, such as manganese dioxide. The

eflEectiveness of a carbon-zinc cell depends largely on the
materials of which the carbon element is made and the skill
used in its manufacture. Burning the carbons too much or
too little in the process of manufacture makes them inferior-
Some manufacturers make inferior carbons and then treat
them with sulphuric acid, to make them operate with vigor
when first installed. Such cells soon become polarized, and
in the course of a few weeks or months are very inferior,
not because of the acid so much as because of the poor
quality of the carbon. Dry cells are very convenient, but as
a rule they do not last as long as wet cells. Sometimes they
can be recharged by sending a current through them in a
direction opposite to that in which they furnish current, but
such recharging does not last long. When dry cells have
run down, the cheapest and most satisfactory ivay in the end
is to throw them away and get new ones. Suitable cells
for bell operation are: Leclanch^, Carbon Cylinder, Fuller
Bichromate, Dry Cells^ Gordon^ and Edison-Lalande. The
two last named are particularly useful on circuits where the
insulation is poor and where there is, consequently, consid-
erable leakage, as, for example, on signal circuits in mines.

37, In a few cases, as in certain burglar*alarm sys-
tems, the circuit is normally closed and the opening of the
circuit interrupts the current. In these systems, the battery
must be capable of furnishing current steadily; that is,
it must be of the chsed-ctrcuii iypet The gtaviiy cell is a
common closed-circuit type and is well adapted for work
where a small steady current is desired; in fact, gravity
cells will get out of order if allowed to stand for any
great length of time on open circuit.

OPERATING BKLL3 FBOM LIGHTING CittCUITS

38. It is sometimes convenient to operate an electric bell
from an incandescent lighting circuit. This may be done
when direct ciurent is used to operate the lamps, but if
alternating current is usedi an ordinary bell will work very

§45

INTERIOR WIRING

poorly, if at all. Of course, it is necessary to use a resist-
ance in counection with the bell in order to limit the current;
the amount of resistance will depend on the kind of bell used,
because some require much more current than others.
Incandescent lamps make a cheap and convenient form of
resistance; Fig. 8 (a) shows a bell a and push button d in
series with four lamps / across a 110- volt circuit. This is
the simplest scheme of connection, but there is apt to be bad
sparking at the contacts on the bell, because the voltage
across the break rises to 110 volts at the instant the circuit

Pio.8

is broken. View (b) shows the bell shunted across one of
the lamps, in which case the voltage at the break is much
smaller. The operation of bells from lighting circuits is not
to be recommended and it will not be allowed by the Under-
writers unless the whole of the bell wiring is installed in
accordance with the wiring requirements for lighting circuits.
Ordinary bell wiring put up with staples, etc. must not be
connected to any source of pressure exceeding 10 volts, and
it would be decidedly unsafe to connect it to a 110- volt circuit.

39. A better method of utilizing the lighting current for
bell operation is through the medium of storage cells, as
shown in Fig. 9. Two sets of cells a, d are connected to
double-pole double-throw switches, as indicated. When both
switches are thrown up, both sets of cells are charged from the
lighting circuit. Normally, one set of cells will be charging
while the other is in use, as indicated bv the position of the
switches in the figure. Of course, if the bell circuits are

INTERIOR WmrNG

§45

such that they will not be used during certain hours each
day, the cells can be charged during this interval and only
one set will be needed. Storage cells are somewhat high
in first cost as compared with ordinary primary cells, but
one storage cell gives about twice the voltage of an ordinary
sal-ammoniac cell, so that only half as many are required for

a given voltage. In Fig* 9» lamps or some other form of
resistance must be connected in series when charging the
cells in order to limit the current. By using storage batteries*
as shown in Fig. 9; the bell wiring is never connected to the
lighting circuits and it does not need to conform to the
Underwriters' requirements for light or power wiring.

ANKUNCIATORS

40, When a number of push buttons are installed, it
is convenient to have an indicating device to show from
which button the bell is rung. This instrument is called
an atmimclator. An ordinary house style is shown ia
Fig. 10. On the face are rows of small windows, before one
of which an indicator appears when the bell rings, showing
from which room the signal has been sent. A handle h at

INTERIOR WIRING

the side is intended to be used to restore the indicators to
their normal position when the call is answered. A view
of the indicator itself is given in Fig* 11. A hinged
arm a carries a card bear-
ing the name or number
of the room to which the
drop is connected, and
is held up in the posi-
tion shown by a counter-
balanced trip / in front
of an electromagnet m.
As soon as the current
passes through the elec-
tromagnet, the trip is at-
tracted and the indicator
falls, being then visible
from the outside through
one of the openings in
the front.

4^. The needle an-
nunciator, Fig. 12, is a
style much used in hotels
and for elevators* The current on passing throiigh the elec-
tromagnet of an indicator attracts a pivoted iron armature
carrying a pointer P on the outside dial, causing it to set in

an oblique position^ in which it
is held by a catch until released
hy pressing the knob k below
the case* Annunciators can be
obtained in almost any desired
finish and for any number of
drops* One type that has lately
become very popular is the
self -restoring' auniinclator.
In the ordinary Instrument, the
drops must always be put back after a call comes in; some-
times this is not done, and consequently one is at a loss to

Fig, 10

Fio, 11

INTERIOR WIRING

§45

know, when several are down, which button has been pushed.
Self-restoring annunciators are constructed so that when a
button is pushed its corresponding drop falls and remains
down until the next call is sent in. This operates a magnet
that moves the restoring device and resets the first drop.
Self-restoring annunciators are somewhat more liable to get
out of order than the simple kind and some of them require
more battery power. They are, however, a great conve-
nience, and are rapidly finding favor. They are wired up
to the buttons in the same way as an ordinary annunciatorp
as the restoring device is wholly within the
annunciator itself and therefore does not
affect the outside connections.

RUXNING BEIili WIRE

42. There are no regulations govemmg
the insulation used on bell wire. That gen-
erally used IS known as annunciaiar wire bix6,
is usually No. 16 or No* 18 B* & S* copper-
covered, with two wrappings of cotton treated
with paraflfin. This wire is cheap, but it is not
moisture-proof j and the insulation does not
adhere very firmly to the wire. However, it
wil! work satisfactorily if it is carefully put
up and is run in a dry place. For good
work, weaiktr-prooi ofiice wire or rubber-cov*
ered wire should be used. The insulation on
the weather-proof wire is heavier than on the annunciator
wire and adheres drmly; it is also damp-proof* If it is neces-
sary to run bell wires where they will be exposed to consider*
able moisture, the best plan is to use rubber-covered wire.

The si^e of wire used is generally No* 16 or No, 18 B, & S.
It will pay to use nothing smaller than No. 16» because the
cost is very little more, the line resistance is thereby reduced,
the batteries work to better advantage, and the line is mechan-
ically stronger. For the main-battery wire in large installa-
tions, No* 14 may be used to advantage.

§46 • INTERIOR WIRING 29

Bell wires are often stapled to woodwork, especially when
bells are installed in old houses. If any stapling: is done,
care should be exercised not to drive the staples so hard that
they cut through the insulation and break the wire. Do not
fasten two wires down under the same bare staple; special
staples, using: a small saddle of leather between the wire and
the top of the staple, are made for this work. When bell
wires are run in new buildings, they may usually be run
througfh holes in the beams, and they should be grouped
together as much as possible. By doing this, the wires are
run in an orderly manner and very little stapling is needed.

In the best class of work, bell wires are sometimes run in
conduits, but no matter how they are run, all circuits should
be carefully tested out after they are put up to make sure
that there are no grounds, breaks, or crosses. See that
all bell wires are kept well away from electric-light wires
and that no push buttons are mounted in the same wall
plate with electric-light switches.

BEIili AND ANNUNCIATOR CIRCUITS

43, Fig. 13 shows a number of connections for simple
bell circuits; for, the operation of such circuits two or three
cells will usually be sufficient. In (a), a single bell is oper-
ated from a single push button; {d) shows two bells operated
in parallel from a single button; (c) shows two bells oper-
ated in series from a single button. When bells are operated
in series, all but one of them should be made single stroke
so that the interruption of the current will be performed by
one bell only; otherwise, the bells will not work satisfactorily
because one may open the circuit at the same instant that
another tries to close it. View (d) shows one bell operated
from either of two push buttons. Views (e) and (/) show
two arrangements for ringing two bells from any one of
three stations. Fig. 14 shows a plan of bell wiring suit-
able for a small dwelling where no annunciator is used.

Fig. 15 shows a method of controlling a bell from two
stations by using two switches a, b. The bell can be rung

INTERIOR WIRING '

§45

from either station independently of the position of the
switch at the other station* Fig< 16 shows a method of
controlling a bell from three stations. It is the same as
Fig. It5 except that a four-point switch is cut in for the
intermediate station. In one position, points 1^2 and 3,4
are connected, as shown, by the dotted lines. In the other
position^ points 1^3 and 2,4 are connected* The connec-
tions shown in Figs. 15 and 16 correspond to those used for

the control of incandescent lamps from two or more points
and by adding an additional four-point switch to Fig, 16 for
each intermediate station the plan can be extended to any
number of stations.

Placing bells in parallel requires a larger volume of cur-
rent to be supplied than when they are in series, because
the total current suttdivides among all the bells. This calls

§46

INTERIOR WIRING

for a large battery and large wires. When the branch
circuit containing one bell is very much longer, and hence
of higher resistance than the branch containing another bell,
the current will not divide equally between the two bells.

nvnf[>porB€lt

He^rOtH'Btli,

fktrDaorP^aii

Pio. 14

and hence the parallel arrangement m^y not be satisfactory
in such cases. Placing the bells in series requires an addi-
tional cell or two, but no larger wire is needed.

Pxo. 15

44. wiring for Simple Annunciator. — A wiring dia-
gram for a simple annunciator system is shown in Fig. 17.
The pushes i, 2, 5, etc. are located at convenient points in

H»--=C

-iSli

"^^^

Pxo. le

the various rooms» one terminal being connected to the
battery wire b and the other to the leading wire / communi-
cating with the annunciator drop corresponding to that

TNTERFOR WIRING

§45

room. The battery wire is run from one pole of the battery
direct to one sifle of each of the pushes* The other side of
each push is then connected to its drop on the annunciator.
A battery of three or four Leclanch^ cells is placed at B in

any convenient location, but
should not be set in a dark
or inaccessible spot or be
exposed to frost.

45. Wlrini^ for Return-
Call Annunciator. — One

of the many methods for
connecting return-call annun-
ciators is shown in Fig. 18,
It requires one leading: wire
from each station to the an-
nunciator and two battery
connections to each station ,

¥\Q. 17

as indicated by the branches from the heavy battery wires.
The annunciator board is divided into two parts — the
upper part having the bell and the numbered drops^ and
the lower the return*call push buttons* Each room is also
provided with a double-contact posh, such as is shown in
Fig* 19* The tongue / makes connection normally with
the upper contact Cy but when pressure is put on the
button k the tongue is forced against the lower contact r'
and connection with the upper contact is broken. The
return -call buttons on the lower part of the annunciator are
of the same description. Assume, in Fig. 18, that the button
in room 1 is pressed; current can then fiow from the -h side
of the battery-annunciator be 11 -drop J-upper contact of but-
ton /'-tongue of button /"-negative side of battery by way
of lower contact on J" since this button is supposed to be
pressed down. This rings the annunciator bell and operates
drop i. As soon as 1" is released, the tongue makes con-
tact with the upper point as indicated. To send the
return, signal button on the annunciator 1' is pressed, thus
allowing current to flow from positive side of battery— bell

§45

INTERIOR WIRING

i-tongue of button i"-tongfue of button i'-negative side
of battery, since button 1' is now pressed down. It will
be noticed that a signal sent from a room to the office

r-^

r^j^

[^ C^ £> ^

MMmL

R'-O

Pio. 18

does not ring the bell in the room but does operate the
atinunciator bell and drop. On the other hand, a call sent
from the office operates the bell in the room but does not

operate the annunciator bell

or drop.

46. Fig. 20 shows another
method of wiring very similar
to Fig. 18, except that two
sets of (iells are used. Bat-
tery A furnishes the current
for sending signals from the
rooms and B for sending signals to the rooms. The batteries
must be connected with their polarities as shown, so that in
case a push in one of the rooms and one at the auniuiQiator

Pio. 19

crW J^M-

■^

MmiW

J L

I ^

1 1 |m|

te:

M IMl IMl

U/no!ps

diim

Fig. 20

^ A/vnff^c^^^h^pOk

Fio.21

S46

INTERIOR WIRING

should happen to be pressed at the same instant^ the two
sets of cells would oppose each other and would not cause
all the drops and bells to operate* This scheme of connec-
tions is used with Holtzer-Cabot» and Partnck Carter and
Williams annunciatorst but those of either make can be con-
nected as in Fig, 18 if
desired. There is an
advantage in having
the cells separated into
two groups because the
sending signals in a
certain installation may
be more frequent than
the return signals, or
vice versa, and each
set of cells can be kept
in a condition suited to
the work it has to do,
independently of the
other set.

47. Fig. 21 shows
a third method of wir-
ing a re turn -call annun-
ciator. H € r e J there are
two leading wires from
each station to the of-
fice and only one bat-
tery wire is required*
Ordinary push buttons
are used* On account
of the necessity of two
leading wires for each
station this plan would in most cases require somewhat more
wire than that shown in Figs- 18 or 20.

48. Wlrlngr for Speakln^-Tube System. — Fig. 22
shows a plan of wiring frequently used in connection with
Speaking tubes. There are five stations with a bell and four

¥iQ.n

INTERIOR WIRINa

§45

push buttons at each. Any bell other than the one at the
calling station can te rung by pressing the corresponding
button, and the bell at any ^iven station can be rung from
any of the other four stations.

49* Bell Wiring for Flats*— Fig. 23 shows a plan of
wiring for door bells in fiats. Four push buttons are placed

at the main-hall entrance. Each
fiat is also provided with a push
button at its front door and a
second push button at the rear
door. The rear-door button
operates a buzzer so that a
signal from it can be dis-
tinguished from a front-door
signal.

50, wiring for Flre-

Alarm Gongs. — The wiring

shol^^l in Fig. 24 is suitable

where fire-alarm gongs are in-

lU r-\JL stalled. All the gongs ring

- rs] tL, when an alarm is sent from a

— E3i — } 1 station and an annunciator is

placed at each station to indi-
cate the point from which the
alarm was sent in. If the
switch at station 5; for ex-
ample, is closed* all three
gongs will ring and drop 3 on
each annunciator will indicate
the point from which the alarm
is sent. The dotted lines indi-
cate another method of install^
ing the battery. If connections a, a^ a are omitted, bat-
teries b, bf b placed at each station, and the main battery
replaced by connection c, the system as a whole will be
more reliable than if a single battery were used, because
if one of the batteries fails it only cuts out of action the

Fig. 23

§45

INTERIOR WIRING

corresponding bell and annunciator and the others continue
to operate.

51. In installing annunciator systems, it is usual to run
the battery wire, which is No. 14 or No. 16 annunciator wire,
through the building at some central portion. If there are
many rooms, it will be advisable to splice on a length of
No. 18 wire to extend from the push in each room to the

tl±

AfMfunekffor

■r

' r«w**b

Pio.21

battery wire. The connection from the other side of the
push button to the annunciator, that is, the leading wire,
should be No. 18. For the return-call system, a battery of
four or five Leclanch6 cells is required.

All wires used in annunciator service should have dis-
tinguishing: colors to prevent confusion. The battery wire
may be blue, the return wire red, and the leading wires

4«B— 32

INTERIOR WIRING

§45

white. This arrangfement will sjeatly simplify the cotmec*
tioQS and reduce the liability of mistake.

52* wiring for Elevator Annunciator^ — The wiring
for an elevator annmiciator does not differ greatly from that
of a simple annuBciator; in fact, the scheme of connections
is essentially the same. A battery wire b. Fig. 25, is run up
the shaft and connected to each push button on the different
floors. The return wires from each button are then carried
to a point a at the middle of the shaft,
where they should terminate in a small
connection board, so that they may be
readily disconnected from the wires in the
cable running to the cage e. The wires
running from the connection board to
the cage are in the form of a flexible
cable, which is made especially for this
kind of work. This cable contains one
more wire than there are push buttons^
because it has to provide for the return
wire r.

SPECLAX APPLIANCES

63» Til© Automatic Drop* — ^For
special alarm purposes, it is sometimes
desirable that the bell should continue to
ring after the push is released. This is
accomplished by the use of an automatic
drop, which closes an extra, or shunt*
circuit as soon as a current passes along
the main circuit. Fig* 26 shows two
views of an automatic drop, A being
a side elevation and B a front view with the cover removed.
There are three terminals on the baseboard; those marked a
and b are connected to the ends of the magnet coil, the
end at t being also connected to the frame /; terminal c
makes connection to the spring contact d^ which is insulated
from the frame and all other wires* The bell circuit is

ll!i!i

Pm. 2&

§45

INTERIOR WIRING

closed first through a-^ by means of the push button; the
armature € Is at once attracted, thereby releasing the rod
piece g^ which falls by gravity and makes contact with the
spring d, establishing a circuit between b and c, which short-
circuits the push button and magnet coil of the drop.

F1Q.3S

-(SV

ff4* The connections for the automatic drop are shown
in Fig. 27, The circuit obtained, on pressing the push but-
ton p, is from the positive pole of the battery B through
the push to the terminal a of the drop, through the magnet

coils to b^ and then through
the bell to the negative
pole of the battery. As
soon as d falls, the magnet
coils are cut out, the cur-
rent being diverted at e,
and passes by way of the
new contact from c to b,
and thence through the bell
and back to the battery.

Vibrating bells are
sometimes made with a
**■ * continuous ringing attach-

ment that takes the place of the automatic drop* A small
lever is mounted near the arnuature of the bell so that when
the armature is attracted the lever is released by the move-
ment of the armature and drops dowOp thus completing

INTERIOR WIRING

the shunt circuit around the push button and allowinif the
bell to rin^ until the small lever has been restored to its
normal position.

55. Two-Point Swl tell.— When two bells are arranged

to rinif from one push button, it is sometimes desirable to
cut one of them out during: some part of the day. For
this purpose a small switch, Fig. 28, is used, by means of

which one bell, when connected
in series with the other, may>{
be short-circuited. The wires
are run to the back of the
switch, one connection being
to the lever arm at a, the other
to the contact piece ^.

56, Boor Openers. — In

F^o.2s apartment houses, banks, and

other places it is often convenient to have the latch on a
door arranged so that the door may be unlocked from some
distant point. For this purpose floor openers are used,
These are made in a number of different styles, the mecha-
nism differing with the different makes. In all of them,
however, the unlocking is effected by means of an electro-
magnet, which is connected to the push and battery in
the same way as an ordinary bell.

BTIRGXiAR AliARMS

5T* Automatic switches may be placed on windows and
doors, in connection with alarm bells, to indicate when
entrance into a building is being forced. There are three
methods of installing these alarms — the open-circuit, the
closed-circuit, and the combined open-and-closed circuit
systems* In the open-circuit system, which is the one
usually employed, the connections are similar to those of an
ordinary electric-bell circuit, the automatic circuit-closing
device being substituted for the push button. There are
many different kinds of window springs made» one of which

§45

INTERIOR WIRING

is shown in Fi^. 29. This is let into the window frame, the
cam € alone projecting; when the window is raised, the cam
is pressed in, revolving about the pin p^ and makes contact
with the spring j, which \% insulated from the plate by a
washer at the lower end and is normally prevented from
touching the cam by an insulating wheel uk The wires from
the bell and battery are connected to the plate and spring,
respectively. The annunciator used is much the same as
that employed for bell work, but additional convenient attach-
ments are usually placed on it, such as a device to
keep the bell ringing until the annunciator is
reset, a clock to connect and disconnect the system
at certain hours, etc. The annunciator is usually
equipped with a small button over each drop,
which when pushed will complete the circuit and
cause the drop to fall if there happens to be any
door or window open. These are very useful for
testing out to see if everything is closed. AH
these appliances belong to the annunciator itself ^\
and do not affect the general plan of wiring, which
is carried out in the same way as for bell wiring.

Pio. 29

68* Open-Circuit System, ^In Fig. 30 is

shown an ordinary annunciator, arranged to be
used as a burglar alarm. During the day, when
not in use, the switch s is placed on the inter-
mediate, or open position, as shown. When clo*
sing the alarm for the night, a silent test is made
by placing s first upon contact a^ and closing the
individual circuit switches k^, ^,, one at a time; if any window
or door on a circuit is open, the annunciator included in that
circuit will allow its shutter to fall, but the bell will not ring.
After all the windows, doors, and individual switches are
closed, the switch s is placed upon contacts. If, during the
eight, any window or door, for instance in the hall, is opened,
one of the contacts €,€ in the hall circuit will be closed, and a
current flowing through line 1 will cause the shutter of the
annunciator a, to fall and the bell v to ringr With some

INTERFOR WIRING

§45

aDnunciators, the bell is arranged to rin^ contintiously when
once it is started. This may be done in various ways, one
of which is indicated by the dotted lines in the figure,
whereby a circuit through the bell v, resistance r, and
battery B is closed when any shutter drops.

atfAsr^m^e

...k.

unei

Lmee^

59# Closed-Circuit System, — ^In Fig* 31 is shown a
Closed-circuit burglar-alarm system, so called because current
nommlly flows through the various circuitSi and the bell
only ringj* when the circuit is opened. The current that
flows nornjally through the various circuits from the

I £

Orcu>f/

urn

JIL ^TS —

Pig, SI

battery B, energizes the relays r., r, and keeps the local

bell circuit open. Should the circuit be opened by opening
a door or window or by breaking a wire, as at €^^ the relay r,
will release its armature and thereby allow current from the
local battery LB to ring the bell v, which will not stop until

§46

INTERIOR WIRING

the switch k^ is opened, the relay circuit closed, or the
battery LB gives out. In this system* the main battery B
must be of the closed -circuit type because it has to furnish a
small current continuously*

60, Open and Closed CI rent t System.— Where a
system is desired to give an alarm, whether the circuit is
opened or closed at a window or door, or the wires broken
or crossed at any point, the arrangement shown in Fig. 32
may be used. Two line wires are necessary; in line A^ are
connected springs €,e,c normally closed, and between this
wife and line Af are connected springs o,o,o liormally open.
If the circuits are in good order, the alarm is set for the
mgbt by closing switch w and pushing the armature of the

L/neM

Fia.32

relay r against the stop d, where it will be held by the cur-
rent that flows from B through /-/-^-r-line N. If the line N
is opened at any spring" ^r or broken at any point, r will
release its armature and current from battery B^ will ring the
bell V until w is opened. If any spring o is closed, current
flowing through ii^-z^line il/^any spring o-Xxxut A^-battery
i7— battery B% will ring the bell. In this case» the two bat-
teries are in series and must, therefore, be connected relatively
as shown. The bell will also ring if lines M and N become
crossed at any point* The dotted line is not necessary, but
with it the system affords still better protection against
tampering with the wires, for, if line M is broken anywhere,

IKTERIOR WIRING

§45

either part into which it has thus been divided is still capable
of sending in an alarm if crossed with line A^ at any point.

It is usual when connecting up burglar- alarm annunciators
to group the windows or doors; i. e., the contacts on several
doors or windows are connected in parallel and attached to
one drop. To provide a drop for each door and window
would require too large an annunciator and would cost too
much for the ordinary run of work*

ELECTRIC GAS LIGHTING

BUHNERS FOR PARAt.Iil]L SYSTEM

61, In the application of electricity to gas lighting, a
spark- IS caused to pass between two conductors, placed near
the burner, at the same time that the gas is turned on* In

the parallel system of lighting,
each burner is independent of all
the others, having direct con-
nection between the battery wire
and ground* Three styles of
burner are used — the pendant^
the raichef^ and the autotnatic
burner.

62. The pendant bnrneF
is shown in Fig* 33. A well-
insulated wire is brought to the
burner and secured under the
head of the screw j, thereby
making* connection to the sta-
tionary contact piece f, which is
fastened by a screw I to frame /
and insulated from it by wash-
ers w. On pulling pendant r
downwards, spring a is drawn
across f, and, on passing off at the upper side, the break causes
a spark that, when the gas has been turned on^ will ignite it.

Fia.aa

§45

INTERIOR WIRING

63. The ratchet burner is very similar to the plain
pendant, but is provided with a ratchet and pawl operated
by a pendant, a downward pull turning on the gas at the
same time that the spark is produced. A second pull extin*
gnishes the gas*

64, The automatic burner is shown in Fig* 34 with
the gover removed. Two wires must be provided, running
from a double push button, one of them leading to the wire a
and the other to b. The circuit from a is through the left-
hand magnet coil c to the
insulated band d, which has
a projection e at one side<
Upon this rests a metal
rod r, bent at the upper
end and terminating in a^
contact piece; at the lower
end the rod is grounded
by connection with the
trame /, Each magnet coil
has an armature g or g*
with a projecting finger on
the inner side. When cur-
rent is sent through the
magnet €, the armature g
is raised and turns the gas
valve V by striking one
of the pins. At the same
time the rod r is pushed
up, thus breaking the circuit at a point where the gas is
escaping and producing a spark that will ignite it. To
provide for certain action, the sparking should continue
longer than the instant of turning on the gas; this is effected
by the use of a spring to restore the circuit. The rod is
forced upwards against the spring s, but when the circuit
is opened at the spark gap, the spring presses the rod and
armature down again, and the circuit being thereby closed,
a spark is again produced on opening. This continues as

Fid. 34

INTERIOR WIRING

§46

lon£f as the push button is pressed, the action being similar

to that of an electric bell. The second coil k is i^ronnded at
the inner end, and when a current is sent through, the
armature ^' is raisedi turning the valve and cutting oflf the
supply of gas* Automatic burners are convenient where it
is wished to light or extinguish a gas jet from some distant
pointy but they are not very safe because of their liability to
leak gas. They are used principally in hallways wbere It is
desired to light or extinguish the gas from any fioor»

ARRANGEMENT OF LIGHTING APPARATUS

65* To light gas by electricity, a spark of considerable
intensity must be produced. This can be done by means
of batteries and induction coils or by an electrostatic dis-
charger. For the parallel system
used with the burners just described,
a spark coll is employed to supply
a good spark. Fig< 35 shows an
ordinary spark coil which is made up
of an iron core about i inch in diameter and 8 inches long,
built up out of soft-Iron wire and wound with five or six
layers of No. 18 magnet wire. The coil M is connected in

Pio. 96

yili — r^

Wwa-m

series with the cells e, as indicated in Fig, 36, The battery
should have at least six cells for satisfactory service. One
end of the coil is connected to the gas pipe p* When the

$45

INTERIOR WIRING

pendant is pulled, the tip makes contact and a current is
esltablished through the circuit. When the circuit is broken,
the self-induction of coil k causes a bright spark at the
break. In case a ground occurred on the wiring, there would
be a steady flow of current from the battery which would
soon run it down. To give notice of such current leakage,
the spark coil can be provided with an armature d that will
be attracted by a steady flow of current in k and thus allow
current from the local battery e to flow through bell /, giving
a signal. The momentary current that flows in k whenever
a burner is lighted would not usually flow long enough to

k ^ ^

^iiiii

-4 — i--- ii>j

JparH

O/f.

PIO.S7

attract d. In more expensive installations, separate wires
are run for both sides of the circuit and the gas pipe is not
used as one side.

66. The wires are usually run on the outside of the gas
fixtures, but they may be concealed, if there is sufficient
room, between the fixture shells and the gas pipe. It is
advisable to use wire provided with good insulation, for
grounds on the fixtures are liable to occur. Where fixtures
are wired on the outside, the wires should be painted or
made with the proper colored insulation, so as not to showy

INTERIOR WIRING

§45

but they must not be painted with bronze or metallic paint,
which would penetrate the insulation and cause g^un^s,
unless rubber-covered wire were used,

67. To make the location of grounds easy, it is advis-
able to run separate wires from a distributing point near the
battery to each fixture or group of fixtures. The wires can
be connected together at that point by means of a connecting
board, at which any fixtiu-e can be disconnected. This
makes the location and removal of g^rounds an easy matter.
Fig, 37 shows the general arrangement of a system using
both plain pendant and automatic burners. The distributing
board is shown at Z?. The automatic burner is provided
with a double push button c. When the dark button is
pressedi the light is extinguished; when the light button
is pushed » the gas is turned on and lighted.

The Underwriters* rules now prohibit the use of electric
gas lighting on combination fixtures that are also equipped
with electric light. There is too much danger of the gas-
lighting wiring coming in contact with the electric-light
wiring. Moreover, where there is electric light on a fixture
there is little need for electric gas lighting because at best,
the only excuse for electric gas lighting is that it makes gae
nearly as convenient as electric light so far as turning the
light on and ofiE is concerned. Electric light has now
replaced gas to such an extent in hotels » theaters, churches,
and other public places, to say nothing of private houses,
that electric gas lighting appliances are going out of use.
These outfits are a continual source of annoyance, unless
they are kept in good condition and they are specially
liable to get out of order in private houses where they
are not, as a rule, properly attended to.

|4fi

INTERIOR WIRING

APPARATUS FOR 8ERIEB LIGHTING SYSTEM

68. The serlest or na^ti, syBtem of gas lighting is
used In large balls, churches, theaters, etc., where many
lights are installed in groups. A fixed spark gap is used at
each burner, both of the points being insulated from each
other and from the gas pipe, except the last point of a
series, which is grounded. The style of burner used is
shown in Fig. 38, in which a and 6 are
the points of the spark gap< To com-
plete the connection between consecu-
tive burners, a fine bare copper wire,
about No. 26 gauge, is stretched across,
being secured through the small holes
at the lower ends of the strips a, h. The
body of the burner is made of some
insulating substance, and a flange of
mica m is added to give further protec-
tion. Since one circuit may consist of a number of burners*
it will be seen that the E. M. F- must be very high to force a
current across so much air space, and to insure success, the
wiring must be installed with the greatest precaution. The
wire should nowhere be nearer to the gas pipe than 1 # inches;
if, however, it is necessary to approach more closely > the wire

Fio. U

-WMr

;::

should be enclosed in glass tubing. A coil giving a 1-inch
spark can light a circuit of about 14 or 15 burners*

The apparatus required for this system of gas lighting
consists of an induction coil i, Fig. 39; operated by a bat-
tery B and used with a condenser c across the spark gap of
the primary p. The condenser cuts down the spark at the

INTERIOR WIRING

§45

circuit-breaker, for this spark would be very destructive in
the case of a large coil. The fine-wire secondary s is

grounded at G, and the other ter-
minal is connected to the line
wire passing to the burners.

69, Frictlonal luactilnes

are also used in the series ligfht-
ing system. These generate
static electricity, and in many
cases are more reliable than in-
duction coils, as there is no bat-
tery to get out of order. One
form of this machine is shown in
Fig. 40. One of the terminals /
is to be connected to the switch
handle s and the other ,^ to
ground. The machine is rotated
by means of the handle kt and
the switch is moved from one contact to the next, lighting
the gas on each circuit 1^ 2^ 3i 4 in rapid succession.

Wia.m

MODERN ELFXTRIC-LIGHTING
DEVICES

LUMINOUS EFFICIENCY

!• Electric lamps are devices for transforming elec-
tric energy into light. Most arc and incandescent lamps,
however, radiate as light only a very small proportion of the
energy supplied them; a large part of the energy is radiated
as heat. Any source of light may be considered as giving out
two kinds of radiation — luminous and obscure. The radiated
energy sets up vibrations in the ether, and those vibrations
which have a wave length lying between certain limits are
capable of affecting the eye and producing the sensation
known as light. All vibrations lying above or below these
limits are useless so far as producing light is concerned.
If A is called the total radiation from a light-giving source,
B the amount of luminous radiation, and C tbe non-luminous,

or obscure, radiation, then A = B + Q and the ratio — is

the optical, or luminous, efficiency of the light-giving
source, because it is the ratio of the radiation that is useful
in producing light to the total radiation. The efficiency of
ordinary light-giving sources, as measured by this standard,
is very low. For example, the luminous efficiency of ordi-
nary incandescent lamps is only a fraction of 1 per cent, and
that of the best arc lamps less than 10 per cent.

There is room for a great deal of improvement in the
efficiency of light-giving sources, and efforts to effect such
improvement have been made largely with a view to finding

Copyrighted by International Textbook Company. Entered at Stationers* Nail, London

166

2 MODERN ELECTRIC-LIGHTING DEVICES §55

an ilium inant in which a higher temperature can be attained
without injury to the material used. Generally, the higher
the temperature of a li^ht-giving source the higher is its
luminous efficiency. All substances, however, do not have
the same luminous eflficicndes at equal temperatures; a
lustrous, metallic surface radiates as light a larger propor-
tion of its total radiated energy at a ^iven luminous tem-
perature than does a black surface, such as carbon, at the
same temperature,

INCANDESCENT LAMPS

METALLIZED-FILAMENT LAMPS

2. The first rncandescent lamps made were very crude
indeed compared to those now in use. The principle on
which the lamps operate— namely, the heating to incandes-
cence of a body in a vacuum by passing an electric current
through it — has not changed, but there have been many
improvements in the processes of manufacture, especially ia
the method of producing the i-acuura and in the methods
of making the bodies, or filaments, to be heated* Better
materials from which to make the filaments have been found,
so that while the first lamps consumed a great deal of energy
and gave off but little light, later ones have greatly reduced
the energy consumption and increased the light output.

The ordinary carbon-filament incandescent lamps usually
consume^ when new, from SA to 3.5 watts for each candle-
power given ofl. If a larger current were forced through the
filaments by increasing the pressure, the candlepower would
increase much more than the consumption of energy; that is,
the efficiency of the lamps would be increased. These lamps,
however, are soon destroyed if run at too high temperature,

3# Prex*^i'£*tioTi of Metallized FUanientg. — Ordinary

carbon filaments are made by squirting a solution of cellulose
through a die and letting it fall in fine threads into wood
alcohol, which hardens the cellulose. The fibers are then
dried, shaped into the desired form for the lamp, placed in a

§55 MODERN ELECTRIC-LIGHTING DEVICES 3

muffle, and heated to the highest temperature attainable with
a gas flame. They are thereby carbonized and are then
known as base filaments. After being prepared in this man-
ner, they are hung in a chamber, from which the air is
exhausted and a thin vapor of gasoline substituted, and are
heated to incandescence by passing an electric current
through them. A dense layer of carbon from the decom-
posing gasoline vapor forms on the filament. This process
is called treating, or flashing, the filaments, after which they
are ready for mounting in the lamps.

Although heating carbon filaments to a high temperature
by passing a current through them injures or destroys them,
it has been found that subjecting them to an excessively high
temperature by the application of heat from an outside source
causes them to undergo a change that greatly improves their
characteristics for lamp filaments. In the new process, the
filaments, in their basic form, are packed in a cylindrical
carbon box, which is fed into the end of a carbon tube. To
the ends of the tube are attached water-cooled copper clamps,
by way of which a large electric current is sent through the
tube after it has been buried in powdered carbon. The
passage of the current 'through the resistance of the carbon
tube raises the temperature inside the tube to between 3,000®
and 3,700® C. The carbon tube as thus used is a form of
electric-resistance furnace. After the filaments have been fired
in this manner for a short time, they are cooled, treated in
gasoline vapor, and again fired in the electric furnace. This
process leaves the filaments covered with a shell of lustrous,
steel-gray elastic carbon in an almost pure graphite form, and
they are then ready for use in the lamps.

4. The ordinary carbon filament has a negative tempera-
ture coeflficient; that is, its resistance decreases as its tem-
perature increases, thus making it very sensitive to changes
of voltage. Filaments that have been subjected to the intense
heat of the electric furnace, as just described, have a positive
temperature coefficient. The new filament also has a lower
' resistance than the older carbon filaments; in fact, when the

46B— 33

MODERN ELECTRIC-LIGHTING DEVICES §55

filaments are finally removed from the electric furnace their
characteristics resemble more nearly those of metal than of
carbon, hence the name luetalllzed fl lament • The word
graphi(i2€d, also sometimes used, more nearly describes the
actual condition.

Metallized-filament incandescent lamps have the same gen-
eral appearance as the ordinary incandescent lamp, except
that they are made only in the larger sizes and some of the
bulbs are tipless. The standard sizes con.snme 50, 100, 125^
187, and 250 watts, respectively, and give off approximately
1 candlepower for each 2*5 watts consumed. By the use of
suitable reflectors the light can be thrown in any desired
direction, so that the concentrated candlepower is much
greater than 1 for each 2.5 watts,

5, Operation of XjatnpSi — The metallized filaments
can be operated at a much higher tempera tnre than the
ordinary carbon filaments; they have also a more lustrous
surface^ offering better properties for radiating light. They
can therefore be operated at a higher efficiency and can also
be made to produce a whiter light, more nearly resembling
sunlight* In spite of the higher efficiency, these lamps have
a length of usefnl life about the same as that of the ordinary
carbon-filament 3.1-watt lamp. Because of the lower resist-
ance of the filamentt lamps with metallized filaments are
not at present made in as small units for standard voltages
as are those having the ordinary carbon filaments.

6. The difference in the color of light given off by ordi-
nary carbon filaments when burning under various conditions
is approximately as follows:

„ , Watts phi*

Color of Light Candlepower

Clear white * ^1,5

White, very faintly tinged with yellow , . 2 to 2*5

Yellowish white . . , , E

Yellowish 8.6

Yellowish, tin^fed with orange 4

Orange yellow , . . , 4*5

Distinctly orange red . , . 5

§55 MODERN ELECTRIC-LIGHTING DEVICES 5

The clear white light, which most nearly resembles smi-
light, is the most desirable; hence, the advantage of opera-
ting at high efficiency is twofold — increased economy and
better light.

7. The objection to operating lamps with ordinary carbon
filaments at a consumption per candlepower of less than
from 3 to 8.5 watts may be seen from the following data
of a 16-candlepower carbon-filament lamp. The figures in
the first line are the watts per candlepower and those beneath,
the corresp9nding useful life in hours. The less the con-
sumption per candlepower the shorter the life.

2.0 2.5 3.0 3.5 4.0 4.5 5.0
28 132 412 1,000 2,005 3,570 6,125

8. The economy in using the higher efficiency metallized-
filament lamps may be readily estimated. A 3.1-watt
16-candlepower carbon-filament lamp consumes in a useful
life of 500 hours 3.1 X 16 X 500 = 24,800 watt-hours, or
24.8 kilowatt-hours. A 2.5-watt 16-candlepower metallized-
filament lamp consumes in the same time 2.5 X 16
X 500 = 20,000 watt-hours, or 20 kilowatt-hours, — 4.8 kilo-
watt-hours less than the carbon-filament lamp. At the prices
usually charged for power for lighting purposes — from 10
to 15 cents per kilowatt-hour — from 50 to 75 cents is saved
during the life of a lamp in the cost of power consumed for
each 16 candlepower given off. However, the smallest
metallized-filament lamp made consumes 50 watts and gives
off 20 candlepower, so that instead of effecting a saving, the
usual result of the improvement will be to obtain more light
at practically the same cost as before.

MKTAI^I.IC-FILiAMENT IjAMPS

9. In the effort to find a more efficient substitute for
carbon for the filaments of incandescent lamps, much experi-
menting has been done with metals having a very high
meltiny: point. Certain rare metals, notably tantalum,
osmium, and tungsten, have been found so well adapted for
incandescent-lamp filaments that some siu"prising results

6 MODERN ELECTRIC-LIGHTING DEVICES §55

have been obtained. It is now possible to make meiallic-
filament lamps that can be operated at even higher efficiency
than the graphitlzed-filament lamps, and that have a useful
life fully equal to and in some cases exceeding that of the ^
carbon lamps*

TANTAT.UM LAMPS

10, Tantalum, — The first metallic*!! lament lamp to
come into commerical use was the lantal urn lamp ♦ Tanta-
lum is a comparatively rare metal of which little was gener-
ally known until Doctor Von Bolton, a German investigator,
found that it possesses very valuable characteristics for
incandescent-lamp filaments. The metal is very heavy, hav-
ing a specific gravity of 16.8; that is, a piece of tantalum
is 16,8 times as heavy as an equal volume of water. As
the specific gravity of lead is only 11,36, tantalum is nearly
one and one-half times as heavy as lead. Tantalum is
malleable and ductile; it can be hammered out into thin
sheets, but being as hard as mild steel, the pounding must
be severe; it can be rolled into very fine wire, w^hich is
stronger than steel. The melting point of tantalum is very
high— nearly 2,300*^ C— and, with the exception of hydro-
fluoric, no acid, even when boiling, will affect it. Tantalum
also has very high electric resistance and expands but
little when heated; its resistance increases as the metal is
heated; that is, it has a positive temperature coefficient.
However, the resistance of tantalum is lower than that of
carbon; hence, tantalum lamp filaments are made longer
than carbon filaments for the same voltage,

11, Bupportliipr Tantalum Filaments, — The low

resistance of the metal makes it necessary that tantalum
filaments, in all except the very low voltage lamps, be
very long. For example, the filament in a 22-candlepower
44-watt 110-volt tantalum lamp is 20 inches long and has a
diameter of ,0018 inch. In spite of the high specific
gravity of tantalum and the great length of a lamp filament
made of this metal, the extremely small diameter makes a

§55 MODERN ELECTRIC-LIGHTING DEVICES 7

filament so light that it requires 20,000 of the 22-candlepowcr
filanients to weiifh 1 pound*

The length of the filament^ together with the fact that it
stretches when hot, makes its support in the bulb a some-
what difficult matten The device generally adopted is
shown in Figr- 1* A central glass rod bears two ^lass sup-
porting rims, from which project laterally evenly spaced

arms made of nickel wire and having hooks at the ends over
which the tantalum filament is wound. The ends of the
filament are connected to the lamp socket by platinum lead-
ing-in wires. The upper support has eleven arms and the
lower one twelve, each upper arm being in a vertical plane
midway between the vertical planes of the two adjacent
lower arms, so that the filament winds on in a zigzag fashion.

12. Character! Btlce of Tantalum Filaments. — The

tantalum filament when new has a perfectly smooth cylin-
drical surface, but as it ages the surface presents a peculiar
glistening appearance, w^hich, under the microscope, appears
rough and pitted. For the first few hours of service, the
filament stretches and hangs loosely on its supports, but as
it grows older it contracts until it is shorter than at firsts

8 MODERN ELECTRrC-LIGHTING DEVICES §55

Fig:. 1 («) shows the aptpearance of a new filament, which is
drawn in loose, easy curves over the hooks, while {d) shows
the appearance of a filament after being in use for some time,
the loops being drawn down to sharp-pointed angles. The
filament finally breaks, but wherever the loose ends come in
contact with some other portion of the filament they immedi-
ately weld fast and the lamp continues to burn, often with
increased candlepower; the filament is shortened, owing to
the cutting out of a portion of -its length, and its resistance
is thereby decreased, but, of course, this shortens the
remaining life. Quite frequently, even after the filament
has been broken several times^ tantalum lamps continue to
give good service for a time. Fig. 1 id shows the filament
on one side of a lamp after it had broken three times and
still continued to do good service. For the sake of clearness
the filament connections on the back of the lamp are omitted.
While new tantalum wire is very strong, it loses nmcb of
its strength and becomes brittle after having served 200 or
300 hours as a lamp filament; hence, while new tantalum
lamps may be handled as freely as carbon-filament lamps,

they should not be dis*
^^ ^ tur be d a f t e r bavin g be en

in service a while* It
also follows that they
are not suitable for use
where there is much
vibration,

13. The curves in
Fig. 2 show the com-
parative resistance char-
acteristics of carbon and
tantalum filaments, as<
20 40 acT'eo loo r2o (4o loo ipo 200 suming that the resist-
Ferc^nt&f Normal r<>m ances are the same at

P"^-^ 100 per cent, of normal

volts* When the voltage is zero, that is, when the filaments
arc cold, the resistance of the tantalum filament is only

§55 MODERN ELECTRIC-LIGHTING DEVICES 9

20 per cent, of its value at normal voltage* while that of
the carbon filament is about 225 per cent, As the volts
are increasetL thereby forcing a current thro ugh the fila-
ments and healing them, the resistance of the tantalum
filament increases, while that of the carbon filament decreases,
as shown by the curves; for example, at 50 per cent, of normal
voltage, the resistance of the tantalum filament is about
82 per cent, of normal, and that of the carbon filament
about 108 per cent*

This resistance characteristj^c of
the two filaments shows that a
tantalum-filament lamp will take
much the greater current ^t start-
ing, that it will reach incandes-
cence more quickly, and that it will
be much less sensitive to slight
variations of the supply voltage;
for, as the volts increase, the re-
sistance also increases, thus tend-
ing to keep the current through
the filament more nearly constant.

14. Fig, 3 shows a complete
22-candlepower tantalum-filament
lamp having a consumption of
44 watts, or 2 watts per candle-
power, and an average life of about
700 hours. This lamp is now sup-
plied by United States manufac*
turers for any voltage from 100 to
130* The bulb is very nearly the same size as that of the
ordinary 16-candlepower carbon-filament lamp.

15, Fig. 4 shows the results of comparative tests of
several tantalum lamps and one carbon-filament lamp*
Curves a and d show the increase of specific consumption
with age; the values of the ordinate s. in watts per candle-
power, are given on the right-hand margin. The tantalum
lamps consumed an average of L85 watts per candlepower

Pm. 3

B^lO^MODERN ELBCTRIC-UGHTING DEVICES ^55 V

H at the start, 2.2 watts at the end of 700 hours, and 2,6 watts ■
^H at the end of 1»200 hours. The corresponding figures for ^M
^H the carbon-filameot lamp were 3.3, 3.7, and 3.9 watts per H
^M candlepower. H
^M Curves r and d show the decrease of candlepower with H
^M increasing age; the values of the ordinates are given on the H
^1^ left-hand margm. The tantalum lanttps gave off about ^^B

j^r&ojL-

II _

—

■ '

•

^^^^^^^^1

rti^i^

!^^^

_fr^

— -

2S (^ ^1
^0 1. ■

^^^^^H

■ -

zr-

Cfe!

fbj

*J^im

w e

f^OM

^ ■ —

\ rf^

^^^^^^H

^^^^

» IC

» 2C

>o ac

» 4C

>0 H

>o «

» -K

)0 8C

x> ec

K) 1Q<

[X» IM

Xl 121

KJ ^^^^^

Hour9 of Burning

Fig. 4

22 candlepower at the start, dropped 20 per cent., or to
17.6 candlepower, in about 850 hours, and were still giving
an average of nearly 17 candlepower at the end of 1,200 hours.
The carbon lamp began with about 17 candlepower, burned
over 900 hours before losing 20 per cent., and was giving
about 13 candlepower at the end of 1,200 hours. This carbon
lamp was evidently an exceptionally good one.

OSMIUM LAMPS

16. Lamps with filaments made of the very rare metal
osmiiim are used to some extent in European countries, and
if the claims made for them are substantiated in practice and
their cost is not excessive, they will probably come into quite
general use. The lamp was invented by Doctor Welsbach,
of Vienna, the originator of the Welsbach gas mantle.

§55 MODERN ELECTRIC-LIGHTING DEVICES 11

17. Ppeparation of OsTninm Filaineiits. — Osmium
has a specific gravity of 22.48, about twice that of lead; it also
has a very high melting point, in fact it is almost infusible.
This metal is malleable and ductile and possesses high elec-
tric resistance. Osmium lamp filaments, however, are not
produced by drawing the pure metal into fine wire as is done
with tantalum filaments. One process is to mix finely divided
osmium into a thick paste and then, under heavy pressure,
force this paste through dies, shaping the threads thus formed
into loops and heating them in a vacuum. The threads then

J5 so

•hi

200 400

800 I200

Fig. 5

1QOO 2000

consist of porous, rough osmium -with a considerable per-
centage of carbon. To burn out the carbon, the filaments
are next placed in an atmosphere containing steam and other
gases and heated by passing an electric current through
them. This is called forming them, and after this process
they consist of pure porous osmium, in which condition they
are mounted in the lamps.

18. Operation of Osmium Lamps. — After the lamps
are put in service, the surface of the porous filaments becomes
gradually more and more smooth, resulting in an increase of
light during the first 200 or 300 hours. Fig. 5 shows the

12 MODERN ELECTRIC-LIGHTING DEVICES §55

variation of candlepower, with life, of a 44-volt 32-caiidle-
power osmium lamp. Beginning at 100 per cent. (32 candle-
power), the light increases until at the end of 250 hours it is
about 105 per cent, (3«^.6 candlepower). From ihis point the
candlepower gradually decreasesi but at the end of 2,000 hours
it has dropped only to about 85 per cent, of its original value.
It is not certain that all osmium lamps will have as long
life as the one whose life curve is shown in Fig. 5, although
the claim is made that with an initial consumption of 1.5 watts
per candlepower some of the lamps burn even 5,000 hours
without losing more than 20 per cent, of their original candle-
power. Of twelve lamps tested in Vienna, the average life
was 2,220 hours, the shortest being 1,793 and the longest
3»036 hourSi respectively, and during this test only three of
the lamps lost more than 10 per cent, of their original candle-
power. The average consumption during life was from 1,8 to
2 watts per candjepower. The British General Electric Com*
pany guarantees their osmium lamps for a life of not less than
500 hours with a consumption of 1.5 watts per candlepower.

19, Osmium lamp filaments when incandescent become
quite flexible, and if the lamp is in a horizontal or an inclined
position, the filaments* unless well supported, tend to droop,
or sag, under their own weight. Moreover, the filaments
are somewhat more fragile than carbon filaments and are
more likely to become damaged in transportation. They are
made in long U-shaped loops, which are so anchored to a
glass rod projecting into the bulb from the base that the lamps
can be burned in any position. The filaments do not, how-
ever, become so brittle with use as the tantalum filaments, and
are more suitable for use %vhere there is vibration. In fact,
osmium lamps have given satisfactory service in car lighting.

Osmium has a positive temperature coefficient; hence,
osmium lamps are not sensitive to slight variations of volt-
age. In fact, they will stand a considerable increase above
their normal voltage without serious injury. Osmium lamp
filaments also weld together when broken, similar to tanta-
lum filaments.

§55 MODERN ELECTRIC-LIGHTING DEVICES 13

TUNGSTEN LAMPS

20. • Tnngrstcn, sometimes called wolfram^ is one of
the so-called rare metals, though it occurs more plentifully
than either tantalum or osmium. Tungsten is steel gray in
color, so hard that it will scratch glass, and very heavy
(specific gravity 19.129). Like carbon, tungsten changes
directly into vapor at a very high temperature (considerably
higher than the corresponding temperature for carbon) with-
out passing through a liquid state. Its specific resistance is
lower than that of carbon; hence, tungsten lamp filaments
must be very long and very thin, as is the
case with all metallic filaments.

21. Tungsten lamps were first pro-
duced in Europe by German and Austrian
inventors. The filaments are made by two
or three methods and, in some types of
lamps, consist of an alloy of osmium and
tungsten. On account of the difficulty of
properly supporting a long, slender filament,
the lamps are not made in small sizes or for
high voltages. The appearance of the tung-
sten lamp first placed on the American market
is shown in Fig. 6. This lamp was invented
by Dr. Alexander Just and Franz Hanaman, and is called the
Just tungsten lamp; it is standardized at 40 hefner candle-
power with a consumption of 40 watts at 100 to 120 volts,
and has a useful life of 1,000 hours.

22. Operation of Tungsten [Lamps. — Well-authenti-
cated tests made in public laboratories in Germany and
Austria indicate that the performance of tungsten lamps, when
compared with that of carbon-filament lamps, is remarkable.
A useful life of from 1,500 to 2,000 hours at less than 1 watt
per candlepower is indicated. Lamps working at .75 watt
per candlepower have been run from 1,000 to 1,100 hours
with a loss of only 3.5 per cent, of their light output, and for
1,600 hours with a loss of 20 per cent.

Pig. 6

V 14 MODERN ELECTRIC-LIGHTING DEVICES §6&^H

^H The curves in Fig. 7 shows the results of official tests H
^H made on the osram iami>. ^1

^^^H

which has a tilament con- H
sisting of an alloy of H
osmium and tungsten. H

The curv^es in (a) show H
thechange of total candle- H
power of two lamps of H
about 28 and 32 hefner H

^^^l

■--,

--^

— 1

^^H

^^^m

"--,

^^B

—

H o 20O 400^^^600 BOO lOQo ^^^^^ fespectively. and ■
^1 **"'* ''"^ those in ib) show the H
^1 chancre in watts ni^r H

hefner. The light output H
increases in each case dur- H
in g the first 200 hours, and H
the consumption per hef- H
ner decreases; the output H
then falls off gradually, H
but has fallen only 5 or H
6 per cent, below the |

""^^

^H ro

— — ^

■

—

^H 0 aoo 400 eoo soo jo

Fm. 7

meanwhile risen to a little less

23 • Tungsten lamps work
or alternating current and are
voltage; in fact, the voltage can
the lamps. Some types of tun
t any position and are not affecl
very excessive. Table I she
raising the voltage on a 17-c
lamp. At the end of the test

The light from these lamps is
ant, but the lamps are so very
some fonn of shades are neces
abundance of tungsten as com
used for lamp filaments, and

^0 initial candlepower at the H
end of 1,000 hours. The H
specific consumption has H

than L2 watts per unit. ^^^M

equally well on either direct ^M

not sensitive to changes of ^M

[ be doubled without injuring H

gsten lamps can be used In H

ted by vibration, unless it is H

)ws the effect of gradually H

;andlepower 20-volt tungsten H

the lamp seemed uninjured, H

exceedingly white and pleas- ^M

brilliant that frosted bulbs or ^M

sary. Owing to the greater ^M

pared with other rare metals ^M

also because of their high H

§56 MODERN ELECTRIC-LIGHTING DEVICES 16

economy and long life, tungsten lamps are likely to come into
more extensive use than the other metallic-filament lamps.

TABLE I
TUNGSTEN LAMP TESTS

Volts

Amperes

Caudlepower

Watts per
Candlepower

20.2

.970

17.1.

1. 138

25.8

1. 140

56.9

.670

32.7

1.300

.484

34.5

1.340

.421

3Q.0

1.440

158

.355

40.6

1.475

185

.322

24. Normal Filament Temperatures. — Table II
gives the approximate true temperatures of some incandes-
cent lamps as determined by the United States Bureau of
Standards, Washington, D. C.

TABLE II
NORMAL BURNING TEMPERATURES

Type of Lamp

Watts per
Candlepower

Volts

Approximate
True Tem-
perature
Degrees C.

Carbon ...

1,800

Carbon ....

3.5

118

1,850

Carbon ....

3.1

118

1,950

Tantalum . .

2,000

Tungsten . .

100

2,300

16 MODERN ELECTRrC-LIGHTING DEVICES §55

THE NERNST LAMP

25, In the incandescent lamps Ihus far considered the
glowing body, or iilament^ is enclosed in a vacuum, because

io open air it would
be oxidized, or btinat
up, by the oxygen in
the air. The Nernst
lamp is properly
called an incandes-
cent lamp, because
the light-giving por-
tion is a solid body
heated to incandes-
cence by the passage
of electric current.
This lamp is the re-
sult of researches
made by Dr. Waller
Nernst. a German
scientist. The dis-
tinguishing features
of the lamp are its
filament, or glower,
the means for making
the glower conduct-
ive, and the fact that
the glower operates
in the open air.

26, Essential
Parts of till" Nernst
Ijatnp. — The esseii'

tial parts of the
Nernst lamp are:
{ I ) the glower, or 1 i g h t-gi vi n s portion; { 2 > th e kea ters , which
raise the temperature of the glowers at starting until they
become conductors; (3) the resistance, or baiiasi, as it is

Fig. §

§55 MODERN ELECTRIC-LIGHTING DEVICES 17

termed by the manufacturers, which steadies the current
through the lamp; and (4) the cut-out device for opening the
circuit through the heaters after the lamp has been started.
All these parts are compactly assembled and enclosed in a
case having a suspension hook, or screw base, and an
enclosing globe attached. Fig. 8 is a view of a medium-
sized Nernst lamp, partly in section, showing the location of
each part, as follows:

a, the suspension eye;

b^ a lamp terminal;

c, the terminal porcelain;

dy the iron cap covering the

lamp;
Cy ballast tubes;
/, the cut-out coil;
g, an armature support;
h, an armature;
iy a silver contact stop;
;, the ballast porcelain;

k, the lamp case, or housing;
/, an aluminum plug;
w, the porcelain contact

sleeve;
«, the lamp petticoat;
Oy globe-holding screws;
py the holder base;
q, the holder;
r, a heater tube;
5, a glower.

27. Nernst Glowers. — The grlowers, or light-giving
portion of the Nernst lamp, are made by pressing through
suitable dies a dough composed of an oxide of some of the
rare metals, such as thorium, zirconium, yttrium, etc. The
porcelain-like strings issuing from the dies are dried, cut
into suitable lengths,
and baked. Terminals
are then attached by
soldering wires to beads
of platinum embedded
in the ends of the
glower. E m b e d d i n g
the platinum beads in *""'• ^

the ends of the glower is found to be preferable to wrap-
ping platinum wire around the ends, because as the glowers
shrink in service the beads are gripped tightly, while the
wire wrappings become loosened. The process of making
the glowers was the most troublesome feature in developing

^K 18 MODERN ELECTRIC-LIGHTING DEVICES §55 ■

^H the lamp» and finding a suitable method of attaching the ter- H

^H minals was a<^peciaUy difTiculL H

^H Fig. 9 shows a pair of glowers a and their accompanying H

^H heater tubes d. Platinum terminal wires c are attached to the ■

^H glowers, and to the ends of these wires are fastened short H

^H copper wires. The copper wires terminate in small, tapered H

" aluminum plutfs (not shown in this figure) suitable for inser- H

tion in receptacles on the porcelain base on which the beater H

tubes and flowers are mounted, ^^^H

28, The g:lowers have an extremely high resistancei^^H

when cold, or at ordinary temperatures, that is, they are^^H
insulators; but when warmed, the resistance decreases as H
the temperature rises until the glowers become good con- H
ductors at about 600*^ or 700° C. The curve in Fig. 10 shows H
the relation that exists between the temperature of a Nemst H

^^H

^^1

g ■; ^ZZ

^^M

^ ^ ~ ' ^

^ lOOO ' --- - --■

X ^ '-^ - ^ -

^^H

^ . -^ ^^^^ ^--«.

^^H

* EWl J

^^H

S *°°T

~!r ^^1

to \^-^ ^ — z

^^1

i _]... - —' -

^^M

X --,.-- :

^^H

q aoo" A

^^H

e — s~ ^ ^

^^H

^ 5: —

^^H

w ^ j-

^^H

^ 700 "-!*,

^^M

*■ "^ — - 1

^^1

g ::::::::::::::L::!e = = ;;:;

^ r-— --.^...^L. ^

^ --= = = ""--- = =i-j^- ^H

^^H

1 ,:_::„:::"^^ .' ■ ~z

^^1

* ._ _

^^H

^^1

^^^ 2G0 ftOO

Ohms per fJuhii

Fig.

glower and its specific resistanc
resistance is about 1,200 ohms p(
temperatures it is much greater
above 60<J° C, the specific resis
being about 225 ohms at 700^^ i
aO ohms at 900° C.

790 iOOO ^^H

e. At 600° C, the specific ^A

^r cubic inch, while at lower ^^H

As the temperature rises ^M

tance lessens very rapidly, ^M

C. and decreasing to about ^^^

MODERN ELECTRIC-LIGHTING DEVICES 19

29. Kern St Heaters*-

Various devices have been
tried for raisinir the tem-
perature of the glowers to
the point where they be-
come conductors. In the
United States, the plan
now followed is to wind
fine platinum wire over
thin porcelain tubes, and
then cover the wire with
a cement paste that will
withstand the intense heat
of the glowers when in
operation and that also
affords a white surface to
reflect the light down-
wards*

Fig, 11 shows the glow-
ers a and the heaters ^ ol a
two-glower lamp mounted
in their porcelain holder d,
which is attached to the
porcelain base d^. The
glowers, located just be-
neath the heater tubes,
are connected to the brass
pieces t\ / attached to the
base. The terminals of the
heater coils are connected
by way of the brass pieces^
(one on each side of the
base) to the prongs H^hL
Prongs /, m, and n are
connected with brass
pieces e, /, thereby form-
ing the terminals of the
glowers* The bolder is

Pm. 13

46B— 3i

20 MODERN ELECTRIC-LIGHTING DEVICES §55

secured to the base by cotter pins <?, which are inserted
througfh the brass pieces.^. The portion of the holder facing;

the glowers is painted withj
a white enamel paste s<:
that it will reflect light.

Fig:. 12 shows the method
of inserting a holder, with
its heaters and glowers, in
a lamp. A six*gIower unit
with a suitable number ^f J
prongs is shown. Thel
prongs enter receptacles
with which they make the
The hand should not be allowed to

Ptg. is

necessary connections

touch the glowers or heater tubes.

30. The smallest Nernst lamp, which is made to compete
with the ordinary incandescent lamp and is fitted with a ba^^e
for screwing into a standard Edison sockets has one glower
surrounded by a helical-formed
heater made of the same materials
as the heater tubes for the larger
lamps. Fig. 13 shows the appear-
ance of the glower a and the
heater b mounted on a porcelain
holder, and Fig. 14 shows a com-
plete lamp. This lamp gives about
the same light as three ordinary
16-candle power carbon*filament
lamps*

31. BalluKt for the Nernst
Lantp.— The rapid decrease of
the resistance of the glowers with
increasing temperature would ren-
der the lamps very unstable were it
not for the bullast. If the glowers were connected directly
across the circuit, they might be adjusted to work all right
with a perfectly steady pressure; \m\ any slight increase of

§55 MODERN ELECTRIC-LIGHTING DEVICES 21

pressure would increase the current through the glowers
and thus increase their temperature. The resulting decrease
of resistance would permit still greater current to flow, and
the process would continue until the glowers became practi-
cally a short circuit across the line.

The ballast consists of pure iron wire mounted in glass
tubes {fj Fig. 8) from which the air is exhausted, the space
then being filled with an inert gas, such as nitrogen. The
resistance of iron wire rises very rapidly as the temperature
of the wire increases. An increase of 10 per cent, in the
current passing through one of these ballasts will cause as
much as 150 per cent, increase in resistance. A small
amount of resistance is therefore sufficient to insure stable
operation, and the efficiency of the lamp as a whole is higher
than if an ordinary resistance were used. By mounting the
wire as described, all danger from oxidation, or burning of
the wire, is removed, and the ballasts will last a long time,
provided the voltage regulation is good.

32. Nernst Cut-Out. — The cut-out consists of an
electromagnet connected in series with the glowers and
arranged so that when current passes through them it will
attract two armatures, one of which is shown at A, Fig. 8,
and open the circuit through the heater coils.

33. Connections for Nernst Lamp. — Fig. 15 (a)
shows a diagram of the connections of a two-glower lamp,
and (d) shows the same connections in a simplified form.
When current is first turned on to the lamp, it passes alter-
nately from the terminals F, G through the armatures C, C,
silver contact points D,D, prongs h,h\ Fig. 15 (a), to the
heater coils ^, b. As soon as the temperature of the glowers
has risen enough to make them conducting, current also
passes from the lamp terminals to the glowers a, a by way
of prong / on one side, and the magnet B, ballast tubes Ay Ay
and prongs w, w on the other side. When the current through
the magnet has become large enoug:h, the armatures C, Care
drawn in by the magnetic attraction to the dotted positions,
thus opening the circuit through the heaters at two points /?, D.

22 MODERN ELECTRIC-LIGHTING DEVICES §55

Cut-out Cci/

Fig. 15

§55 MODERN ELECTRIC-LIGHTING DEVICES 23

The armatures are suspended loosely from a single point,
so that they swing outwards against the contact points when
the magnet is not excited; the single loose suspension also
prevents humming, which would otherwise be caused by the
alternating current in the coil. The temperature inside the
lamp when operating is about 110° C, and to protect the wire
of the cut-out coil from the heat, it is covered with cement.

34. Characteristics of the Nernst Lamp. — In Fig. 16
is shown a curve that illustrates graphically the flow of

a£

ax}

— ,

3 2j0

^ in

10 20 30 40 50 OO lO BO 90

Seeondt

Pio. 16

current through a six-glower 220-volt lamp from the time it
is switched on until the lamp is running steady on its normal
current — about 2.3 amperes. When first switched on, nearly
3.5 amperes flows through the heater tubes. The resistance
of the platinum wire on the heaters quickly rises and brings
the current down to about 1.3 amperes, which continues until
at the end of 26 seconds the glowers begin to take current.
The total current then gradually rises until, after a little
over 30 seconds, the current in the glowers reaches a value
high enough to cut out the heaters, when the total current

24 MODERN ELECTRTC-L[GHTrNG DEVICES §55

through the lamp decreases abruptly by the amount that the
heaters were taking:. The current through the glowers con-
tinues to increase, until at the end of about 40 seconds all
the glowers are burning full brilliancy and the resistance of
the ballast has risen enough to prevent further rise of
current. From this time on there is a slight rise in the
resistance of the ballasts, lamp connect joas^ etc., until the
whole lamp has reached its maximum temperature and
the current has fallen to its normal value.

35. Nernst iamps are made with one, two, three, fonr»
or -six glowers » giving hemispherical candlepowers of very
nearly 35, 75, 125, 190, and 300, respectively. The efficiencies
of the lamps steadily increase with the number of glowers,
the approximate consumption of energy in the various sizes
in the order named being* respectively, 2,4, 2,2, 2,1, LK5,
and 1,75 watts per hemispherical candlepower. This increase
in efficiency is due largely to the fact that the several glowers
tend to heat one another.

The high efHciency of the Nernst lamp may be ascribed to
the high temperature at which the glowers work, and to their
ability to radiate a large proportion of the energy supplied
them as light. The color of the light approximates closely
to that of daylight, and hence is desirable for store or art-
gallery illumination, where the correct determination of color
is of importance. As an offset to these advantages, the Nernst
lamp, in comparison with the incandescent lamp, is some-
what complicated, and high in first cost, although the parts to
be renewed can be replaced at slight cost after the lamp is
once purchased, because allowance is made for the scrap
platinum in the burned-out parts. The slowness of starting
13 also a disadvantage for some kinds of illumination* partic-
ularly in theaters, or in any other place where it is desired
to switch lamps on and off frequently.

36. The lamps are made for 110 or 220 volts alternating
current J the llO-volt lamps can be adjusted for any voltage
from 100 to 120^ and the 220-volt lamps for any voltage
from 220 to 240. For best results the voltage must not be

MODERN ELECTRIC-LIGHTING DEVICES §55'

permitted to vary more than 3 per cent, above or below that
for which the lamp is adjusted. Each 110-volt glower takes
approximately ,8 ampere, and each 22()-volt glower, approxi-
mately .4 ampere. More satisfactory service is obtained
from the 220-volt lamps. A single-glower lamp for outdoor
service on series-circuits is also made. This lamp is made
both for 26 volts 6.6 amperes and for 23 volts 7,5 amperes.
All sizes, except the low-voltage series-lampj are made in
two styles, for either indoor or outdoor service, the difference
being almost entirely in the style of casing used to enclose
the lamp.

37 1 Li^ht Dlstrlbiitlon^^-Owing to the reflecting sur-
faces just above the glowers, nearly all the light from a
Nemst lamp Is given off in the lower hemisphere. The light
is very evenly distributed below the lamp in the vertical plane,
as shown by the heavy curved line in Fig, 17 (a), where the
candlepower given off in various directions by a three-glower
lamp is indicated by the numbers in the vertical column.
There is a slight excess of light immediately below the lamp.
Fig, 17 (6) shows the horizontal distribution about a three*
glower lamp; the light given off parallel to the glowers is
much less than that given off perpendicular to them.

38* Care of Nernst IjainpSi— Nernst lamps should
have regular and systematic attention while in operation.
There should be kept on hand a supply of parts likely to be
needed, such as glowers, heaters, holders, ballast, glass-
ware, etc., the number of extra parts depending on the number
of lamps in use. The attendant should have a suitable kit
of tools, and regular, systematic visits should be made to
each lamp. He should carry with him a supply of parts most
likely to be needed, including a number of repaired holders »
complete with heaters and glowers, and should inspect each
lamp as follows:

L Determine whether all heater tubes become red when
the current is turned on; if not, the holder should be replaced
with a new one. After the lamp has been in use some time,
the holder and heater tubes become blackened by a deposit

§55 MODERN ELFXTRIC-LIGHTING DEVICES 27

of oxide of platinum from the glower terminals. This deposit
should be scraped off or a new holder substituted, so as to
keep the reflecting surface good.

2. Inspect lighted lamps with colored glass to determine
condition of glowers.

3. Change holders in a six-glower lamp if two glowers are
out; in a four-, three-, or two-glower lamp if one glower is
out; and in a one-glower lamp if the glower does not light.

4. After replacing the holder, see that all glowers light
up; if any does not, the corresponding ballast is burnt out
and must be renewed.

5. All defective holders should be returned to the repair
bench. The shades and glassware should be cleaned as often
as necessary — at least once a month.

TUBE LIGHTING

39. For two centuries or more it has been known that an
electric discharge through a tube of rarefied gas, or vapor,
causes the gas to become luminous. Within recent years,
much experimenting has been done, with a view of develop-
ing a practical illuminant by using a tube of incandescent
gas. It has been found that the luminous efficiency of a
vacuum tube is 25 or 30 per cent. — many times better than
the best arc or incandescent lamps. The prediction is freely
made that further investigation will enable the production of
a vacuum-tube light far more efficient than anything yet
produced.

When light is radiated from a point, the intensity of the
light striking an object at a distance from the source of light
varies inversely as the square of the distance; hence, in order
that objects at a considerable distance may be well illumi-
nated, the source of light must be dazzlingly bright. When
the source of light is extended over a considerable space, as
in a tube of light, the law of inverse squares does not hold
true; the light falling on an object at a distance from the
source is greater than given by this law. Moreover, from
such a distributed source, light is given off in all directions

28 MODERN RLECTRrC-L!GHTlNrr fJEVICES §55

perpendicular to a considerable length of lube, and sharply
defined lights and shadows ^re avoided* This quality adapts
tube lightini.r to rooms where there are many obstnictions to
the distribution of light from concentrated sources, as in
rooms where much machinery is installed.

Two principal types of tube lights have thus far come into
practical use: the mercury -vapor lamp in which a column of
mercury vapor is heated to incandescence by the passage of
a current of electricity through it, and the Mwre eieciric Hgki
in which the incandescent body is a tube of rarefied gas con-
sisting almost wholly of air. Far less heat is required to
raise to incandescence the temperature of a column of rare-
fied vapor or air than a solid, such as used in incandescent
and arc lamps; this accounts for the higher efficiency of the
vacuum-tube lamp, _^

MERCURY- VAPOR LAMP8

40. The mercury-vapor tube lamp as used in the

United States was invented and developed by Peter Cooper
Hewitt: hence, it is commonly known as the Cooper Ilovvltt
iriiup. The standard types of this lamp consist essentially
of a clear glass tube 1 inch in diameter, with a light-giving^
portion from 17i tu 45 inches long. In each end of the tube
is sealed a platinum wire that terminates in an iron or mer-
cury electrode, very similar to the electrodes of the Cooper
Hewitt mercury-vapor converter; in fact, the idea of using
the mercury arc to convert alternating current to direct cur-
rent was conceived while experimenting with mercury- vapor
lamps*

UESCRIFTIOBT

41. Type H Lamp. — Mercury-vapor lamps are made
in three standard sizes, each designated by a type letter;
namely, types H and A" for direct current ^ and type C for
alternating current.

Fig. 18 shows a typa H lamp complete with the canopy j
containing the adjusting and regulating devices; a is the
holder without the reflectori which is normally supported

§55 MODERN ELECTRIC LIGHTT NO DEVICES 29

between the holder and the lamp tube b. The holder is
hinged at its middle point €, and is provided with a suitable
stop, so that when in operation the lamp remains in an
inclined position. The anode d is a piece of iron, and the
cathode is mercury contained in the blackened bulb e. The
chain / serves to pull down, or tilt, the lamp when starting it.
Two type H lamps in series * with tubes 17i inches long.
are used on circuits where the voltage is from 9S to 106, and

Pro. IS

two 20f-inch tubes are used on from 106- to 122-voIt cir-
cuits. At 110 volts, the two lamps consume 3,5 amperes, or
385 watts, and give off 300 spherical candlepower each, or a
total of 600 candlepower, thus making the specific consump-
tion ,64 watt per candlepower. A lamp of this kind, with a
special resistance in series, can be used on from 98* to
122- volt circuits, and four lamps can be used in series on
from 196- to 244-volt circuits.

30 MODERN ELECTRIC-LIGHTING DEVICES §1

42. l>'ije K Ltinip. — The type K iBtnii has the same
general appearance as the type H, but the light-giving por-
tion of the tube is 45 inches long. Type K lamp can be
used singly on from 98- to 122*volt circuits, or two in series
where the voltage is from 196 to 244, With one of the two
lamps shunted by a special resistance, the other can be used on
from 196- to 244-volt circuits. P^ach lamp consumes 385 watts
(3i amperes at 110 volts) aftd gives off 700 candlepower,
making the specific consumption *55 watt per candlepower-

43, Type C Lamp. — Fig, 19 shows a type C Iam|> for

use with single^phase alternating current only. The general
appearance is very similar to that of the type H or type K

Pjg 19

lamp, except that the type C lamp combines the features"
of the direct-current lamps and the mercury- vapor converter,
and hence has three anodes, one a for starting and two d and c
for operating the lamp. The complete lamp has a canopy
not shown in the figure. A resistance ti in series with the
anode a prevents the flow of an excessive starting current.
The length of the light-giving portion of the tube is 28 inches.
With each lamp is supplied an autotijansformer, making the
lamp suitable for use singly on from 98- to 244*volt circuits.
The lamp consumes 3k amperes on 110 volts and has a power
factor of 71 i per cent., making the actual consumption
3J X 110 X .715 = 275 watts. The output is 425 spherical
candlepower; hence, the specific consumption is .64 watt

per candlepower*

§55 MODERN ELECTRIC-LIGHTING DEVICES 31

44. Cooper Hewitt Lamp Reflectors. — Fig. 20 shows
the different forms of reflectors used with mercury-vapor
lamps. The flat type is supplied where a medium distribu-
tion of light is desired; the curved type is used for concen-

FiG. 20

trating most of the light immediately under the lamp; and the
adjustable type permits almost any desired distribution to be
obtained. With light-colored walls and ceiling, best results
are obtained without the use 6f reflectors.

CONNECTIONS

45. Fig. 21 shows a diagram of the connections of two
type H lamps in series, on a 110-volt circuit. A ballast a,
very much like that used in the Nernst lamps, tends to keep
the current nearly constant through considerable variations of
the voltage. A resistance b in series with both lamps helps
to steady the current and prevents it from being excessive
at starting. Inductance, or reactance, coils c, c', also in series
with the lamps, prevent sudden fluctuations of current and
act as mag^nets to hold the automatic switches d d' open
while both lamps are in operation. If one lamp is out of

S2 MODERN ELECTRIC-LIGHTING DEVICES §55

PlO 31

Pig. 22

§55 MODERN ELECTRIC-LIGHTING DEVICES 33

service for any reason, its inductance coil carries no current
• and its automatic switch remains closed, thus allowing the
current from the other lamp to pass around the idle one
through a special shunt resistance e or e' , It is thus possi-
ble to burn either lamp singly if desired. Two pair of type H
lamps in series, each pair connected as shown in Fig. 21,
can be used across from 196 to 244 volts. The connec-
tions for two type K lamps in series are very nearly the
same as for two type H lamps. When one lamp of either
type is connected for use alone, the automatic switch is
omitted, but a resistance and an inductance are used in series
with the lamp.

46, Fig. 22 shows a diagram of the connections of a
type C lamp. The connections are the same as those of the
single-phase mercury-vapor converter, except that in the
lamp connections a ballast is used in the line from the cath-
ode to the autotransformer. The autotransformer shown
is suitable for use on 110 volts; a different one is used
for 220 volts, the transformation ratio being such that
the pressure across the lamp terminals is 172 volts in
each case.

47. The adjusting and regulating devices for each lamp
are arranged in a compact group called the auxiliary, which
is usually placed in the large canopy above the lamp. Fig. 23
shows the inner parts of the type C lamp, the arrangement
of which is typical of all. A plate a is fastened to the ceil-
ing, a shield b of sheet iron and asbestos comes next, and
the plate c to which the resistances, inductances, etc. of the
auxiliary are attached is then fastened to the ceiling plate.
The asbestos shield protects the ceiling from heat that might
be generated in the auxiliary. The plate c carries a crow-
foot d, into which the suspension bar c is screwed. The
parts are shown suspended in the order in which they go
together. When assembled, the canopy covers all the parts,
as shown in Ficj. 18. The position of the lamp is indicated
in Fit,^ '2:?^ liy dotted lines, and the holder, reflector, clamps,
etc. are shown.

34 MODERN ELECTRIC-LIGHTING DEVICES §55

When the ceiling is fireproof, the plate is attached to it by
means of expansion bolts or other suitable devices; when
the ceiling plate is attached to an outlet box, an insulating
joint is used. The auxiliary can be screwed direct to wooden

Fia. 28

ceilings without the use of a plate, but it must be spaced
4 inch from the ceiling by porcelain insulators, and the
asbestos shield must not be omitted.

48t In Fig, 24 is shown a diagram illustrating the relative
location of the various parts of two type H lamps. The

a
a
n
a
□
□

4rtB— 35

m MODERN ELECTRIC'LIGHTING DEVICES §55

auxiliary of one lainp contains the ballast a, and that of the
other lamp contains the series-resistance ^ (see also Fig. 21);
hence the names, ballast auxiliary and resistance auxiliary.
Each auxiliary is provided with inductances c, c^ and shunt
resistances e,€\ each in two parts; also a canopy, shieldi and
plate like the ones shown.

In assembling a pair of lamps, the canopy is first slid
down over the suspension bar, which is then screwed tightly
into its auxiliary. The two wires protruding from the top of
the suspension bar are provided with terminal plugs, which
fit into holes in the binding posts to which they should be con-
nected, the posts being marked + and — . In all cases, the
wire from the positive end of the lamp should be connected
to the positive postj and the wire from the negative end to
the negative post. A wire connection is made between the
posts marked B on the ballast auxiliary and the post marked
y? on the resistance auxiliary* and the wires from the supply
circuit are connected to the remaining posts, the positive
to the ballast auxiliary and the negative to the resistance
auxiliary.

The clamps holding the tubes should be left loose enough
so that the tubes can be turned easily; alsoj the tubes should
remain tiltedi as shown in Figs. 18 to 24, so that the mercury
will remain in the cathodes. It may be necessary in some
cases to add a small weight to the cathode end to keep it in
the lower position.

OPERATION

49. Before starting mercury^vapor lamps, it should be
ascertained that all connections have been properly made.
The polarity of the direct-current lamps should be verified
with considerable care, as an attempt to start with the cur-
rent flowing in the wrong direction will melt the end of the
negative leading-in wire, break the glass, and thus ruin the
lamp. In starting, close the main switch, pull down on
the chain until all the mercury has run from the cathode to
the anode end of the tube^ and then allow the tube to fall
back slowly to its normal position. When the mercury forms

§55 MODERN ELFXTRIC-LIGHTING DEVICES 37

a continuous stream between the electrodes, about double
the normal running current flows through the lamp, and
when the stream is broken, the tube at once becomes filled
with a glow of light.

In some types of lamps, a magnet is so arranged that
when the main switch is' closed the lamp is automatically
tilted. In all cases, the lamp, after being tilted, should
promptly return to the normal position with the cathode end
down; it should not be permitted to burn long in any other
position. The overload at starting will injure the lamp if
maintained long; that is, if the tube is held for some time in
a horizontal position. •

COMPARISON WITH OTHER I^IGHT SOURCES

50. The principal advantages claimed for the Cooper
Hewitt mercury-vapor lamp are its high operating economy,
uniform distribution of light, and the ease of the light to
work by. The chief disadvantage is the absence of red rays,
which gives the light a ghastly greenish appearance and ren-
ders it useless where colors must be distinguished. In such
light, red appears as dark purple, and any color of which red
is an element is distorted.

In economy, the mercury-vapor lamps are much superior
to any of the older forms of electric lights, as may be seen
by comparing the energy consumption per candlepower of
the mercury 'lamp with that of the incandescent and arc
lamps, as already given. Less than 1 per cent, of the
energy supplied to carbon-filament incandescent lamps is
converted into light, all the remainder being converted into
heat. Of the energy supplied to mercury-vapor lamps, about
20 per cent, becomes light and 80 per cent. heat. The mer-
cury-vnpor lamps are therefore comparatively cool and heat
up the surrounding air much less than either incandescent or
arc lamps {giving the same light output.

51. The superior distribution obtainable with tube light-
ing is illustrated, in the case of the mercury-vapor lamps,
by the lighting of presses in some of the large printing

3S MODERN ELECTRICHGHTING DEVICES §55

establishments. To light such machinery witli ordinary incan-
descent lamps requires the installation of many lamps inside
the presses. For example, it was estimated that forty incan-
descent lamps would be required to illuminate each of four
larg:e presses in one office, and that it would be necessary to
drill 450 holes in the framework of each press to install the
necessary conduits. In addition to these lamps^ ten enclosed*
arc lamps would have been needed to give the room suffi-
cient general illumination. Instead of adopting this scheme
of lighting, twenty-six type H mercury-vapor lamps were
installed; the presses are thoroughly well lighted and no
holes in the*frames were necessary. The incandescent and
arc lamps would have required about 15 kilowatts of energy*,
the mercury lamps require about 5,5 kilowatts.

52. The light from the mercury -vapor lamp is easy on
the eyes for several reasons: it is very steady, there beinir
no flicker or perceptible variation whatever; the source is
not so dazzling as to cause the pupils of the eyes to contract
and thus shut out the reflected light from the objects it is
desired to see, such as printed pages* drawings* machinery,
boxes or bales of goods, or whatever it may be; ihe prevail-
ing color of the light is green, which is best suited to the
eyes, while the trying red rays are entirely absent; and as
the source is distributed, there are few sharp contrasts
between lights and shadows to tire the eyes in making
continuous adjustments.

For factories* warehouses, depots* offices, drafting rooms,
press rooms, reading rooms, and all places where color
distortion is not objectionable, this form of light is very
desirable. Many attempts have been made to use a sub-
stance for the cathode that will give off all the colors in
about the proportion that they exist in sunlight, but nothing
so desirable as mercury has yet been found*

§55 MODERN ELECTRIC LIGHTING DEVICES 39

MOORE LIGHTING TUBK9

53. The Moore electric light is a system of artificial
lii:hting in which the source of light is the rarefied^ non-
metallic* gaseous contents of long glass tubes, made luminous
by the passage of an electric current. The Moore tube can
be made in many sizes and shapes, but usually it consists of
a clear glass tube 1} inches in diameter and whatever length
is desired up to 2(X) feet. The tube is usually placed near
the ceiling, the two ends entering a sgiall steel terminal box
placed in any convenient location*

54- Theory of the Moor© Llf^ht. — To explain the
theory of the Moore lamp, reference is made to Fig* 25,
which shows the appearance of a series of discharges of
electricity in air at atmospheric pressure. If the difference
of potential between two points or terminals in open air is
gradually raised, sparks will finally jump from the positive
terminal across the intervening air space to the negative
tarminaU as shown. The path of the discharge will not be

a straight line, for the electricity will seek the path of least
resistance* which includes particles of dust that may be
floating in the air. The same tendency is seen when a
lightning discharge passes in a zigzag path from cloud to
cloud or from a cloud to the earth.

If the two terminals are sealed in a glass tube and the air
is gradually exhausted from the tube, a condition will soon
be reached where the discharrres, instead of following zigzag
paths* as in open air. will become straight and continuous and
will fill the tube with a glow of light. The electromotive

40 MODERN ELECTRIC-LIGHTING DEVICES §55

force required to cause the discharge changes as the degree
of exhaustion, or the pressure, of the air in the tube changes.
At fifiit the necessary electromotive force decreases rapidly
as the pressure decreases, but a condition is soon reached
where the electromotive force is a minim um, and the tube is
completely filled with a bright glow. H the air pressure is
further reduced, the electromotive force will have to be
increased and the !ig:ht will be less brilliant. For best
results as a light source, therefore, the vacuum in the tube
must be maintained at a dehnite pressure.

The color of the light emitted when the tube contains

^\ r,

Fio. 2fi

only rarefied air is a rosy pink, but by introducing a small
quantity of a suitable gas, the color can be made any shade
desired; the light, in fact, can be made pure white. The
coloring gas soon becomes exhausted and must be frequently
renewed.

55, Moore Tube Connections. — Fig. 26 shows the
very simple connections of a Moore tube. The pressures
required are usually higher than are practicable with direct
current. Low-potential alternating current, such as is per-
mitted by the Fire Underwriters' rules to be brought inside
buildings for incandescent lighting, is led through fuses

§55 MODERN ELECTRIC-LIGHTING DEVICES 41

and a switch tnlo a fireproof and danger-proof box a and
through the primary coil of a potential-raising transformer^.

The secondary coil of the transformer terminates in carbon
electrodes in the ends of the tube cc, inside the box. No
wiring is necessary, except to bring the low-poteniial mains
to the box» thus making the system very safe. Fig. 27
illustrates an interior view of one of these terminal boxes,
which has been in successful commerical use for several years.

Pig, 27

When the main low-potential switch is closed, the tube
lights up immediately with a glow that can easily be regu-
lated, so that it will give any desired intensity from
2 to 25 or 30 candlepower per linear foot of tubing. The
actual current passing through the tube, assuming that it is
radiating 15 candlepower per foot, is about i ampere, vary-
ing somewhat with the color of the light desired*

56. Vucutim lU*^iil»tor. — The passage of electric cur-
rent through the tube in a Moore light soon burns out the
small quantity of air or other gas needed to maintain the
conductivity, and it is necessary to admit a minute quantity to
the tube at intervals, or the current will soon cease to floWi

42 MODKRN ELECTRICLIGHTING DEVICES

The vaettutii reirulator, shown in section in Fig^. 28» is a
device for automatically feeding air to the tube. The vac-
uutn is maintained at a little above the point of least
resistance; therefore, as the degree of exhaustion increases,
the resistance decreases and the current increases*
The regulator consists of a valve operated by an electro-
magnet connected in series with the pri-
mary or the secondary of the transformer
feeding the lube* A porous carbon plug a
is sealed into the top of a glass lube b^
around which is an annular space filled
with mercury r. Into the annular space
extends a movable tube d, the other end
of which is attached to the core e of the
magnet. As the excitation of the magnet
changes, the core moves up or down^ thu^
moving tube d up or down in the mercury.
The surface of the mercury is thus lowered
or raised.

Above the surface of the mercury is a
space filled with air or other gas, and when
the tip of the carbon plug is exposed an
extremely small quantity of the gas filters
through the plug and passes' into the light-
ing tuhe. By means of a stop-cock f^ the
regulator can be shut off from the lighting
tube, If the tube is fed with pure air. the
Hght will be a rosy pink; if the air supply
is first passed through phosphorus» the
oxygen is withdrawn, leaving only nitro-
gen to enter the tube, and the light will
then be yellowi which is the most econom-
ical color; or, the lube can be fed with carbon-dioxide gas*
generated by the contact of a piece of marble with a little
hydrochloric acid, in which case the light will be pure white.
Tn operation, the valve acts about once a minute: the cur-
rent gradually rises until the valve acts, then gradually falls,
as the newly admitted gas diffuses through the tube, until

Pm. 28

MODERN ELECTRfC I.trrirriNG DEVICES 43

the degree of exhaustion begins to increase again, thus
working between fixed limits. No variation in the brilliancy
of the tube can be detected, and in spite af the continual

admission of new material, no change can be not iced except
a deposit near the electrodes, and this is very slight* even after
lon£:<ontinued use*

44 MODERN ELECTRIC-LIGHTING DEVICES §55

57, Applications of tlic Moore Tubes,^ — Fig. 29 shows
the Moore tube light in the main-corridor entrance to Mndison
Square Garden, New York City. This tube is 100 feet long
and is arranged in the form of a rectangle hung near the
ceiling.

In Fig. SO is shown an artificial skylight for photographic
purposes » made by bending a Moore tube back and forth
over the surface of a window-like box. This skylight is
located in one of the large New York City photograph
galleries, and after 2,500 hours' service, extending over

Fig. tQ

a years, it showed no change in its conditions or its light
output, and indicates indefinite life. A modified form of this
device, in which the box carrying the tube is mounted in a
frame so that it can be adjusted to any angle, is used by
many photographers as an artificial photographic window.

Fig. *^1 illustrates an adaptation of a Moore tube to electric
advertising, to which it readily lends itself, as it can be bent
into any form desired. This form of light is also applicable
to large areas where unifortn light is desired, such as stores,
offices, restaurants, public halls, churches, theaters, libraries »
art galleries, subways, and even to street lighting.

1 55 MODERN ELFXTRTC-LIGHTING DEVICES 45

The longer tubes* such as shown in Fig, 29, arc sent out
from the factory in sections 8 feet 6 inches long, and are
united into one continuous air-tight tube, being exhausted
when mounted in their permanent location. This makes the
system somewhat troublesome to install, but the expense is
less than that of a first-class system of incandescent lighting,
including vviringt fixtures^ and shades.

Fig. 31

58, Characteristics of Moore Tubes. — Moore light-
ing tubes require alternating current at any of the frequencies
ordinarily used for incandescent lighting. If the supply
current is direct, a motor-generator, dynamotor, or rotary
converter must be used to transform it into alternating cur-
rent. Direct current, however, could be used in the tube,
provided sufficient voltage could be obtained. The voltage
required depends on the length of the tube and on the
brilliancy at which it is operating. Curve a. Fig. 32, shows
the volts at the tube terminals when operating at 12 hefners
per foot. A tube 100 feet long requires about 7J50 volts,
or 71,5 volts per foot; a tube l''>0 feet long, about 9,750 volts, or
65 volts per foot; and a tube 200 feet long, 12,250 volts,
or 61.3 volts per foot.

W Tn MODERN ELECTRIC^LIGHTING DEVICES %^h 1

H Curve d. Fig, 32, shows the low tension, or priniary,
H amperes at 220 volts for different lengths of tube operating
B at 12 hefners per fool, and curve r shows the total energy
H in kilowatts* Since the supply voltage remains constant
B and the energfj' supply increases with the length of lube, the
B primary amperes must increase.

B 59* The brlUlaucy uf the tube in the Moore light
B increases slightly during the first 100 hours of service, and
B After that remains fairly constant with constant voltage. The

1 '^

1 lill

H 25 e KKWO

.jii

^X'

\r^

sJS^

5j»^

EP*""^ 1

B ^ ^'^^^

SKprr

Hcfnt

r d

light outE
increase it
erable var
the tube
linear foo
looking d
The ef f
100 hours
chnnge di
remains cc

26 50 75 too 1^15 fBO t7C 20O 22S
Length uf Tu^e in J'\'fi
FtG. 32

mt increases about in direct proportion to the
1 voltage, and the tube is not injured by a consid
iation of voltage. The g^reatest brilliancy at whict
can be made to burn (about 30 candlepower pei
t) is not great enough to strain the eyes whet
ireclly at it.

lelency of the tube also increases during the firs

of service, but afterwards there is no appareu

a ring the life of the lamp, provided the voltag<

mstant. Increased voltage causes not only increasec

\
r
1

t
t

§55 MODERN ELECTRFC LIGHTING DEVICES 41

bri]lianc7« but also increased efficiency. The efficiency of long
tubes is greater than that of short ones* Curve d. Fig* 32,
shows the relation existing between the length of a tube and
its consumption of power at 12 hefners per foot.. A tube
50 feet long consumes about 2 watts per hefner unit; a tube
100 feet long* 1.6 watts per unit; a tube 150 feet long»
L35 watts per unit; etc* Recent tests made on a 179-foot
tube that had been in use 1»000 hours showed a power con-
sumption of 1.S5 watts per hefner» at a brilliancv of 13 hefners
per foot of tube* This lube was giving an orange-tinted
light: when producing white light, the efficiency is lower*
The power consumptions here given include that of the
transforming device.

Among the objections to the Moore tube are the fact that
it can be used efficiently only in large units and its low power
factor — 60 to 75 per cent* In many installations, the first
objection is not serious, since the demand for large units,
especially those having a distributed light source, is greater
than that for small ones; the second may, perhaps, be largely
removed with further developments.

FLAMING-ARC LAMPS

60, Up to 1894, the only arc lamps used in the United
States were of the open-arc type. During the succeeding
10 years enclosed- arc lamps came into general use and grad-
ually, with the exception of a few isolated cases, displaced
open-arc lamps. Many varieties of enclosed-arc lamps are
in use, most of them differing from one another only in
mechanical details* There are differences in the methods of
making up magnet coils and resistances, of insulating the
electric circuits, adjusting and regulating the arc, enclosing
the arc. etc*, but the general principles on which nearly all
enclosed-arc lamps operate are practically the same.

The chief reason for displacing the old-style open-arc
lamps was the superior steadiness and quality of the light
furnished by the enclosed-arc lamps, though the decreased
cost of repairs and maintenance of the newer lamps was an

4S MODERN ELECTRIC-LIGHTING DEVICES §66|

itnportant consideration, especially in countries where labor
costs are high.

61. Theory of Flauilii^'Are Lamps. — All attempts to
operate the old-style open-arc lamps with an arc longer than
about i inch resulted in a waste of energy. The additional
power required to force the current through the longer arc
was expended in a stream of hot gases, with but little
increased light and greatly increased flaring and unsteadi-
ness. The idea of inserting in the stream of hot' gas a sub-
stance that would be heated to incandescence, and that would
at the same time so increase the conductivity of the gas that
the arc would remain steady, is an old one, but only within
recent years has it been made practicable.

It has been found that if the carbons are impregnated with
suitable mineral salts, the heat of the arc will vaporize the
salts and heat the vapor to incandescence. The electrodes
cjn then be drawn farther apart, producing a luminous arc
from t to 2i inches long; The color of the light from such
an arc can be controlled to a considerable extent by the selec-
tion of the salts with which the carbons are impregnated.
The salts most commonly used are those of calcium and
magnesium. Lamps using such carbons and producing such
arcs are usually called flaiiiiu|sr-arc lamps; a more nearly
correct designation, also sometimes used, is lu ml nous-are
laniiis.

When the carbons burn, the salts are converted into vapor,
which not only becomes incandescent, thus making the arc a
brilliant flarae of light, but also afTords a path of compara-
tively low resistance between the electrodes, so that the arc
is much more steady than with pure carbons* The burning
is accompanied by the production of noxious fumes, a con-
siderable quantity of ashes, and particles of slag^ or scoria.
The fumes render such arcs somewhat objectionable for
indoor use, except in the small sizes, and also prevent
enclosing the arc. The ashes are deposited largely on parts
of the lamp immediately above the arc, and being white,
assist in reflecting the light downwards.

§55 MODERN ELECTRIC4.IGHTrNG DEVICES 49

62, Doseiiption of Flaming- Arc Xjamin— If both
carbons are impregnated and are arranged coaxially* that is,
with the positive carbon above the negative i as in ordinary
arc lamps, the scoria forms on the end
of the lower carbon as a hard bead*
which hinders the flow of current. To
prevent this, one inventor has placed
almost all the trapregnating salts in the
positive carbon, which is made the lower
electrode in the lamp; the scoria then
drops harmlessly away from the elec-
trodes. The arc in such lamps is drawn
to about I inch and has the appearance
shown in Fig* 33*

63* In most flaming-arc lamps, the
carbons are arranged side by side and
are slightly inclined so that the lower
ends approach each other at an acute
angle* as in Fig* 34, All scoria then drops away from the
carbons as soon as formed* In direct-current lamps, the

FiQ. $3

^safima^

Ptg. U

FtG, ftS

positive carbon is slightly larger than the negative* so that
both burn away at nearly the same rate; in alternating-current
lamps, both carbons are the same size.

60 MODERN ELECTRIC LrGHTING DEVICES §55

The arc assumes the form shown in Fig, 35; its natural

tendency is to pass across the shortest space between the
electrodes j but it is prevented from doing^ so and is made to
bow downwards from the carbon tips by magnets, which cause
lines of force to pass across the path of the arc. The arc is
thus forced in the same direction as would be a conductor
carrying a current through the same field in the direction the
current is flowing through the arc. By varying the strength
of the magnetic field, the arc can be made to assume the
form desired,

64< In the ordinary arc lamp, a large part of the light
comes from the incandescent carbon tips, especially from the
crater in the positive carbon. If the carbons are arranged
coaxially, much of the light from the carbon tips is cut off
by the lower carbon; if both carbons feed downwards, as in
Fig. 35j there is nothing to interfere with the downward
passage of all the light from both carbon tips, as well as that
from the flame. About three-fourths of the light from a
flaming-arc lamp comes from the flame itself; the remainder,
coming from the incandescent carbon tips, contains an excess
of violet rays, which improve the general quality of the light.

65* If permitted to enter the top of the lamp freely, the
fumes and ashes from the impregnated carbons would be
injurious to the mechanism. Moreover, in order to prevent
too rapid consumption of the carbons, it is necessary to
shield the arc as much as possible from air-currents. An
economizer, that is, a chamber made of a material not
easily affected by heat (see Fig. M), surrounds as much of
the arc as is necessary to shield it from air-currents, and affords
a surface on which most of the mineral vapor is condensed.

EXCELIiO FIvAMING-ARC LAMP

66» ExeeUo Dlreet-Curreiit liamp. — All flaming-arc
lamps have many points of resemblance. Most of those first
developed are made in Europe and have somewhat com-
plicated regulating mechanism. Fig. 36 shows the prin-
cipal electrical connections and mechanical details of the

MODERN ELECTRIC-LIGHTING DEVICES 51

Mathiesou direct -current lamp sold in the United States
under the trade name Excello. A shunt magnet a and a series
magnet b are arranged at right angles to each other, and
between them is an armature c pivoted at d and having arms
e and /. When current is switched on to the lamp, the shunt
magnet a is excited
and armature c moves
toward it, lifting arm/ , ^ ^_

against the retarding ^^

influence of the dash-
pot g. Attached to
arm / is a rod hy the
lower end of which is
fastened to a slider /'.
When the rod is
raised, the slider,
through which the
negative carbon
passes, is drawn hori-
zontally toward the
positive carbon and
the carbon tips are
brought together,
closing a circuit be-
tween the two lamp
terminals through
magnet b and the car-
bons. A momentary
starting current 40 per
cent, in excess of nor-
mal value causes the
series magnet h to
overpower magnet a,
and armature c is drawn back, the rod h lowered, and the
slider / shifted outwards in a horizontal plane, thus separa-
ting the carbons and starting the arc. The current imme-
diately drops to normal value. Armature c then remains
floating between the series and shunt magnets.

Fk;. 3r.

46B— 3(5

52 MODERN ELECTRIC-LIGHTING DEVICES |BS'

As the ends of the carbons bum away and increase the
length of the arc» the shunt magnet a becomes stronger
until armature e is drawn over so far toward a that the arm €
causes the detent /' to release the feeding: gear. This gear
consists of wheels and pinions controlling the movements of
drum i, around which is coiled the chains that support the
carbons. When the carbons have fallen until the arc is again
shortened to the proper length, armature c is drawn back
automatically until the detent /' arrests the movement of the
gear. As the carbons fall, a detent, or tripping pin, attached
to a third chain passing over the drum / gradually rise^ in
the center tube, and when the carbons are consumed the pin
has reached the position p, where it raises the stud g and
opens the switch m in series with the shunt magnet a.
Armature c is instantly drawn to its extreme position toward
magnet b, forcing the slider i over so that the carbons are
separated as far as possible , and the arc is broken. Coil ^',
in series with the arc, supplies the magnetism required to
keep the arc blown down to the ends of the carbons. The
higher voltage lamps have an additional blow-out coil n in
series with a switch o across the circuit. While the lamp
is operating, the shunt magnet a attracts the rear end </ of
the switch, which is thereby held open; as soon as magnet a
is cut out, switch o closes and coil n assists in blowing out
the arc.

G7- Excello Altematlnpr-Ciirrpiit Lamp. — In Fig. S7

is shown the arrangement of the wiring and mechanism in
an alteruatlngr-eurrent lamp. A shunt magnet a is con-
nected directly across the lamp terminals through the
switch wi, while a magnet b is connected in series with the
blow-out coil ^' and the arc, these connections being similar
to those of the direct-current lamp* A copper disk r is
arranged to rotate near the poles of magnets a and ^.
Alternating magnetism in the poles sets up eddy currents in
thediski and the reaction between these currents and the mag-
netism causes the disk to rotate, the direction of rotation
depending on the relative strength of the magnets. When the

§55 MODERN ELECTRIC-LIGHTING DEVICES 63

lamp is ready for operation ^ the carbon ends are in contact,
and when the lamp h switched on to the circuit^the resistance
through coils 6, i>' and ^
the carbons being low *-= — t-
— a considerable cur-
rent flows, and series
magnet b is strongly
excited. This causes
wheel € to rotate in a
direction to wind the
chains on the drum i
and draw the carbons
apart* thus striking the
arc. The voltage
across the arc soon
causes the shunt mag-
net a to become ex-
cited enough to balance
the effect of the series
magnet i> on the rota-
ting disk» which there-
fore comes to rest with
the proper length of
arc. The two mag-
nets act differentially
on the disk while the
lamp is operating and
automatically keep the
arc adjusted. When
the carbons are burned
out, the pin on piston^
lifts the stud q and
opens the switch m in the shunt circuit: the series magnet at
once causes the carbons to be separated so far that the arc is
broken.

Fjo. a7

68. Kxcello Lamp Economizer^ — Fig. 38 (a) shows
a view of the economizer a and the carbon tips while the arc

54 MODERN ELECTRIC-LIGHTING DEVICES §55

is burning; ^ is a blow-out coil, consisting of a few series*
tums to hold the arc down on the carbon tips and a number
of auxiliary shunt turns that are used only to help blow outj
the arc when the carbons are consumed. Rods ^, c are m\
part of the framework of the lamp, and d, d are the carbons.
Fig. 38 {^) shows the position of the carbon ends when they
have been automatically separated and the arc disrupted.

fa>

Pio, »

Suitable ventilatinir holes are provided around the econo-
mizer for the escape oi gases, and the pan underneath the
globe (not shown} contains holes to admit the air needed
by the arc. The globe surrounds the arc and fits tightly
inside the rim i^. All the lamp mechanism is housed as com-
pletely as possible, to protect it not only from the weather,
in case of outdoor lamps, but also from the fumes of the
lamp.

56 MODERN ELECTRIC-LIGHTING DEVICES §55

THE BECK LAMP

69» Fig. BB {a) and (d) are front and rear views of the
interior of a Beck direct -current flaming-are Intnp, with

resistance on spools ^ such that the lamp can be operated
singly on a 110-vok circuit. Without the resistance* this
lamp is suitable for use on from 55 to 65 volts, two in series
on from 110 to 120 volts, or four tn series on from 220 to 240
volts* The resistance may be connected in either the posi-
tive or the negative line. Assuming that it is in the positive
line, the current passes through the resistance and enters the

positive terminal of the
lamp, through which it
takes the following path:
positive cable a, carbon
holder ^, and carbon ¥-
arc r-negative carbon d,
holder d\ and cable e
[shown only in (^)]-arc
blow-out coil /-lifting
magnet ^-arc blow-out
coil /'-cable k, to the neg*
ative terminal.

Fig, 40 is a view of the
bottom of the lamp, show-
ing the economizer A and
the carbon tips as they
rest together when the
lamp is ready for oper-
ation. When the current is switched on, the magnet j'.
Fig, 39 M, lifts the rod /, Fig. 39 (^), which turns the
casting j on the pivot k, causing the pin / to move the
casting m and its attached porcelain piece* through which
the negative carbon passes, away from the positive carbon,
thus striking the arc. A dashpot g'' steadies the movements.
The rods n, n are so fastened in the top of the lamp as to
allow them to swing outwards at the bottom. White the
lamp is operating, some of the magnetism produced by the

Fio. 40

§55 MODERN ELFXTRIC-LIGHTING DEVICES 57

blow-out coils /, / follows down the side rods to the bottom
of the lamp, and enough of it crosses the space between the
carbon tips to force the arc down, so that it forms a bow, or
inverted arch, between the tips.

70. Running the whole length of one side of the positive
carbon is a rib that rests on a cone-shaped metal wheel o.
Figs. 39 and 40. This rib burns to a fine point where it rests
on the wheel, gradually crumbles off, and allows the carbon
to drop slowly. The two carbon holders are connected by
a chain, as shown diagrammatically in Fig. 41.
The chain is insulated from each holder and
passes around two pulleys /, p' — one in the top
of the lamp and one in the bottom. When
the ribbed carbon drops, the chain moves over
the pulleys and permits the other carbon to
drop an equal amount, so that the two feed
down together.

When the carbons are burned as short as
they can be without injuring the lamp, a pro-
jection on the positive holder pushes the neg-
ative holder to its extreme outward position,
making the arc as long as possible, after which
the projection g. Fig. 39 (a), on the positive
holder touches the contact piece r, which is
connected through the fuse s and cables / and h
to the negative terminal of the lamp. This
short-circuits the lamp, puts out the arc, and at
the same time blows the fuse. As the carbons
are held apart, the arc cannot start again.

A sheet-metal casing encloses the lamp
mechanism, and a large translucent globe sur-
rounds the arc and protects it from air-currents. The size
and appearance of the completed lamp do not differ
materially from those of ordinary arc lamps. The alter-
nating-current lamps operate on the same general principles
as the direct-current lamps, very few minor changes being
necessary.

Fig. 41

68 MODERN RLFXTRIC LIGHTING DEVICES §55

CHARACTEni8TICS OF FLAMING-ARC liAMPS

71. Impregriutted Carbons, — The I mpreipii a ted car-
bons used in nearly all flaming-arc lamps consist of three
zones, or layers: (l) An inner soft core made of a mixture
of carbon and salts of calcium, magnesium ^ or whatever
metal is required to give the desired color; (2) a layer of
the same materials more firmly compressed; (3) an outer
layer of firmly compressed pure carbon, giving mechanical
strength to the whole. In some cases^ in order to reduce
the resistance, the' carbons have a metallic core. Fig, 42

Pig. «

shows a pair of carbons, such as used in the Excello lamps,
broken in pieces to show the metallic core*

The impregnated carbons used in flaming-arc lamps are
expensive and they last only from about 8 to 20 hours,
according to their length and the quantity of current in the
arc. If used for street lighting, it is necessary to trim most
flaming-arc lamps about every dayi as was done with the

TABF^K in
COMPABATIFE LAMP TESTS

CompariBOQs

Mean amperes . , . , .

Mean volts at the arc ..,....*.
Mean watts at the arc .*..,...,
Mean spherical candlepower .,.,..
Mean lower hemispherical candlepower .
Watts per mean spherical candlepower . .
Watts per mean hemispherical candlepower

Fkamiti£f
Arc

360

1,020

1,560

353

Enclosed
Arc

81
413

260
X.59

§55 MODERN ELKCTRK-LIGHTING DEVICES 59

old-style open-arc lamps. The cost for maintenance is
therefore high. Some lamps have been arranged with a
magazine holding a number of car-
bons in such a way that as soon as
one pair is exhausted another pair is
automatically substituted.

72. CandlepoMrer and Distri-
bution.— The data given in Table III
are from tests made by the Electrical
Testing Laboratories, New York City,
on a flaming-arc lamp (the Excello)
and on a direct-current enclosed-arc
lamp.

The distribution of light as determined by the tests just
mentioned is illustrated graphically in Fig. 43. The arcs of
circles represent the intensity of the light in candlepower,

■Vr"

400

'vxir

000

y(F)

IQOO

76*

atf

Fio. 48

as shown by the figures along the left-hand margin. The
center o shows the position of the lamps, while the full-line
curve a represents the light given off by the flaming arc,

60 MODERN ELECTRIC-LIGHTING DEVICES §55

and the dotted curve b, that given oflF by the enclosed arc.
The two curves have the same general shape^ showing that

the light is distributed from both lamps in very much the
same way; but the flaming arc gives off ne^^rly six times as
much light as the enclosed arc. The maximum light from
the flaming arc is given off in the angular space between
30° and 75° below the horizontal, and decreases slightly
directly under the lamp. The fiaming-arc lamp had an
opalescent globe, and the enclosed-arc lamp had an opales-
cent inner globe but no outer globe.

The distribution of light from a flaming-arc lamp with
downward^eedlng carbons and no globe is shown by curve a.
Fig. 44, Curve ^ shows the distribution and the relative
intensity of light from an old-style open-arc lamp, and
curve € the corresponding quanlitiess for an enclosed-arc lamp.

73, The effect of impregnating the carbons with differ-
ent light-producing minerals is shown in Fig. 45. The

same lamp with dif-
ferent sets of carbons
was used for each
curve, and the lamp
consumed the same
power in each case.
The white light,
curve a, was produced
at an expenditure of
1.202 watts per spher-
ical candlepower; the
red light, curve b, at
L03 watts; and the yellow light, curve c, at .716 watt.
These curves were taken with an alternating-current lamp
consuming 578 watts*

|55 MODERN ELECTRIC-LIGHTING DEVICES 61

CARBONE ARC LAMPS

74. The Carbone arc lamp is the result of an attempt

to secure with pure carbons the advantages of downward-
feeding inclined carbons and also freedom from interference
with light reflection from the carbon tips. From 80 to 90
volts are used across the arc. which is forced down to the
carbon tips by suitably arranged magnets. Fig, 46 shows
the position of the electrodes a and
the mag^nets^, b for steadying the arc.
Most of the magnetism traverses the
iron ring c, but holes d^ d increase the
rdmta7U€ of the ring, that is, its oppo-
sition to the passage of magnetism,
and enough lines of force leak across
from one side of the ring to the other
to cause the arc to spread out and
bow downwards in the form of a
spherical segment. An economizer fits inside the iron ring c
around the carbon tips.

Considerable advantage is obtained over the ordinary arc
lamp, and although the efficiency is not so high as with
impregnated carbons in the flaming-arc lamp, the Carbone
lamp has the advantage of using very much cheaper car-
bons. Table IV gives comparative results in hemispherical
candlepower.

TABLE IV

Fig. 4fi

COMPAKISON OP VARIOLTS ARC LAMPS

Candlepower

per Watt

Watts per
CaadJepower

Ordinary open arc . .
Enclosed arc . , . .
Carbone arc ....
Impregnated-carbon
arc

200

259

1-54
0.77

2.24

578

^65
13

•445

^173

62 MODERN ELECTRIC LIGHTING DEVICES §56

MAGNETITE IjUMINOU8-ARC I.AMP

75- In any electric arc, the material that supports the arc
isfines from ihe negative electrode as a high-velocity arc
blast, wliich strikes the positive electrode and heats it.
Unless the positive electrode is large enough to conduct this
heat away, it may get hotter than the negative electrode, as
is the case with ordinary arc lamps, in which the positive
carbon is burned away nearly twice as fast as the negative
carbon. The size of the positive electrode may be made
such that it will wear away but very little; if too large,
the material from the negative electrode will be deposited
on it.

The magnetite lumlnoiis*arc lamp developed by the
General Electric Company has a copper positive electrode
larg^e enough to be practically unaffected by the arc; also a
negative electrodCi made up by packing in thin iron tubes,
8 inches long by I inch diameter, very finely divided
magnetite, or black oxide of iron, in which are mixed small
quantities of salts of chromium, titanium, etc. Pure mag-
netite does not give such high efficiency nor produce so
steady an arc as that containing the other salts mentioned.

76* In Fig, 47 {a) is shown a luminous-arc lamp com-
plete, and in {b), the interior with the globe and casings
removed. At a is shown the series magnet; b^ the shunt
magnet; e, the starting magnets {one directly back of the
other); d, the dashpot; r, the adjusting armature disk, lor
regulating the frequency of the automatic arc adjustments;
/, an adjustable stop, for regulating the length of the arc;
^, the starling resistance, of which there are several spools;
h, an iron box^ through a slot in which extends the positive
electrode / — a copper bar; j, the negative electrode; k, the
tripping rod; and /, a central tube, or chimney, for discharging
the gases from the arc out of the top of the lamp. These lamps
are used only with direct current, either in series on constant-
current circuits or in multiple on constant-potential, 110- or
220- volt circuits..

%r,r, MODERN ELECTRIC-LIGHTING DEVICES 63

FiQ. f!

64 MODERN ELECTRrC-LIGHTING DEVICES §55

77, Fi^. 48 is a diagram of connections of a cau&taiii^
current lumiii<His-are luiiixi. When the lamp is idlei

the carbon blocks m
are in contact, and
when the current is
switched on, it takes
the path from the
positive terminal
throngh the starting
resistance ^-the car-
bon blocks m-and the
starting magnets c,
to the negative ter-
minaL The starting
magnets lift their
armature n, thus rais-
ing the negative elec-
trode / until it makes
contact with the posi-
live electrode /. The
^^^^::d_l larger part of the cur-

J^'**- *^ rent then takes the

path from the positive terminal through the series magnet a
and the electrodes to the negative terminal. The series
magnet lifts its armature and separates the
carbon blocks^ thus cutting the shunt mag-
net S into circuit in series with the starting
resistance and the starting magnets. When
the carbon blocks separate, the addition of
the resistance of the shunt magnet to the
circuit through the starting magnets so
weakens them that the armature n drops
back instantly about A" inch and then slowly,
as the dashpot retards the motion, until the
arc is about i inch long and has the appear-
ance shown in Fig. 49. The flame is very ^^^ ^^
brilliant and the light nearly whke. This lamp has proven
very successful for street illuminationi

§55 MODERN ELECTRIC-LIGHTING DEVICES 65

78, The voltage across the lamp terminals at the start is
about 76, As the arc len^^thens, owing to the burning away
of the negative electrode » the voltage gradually rises until it
reaches a fixed lira it ♦ when the shunt magr^et acts to close
the carbon contacts^ thus short-circuiting the shunt magnet
and permitting the starting magnet to again adjust the arc.
This feeding occurs about once every hour.

Each negative electrode lasts from 150 to 200 hours; a
positive electrode lasts about 4,000 hours. There is some
residue from the burning, most of which falls into a tray in
the bottom of the globe.
This tray should be cleaned
and the globe brushed out
at each trimming; also, the
center tube should be
cleaned by running a small
brush through it.

The constant-current
luminous-arc lamps con-
sume about 320 watts and
give off about 400 spherical
candlepower, the specific
consumption being about
.8 watt per caudlepower.
The output of light is
slightly greater than that
of a 340-watt open-arc lamp
or a 460- watt en closed-arc
lamp, and the distribution
is better.

In a later type of mag-
netite luminous*arc lamp,
the positive electrode,
consisting of convoluted
strips of laminated copper
lower element of the lamp,
is connected to the
upper elemenl. The

Ftc. 60

and iron, forms the stationary

and the magnetite tube, which

negative lamp terminal,
feed is downwards, which

forms the
somewhat

66 MODERN ELECTRIC-LIGHTING DEVICES §55

simplifies the lamp mechanism,
also obtained.

Better light distributian ts

79» Automatle Mercury-Vapor Lamp. — ^The Cooper

Hewitt type P lamp is so constructed that on closing the
switch it will operate without the necessity of lilting the
tube. In Pig:. 50 is shown the lamp mechanism, and in
Fig. 51 the connections of the operating devices. Corre-
sponding parts in the two figures are lettered the same. In
Fig. 50i a is the ceiling plate; ^, the insulating joint; r+ and
^^ 1 Figs. 50 and 51, are the lamp binding posts; d, a resist-
ance coil; e, the shifter, or circuit interrupter; /and f\ the
inductance coils; £, the ballast; and A, an armature, which is
drawn toward /,/' when these coils are energized.

The positive lamp terminal r+, Fig* 51, is connected to

Pio. fi]

terminal 1 or terminal 2 on the resistance coil, depending on'
the voltage of the circuit. The shifter consists of a glass
vessel containing two electrodes, which are connected by
mercury when the lamp is not operating. This vessel is
mechanically connected to armature h and is rotated on its
axis when h is drawn up; an indentation in the glass vessel
then divides the mercury stream into twx> separate bodies
and the rotation also causes the mercury to fall away from
the contacts, thus opening the circuit through the shiften

§56 MODERN ELECTRIC-LIGHTING DEVICES 67

The lamp is started as follows: Close the switch; current
now flows from r-h through 1 or 2-3-4-e-5'-f-f'-g-€'~, The
inductance coils are energized and armature // is drawn up,
thus rotating shifter ^, breaking the circuit through the
shifter, and impressing a high electromotive force, due to
the kick of the inductance coils /, /', on the lamp tube termi-
nals. The positive side of the lamp mechanism is connected
to the positive tube terminal by path 6-7-8, and to a starting
band, consisting of a metallic coating painted on the outside
of the enlarged chamber on the tube, by path 6-7-9-10.
The negative side of the lamp mechanism is connected to
negative tube terminal //. The high electromotive force set
up between 8 and 7/, and 10 and 11 overcomes the resistance
between the tube terminals and starts the arc. The starting
band assists by concentrating the stress, due to the kick of
the inductance coils, at the surface of the mercury in the
negative electrode, thus causing minute sparks at the mer-
cury surface. As soon as the arc starts, the path of the
current that maintains the arc is c-f -l-6-7'S-tuhe-ll-12-

40B— 37

ELECTRIC SIGNS

FIXED ELECTRIC SIGNS

1. Electric signs are of almost endless si7.es and varie-
ties and some very striking effects are produced with them.
There are many patented devices in use for producing
electric-sign effects. While only a few of these are described
in this Section, yet there is abundant chance for the elec-
trician or wireman to exercise his ingenuity in devising; new
arrangements and devices to catch the pubUc eye. The
descriptions that follow are suggestive of innumerable
schemes. There are two general classes of electric signs:
those that have a fixed display and those that change either
automatically or at the will of an operator,

2. Fixed electric sl^ns may be classified as those iq
which the lights are arranged to illuminate a printed or a
painted sign; those in which the lamps are concealed behind
letter^shaped openings covered with translucent material
through which the light shines; and those in which the
lamps themselves are arranged in the form of letters* the
bulbs being displayed. Combinations of any two or more
of these methods may be used.

The user of an electric sign is addressing the public, and he
naturally desires to address the greatest possible number of
people for the longest possible time and in the most impress-
ive way. The sign should be designed wnth these points in
view, A sign that is legible only for short distances or only
during the night while the lamps are burning is, generally
speaking, of less value than one that can be read distinctly
from a long distance and that is visible either by day or night,

Ci^^ijFhifti ^y fntermuiiiyHitt To^M^tbook Cump^any. Eh tired at Staintners' ffati> London

iS6

ELECTRIC SIGNS

§56

n-IiUMINATED SIGNS
3* Fig. 1 shows a sign that is distinct and legible either

by day or night and that can be arranged single-faced or
double-faced; that is, so that it can be read from one direc-
tion or from both. This sign consists of white betters on a
blue enameled background surrounded by a border in which
is placed a number of incandescent lampSi which are so
arranged that the letters are brilliantly illuminated while the

»*;

DRY GOODS

lamps are burning* The lamp sockets and wiring are con-
cealed behind the border, and the wiring is very simple.

The making of such an enameled sign is an expensive
operation, requiring special tools and facilities, but any
electrician assisted by a sign painter should be able lo make
up a sign similar to that shown in Fig. 1. A modification
that might in some cases be an improvement would be lo
arrange shades over the lamp bulbs, so as to conceal them
from view and at the same time throw the light on the letters.

TRANSPARENT SIGNS
4* One sign manufacturer has had patented a method of

Fro. 2 1f^

making electric signs in which the letters or characters are

§56

ELECTRIC SIGNS

Fw. 3

ELECTRIC SIGNS

§56

outlined by a raised molding, leaving a hollow central portion
that is covered with a light-tinted, wire-woven, translucent
substance, behind which electric lamps are arranged. Fig. 2
shows a sectional view of a letter; a is the molding, of which
the face ^is covered with gold leaf and the side c tinted to
harmonize with the dark background d. The letter-shaped
opening outlined by the molding is covered with the trans-
lucent material e, back of which the lamps are placed. The
hooks / and g- enable any number uf letters to be interlocked.
Fig* 3(a) show^ the appearance by daylight of a sign made
of such letters^ and U) shows the same sign at night.

5. Combination 8l|^n.— Fig. 4 shows sectional views
of a patented device in which electric lamps are used, both
to illuminate a painted sign and to light a transparency;
(a) shows a single-faced sign, and (^) a double-faced sign.
In (a) the transparent sign b forms the front wall of a casings
across the opposite upper corner of which is a reflector sur-
face c that throws the light of the row of lamps d? out through

i56

ELECTRIC SIGNS

the transparency* Behind the lamps is a curved or V-shaped
rejector c, which may be turned at any desired angle to direct
a proper portion of the light on the painted sign / below the
casing. The lamps are invisible, while the signs are well
illnminated. The double-faced sign h is practically a duplicate
of the single-faced sign. Transparent signs b are placed in
each side of the hood, or casing, and there are two painted
signs / and two rows of lamps d^ each row having its curved
reflector e. ^

EXPOSEI1-BUI.B SIGNS

6* One lamp may be used to illuminate a considerable
portion of a painted sign or a transparency; but in order to
form a letter of exposed lamp bulbs so that it will be intel-
ligible at night, several lamps ^ ^ -^ Q d

Q
Q

Q Q Q

must be used. It is an object

to keep the number of lamps

as small as possible, not only

to reduce the cost of the sign, ^ ^

but also to keep the cost of

operation down* In Fig, 5 {(t)

is shown the result of an at- Q Q Q Q

tempt to make the letter £ ^^^ (^^

with only six exposed lamp *'*'

bulbs and no reflecting surfaces, while in (b) is shown the

number and arrangement of lamps necessary to make the

letter legible.

7, By enclosing the lamps In boxes having the shape of
the letter to be produced, and by using reflecting and distrib*
uting surfaces so that the light can be thrown only in the
outline of the letter, fewer lamps may be used. Fig, 6 {a)
shows a section of a patented letter that in reality is a com-
bination of a transparency and an exposed-bulb sign. The
letter, as patented, consists of a galvanized-iron body a with
a translucent face b through which the ends of the lamp bulbs
protrude* A white reflecting surface r and the white inner
surfaces of the box throw nearly all the light out through the

BLECTRIC srONS

156

translucent surface. Fig. 6 (A) shovv^ a 24-iiich letter ^ made

in this way atid lighted with only sev.en lamps. The trans-
lucent faces are white, so
that the letters are equally
legible hy day or night.

8, D ou hi ed -Paced
Sli^tis. — Individual letters
are sometimes cut irom
wood, painted with white-
enamel paint so that they
win be distinct in daylight,
and covered with incan-
descent lamps, which bring
out the outlines of the let-
ters at night. In making
up doiible-faeed hI^iib,
of letters made in this
way, it is well to bear in
mind that the letters .4, H^
/,M.O,T.UJ\ n\X\ and
>" appear the same whether
viewed from the back or
the front* ft is often pos-
sible to use both face^ of
these letters. The other
letters of the alphabet
must be cut from material
thin enough » so that when
two letters are placed back
to back they will have the same thickness as the double-faced
letters.

Fig. 7 shows a large sign on a prominent corner in
New York City. The letters are cut from 2- inch seasoned
lumber, painted white, and fastened to a wide strip of bar
iron, which serves to hold the siirn in position. On the faces
of the letters are rows of incandescent lamps, which make
the sign very conspicuous at night. The dentist sign a short

ELECTRrC SIGNS

§56

distance from the comer is one of the type described in
Art. 3*

9, E^aniples of I/ari^e Stitns, — The immense Butterick
sign, Fig. 8, on the side of the Butterick Building, in New
York City, can be seen from the New Jersey shore within a
radius of several miles. The first letter is 68 feet high, while

Pio. 8

the others are t50 feet. The two lines of lamps inscribinff the
outlines of the letters are 5 feet apart. The letters are painted
in fast black on the brick wall. A light steel box construc-
tion about 6 inches high is spaced about 6 inches from the
wall, to which it is fastened by means of expansion bolts.
The box construction is made in sections about 10 feet long,
with lamp sockets every 18 inches, and is placed around the

§56

ELECTRIC SIGNS

outlines of Ihe letters. There are twelve hundred 4-candle'
power lamps controlled by three switches, each switch having
a separate panel box. From one panel runs twenty*fonr cir-
cuits and from each of the other two, sixteen circuits. The
wiring is carried through the interior of the sign boxes.

10. The New York Edison Cofnpany has erected a sign,
shown in Fig. 0» at its coal-storage plant at Shadyside» New
Jersey, which can be seen plainly tor several miles up and

|*g«EDisONCO

55DUANEST

Pxo. V

down the New York side of the Hudson River. To support
this sign, a framework requiring over 70,0()0 pounds of steel
was put up. The sign contains eighteen hundred 8-candle-
power lamps, A special 7.>kilowatt generator and engine is
used to supply the electricity*

The lamps used for electric signs are usually of smaller
candlepower than those used for ordinary illumination; 4-, 6-,
and 8-candlepower sizes are common. Sign lamps also have
shorter and thicker bulbs, with the filament so coiled that
the larger part of the light will be thrown out at the end.

■ft

ELECTRIC SmNS

§56

CHANGEABLE SIGNS

CHANGES in INTENSITY OF LIGHT

THEIIMO^TATS

11. The fixed, or permanent, signs thus far described
may be made very attractive and of considerable va3tie lo
the advertisers; but im sign arrests the attention of passers-
by as does one in which there is apparent animation ^ espe-
cially if the changes or motions are surrQiinded with an air
of mystery. In electric sigfns, changes so slight as the light-
ingf and putting; out of the lamps or changes in the intensiiy
of the light will arrest the attention lon^r enough for the
passer-by to read what the advertiser has to say. Automatic
devices may be arranged to switch off all the lamps of a sign
together or part of them at a time- This is frequently done
by means of a therniostnt, an instrument in which an
electric current heats a metal and causes it to expand until a
circuit-opening device is made to operate so as to close or
open a circuit, after which the heating current is cut off or
so reduced that the metal cools and contracts and the device
is operated in the reverse direction; this throws the heating
coil into circuit again, and the series of operations are
repeated indefinitely.

12. The ThennobUnk, — ^Fig. 10 U) shows a form of
thermostat having the trade name thtirinobiltikt and (^)

shows the connections with a circuit of lamps. This device
consists of metal strips arranged in the form of a triangle,
around one leg of which is wound a coil a of fine wire that
forms a part of a circuit through the lamps. When the cur-
rent is first svvitclied on, the end ^ of the triangle does not
quite make contact with the end of a screw ^ with which one

§56

ELECTRIC SIGNS

end of the lamp circuit connects: but a smaH current, not
enough to light the lamps, flows through the coil a and heats
it. The heat causes the metal around which the coil is
wound to expand until the end of the triangle swings over
and touches the contact screw b-\ current enough to light
the lamps then flows through the side r and the contact
screw. The coil a, being shunted by the side c^ soon cools
and the triangle springs back to its normal position, thus

breaking the contact between b and ^' and putting out the
lights. This process is repeated indefinitely or until the
whole circuit is switched off.

In another form of the same device, a central tongue is
made to swing both ways by the influence of a heating coil,
one of two circuits being closed immediately after the other
is opened. A retarding device holds the contact closed in
either position until th§ pull becomes strong enough to open
it with a snap.

13, I.atnps With Thei-rnostats.— It is now possible to

obtain incandescent lamps that have U-shaped bimetallic
thermostats in the bases, made as showm in Fig. 11, The
two metals of which the U-shaped piece is formed have
different rates of expansion under the influence of heat

ELECTRIC SIGNS

The U is wound with a coil of wire a connected in series
with the lamp filament. When the lamp is connected to the
circuit, it lights for an interval, until the coil heats and
causes the U to spread and open the circuit, as shown

FIG. n

at d^ This stops the flo%v of current through the filament'
and puts out the lamp; the heating coil a soon cools and the
contact ^ closes, thus again lighting the lamp. By means
of an adjusting screw c the rapidity of the flashing may be
regulated. The contact points at ^ are tipped with platinum,

14* Double-Filament Lamps. — Fig. 12 shows a sign
lamp having a large and a small filament* The base contains
a thermostat that causes the two filaments
to light alternately. While on the circuit,
such lamps are never entirely dark* but
the intensity of the light changes enough
to draw attention.

15, Turnip Slfrn Ijanip^;* — Fig. IZ
(a) and {^) shows aide and end views of
a turnip ai^n lanixi^ so called because
of its shape. The base contains a ther-
mostat, and on the end opposite the base
is a letter, word, or sentence to be dis-
played. The continual flashing calls atten*
tion to the advertisement,

16- Thermal Flashers* ^^Not over

2 amperes current can be broken by the

Fio. 12 thermostats thus far described, as the

sparking, if a larger current were broken, would soon destroy

the contacts* In Fig, 14 (a) is show^n a thermal f lusher

made by the Solar Electric Company that will break

ELECTRIC SIGNS

10 amperes, and in (^) is shown connections to a circuit
of lamps* The carbon contacts a are normally separated,
the upper one being fixed in position and the lower one
attached to one end of a spring lever ^» the other end of
which is fixed at c* Near the fixed end of the lever d is
attached the end of
an expansion %vire d
that passes down
through a tube and
pulls the lever b
downwards against ^
the opposing action |r
of a spring e, which \
may be either coiled,
as shown, or flat*
Around the expan-
sion wire inside the
tube is a coil of fine
wire, called the beat-
ing, or resistance,
colli one end of which
is in connection with
the fixed end of the
spring lever 6 and the
other in connection
with the upper, or
fixed, carbon block a.
These connections
make the resistance
coil a part of the
circuit through the
lamps.

When current is turned on. it flows through the heating
coil, which does not permit the passage of enough current
to light the lamps of the circuit; but as the coil heats, the
expansion wire inside stretches until the carbon blocks are
drawn together by the spring e and the lamps light. The
heating coil, now being shunted by the lever d and the carbon

Tto. 13

§56 ELECTRIC SIGNS 15

blocks* soon cools, and the expansion wire contracts and
pulls down on the lever against the combined holding power of
the permanent horseshoe magnet /and the spring e. The pull
of the expansion wire finally becomes so strong that the car-
bon blocks separate with a quick break. The resistance coil
immediately begins to heat again and the process is repeated.
Adjustments can be made on the regular flashers so that the
lamps will light from eight to fourteen times per minute and
so that they will remain lighted any desired portion of the
time, from 50 to 90 per cent. Special thermostats of this
type have been made to work once a minute and others to
work fifty-six times a minute.

MECHANICAL FLASHERS

17. Double- Pole Flasher. — Various mechanical
devices are in use for flashing lamps automatically. Figs. 15
and 17 show devices made by the Electric Motor and Equip-
ment Company. In Fig. 15 {a) is shown a three-clreult,
double-pole, commutatiiis switch, or flasher, and
in (^), a similar switch with the motor and one end casting
removed. The rotation of the motor is transmitted through
the belt and worm-gear to the shaft a, on which are as many
disks b as there are circuits to be controlled. In Fig. 15 (/>)
only two disks are shown in place, the third being removed
in order to show the mechanism. Near the rim of each disk
is a series of holes, in any of which may be placed the
pinions of steel rollers c. The rollers may be placed on
either side of the disk, and the pinions are secured in place
by screws through the rim of the disk, as shown at c' ,

When the roller on one side of the disk presses against
the jointed links d and forces them down until they are in
line with each other, the switch arm € is forced over until the
blades e' enter the spring clips /. The springy is then under
tension, tending to open the switch. A smaller shaft h
below the main shaft a carries castings, each of which has
two cams i,j. There are one set of links and one pair of
cams for each disk. The links and cams shown in Fig. 15 {b)

46B— 38

§56

ELECTRIC SIGNS

next strikes them. The condition shown is that just after
the switch has been opened and before the cams have
snapped back into place.

18. The two blades ^, Fig. 15 (^), of each switch are
insulated from the arm e that carries them. When the switch
is closed, each blade makes contact with two clips /, as shown
diagrammatically in Fig. 16. The upper clip of each pair
is connected to the sup-
ply line, and the lower
one to the lamp circuit.
Each switch is there-
fore double pole.

19. 81n»le-Pole
Flasher.— Fig. 17

shows a portion of a

smaller flasher that is

single pole. The shaft a

rotates and carries with

it arms b, b\ etc. Arm b

strikes against and

raises a projecting

switch arm c, and closes

a switch against the

action of a heavy coiled spring d tending to open it. The

switch is locked in the closed position by a hook on one

end of a casting <r, on the other end of which is an arm

ay:ainst which the arm b' strikes at the proper time, and

thus tips the casting enough to release the switch and allow

it to fly open. After the arm b' has passed, the hooked end

of the casting is held up in position by a lighter coiled

spring /, and is ready to catch the switch for the next

operation.

20. Time Switches. — Fig. 18 shows the principal parts
of an nutoniatie time switch, consisting of an ordinary
double-pole knife switch, with the handle at right angles to
its ordinary position, and a device that opens the switch auto-
matically at a set time. In the position ordinarily occupied

spring

PlO. 16

ELECTRIC SIGNS

§56

by the switch handle is a special casting having a lip a
that hooks behind the end of a lever b and holds the switch
closed against the action of a spring c that tends to open it-
Above the switch is a shelf bearing two pedestals d\ the
shaft supported by the pedestals carries on one end a slotted
rectangular block e and on the other end a cam /, An ordi-
nary alarm clock is placed on the shelf between the springs^,

fju. n

so that the thumb piece for winding the alarm fits into the
slot in the block e. When the alarm goes off, the thumb
piece turns and causes the cam / to move the lever 5 enough
to release the switch, which immediately flies open* A coiled
spring h causes the lever b to return to its original position
as soon as the pressure of the cam / is removed.

By the use of time switches^ lamps may be left burning at
nightt to be automatically thrown off at any desired time.
Similarly arranged switches are made both for closing and

ELECTRIC SIGNS

for opening circuits, so that lamps can be made to light
automatically at one hour and £0 out at another. These
switches are useful (or lighting the lamps of a sign or those

in show windows on Sundays and holidays, and then extin-
guishing them after the travel by the store has nearly ceased

for the night.

CHANGES IN DI8PLAT

BLBLIGIIT SYSTEM

21 » There are in use many systems and devices by
means of which the wording of a sign may be changed.
The Elbllglit isystetn consists of lighting boards » cables »
and lamps with two-pin terminals*

The lighting boards are made by laying conductors a^a^
Fig. 19» side by side parallel with each other, and so con-
necting them by suitable terminals to a source of electro-
motive force that adjacent conductors will be of opposite

ELECTRIC SIGNS

§56

polarity. Between the conductars is insulation d, t. The
conductors are stranded, and when the board is compressed

thev flatten out tin HI

J J

FfG. 19

ihey are separated by
about i inch of in-
sulation.

22. The Elbltght
cables are made in a
similar m anner.
Many strands of bare,
fine copper wire are
braided together as
a cable and insulated, two insulated cables being fastened
side by side when in use, as shown in Fig. 20. Fig, 21 (a)
shows a lamp for use with a lighting^ hoard, and {h) shows a
method of^ fastening the lamps to the cables. The lamp
bases are porcelain
and the prongs phos-
phor-bronze. The
braiding of the cable
strands is such that
under ordinary con-
ditions the prongs are
firmly held without
the clamp* The in-
sulation on the cable
is of a high-grade
rubber, so that holes
formed by the lamp
prongs close imme-
diately when the
prongs are with-
drawn.

All that is required ^^^' ^

to light lamps with either the board or the cable is to thrust
the prongs through the insulation until they come in contact
with the copper* In the board* the insulation between the

156

ELECTRIC SIGNS

conductors usually consists of hard fiber or some other
material that the prongs wiil not easily penetrate ^ so that
short circuits are rare.
Lamps may be ar-
ranged on the board
in the form of any
letter, figure » or char-
acter desired and may
be changed, without
great expense, to any
other design. The
cable is more useful
for electric ornamen-
tation than for electric-sign work, as it may be draped or
looped along the walls of a room or a building, wound
around pillars and cov^ered with evergreen, with lamps stuct
in at intervals, etc.

Pig. 21

TALKING SIGNS

23» Moiioprrain Letters. — Various
other devices are in use by which the
positions of the lamps in a sign may be
changed so as to display different let-
ters; but to make such changes requires
considerable time and trouble. Fig; 22
shows a group of twenty-one lamps
arranged in metal troughs, or boxes,
whose inside surfaces are whitened with
a vitreous substance like enamel, so that
they reflect the li^cht outwards. This
device, including the lamps and boxes,
is called a iiicmo^rivin letter, or simply
a niano^riim; with it» by lig'hting dif-
ferent groups of lampSt may be dis-
played any letter of the alphabet. In
order to show any desired letter, il must be possible to con-
trol the lighting of each lamp independently of the others

ELECTRIC SIGNS

$56

§5*^

ELECTRIC SIGNS

(with one exception). This necessitates a separate wire from
one side of each lamp socket to a suitable controlling^ device,
but the other side of each socket is connected to a common
wire that leads directly to the supply circuit. The con-
trolling devicet or commuiaior, automatically changes con-
nections so as to display letters in any desired order,

24. Fig. 23 shows the complete wiring of one monogram,
with the exception of the lamp connections of the wire a
common to all lamp sockets; these connections are omitted
for the sake of clearness. The individual wires from
the lamps lead to a series of binding posts 1 to 20 on the
commutator* The two lamps numbered 5 m the monogram

are never lighted separately; hence, a common wire connects
them with finger number 5 on the commutator. This is the
exception previously referred to. Including the wire a
common to all lamp sockets, there are twenty-one wires
leading to each monogram, A wire a^ connects the commu-
tator with the side of the supply circuit opposite that with
which the common wire a is connected. Circuits b lead to
other monograms in the same sign; one wire of each circuit
connects with one terminal of each lamp in a monogram and
the other with the commutator belonging to that monogram*
Each monogram circuit is connected to the supply circuit
through double-pole cut-outs r . Another branch circuit leads
to the motor that operates the commutator,

ELECTRIC SIGNS

§56

ii * ii

J_U=**-i'

25. The commutator consists of a series of contact fin-
gers» or springs, and a device for forcing them into a position
where they close the circuits throug^h the lamps. Fig. 2-4
is a view of two commutators, one having a letter bar a in

position. The contact

fingfers are arranged
uodernealh the slate
top if. The rolled-steel
letter bars» each having
projections for raising
the fingers necessary to
light a letter, are slipped
into slots in the rims of
the wheels r, and are
held in place by spiral
springs d around the
end wheels of each com*
mutator. On the left-
hand commutator these
springs are shown off
the slotted wheels and
hanging on the shaft*
The shaft is rotated by
means of a motor, not
shown, so that succes-
sive letter bars are
brought under the
fingers,

26. Fig. 25 is a
diagram showing a
cross-section of the
commutator; (a) shows
a projection on a letter
bar a just as it begins to raise a finger d, and id) shows the
finger raised to its full height. The letter bars do not make
electrical contact with the fingers, but strike against metal
shoulders e that are insulated from the fingers.

§56

ELECTRIC SIGNS

The fingers are phosphor-bronze springs clasped loosely
about a bar /running lengthwise of the commutator. When
a finger is raised, one end makes firm contact with a brass
stripy on the under side of the slate cover. A single bind-
ing post // in connection with this brass strip serves for the
common wire a\ Fig. 23, connecting the commutator to the
supply circuit. The other end of the spring d. Fig. 25 (^),
makes contact with the round head / of a binding post /, one

Fi(i. 26

of the twenty posts with which the lamps of the monogram
are connected.

27. In Fig. 26 is shown a diagram of the connections
that are active when the letter H is displayed. The letter
bar a has projections that lift the fingers corresponding to
the lamps needed. The lamps are numbered, and correspond-
ing numbers are shown on the bar projections. This diagram
represents conditions at one instant while the commutator is

26 ELECTRIC SIGNS §56

turning; as this bar passes out from under the springs, all
the lamps go out, but immediately another bar with other
projections moves under and another letter is displayed.

28. Each commutator holds forty barsj hence, each
monogram can be made to display forty separate characters,
A number of monograms arranged side by side with all
their commutators operated by a single motor constitutes a

INTERNflTIONRL

■

CORF^ESPONDENCE

cr 1 vj i"*' '*"' 1 cr

Z? L- n U •-•L-I?

■

SCRRNTON. PR.

FiO. 27

talking sl^Uf and may be made to flash forty words oi
sentences in succession. The same series of expressions
may be flashed a whole evening without any supervision
whatever from an attendant, or the attendant may substitute
other bars as often as desired so that new expressions wil
be displayed. Fig. 27 shows four of the forty expression:
one sign may be made to flash every night* ^

§56

ELECTRIC SIGNS

29. Talklnic Clock. — Fig. 28 show» an arrangement of
electric lamps for displaying time; {a) and (A), respectively^
show two successive displays. The lamps are differently
arranged than in the letter monograms previously described,

o «^^^^H

^HMMH

puyi^

^ «?9MP

P^niSP^^*

• a O • »

0 a a

• >

0*0 4>«» a

•oa ^ g

^>a ^^^

• ' : ^

0 i»ii» .^ ij

^ 0 ^

D^pji a

0 #«> ^ 4

^^K^ **

«» ^ «»

/&J

FjO. 2S

and each group contains only the number of lamps needed
for the figures it must display- For example, the first
group displays only the figure I, and hence contains but
a single row of lamps; the second and fourth groups must

ELECTRIC SIGNS

be capable of displaying any numeral from 0 to B, inclu-
sive, and the third group any numeral from 0 to 5, inclusive*
A commutator operated in synchronism with the movements
of a clock changes the contacts so that the time display is
changed once every minute,

30i CarrlBge Calls, — Fig. 29 shows a carrla|2re call

that is very useful where a number of carriages are waiting

Fio. 2^

for persons emerging from large assemblies, as at theaters.
This call consists of three groups of lamps arranged in
boxes with reflecting interiors and frosted-glass covers.
The lighting of the lamps is controlled by a device some-
what similar to the commutator used with the talking sign,
except that the carriage-call controlling device is operated
by an attendant. Any number from 0 to 999, inclusive, may
be displayed on the call shown. On arrival, each carnage
occupant and driver is given a number, and when the carriage
is wanted this number is displayed on the carriage call, which
is in plain view of all the drivers.

ELECTRIC HEATING

HEATING EFFECTS OF ELECTRIC
CURRENTS

1. When a current of electricity flows through a con-
ductor, work is done proportional to the square of the
current /, the resistance R of the conductor, and the time /;
that is, the work in joules is equal to P Ri, where / is in
amperes, R in ohms, and / in seconds. All this work is con-
verted into heat, which raises the temperature of the conductor
and its surroundings.

In the generation and transmission of electricity, this pro-
duction of heat is very undesirable and is avoided as much
as possible by using conductors of low resistance or by
transmitting the energy at high pressure and correspondingly
low current. Ordinarily, in transmission work, the size of the
conductors to be used is determined by the allowable pressure
drop rather than by the heating effect, but it is sometimes
necessary to consider the heating effect of electric currents.
This is especially the case when wires are to be used in
underground ducts, in molding, or other confined locations.

2. When the temperature of a wire is higher than that of
its surroundings, heat escapes from the wire. A wire with
a rough and blackened surface loses its heat more rapidly
than one with a bright, shiny surface. Table I gives the
heating effect of currents in bright and black wires, respect-
ively, in still air. The fi^^^ures in the body of the table are
the diameters of the wires in mils. For example, to carry
1,000 amperes with a rise of 80° C. in still air requires a

Copyrighted by International TextbixtA C 'ompany. Entered at Stationers' Hall, Ijondon

IWI

DKATtNG KPKFCTH nr CUR RENTS

EUk in T^raper»tttfe

Degrees CentiicmdF

Amperes

Height

Bkkdc

Brl^t fita^k

Bright

Bt«:k

Brii^t

Black

Dmmetcnof ¥

riTts. u^

t,ooo

968

911

7SO

9JO

878

7^3

©oo

593

S44

6qs

«So

«ss*

Hog

mil

800

It«W

S^3

771

6jS

TS^i

950

' 785

734

610

700

96a

900

74a

696

Sto

650

910

850

708

660

S50

600

858

800

66^

6j|

SiS

srs

775

ft4«

ftoj

SOJ

sso

995

080

808

750

628

583

4S8

S*5

97^

048

780

735

607

5*^3

461

500

960

9'S

751

700

S84

54J

45S

47S

9*5

S80

7'3

&75

S6j

5^3

4J9

450

S05

S4,l

t>g6

648

541

501

4J«

4:^5

McJ<

bbq

O^o

S^o

479

4or.

400

\ .OOQ

^^o

770

h^t

59^ 498

457

387

m$ ,

950

7.^i '

fti2

564

475

435

369

JSo

900

74S

fHJO

5^^

536

45^

4^3

350

.US

Sso

70H

fJ=;4

S50

S06

4?8

390

331

3*»

«oo

61s

5^9

475 ! 4P3

i*^

313

^75

7S0

638

575

4H7

444

377

341

^93

J50

696 1

s»f*

534

453

41J

351

317

373

235

ri4.'

545

A9A

4tg

379

333

agi

^53

JOO

500

453

3f'4

345

-0

265

239

'75

.5if>

454

4Crfi

34t> 1

^\iti 2t^

239

308

150

47c

404

:-i 2 2n

2ia

t94

'^5

40H

35^

3°H

270 :

2^5 JO(>

182

iGi

100

343

300

^5S

llh

195 170

150

i3S

3t5

27^

^37

J6^ '

i7iS 1 158

^17

>23

386-

24Ei

214

igfi

H'^i

JJ4

tia

^59

JJO

t(3Q

"70

1^7

I JO

100

fK)

^sfi

«ai

th;

15^ ,

1^5

1 12

H/i ,

ih;

iVJ

^3<3

|Qf>

K-

l.M^

14^^

117

lO.'^ 1

86 7K 1

fiS

f*l

(<^CJ

II 1

tiO N5

U(> 1 (t6

4«

JC)

7fi

fU Oo

45 44

3^1

IS j

37 35

§57

ELECTRIC HEATING

300
280
260
240
220

200
190
180
170
160

150
140

130
120

no
100

90
80
70
60

50
40

20
10

TABLE II
HEATING EFFECTS OF CURRENTS

(Carrying Capacity of Insulated Wire in Moldings)

Rise in Temperature. Degrees Centigrade

Diameters of Wires. Mils

445
431
417
400

362

343
322
300
275

250
217
178 I

78 I

448
437
425
411

398 364

383
370
354
339
322

302
284
264
242
220

436

414
403
391
378

351
338
322
308
292

276

259
240
220
195

195 175

169 I 144

136 I 115

100 ! 71

446

411

386

427

393

369

450

409

375

352

430

390

356

Z2^Z

408

370

^Z7

315

386

350

317

295

375

339

308

286

364

328

298

277

352

Z^7

287

266

340

305

276

256

326

293

265

244

312

281

253

232

300

269

240

220

285

255

228

208

270

240

214

195

253.

223

200

182

237

208

185

168

218

192

169

153

198

174

152

139

175

^55

135

122

152

132

118

104

128

100

250
241

230

220

208

195
182

168
154
139
123
108

75
58
40

367 '

350 I

315 '
298 I

354
338
321
304
285

280 1 268
270 I 258
260 I 249

239
229

218
206

195
182
170

158
143
130
116

lOI

86
70
54

40B— 39

^^^ 4

ELECTRIC HEATING

§"^B

TABI.E III

^B DIAMETERS OP WIR]!!; OF VARIOITS MATBRtALa ^^H

THAT W1L1> BE FOSfiU BY A CURKEHT OF

^^^^H

G^VEN STRENGTH

^^^^

(W.//. Preece.F. R, S.)

1 1

DiAmct«r», Inch ^^^B

E
1 ,

1
1

I 1

.003 1

.0036

■OOJ3

■0033

■^1%

.0047

.0073

.0083

.oo8t H

.OOJ4

,0041

^ooSJ

'^U

.0056

.0074

o"3

.0132

,0128 H

.0044

.0054

,007

,0069

.0074

.i)097

.0149

0173

,0168 ■

'^53

.0065

.00S4

.0084

.0089

.0J17

,0181

.02 1

0203 ^^H

~ s

.006a

.0076

.oogS

.0097

.0104

.0136

*03I

.0343

^^H

.OC98

.013

OI5S

.0154

.0164

,0216

0334

.03S6

037s ^^B

.0129

.0158

.0203

.0202

.0215

,0283

^^437

.0506

0491 ■

.0156

.0191

.0246

.©245

.0261

0343

0529

.0613

^595 ■

.oiSi

.02^2

.0286

.0284

^0303

.0398

.0614

.0711

.069 ■

.0205

.02$

"^m

.032

-0343

■^45

.0694

0803 1

0779 ■

.0227

.0277

03S^

-0356

0379

.0498

.0769

.089

,0864 H

.0248

'O30J

.0391

.0388

.0414

0545

.CS84

■0973

0944 H

.026S

^0328

0433

.04*

H044S

.0589

0909

,1052

.02 ss

*o3S^

.0454

045

■04S

0632

0975

1129

^^5 H

*o5^5

'O397

0513

*i5*^

.0542

.0714

. I lOI

1*75

■

.036

,044

.0568

,0564

.0601

.0791

.122

1 413

OJ94

,0481

.0621

.o6j6

.0657

.0864

■U34

1544

1499 H

.0426

.052

.067a

.0667

.0711

0935

1443

.1671

.t6ti ^1

100

0457

.0558

.072

07^5

,0762

aoo3

-1548

.179a

1739 H

120

.05! 6

^063

.0814

,0808

.0861

-1133

a 748

.2024

19^4 ■

^0573

.0698

0902

,0895

•0954

^^ni

'937

2243

.3176 H

t6o

.0625

■0763

.0986

,0978

J043

.2118

2453

2379 H

tSo

.0676

.0826

.1066

.1058

.1128

.1484

.2291

2652

^573 ■

200

.0725

.0886

.1144

1135

.121

-159*

3457

2845

.276 H

335

.0784

0958

*^37

.1228

^^'^^

.1722

.2658

'30/7

.2984s ■

250

.0841

.107B

1337

.1317

.1404

.1848

^3851

ll^^'

3*°3 1

275

.0897

,1095

1414

,1404

1497

.1969

^l^l^

35 *»

•3417 ■

300

09s

.1 161

M9S

,14^7

.1586

.20S6

.322

'372S

.3617 ■

1^ J

157

ELECTRIC HEATING

bright wire 911 mils in diameter, but a black wire of only
750 mils diameter will carry the same current with the same
temperature rise. Table II gives the heating effects of elec-
tric currents in insulated wires used in moldings. Heat
escapes more readily from a wire to its insulation and the
moldings than from a bright, bare wire to still air; for

TABLE IV
CARRYING CAPACITY OF GERMAN-SILVER WIRE

Number
B. &S.

Circular
Mils

Maximum Current
Amperes

Feet per Ohm

10,381

6.8

60.90

8,234

5-7

47.60

6,529

4.8

37.80

5.178

4.0

29.90

4,106

3.4

23 70

3.257

2.8

18.80

2,583

2.4

14.90

2,048

2.0

11.80

1,624

1-7

9.40

1,288

1.4

7.25

1,021

1.2

5.91

810

i.o

4.69

643

.83

3.72

509

.70

2.95

404

.59

2.33

320

.49

1.85

254

.42

1.47

201

.35

1. 16

example, according to Table I, to carry 300 amperes with 40° C.
temperature rise in still air requires a bright wire 475 mils in
diameter, while according to Table II an insulated wire in
molding to do the same thing need be only 41 1 mils in diameter.

3. Table III gives the currents that will just fuse, or
melt, wires of different materials. The fusing effect of a

ELECTl^TC HEATING

[57

current depends on the readiness with which heat can escape
from the wire. If a very short wire is clamped between
terminals, heat will escape to the terminals; if a fuse is
installed where air circulates freely, the air-currents wiU
carry away heat^ etc. For these reasons, fuses must be of
sufficient length so that the heat imparled to the terminals
cannot appreciably change the melting point; they must also

TABLE V
CARRYING CAFACITY OF GALVA XI ZED-IRON WIRE

Number

Washburn & Moen

Gauge

Circular
Mils

Maximtirn
Current
Amperes

F^t per
Ohm

' 59-536

515

6450

5o,6as

4SS

5490

ft S

43.849

40.0

463.0

1 '

36J64

3S-5

J9S0

[ ^

3^ 329

31^3

337*0

1 '

a6,244

^7-5

2$3 <9 H

^ 9

2J,go4

23^8

236.0 ^*

18,225

20,6

196.0

14,400

i6-9

15s 0

n.025

tj S

1 19.0

8.464

X0.7

91 4

6,400

8-4

69 1

5^184

7't

56.0

3.969

42. s

2.916

4.3

3^'4

be installed where air-currents cannot affect them. Fuses,
therefore, are usually 1 inch or more long and are enclosed.
In the absence of air, a conductor will carry a much larger
current without fusing than if air is present. For this
reason, in rheostats and electric-heating apparatus, where a
high current density in the conductors or an intense heat is
desirable, the wire is embedded in cement, enamel, or other
substance, which not only insulates the conductors, but also

§57

ELECTRIC HEATING

excludes the air from around them. The incandescent lamp
affords an example of the advantage of excluding air from a
highly heated conductor. If even a very small quantity of
air remains in a lamp globe, the life of the lamp will be

TABLE VI
CARRYING CAPACITY OF TINNED-IRON WIRE

6
2:

Area

Circular Mils

1^^

Maximum
Safe Current With ,
Iron Frame
Amperes

i
1

' Ohms per Inch
of a Spiral Wound
on .4-Inch Mandrel

J6.509

17.40

30.30

43-6

350.00

.04000

.0050

13-094

14.60

17.10

36.6

173^00

03300

.0066

lo.jSi

13-30

14.30

30.8

137^00

02751

^0095

S.334

10.30

13. 00

2S-8

iq8.oo

.02183

-0131

6,529

8.70

10.10

31.7

86,40

01730

.0182

5-178

730

S.50

18.3

68.50

.01372

.0245

4,106 1

6, 10

7.10

'5-3

54-30

,01089

'^3$3

3i257

S'lo

6.00

ia.9

43-10

.00863

.049a

2.583

4'3o

5.00 '

10.8

34 10

.00685

.0690

3,048

3.60

4.30

37.10

■00543

, .0960

1 1634

3,00

350

7.6

31,40

.00430

■1345

1.28S

2.50

2.90

6.3

16.50

.00341

.1963

1*021

2. 20

3.50

5-4

13 50

-00271

.2636

8[o

I. So

3.10

4-5

1070

.00231

■3735

643

1^50

1 77

3-8

8.49

,00184

.5320

509

1^30

I 49

3-3

673

.00146

7350

404

T.08

1.20

2-3

5-34

.00116

1-035

much shortened; and if the filament were in open air, it

would immediately be consumed.

4. The resistance wire in rheostats and in electric-heat-
ing apparatus, if properly protected from the air, may be

ELECTRIC HEATING

§57

operated at red heat without material injury; but this is sel-
dom done, because it is difficult to maintain good insulation
at such high temperatures, and, moreover, such intense heat
in these appliances is seldom necessary* Tables IV, V, and
VI give the safe carrying capacities of various materials used
for rheostats and electric-heating appliances. These figures
are for continuous service in open air; for intermittent
service » as in motor-starting rheostats, or for service in the
absence of air, considerably more current can be carried
safely, as indicated by the fifth column in Table VL

APPLICATIONS OF ELECTBIC HEAT

GENERAL CONSIDERATIONS

5, Aclvantai?es. — In the electrical devices thus far con-
sidered, the development of beat has been an undesirable
incident rather than an object* Under some conditions, how-
ever, it becomes highly desirable and possibly economical to
convert electricity into heat- Some of the advantages of
electric heat are as follows: (1) Its instant availability on
closing a switch; (2) its perfect control ^ as heat may be
obtained by its use in almost any intensity desired; (8) its
perfect adaptability, as it may be applied to the exact location
desired and in such a way that only very little heat escapes
to the surrounding air or other objectsj (4) the absence of
smoke, flame* dust, poisonous gases, etc.; (5) the absence
of fuel, ashes, etc. to be handled, or fires to be maintained;
(6) the decreased danger from fire or explosions.

6» Effect on Central station* — The applications of
electric heat are very numerous, and fortunately for the
interests of central^station owners and managers, most of
these applications call for electric power during those hours
when the station and the transmission system are not other-
wise loaded to their full capacity. The addition of a day load
to an ordinary lighting station is a source of considerable

§57 ELECTRIC HEATING 9

profit to the station, inasmuch as such a load calls for no addi-
tional investment in ^eneratins: equipment or in transmission
lines, but permits the use of apparatus already installed at
more nearly a constant load. With a good day load of motors
or heating apparatus, engines and generators that would
otherwise be idle and useless all day may be kept running at
a considerable profit.

It is evident, then, that a station can afford to sell power
during its periods of light load cheaper than during its max-
imum load, or, as commonly called, its peak of load; and many
stations, in order to encourage a day load, offer special rates
or other inducements for the use of motors, heating appli-
ances, etc. that are ordinarily in use only during the day.
Central-station managers should therefore be familiar with
all electrical devices that may add to day loads, and should
lose no opportunity to impress the public with the advantages
to be obtained by the use of electricity. Electric heating
presents a very promising field for such work.

7. Relative Costs. — The greatest arguments in favor
of electric heating are its convenience and cleanliness; these
in many cases are sufficient to overbalance the objection of
increased cost. The relative cost of heating by electricity
and by burning coal or gas depends on the continuity of the
service required, as well as on the relative prices of electric
power and of fuel. If a small amount of heat is required
intermittently for short periods only, as for heating flat irons,
it may prove more economical to use an iron that is heated
electrically rather than to maintain a fire in a range, with its
great waste of heat. In any case, it has been found that electric
power at 2^ cents per kilowatt-hour is about equal to gas at
$1 per thousand feet, and that for cooking and miscellaneous
heating, electric power at 4 to 5 cents per kilowatt-hour can
compete successfully with coal at from $6 to $7.50 per ton.

ELECTRIC HEATING

§57

THAWING FR02EX WATER PIPES

Ceueral Method, — The process of thawing frozen

water pipes by electricity consists simply in sending through
the pipe a current of electricity large enough to heat it.
Alternating current is generally used, because almost any
current strength desired can be easily obtained. In cities
and towns where the winters are severe, many of the central
stations provide special transformers, each having a sec-
ondary winding of a few turns of very heavy copper capable
of carrying large currents, A transformer, together with the
necessary cables, terminal clamps, measuring instruments,
rheostats, etc., is mounted on a wagon or sled, and one or
more such outfits are kept in almost continuous use through
the freezing weather.

When a request is made for the services of the pipe^haw*
ing outfit, it is hauled to the desired place, the terminals of
the primary coil connected to the high-voltage lighting cir-
cuit, the terminals of the secondary coil to the frozen section
of the pipe, one at each end, and an electric current of the
proper strength turned on* The current strength should be
suitable for the work to be performed; a large pipe of low
resistance will require a larger current than a small pipe.
Too large a current may injure the pipe; hence, it is better
to use a more moderate current for a longer period of time*
The length of time required to produce running water in
pipes that are frozen solid varies inversely as the square of
the current used,

9* Pipe-Thavring Data. — Table VII gives figures
obtained in practice, showing the diameters and lengths of
frozen pipes, and the amperes, volts, and time required to
produce running water in each size. These results are prob-
ably a fair sample of what will always be obtained in prac-
tice! hut are too inconsistent to permit the making of definite
rules to be followed in all cases. For example, a 1-inch
pipe 700 feet long embedded in solidly frozen ground
required 175 amperes for 5 hours, while another pipe of the

TABLE VII
PIPE-TII AWING DATA

1
Diameter

Inches

Length
Feet

Material

Amperes

Volts

Time
Minutes

Lead

250

Iron

250

Iron

300

100

Iron

150

180

Lead

185

Iron

300

Iron

320

110

Iron

100

Iron

300

100

Iron

135

100

Iron

300

150

Lead

250

200

Iron

200

Iron

120

240

Iron

250

Iron

120

250

Iron

400

380

Iron

300

Iron

140

220

Iron

280

100

Iron

175

220

150

Iron

200

150

Iron

280

120

220

Iron

105

250

Iron

400

250

Iron

500

600

Iron

700

Iron

175

300

^30

Iron

340

Iron

2,000

180

Iron

500

120

Iron

160

300

Iron

250

150

800

Iron

300

180

400

Iron

800

700

Iron

1,000

2,400

KLECTRIC HEATING

SS7

same diaraeter and 600 feel long, but much less solidly
frozen, required only 60 amperes for 1 hour. It is very

seldom that an ordinary house pipe requires more than from
30 to 50 volts and 300 amperes,

10. Thawltiaf Tt-ausfornierft,— 'The tba^vltig tt^tis-
former should be compact and easily portable* If specially
designed, the transformer usually has a large magnetic leak-
age, so that with heavy secondary currents there will be a
considerable drop of voltage; in facti such a transformer
may be short-circuited for several minutes without injury.
This design makes the transformer so bulky that it is used
only for work requiring fairly low secondary voltages; for
higher voltages, an ordinary lighting transformer with a
choke coil in series is used. The choke coil accomplishes
the same object as the magnetic leakage in the special
transformers*

Hi Conneetions* — ^There should be very little resist-
ance in the secondary circuit; that is, the secondary mains

should be short, and
all contacts should
be made secure. In
thawing house pi-
ping, one secondary
lead is usually con-
nected to a faucet and
the other to the pipe
where it enters the
house, to a hydrant,
or to a faucet in a
neighboring house,
the object being to
send the current
through all the frozen
section. In thawing
street mains, connections may be made to two hydrants or to
one hydrant and the pipe beyond the frozen section^ as shown
in Fig. 1-

\fQrmmr

PlO. 1

§57

ELECTRIC HEATING

WEIRDING

12. Thomson Welding: Process. — By the ordinary
process of welding, two pieces of metal are heated to the
proper welding temperature and then, while still hot, are
hammered together as one piece. Many welding operations
that would be very difficult by this process may be easily
performed by aid of electric current; that is, by the process
of electric Aveldlii^.

The Tlioinson ^^eldliiK process, which is more widely
used than any other, is illus-
trated in Fig. 2. Alternating
current is used for the same
reason as given for its use in
thawing frozen water pipes;
namely, because a large current
at a low voltage is thereby easily
obtained. The current from an
alternator a flows through the
primary coil ^ of a transformer b
by way of a switch o, A reg-
ulator f — preferably an adjust-
able reactance coil, though an
adjustable resistance could be
used — enables the primary cur-
rent to be adjusted as desired.
The laminated core c passes
through both the primary coil d
and the secondary coil c. The
secondary coil consists of a
very few turns, sometimes only one, of heavy copper, and
has its terminals connected to the water-cooled clamps f^g
holding the pieces /, ;;/ to be welded. Handles h,k operate
the cams, by which pieces A ni are clamped. One clamp
is movable, so that the pieces may be forced together
when hot enough; this is sometimes done by hand and
sometimes automatically by air pressure, weights, or
springs.

Fig. 2

ELECTRIC HEATING

13p Only a very low voltage is needed in the secondary
circuit, but a current as high as 60,000 amperes per square
inch naay be necessary in welding sorne nietals, as for
example, copper, A low frequency, 50 cycles or less is pre-
ferred* especially for heavy work where the current density
is very great, because high frequency together wjth high-
current density causes high-inductive effect with a corre-
sponding reduction of the power factor of the system.

Fig. S

14p Fig. 3 shows a Thomson welder for miscellaneous
work up to 6-square-inch cross-section, A Hat iron hoop is
shown in position for welding, hut different forms of clamps
permit the handling of a variety of work. The transformer
is contained in the base a of the welder, and the work is
held by clamps d, e, operated by handles d, e. A lever / and
a toggle ^ serve to force the clamp c toward d when the
proper heat is attained. Water is circulated through the
clamps by means of pipes /r, /t\ h^ The pipe A' is a piece of
rubber hose, which affords the necessary flexibility and also

(57

ELECTRIC HEATING

prevents the passage of current between the clamps by way
of the pipe. The current can pass from one clamp to the
other either by crossing the joint to be welded or by going
around the unjointed portion of the hoop; much the larger
portion takes the shorter path across the joint between the
clamps and heats the abutting ends of the hoop. The welder
just described ts a simple type; for some special work,
welders are used in which hydraulic pressure is applied and
regulated automatically.

15* Welding Transformer, — In Fig. 4 is shown one
style of welding transformer that wiU illustrate the principles
of all. This transformer has two laminated coreSi one of

Fig. 4

which is shown at a. Linked with each core is a heavy
copper casting d that forms the secondary winding of only
one turn* A slit f between the clamps d compels the second-
ary current to pass through the work held between the
clamps. The primary coil is not shown in the figure^ but
its place is in the recess shown in the secondary casting.
In such a transformer there can be only very little magnetic
leakage, and the secondary current may be very large. The
secondary circuit of a welding transformer may take any
form most convenient fur clamping and holding the work.

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sptrao^-ioo^

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§57

ELECTRIC HEATING

16* Power Roqiilred for Eieetrle Weldlnic. — The
time required for making a weld varies inversely with the
amount of power supplied; that is, the greater the power
the shorter the time, and the less the power the longer the
time, Metals that are deteriorated by being heated, such as
copper, brass, and tool steel, must be welded rapidly* The
pressure must be great enough to crowd out from the weld
all metal harmed by the heat.

Table VlII, given by the Thomson Electric Welding Com-
pany, shows the power required for welding iron, copper, and
brass of varying cross-sections. Tests have shown that from
70 to 75 per cent, of the power supplied is actually used in
making the weld, so that there is comparatively little heat
wasted. Although there is a great loss of heal in the steam
engine, and also some loss in the dynamo, it has been found
that the fuel cost for electric welding: is but little more
than for welding by the ordinary process ^ because in the
electric process, nearly all the heat is applied just where it
is wanted.

17. AdTanta^es.^ — Electric welding is especially
adapted to intermittent work and to making welds where it
would be very difficult to apply the heat by any other
method. When metals are heated by electric current, the
central part gets hot first; hence, electric welds are solid
throughout. Welds made by the external application of heat
are often imperfect in the center, leaving the joint weak,

18* Rail Weldlnff. — ^A special application of the Thom-
son welding process is the joining of steel rails, thus making
the track one continuous piece. When rails are surrounded
by paving, it has been found that they can be joined in this
way without being thrown out of line by the expansion and
contraction due to heat and cold. Before the weld is made,
the surfaces to be welded are thoroughly cleaned either by
grinding or by means of a sand blast*

A special form of welder is suspended from a boom car-
ried by a car designed for the purpose; the contacts of the
welder are brought against opposite sides of the rail, and, by

ELECTRIC HEATING

§57

means of the current, two pieces of iroaare welded on at the

joint, one piece on each side. When the pieces have been
heated to a welding heat» pressure is applied by means of a
hydraulic jack, A joint made in this manner on a 70*pound
rail will stand a strain of 279,000 pounds, whereas the max-
imum strain placed on the rail on account of variations in
temperature is 150.000 pounds*

The current for weMing is obtained from a transformer,
the primary of which is supplied from a rotary converter
that takes direct current at 600 volts from the trolley line
and converts it to about 300 volts alternatingf. The average
current supplied to the primary of the transformer during a
welding operation is about 650 amperes. The electrical
conductivity of the joint is as great as that
of the rail itself, and under proper con-
ditions four joints per hour can be made.

BM^m^fm^

ANNEALING

19, Electric annealing:, another
application of electric heatingf, is a proc-
ess by which parts of steel plates or cast-
ings on which it is desired to perfortnJ
^*°^ ^ machine work are softened. The heavy"

secondary terminals of a special transformer are placed on
the part to be softened, as shown in Fig. 5, and a large cur
rent sent through it. The part is thereby heated and soft-"'
ened, but other parts of the casting are not affected.

ELECTROLYTIC FORGE

20* An electrolytic forise, or tempering; bath, con

sists of a metallic-lined vessel containing water or a snitabk
solution. The solution is made the positive electrode of a
direct-current dynamo, while a piece of metal to be heated is
made the negative electrode. Fi^, 6 illustrates the device;
the piece of metal a rests on a contact bar t\ to which the
negative side of the circuit is connected, and extends into

§57

ELECTRIC HEATING

the liquid b* The vessel r has a metal lining </, to which the
positive side of the circuit is connected*

When the metal is plunged into the liquid and touc^ied to
the rod t, a current begins to flow through the liquid to the
rod and a layer of hydrogen gas immediately forms around
the submerjjed portion. The gas introduces so much resist-
ance between the metal and the liquid that intense heat is

developed at the surface of the metaL By adjusting the
strength of the current and the time it is allowed to flow, any
required dejjree of heat can be obtained, even to melting the
metaL This is called the llolio iiroeess, after its discoverer,
Paul Hoho. In a modification of the process, the metal is
brought in contact with only the surface of the liquid » and
the liberated hydrogen is burned, thus helping to raise the
temperature of the metal.

21« By the Hoho process, metals may be tempered with
a great degree of accuracy* The current may be adjusted
until the submerged portion of the metal is at the proper
temperature and then shut off, leaving the metal in contact
with cold water or tempering solution and thus tempering it.
Any composition it is desired to use in tempering may be
dissolved in the liquid. The heating is under such perfect
control that the tempering may be carried to any desired
depth from the surface of the metal. Suitable insulating

4(Ul-^0

ELECTRIC HEATING

§57

shields placed over portions oi the metal prevent the
development of heat on surfaces that are not to be tempered.
Large surfaces, such as the wearing surfaces of steel rails,
steel axles, shafting, cannon, etc, may be tempered by
exposing small portions at a time to the action of the
current and the tempering bath, the remaining portions
being covered with shields.

By the Hoho process, metals are heated in an envelope of
hydrogen gas, which prevents oxidation and thus makes this
process very desirable for all operations where oxidation is
objectionable. Soldering is one such operation, and metals
that are very difficult to solder by any other process can be
easily soldered by using an electrolytic forge.

FURNACES

22- When current is made to flow across an air gap
between two electrodes, an dec trie art\ a bow-shaped f!ame of
great brilliancy and intense heat, is produced. The temper-
ature of the electric arc is the highest attainable, being in the
neighborhood of 3, .500° C: and in an electric funiacc, in
which the arc is confined in an enclosed space^ any known

g^^s?S5r^

substance can be melted or vaporized. Carbon is nearly

always used for electrodes, as it will best withstand the heat.
Pig. 7 shows a simple form of electric furnace, consisting
of a crucible a of refractory material surroimded by firebrick
and covered by a fireclay slab h. Carbon rods c, d enter from
each side and form the electrodes. The arc is started either
by sliding one carbon in until it touches the other and then

§57 ELECTRIC HEATING 21

withdrawing it, or by placing a very small carbon rod, say
about tV inch in diameter, between the carbon points before
turning on the current; when the current is turned on, the
small i;od will very soon burn out and the arc will start.

In some furnaces, the crucible, or containing vessel, is
made of carbon and forms one electrode. Many styles of
electric furnaces are in use in electrometallurgical and electro-
smelting work. They enable the production of high temper-
atures in very confined spaces and without the admission
of air.

AIR AND WATKR HEATING

AIR HEATING

23. It requires an expenditure of 18 watts (18 joules per
second) to raise the temperature of 1 cubic foot of air 1° F.
per second. From this may be calculated the exact power
required to raise the temperature of a room a definite
amount, provided the room is tightly closed and has non-
conducting walls so that no heat can escape. If the room is
ventilated, or if the walls conduct heat readily and the rate
at which heat escapes cannot be determined, it is impossible
to calculate the amount of heat required to raise tlie tem-
perature to a given point or to maintain it after being raised.
Less heat is required to maintain the temperature of a room
at a given value than to raise it to that value from a lower
one; also, the quantity required for such maintenance is
inversely proportional to the amount of ventilation and to
the temperature of the outside air.

Example. — It is desired to raise the temperature of an electric oven
6 ft. X 10 ft. X S ft., inside dimensions, from 6()° to 175° F. in ^ hour,
the heaters being supplied with current at 5(X) volts, (a) Assuming
that no heat is lost, what will be the total current required to heat
the oven? {f?) If two heaters are used in parallel, what will be the
resistance of each?

Solution. — {a) The cubical contents of the oven is 6 X 10 X 8
= 480 cu. ft. The total rise of temperature is 175 - 60 = 115° F., and at
18 joules per cu. ft. for each degree, there would be required for 1 sec.

ELECTRIC HEATING

§57

18 X 480 X 115 = 993,600 joules. Since this energy is to be enpendeil
in i br., or l.ROO sec, the joulejs per set\, or the watts, raust be
9£©,6O0 -4- l,80n ^ 552; and the current at .^00 volts is 552 ^ 500
s= L104 amperes. Ans,

[it) The current taken by each heater ts 1 . 104 -s- 2 = .562 aropere* and

the resistance of each heater by Ohm's law, I^ ^ -j^ (s ^^ = 906 ohms,
nearly, Ans,

In the foregoing example and solution no account is taken
of the heat absorbed by the walls of the oven or of that
which escapes to the outside air. The quantity of heat
actually required would be considerably greater than indi-
cated by the estimates just stated; in practice, it is best* in
case the exact quantity has not been experimentally deter-
mined» to install with each heater a regulator by means of
which tihe current can be adjusted to suit the requirements.

24. liumlnoiis Radiator. — Every electrical device in
which there is any considerable expenditure of energy gives
off heat to the surrounding air, even though the device is not
intended for this purpose. About 97 per cent- of the energy

expended in electric lamps h
converted into heat. This
fact has been made use of in
the manufacture of lumi-
nous radliitorBt such as
shown in Fig. 8. Three or
more large incandescent
lamps, especially designed
for the production of heat
rather than light, are assem-
bled in an ornamental cast*
iron casing. Back of tlie
lamps is a polished copper re-
flector, which throws most of the heat out in front of the heater*
These devices are made in two sizes, consuming, respectively,
750 and 1500 watts on either 110- or 220-volt circuits.

25, Car Heater » — ^A type of car heater, for use with
direct current only, is shown in Fig. 9. The resistance wire

Fig. S

\b7

ELECTRIC HEATING

is wound in a long helix with a central flexible insulated cord a.
The helix is looped over porcelain insulators attached to oppo*
site sides of steel strips ^, and the whole is protected from

Pto, 9

accidental contact with persons or clothing by suitable gra-
tings. This style of heater is unsuitable for alternating cur*
rent on account of the high self-induction of such a winding.
Many other types of air heaters are in use for electric-car
heating.

26, Economy. — At the prices usually charged for energy ,
the cost of heating by means of electric air heaters is too high
to make them economical for continuous use in heating dwell*
ing houses and living rooms? but for removing the dampness
from living rooms during the summer and for use for short
periods only during the cool days of late spring or early fall,
they are practicable.

WATER HEATING

27* It has been found by careful measurement that the
conversion of 778 foot-pounds of work into heat mill produce
exactly the quantity of heat required to raise the temperature
of 1 pound of water 1° F.; hence, 778 foot-pounds is calfed
the meckanifai equivaleni of iwai^ There is .737 foot-pound
in 1 joule; hence» the mechanical equivalent of heat expressed
in electrical units is 778 -=- .737 = 1,065 joules. As 1 gallon
of water weighs 8.34 pounds, it requires the conversion of
8.34 X 1,055 = 8,798.7 joules into heat to raise the tempera-
ture of 1 gallon of water 1^ F. Since 1 joule is equal to

ELECTRIC HEATING

§57

1 watt-second, and there are 3,600 watt-seconds in 1 watt-
hour » 8 J98.7 -I- 3,600 = 2.444 watt*hours will be required for
1^ P. rise in the temperature of 1 gallon of water, provided
there are no heat losses.

As a matter of fact, in practical heating operations, consid-
erable heat is always lost; the containing vessel absorbs some
heat, while some escapes to the surromiding air. The actual
efficienciesof commercial electric water heaters varies between
wide limits. Assuming 80 per cent, as a fair average^ the
energy required to raise the temperature of 1 gallon of water
from 50^ F. to the boiling point, 212° F., or a total nse ot
162^ F., is 162 X 2.444 X W = 495 watt-hours.

The power required depends inversely on the lime in which
the work must be done; for example, in the preceding prob-
lem, if the gallon of water is to be boiled in i hour, 2 X 495
= 990 watts will be required » and if in i hour, 4 X 495 = 1 ,980
watts will be required.

Example*— (a) Assuming that an electric water heater has an effi-
ciency of 85 per cent.* how much power in watts will be required to
raise the temperature of 2 quarts of water from Ml*^ P. to boiling point
In 20 minutes? {&) What will be the cnrrcnt at 220 volts?

Solution.— (fl) Since 2 qt. - | gal., | X 2.44-1, or 1-222 watt-
hours, is required for each degree rise without any losses. For
212 - 50, or 162'' rise, there will be required 162 X 1.222 = 198 watt-
hours at 100-per-cenc. efficiency. At 85-per-cent. efficiency, the energy
roust be 198 X W = ^^^ watt-hours. If the work roust be done in
20 rain., or } hr.. the power must l>e ^ X 2:i"i = 6119 watts. Ans.

W The curTent at 220 volts will be 699 -r 220 ^ 3.2 amperes,
nearly* Ans,

HEATING APPLIANC1C8 FOR BOMESTIC USE

28, All ^electric-heating devices for domestic use may
be classified as lighting-t;irciiit devices and heating-circuit
devices. The li^litlripr-t^irciilt devices are those which
take about 500 watts or less* and which may be connected to
the ordinary branch circuits without any special wiring. The
heatfngf-clrciilt lie vices require special circuits, as the
ordinary branch*lighting circuits are not of sufficient capacity.

§5? ELECTRIC HEATING 26

In view of the fact that the use of domestic electric-heat-
ing devices is constantly increasing, new dwelling houses
should be provided with special heating circuits having out-
lets wherever large heating appliances are to be used.
Architects and electrical contractors should urge this matter,
as the installation of such circuits may. save considerable
future annoyance and expense

29. Among the many electrical devices for domestic heat-
ing may be mentioned flat irons, coffee pots, teapots, water
heaters, chafing dishes, stoves, plate-warming closets, grid-
dles, warming pads, curling-iron heaters, etc. In such devices,
the heating circuits are arranged as closely as possible to the
surfaces to be heated, so as to make the efficiency of con-
version from electricity into useful heat as high as possible.
Generally, each manufacturing company has adopted a dis-
tinctive method of making and insulating the resistances.

30. Ilcatliiii: Units. — The General Electric Company
makes a cylindrical unit by winding flat resistance ribbon
edgewise in the form of a helix on an arbor, and holding the
turns rigidly in place, and at the same time insulating them,
with a cement; the whole forms a solid tube, which is
wrapped in a thin sheet of mica
and enclosed in a shell, or car-
tridge, as shown in Fig. 10.
These units are inserted into
close-fitting chambers in flat

irons, stoves, or other devices, and are readily replaced if
they burn out.

The same company makes a flat heating disk by insula-
ting the surface to be heated with an application of quartz
enamel — made by mixing finely divided quartz grains with
an insulating enamel — and then winding resistance wire
spirally on the enamel. The wire is held in place by apply-
ing another coat of enamel over it. The Simplex Electric
Heating Company employ the same method, except for
differences in the quality of the insulating enamel in which
the resistance wire is embedded and sealed.

ELECTRIC HEAT[NG

§57

31« The Prometheus Kentltijir unit, shown in Fig. 11,
consists of a strip of mica carrying a thin layer of non-

oxidizable metal firmly secured
to the mica by a process of
firing. This conducting strip is
protected by another piece ui
mica placed over it, and the
whole is bent into any desired
form and enclosed in a metallic
casing.
The resistance used by the
Hadaway Electric Heating Company is composed of iron strip,
or ribbon I with deep, narrow notches punched in the edges.
as shown in Fig. 12. This ribbon is first insulated by a

Fig. U

DTI

wrapping of mica, and is then laid in molds, where the metal
of the healing device is cast around it, thus making the
resistance unit aa

integral part of
heater.

the

32. All heating
resistances for use
with alternating cur-
rent should be non-
inductive, as the
production of heat
depends only on the
square of the current
and the ohmic re-
sistance; inductances
would cause voltage

losses that would result in no additional heat. Non-inductive
ejects are produced by making the current follow a zigzag

§57

ELECTRIC HEATING

path, as suggested in Fij?. 12; or, if the resistance is in the iDrm
of a helix, by making the winding snch that the current raust
travel an equal nunnber of times each way around the helix.

33. Fig. 13 shows the method of applying the General
Electric cylindrical units to the bottoni of a glue pot. 1q

Fio. 14

some utensils the \inits are so applied as to be almost
entirely surroiifided by the liquid to be heated. Fig. 14 {a]
shows the interior of a Pacific Heating Company flat iron,
showing the positions of the two heating units, and id)
shows the complete iron with its end so shaped that the
iron will stand vertically when not in use* This method of
locating the heating units in the iron causes most of the heat
to be developed near the point and along the edges of the
iron, where it is most needed. The stand, by holding the iron
in a vertical position, enables the heat to escape more easily
when the iron is not
in use, thus avoiding
the danger of a burn-
out if the current is
left on,

34, Flat*Iron
Btand mid Heater*
When a flat iron is in
use, heat escapes from it much more rapidly than when it
is idle; hence, more rapid developmeat of heat is required

Pio. 1^

ELECTRIC HEATING

§57

in order to keep up a given temperature. If an electric flat
iron is allowed to stand idle in a horizontal position with the
same current flowing through it as is required while it is in

use» the iron will over-
heat. Fig. 15 shows
a simplex Ktaml for
an electric flat iron; a
switch a is so ar-
ranged that tlie act of
setting the iron on
the stand cuts an ad-
ditional resistance in
series with the heal-
^^^^' '^^ ing circuit of the iron,

so as to prevent overheating and at the same time save current*
Fig. 16 shows a Hmliiway lieiiter for four ordinary irons.
Similar heaters are made for any number of irons. An
objection to this plan is that the heater remains in operation
while the irons are in use. and some heat is thereby uselessly
dissipated to the sur-
rounding air,

35« llontln^ Pnd,
Fig, 17 shows a lit'iit-
IbIC pu«l to be used as
a substitute for a hot-
water bottle. This ap-
pliance is very useful
in hospitals and in
private homes. Flex-
ible resistance wire is
embedded in non-com-
bustible insulating material^ and the same material covers
the leads far enough from the pad to avoid all danger of
burning the bed clothing.

Fig. 17

§57 ELECTRIC HEATING 29

MISCEIiliANEOUS HEATING DEVICES

36. Prlntlnic and Binding Machinery. — Other appli-
ances that will assist in building up a day load, provided
they can be introduced in sufficient number, are heating
devices for use in printing and bookbinding establishments;
also irons, hot rolls, etc. for laundries, hatters' tools, tailors'
irons, glue pots, soldering irons, cigar lighters, etc.

In a printing and bookbinding establishment there are
a great many calls for heat, most of them of an intermittent
nature. Electric heaters have been found very desirable for
such work, on account of the perfect control and ready
adaptability of the heat. The Government Printing Office at
Washington, D. C, probably has the most extensive equip-
ment of electrical devices for use in printing and bookbind-
ing; these devices range in energy density from .75 to 4 watts
per square inch of superficial area of the heaters.

37. I^anndry Machinery. — Electric laundry machin-
ery has proved to be economical and satisfactory in service,
as well as a source of income to the central station. Many
laundries are equipped not only with electrically heated fiat
irons, but also with electrically heated ironing rolls. It is
evidently a simple matter to arrange an electric-heating cir-
cuit inside an iron cylinder, so that the surface of the cylinder
can be kept as hot as desired. Suitably arranged slip rings
and brushes conduct the current from the stationary part of
the circuit to the revolving part.

38. Power Consumption. — The power consumption

of electric-heating appliances varies so much with the size of
the heater and the rate at which it is designed to furnish heat
that it is impossible to give any figures that are generally
applicable. The following, however, may be useful: Flat
iron, family size (0 pounds), 500 watts; chafing dish, 3-pint
size, 500 watts; water heater to raise the temperature of
1 quart from 00° V. to 212° F. (boiling point) in 10 minutes,
ih)i) watts; glue pot, 1-quart size, 440 watts; soldering iron
(Vulcan), equivalent of 3-pound soldering copper, 150 watts.

A SERIES

QUESTIONS AND EXAMPLES

Relating to the Subjects
Treated of in this Volume.

It will be noticed that the Examination Questions that
follow have been divided into sections, which have been
given the same numbers as the Instruction Papers to which
they refer. No attempt should be made to answer any of
the questions or to solve any of the examples until that
portion of the text having the same section number as the
section in which the questions or examples occur has been
carefully studied

STORAGE BATTERIES

EXAMINATION QUESTIONS

(1) Why does the density of the electrolyte in a lead-
snlphuric acid battery vary with the charge and discharge?

(2) (a) What is meant by the ampere-hour efficiency of
a storage battery? (d) What are fair average values for the
ampere-hour efficiency?

(3) (a) What is meant by sulphating? (d) What are
some of the causes of sulphating? (c) How may the sul-
phate be removed in case it has not gone too far?

(4) (a) What is meant by gassing? (d) When does
gassing occur?

(5) How is the output of a storage battery affected if the
battery is discharged at rates higher than the normal?

(6) (a) What are the indications of a full charge? (d)
About what value will the voltage per cell have at the end of
a charge at normal rate, assuming that the battery has been
in use for some time?

(7) Point out the difference between the Plants and the
Faure types of accumulator.

(8) What is the voltage below which cells should not be
discharged?

(9) Explain the action of the differential, storage-battery
booster and illustrate by means of a diagram of connections.

(10) What are the principal materials used for pasted
Storage-battery plates?

STORAGE BATTERIES

§27

(11) {a) What should be the specific gravity of the elec-
trolyte when the cells are fully charged? {d) How is the
specific gravity measured?

(12) (a) For what purpose are end-cell switches used?
id) Make a sketch of connections and explain the operation
of a simple end-cell switch,

(13) (a) When an ordinary storage battery is charged^
what substance is formed on the positive plate? (^J What
is formed on the negative plate?

(14) Name four ways in which storage batteries are com-
tnonly used in connection with electric-light or power systems.

(16) (a) How does the voltage of an ordinary storage
cell vary as the cell is discharged? (d) What is the limiting
discharge voltage on which the rating of storage cells is

usually based?

(16) Make a diagram of connections and explain the
operation of a compound-wound, storage-battery tiooster.

(17) In a certain storage cell of the lead-sulphuric acid
type, the positive plates have a total area of 2,500 square
inches. What would be a fair value for the normal discharge
current for this cell? Ans* 100 amperes

(18) Why is it not advisable to overcharge a battery?

(19) (a) Under what circumstances is the constant-cur-
rent, storage-battery booster used? (d) Explain the action
of this type of booster and illustrate by referring to a diagram
of connections.

(20) (a) What is meant by the watt-hour efBciency of a
storage battery? (d) What are fair average values for the
watt-hour efficiency?

INCANDESCENT LIGHTING

(PART 1)

EXAMINATION QUESTIONS

(1) ^a) Name the principal parts of an incandescent
lamp, id) Of what is the filament made? (c) What
material is used for the leading-m wires and why is this
material used?

(2) (a) What three styles of lamp base are in most
common use? (d) Which, one of the three is used to the
greatest extent?

(3) (a) What is the common unit used for expressins:
the brightness of a source of light? (*) To how many
Hefner units is 1 standard candle equal?

(4) (a) What is a photometer? (d) Describe the Bunsen
photometer.

(5) A photometer bar is divided into 500 equal parts and
a standard lamp of 32 candlepower is placed at one end.
The lamp to be measured is placed at the other end, and it
is found that the screen becomes balanced when it is 350
divisions from the standard. What is the candlepower of
the lamp under test? Ans. 5.88 c. p.

(6) (a) What is meant by the mean horizontal candle-
power of an incandescent lamp? (d) How is the mean hori-
zontal candlepower usually measured?

(7) If a certain object is 10 feet from a source of light,
how many times will the illumination on it be reduced if it
is moved to a distance of 35 feet from the source?

i»

46B— 41

:iNCANDESCENT LIGHTING

§32

(8) In making photometer tests on iocandescent lamps*

what three requirements should be fut filled in order that the
photometer screen may be set with a fair degree of accuracy?

(9) (a) Is the hot resistaoce of an incandescent lamp
gfreater or less than the cold resistance? (d) What is the
approximate hot resistance of an ordinary 16H:;andlepower,

110-volt lamp?

(10) A 32-eandlepower, 220-volt lamp requires 4 watts
per candlepower. What current will 160 of these lamps take
on an ordinary two-wire system? Ans* 93.09 amperes

{11) (a) What do you understand by mean spherical
candlepower? (d) Are incandescent lamps usually rated by
their mean spherical candlepower?

(12) (a) What voltages are ordinarily used for operatiog
incandescent lamps? (^) Give a table showing: the approx-
imate current required by some of the ordinary sizes

of lamps.

(13) (a) About how many candlepower per square foot is
required for the illumination of ordinary rooms with ceilings
about 10 feet high? (^) How many candlepower per square
foot is required for brilliantly lighted spaces such as ball-
rooms, etc?

(14) (fl) Of what does the light-giving element of a
Nemst lamp consist? (h) Why does the glower have to be
heated in order to start the lamp?

(15) {a} Why is it necessary to use a resistance or
ballast in series with a Nemst lamp glower? (^) What
is the power consumption per mean hemispherical candle-
power of the Nernst lamp?

(16) If an incandescentf lamp has a life of 800 hours
when burned at an efficiency of 3 watts per candlepower,
w^hat would be its approximate life if burned at an efficiency
of 4 watts per candlepower? Ans. 3,370 hn, approximately

INCANDESCENT LIGHTING

(PART 2)

EXAMINATION QUESTIONS

(1) Under what circumstances are frequency changers
sometimes used for electric-lighting work?

(2) (a) Make a sketch showing how you would connect
two large transformers on a single-phase system to feed

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three- wire secondary mains, {b) What are some of the
advantages jjained by supplying customers from secondary
mains rather than from a number of small transformers?

188

INCANDESCENT LIGHTING

§33

(3) Describe, briefly, two methods of operating a three-
wire system by means of a single 220-volt dynamo with
auxiliary apparatus to take care of the unbalancin^r.

(4) (a) What is the feeder-and-main system of distribu-
tionf (d) What are its advantages?

(5) Describe the Westinghouse method of operating
incandescent lamps in series on constant-potential, altema-
ting-curreot systems. Illnstrate by means of a sketch.

(6) Fig. I shows a two-wire 110-volt system, the number

of lamps operated and the various distances being as shown.
The total allowable drop from the dynamos to the lamps
is not to exceed 12 volts. The drop in the house wiring
is to be 1.5 volts, the drop in the mains 3,6 volts, and the
balance of the drop is taken up in the feeders. Calculate
the size of wire required for: (a) the feeders; (^) the
mains D; U) the mains £[ (d) the mains /\

(a) 2.50,714 cir. mils
A„^ . (A) 277.714 cir. mils
^^^'(c) 185,143 cin mils

(d) 123,428 cin mils

(7) The pressure on a long-distance electric-light feeder
is to be raised 25 volts by means of a booster. The maxi-
mum current to be supplied to the feeder is 500 amperes.
What must be the capacity of the booster » in kilowatts?

Ans. 12.5 K. W,

(8) Draw a simple diagram showing how to connect
a shunt-wound booster so as to raise the pressure on a two-
wire circuit.

(9) Fig. II shows a three- wire system* The main feed-
ers C run to a junction box y, from which current is
distributed to the house wiring F by means of the mains Z>,
Current is also supplied from J to the lamps E uniformly
distributed as shown. The drop in the feeders C (L e-, the
drop on one side of the circuit) is to be 6 per cent, of
the lamp voltage, and that in the mains Z>, 3 per cent, and
in mains Et 5 per cent. The distances and tiumt>er of lamps

INCANDESCENT LIGHTING

supplied are as shown in the figure. Calculate: (a) the
size of feeders C; (d) the size of mains D; {c) the size
of mains B. [ (a) 54»785 cir. mils

Ans.{ (d) 122,727 cir. mils
I (c) 12,371 cir. mils

(10) Three thousand 16-candlepower incandescent lamps
are to be operated at a point 9,000 feet from the station.
The total loss in power is to be limited to 15 per cent..

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10 per cent, of which is to be lost in the transmission line
and 6 per cent, in the secondary wiring and transformers.
The lamps require 3.5 watts per candlepower, and the
voltage at the end of the line is to be 2,000. Find the size
of the line wires required if the single-phase alternating-
current system is used.

Ans. 85.700 cir. mils; a No. 1 B. & S.

(11) Can a three-phase alternator be operated as a single-
phase machine, and if so, about what percentage of its
rated output will it deliver when so operated?

INCANDESCENT LIGHTING

§33

(12) Show how grounding the secondary of a trans-
former prevents danger from shocks due to accidental
contact between the primary and secondary circuits-

(13) State why it is not advisable to fuse the mam
neutral wire on large three-wire direct*current systems,

(14) Make a sketch and explain the operation of series
incandescent circuits as used with a constant-current trans-
former,

(15) For what kinds of lighting work is the series
incandescent system well adapted?

(16) In case a balancer is used on a three-wire system,
how should the circuit-breaker that protects it be arranged?

(17) Make a sketch of the connections and describe the
method for measuring the core loss of a transformer-
CIS) How should the insulation of a transformer be

tested?

ARC LIGHTING

(PART 1)

EXAMINATION QUESTIONS

(1) Name some of the things that will cause bumed-out
shunt coils in series arc lamps.

(2) What are some of the main points of difference
between an alternating-current, constant-potential, enclosed-
arc lamp and a direct-current, constant-potential lamp?

(3) What should be the length of arc: (a) for a 2,000-
nominal-candlepower series arc lamp? {d) for a 1,200-nom-
inal-candlepower lamp?

(4) What is likely to happen if constant-potential, en-
closed-arc lamps are operated on a higher voltage than that
for which they are adjusted?

(5) (a) What is meant by a carbon-feed, enclosed-arc
lamp? id) What are some of the advantages of a carbon
feed?

(6) At what current and voltage are series enclosed-arc
lamps commonly operated?

(7) (a) Why is a single coil in series with the arc inca-
pable of regulating a series, constant-current arc lamp?
(d) Explain the action of a simple, differential, series arc
lamp.

(8) Make diagrams showing how to connect arc lamps
on: (a) a direct-current, constant-potential system; (d) a
constant-potential, alternating-current system.

181

ARC LIGHTING

(9) (a) Why is it necessary to have ao atttomatic cut-out
in series arc lamps? (*) Why is it necessary to use a start-
ingf resistance in some styles of series arc lamps?

(10) (a) How may the voltage at the arc on a General
Electric constant-potential, direct-current, enclosed-arc lamp
be adjusted? {^) How may the voltage be adjusted on the
General Electric cons tant-potential^ alternating-current lamp?

(11) (a) What is a multicircuit arc machine? (A) Explain,
by means of diagrams, the operation o£ two arc circuits from
one machine and point out the advantages that are claimed
for this method of operation.

(12) How many watts, approximately* do the following
lamps consume: (a) a S.OOO-nominal-candlepower* open -arc
lamp? (^) a 1,200-nominal-candlepower open-arc lamp?

( 13) (a ) Of what are ordinary arc-lamp carbons generally
made? (^) Why do encIosed*arc lamps require a higher
grade of carbon than open -arc lamps? ic) What material is
generally used for making enclosed-arc lamp carbons?

(14) (a) Make sketches showing at least three of the dif*
ferent methods of arranging the carbons for searchlights or

other projection apparatus* (^) What is a Man gin mirror?

(15) (a) In direct-current lamps, why should the upper
carbon always be connected to the positive side of the line?
(d) How would you find out whether a lamp were burning
"upside down*' or not?

(16) Does the direct-current enclosed arc form a well-
defined crater like the direct-current open arcj and if not*
what shape do the carbon points assume?

(17) What amount of current do open-arc direct-current
series lamps usually take?

(18) (a) What is an enclosed arc? (^) How does the
consumption of carbon in an enclosed arc compare with that
in an open arc? (c) Give a description of the general
arrangement of an enclosed arc?

S84 ARC LIGHTING 8

(19) What are the characteristic features of a direct-
cnrrent arc formed in open air between carbon points?

(20) (a) What is the approximate temperature of the
electric arc? {i) Does an arc lamp usin^ a large current
produce a hi^fher temperature at the arc than one usingf a
small current? (c) What is the effect of increasing the cur-
rent supplied to an electric arc?

(21) (a) In what direction does an open-arc, direct-
current lamp throw the greatest amount of light? (d) Why
should reflectors be used with alternating-current arc lamps?

ARC LIGHTING

(PART 2)

EXAMINATION QUESTIONS

(1) In Fig. 37, where would the plugs be inserted if
machine A were connected to circuit I' and if machine C
were running circuits 2^ and 3' in series, machine B being
shut down?

(2) {a) Into what two classes may constant direct-cur-
rent arc machines be divided? (b) Name some common
makes of machine belonging to each of the classes.

(3) For what are transfer boards used in connection with
arc-light switchboards?

(4) How would you locate a ground on an arc line by
using a voltmeter?

(5) Give a general description of the method by which a
Brush arc machine, equipped with an oil regulator, is made
to regulate for constant current.

(6) Name some of the chief points of difference between
the new and the old styles of Brush arc dynamo.

(7) Name some of the precautions to be taken when con-
necting up circuits and dynamos on an arc plug switchboard.

(8) Why is it necessary to provide constant direct-ciu:-
rent arc machines with a regulator?

(9) On the board shown in Fig. 29. what will be the
position of the plugs when machine A is operating circuit 1
alone, circuit 2 being dead, machine B operating circuits 3
and 4 in series, and machines C and D shut down?

ARC LIGHTING

886

(10) If at ternatin ^-current, series arc lamps are to be
operated, is the alternating current usually generated at

constant potential or constaat current?

(11) Name some of the methods that may be used
for operating series arc lamps from constant-potential
alternators,

(12) Describe the method of locating a break in an arc*

light line by using a magneto-belL

(13) ia) Why is it that in some cases two arc machines
will not regulate well when nm in series? (i) How would

you remedy matters?

(14) How would you right matters if the polarity of a
series arc machine should become reversed?

(15) Describe how you would locate a ground on an arc-
light line by using a magneto-bell.

(16) What style of switch must be provided where series

arc-light circuits enter a building?

(17) Explain the differential method of locating grounds
on a series arc-light circuit-

(18) Explain the operation of the Western Electric regu-
lator for constant, alternating-current, arc-light circuits.

(19) Make a sketch showing how a 110-volt, constant-
potential, alternating-current arc lamp can be operated
from a 220-volt circuit by the use of an economy coiL

(20) (a) What is a balancing coil? (A) Make a sketch
showing how a three-wire, alternating-current circuit 'can
be operated from a two-wire circuit by means of a bal-
ancing coilp

(21) Make a sketch showing the connections and instru-
ments required for the operation of a series arc-light circmt
supplied from a constant-current transformer.

INTERIOR WIRING

(PART 1)

EXAMINATION QUESTIONS

(1) In wiring a building: for incandescent lamps, why is
it important to have the drop in the various circuits limited
to a small amount?

(2) (a) For what class of work is slow-burning weather-
proof wire allowable? (t) How must this wire be supported?

(3) Where do the Underwriters* rules require cut-outs to
be placed?

(4) How would you calculate the sizes of wire required
for house wiring on the three-wire 110-220- volt system?

(6) (a) For what are cut-outs used? (d) How are they
usually constructed?

(6) What are the Underwriters' requirements relating to
joints for wires used in connection with interior wiring?

(7) A pair of feeders are to be installed in a factory
building to carry current for five hundred 16-candlepower
110-volt lamps from the dynamo room to a center of distri-
bution situated in another building; the total distance (one
way) from the dynamo room to the center of distribution is
400 feet and the drop is to be limited to 5 volts: (a) What
size wire will be required? (d) What size wire would be
required if the carrying capacity alone were considered?
Assume that weather-proof wire is used.

INTERIOR WIRING

§43

(8) Is the carrying capacity of rubber-covered wire as
Ifiveo by the Underwriters as large as that o£ weather-proof
wire? If not, why?

(9) Are the odd sizes of wire between Nos. 7 and 14
nsed for interior wiring? If not, why?

(10) In laying^ out the branch circuits, what determines
the number of lamps to be allowed on any one circuit?

(11) Into what three general classes may fires caused by
defective wiring t»e divided?

(12) Fig, I shows a wiring plan of a network that sup-
plies current to UO-volt lamps and motors as indicated;
(a) Make a sketch and indicate the current flowing at
a,^fC,d,and^, id) Mark the sizes of wire necessary for
the various parts of the system in accordance with the

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Underwriters' requirements, assuming that rubber-covered
wire is used and that current-carrying capacity alone is con*
sidered, U) Show where main cut-outs or branch blocks
will be required and the size of fuses to be used in order to
protect the wire. The individual fuses at the arc lamps and
motors need not be indicated,

(13) What are the four most important things to be
considered when installing a job of wiring?

INTERIOR WIRING

(14) When may single-pole switches be used in an
interior-wiring installation?

(16) (a) What is the smallest size of wire allowable for
interior- wiring work outside of fixture wiring? (d) If no
requirements must be met in regard to line drop, what
determines the minimum sizes of wire to be used for a
given installation?

(16) Why should the two sides of a circuit always be run
in the same conduit when alternating current is used?

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(17) {a) Why should unprotected wires never be laid in
plaster? {b) Why should lelectric-light wires never be
fastened with staples?

(18) In Fig. II, point out the places where the Under-
writers* rules are violated and state how you would remedy
the defects. All wire is supposed to be rubber-covered.

(19) For what kinds of service are Edison plug fuses
suitable?

(20) Under what conditions may a cut-out be omitted
when a change is made in the size of wire?

INTERIOR WIRING

(PART 2)

EXAMINATION QUESTIONS

(1) By the aid of Table I, determine the size of wire that
would be required for a line (2 wires) extending: a distance
of 120 feet and carrying: 30 amperes with a drop not exceed-
ing 3 volts. Ans. No. 6 B. & S.

(2) After a building has been wired, what tests should
be made?

(3) (a) What tests and observations does the Under-
writers' inspector usually make? (d) When should con-
cealed work be inspected by the Underwriters* inspector?

(4) What instrument is generally used in testing out
connections, and also in testing for grounds and crosses?

(6) What size B. & S. copper wire should be used, allow-
ing a drop of 2 volts, to supply a group of eighty 110-volt
16-candlepower incandescent lamps at a distance (one way)
of 200 feet? Each lamp requires i ampere.

Ans. No. 1 B. & S.

(6) What will be the current in the outside wires of an
evenly balanced three-wire system supplying sixty lamps, if
each lamp requires 52 watts? There is a drop of 2 volts in
each outside wire to load center, and the pressure between
the outside wires at the center of distribution is 220 volts.

(7) Determine, by means of Table II, what size of wire
would be required to transmit 30 amperes a distance of
120 feet (one way) with a line drop not exceeding 3 volts.

Ans. No. 6 B. & S.
iii
46B— 42

INTERIOR WIRING

§44

(8) Calcalate the size of wire necessary to supply fifty
16-candlepower 110-volt lamps located in a gfroup at a dis-
tance of 150 feet (one way) from the center of distribution,
allowing a drop not to exceed 2 volts* Ans, No, 4 B, & S.

(9) In a building already wired » the drop in a certain
feeder, extending a distance of 100 feet (one way), is excess-
ive. The feeder, which consists o£ a No* 6 wire, carries
40 amperes. What size of wire should be connected in par-
allel with the No. 6 wire so as to reduce the drop to 2 volts?

Ans. No. 8 B, & S.

( 10) What are the Underwriters' requirements: (a) about
supporting wires in damp places? (d) about the use of
cut-outs and rosettes In damp places?

(11) (a) Where may wooden molding for wires be used?
(d) Where must it not be used?

(12) What two important conditions necessitate addi-
tional precautions for ship wiring?

(13) (a) What appliances do the Underwriters require to
be placed at a convenient point near where the wires enter a
building in addition to the meter that is usually installed?
(i) In what order should these appliances be placed?

(14) Make a sketch showing how a lamp or group of
lamps may be controlled independently from two different
points.

(16) Why should good metallic connections be made
between all metal conduit pipes, outlet tioxes, etc. and the

ground?

(16) What kinds of conduits for concealed wiring are
now approved by the Underwriters?

(17) What is the so-called loop system of wiring?

( 18 ) What must be done when the size of wire is changedf
at a junction box?

(19) What precautions must be taken at outlets wher^

th? wiring w QU the concealed knob-and-tube plan?

§44 INTERIOR WIRING 8

(20) How must wires be supported in concealed knob-
and-tube work?

(21) Why will two wires safely carry more current than
one wire of equivalent cross-section?

(22) A wireman having: at hand only some No. 14 wire
desires to run a line a distance of 100 feet to supply fifty
16-candlepower lamps requiring i ampere each. How many
No. 14 wires must be run in multiple in order to have a drop
of about 3 volts?

(23) In damp places: (a) what kind of sockets must be
used? (d) how should they be put up?

(24) (a) Where may single-pole switches be used?
id) Why are they used when possible in preference to
double-pole switches?

(25) Why is it that No. 14 wire is generally used for
lamp circuits in all ordinary dwelling houses?

INTERIOR WIRING

(PART 3)

EXAMINATION QUESTIONS

(1) Where it is necessary to install wires very cheaply
for temporary or occasional use and for some special pur-
pose, such as the illumination of the outside of a buildingf,
what are the important items to be kept in view and what
are not so important?

(2) What are considered as high-potential circuits?

(3) Why cannot the same protective devices be used on
constant-current as on constant-potential circuits?

(4) What sort of switches must be used for constant-
current systems?

(5) (a) What is a self-restorins: annimciator? (i) What
are its advantag^es?

(6) To what class of work is the use of high-potential
direct current almost exclusively confined in the United
States?

(7) Why do the Underwriters' rules prohibit the opera-
tion of motors or lights from street-railway circuits, except
on street cars, in car bams, or railway power houses?

(8) {a) How must a motor and starting resistance box
be protected? (b) When may single-pole switches be used
with motors?

(9) Why is it bad practice to bring the wires of high-
voltage systems inside a btiilding?

INXERIOR WIRFNG

S4S

(10) (a) Name two kinds of stage dimmefs, (^) With
what current s^rstems may each be used?

(11) Is it allowable to install electric gas-lfghtrng appa-
ratus on fixtures wired for electric light?

(12) What kind of wire is the best to use for bell and

annunciator work when it is run in wet places?

(13) Under what conditions may the circuit -breaker
used with a motor take the place of the tnaln switch and
cut-out?

(14) What are the ordinary requirements connected with
the Installation of transformers?

(15) If metal staples are used to fasten down bel! and
annunciator wires, what precautions should be taken?

(16) When incandescent lamps are connected in series
in a circuit, state at least two of the Underwriters' rules
concerning such work.

(17) In series gas-lighting systems, why is it necessary
to insulate the wires very carefully?

(18) What precautions must be taken when wiring
motors?

MODERN ELECTRIC-LIGHTING
DEVICES

EXAMINATION QUESTIONS

(1) (a) Why were not the old-style open-arc lamps
operated with an arc longer than i inch? (d) What change
has been made that makes it possible to operate arc lamps
with arcs 1 inch or more in length?

(2) Describe a system to be followed by an attendant in
inspecting and repairing a Nernst lamp.

(3) {a) Describe the light obtained from tungsten lamps.
(d) Why are tungsten lamps likely to come into more general
use than any of the other metallic-filament lamps?

(4) (a) Of what materials are the electrodes of a mag-
netite arc lamp made? (d) Why is not the positive electrode
in this lamp destroyed by the arc?

(5) What is meant by luminous efficiency as applied to a
source of light?

(6) Describe the connections of two type H mercury-
vapor lamps in series. Make a rough sketch.

(7) (a) What is the economizer in a flaming-arc lamp?
{b) Why is it especially necessary to house all the mechanism
of a flaming-arc lamp?

(8) (a) What is the Moore electric light? {b) How can
the color of this light be controlled?

j|65

2 MODERN ELFXTRIC^JGHTING DEVICES §55

(9) How does the preparation of metallized ^laments for
incandescent lamps differ from that of the ordinary carbon
filaments?

(10) Name the essential parts of a Nernst lamp*

(11) {a) Of what does the ballast in a Nernst lamp con-
sist? (t) For what purpose is the ballast used?

( 12) Describe a process of making osmium lamp filaments.

(13) (a) What object has been attempted in the Carbone
arc lamp? {&} How dues this lamp compare with other arc
lamps in efficiency and in cost of maintenance?

(14) Describe briefly the advantages and disadvantages
of mercury -vapor tube lamps, naming three advantages and
one very marked quality of the light that renders this lamp
useless in some locations.

(15) {a) What characteristics have metallized filaments
that g:!ve them their name? (d) What other name would
more nearly describe their condition? (c) What tw^o chief
advantages have metallized-filament lamps over the ordinary

carbon -filament lamps?

(16) In flaming-arc lamps, how is the arc made to bow
downwards from the tips of the inclined carbons?

(17) Describe briefly the process of making the glowers
for Nernst lamps.

(18) To what places is the Moore light applicable?

(19) (a) What rare metals are most used for incandes*
cent-lamp filaments? (d) Why is it difficult to make metallic-
filament lamps for high voltage or small candlepower?

(20) Why can better illumination be obtained from a
tube of incandescent gas than from a concentrated source
of light?

ELECTRIC SIGNS

EXAMINATION QUESTIONS

(1) Describe an electric carriage call.

(2) How is the quick-break feature obtained in the Solar
Electric Company's 10-ampere flasher?

(3) {a) What is a monogram letter as used in elec-
tric talking signs? (d) Describe briefly the connections
necessary.

(4) What letters may be made so that they will appear
the same when viewed from either side?

(5) (a) Describe the making of an Elblight lighting cable.
id) How are lamps connected to the cable? (c) Where
are these cables and lamps most useful?

(6) How may the time be automatically displayed by
means of electric lamps so that it can be read from a
distance?

(7) When exposed lamp bulbs are used, what may be
done to reduce the number of lamps necessary to display
the letters properly?

(8) (a) What is an automatic time switch? (d) Mention
an instance where a time switch is useful.

(9) What is a talking sign?

(10) Into what three classes may fixed electric signs be
divided?

156

ELECTRIC SIGNS

1 56

(11) How do the lamps used in electric signs diifer from
those used for ordinary illumination?

(12) 0£ wbat does the commutator used with a mono*
gram letter consist?

(13) (a) What is a thermostat? (d) Make a sketch of
the connections of a thermostat and describe its operation*

(14) What points should be kept in view in designing an
electric sign?

ELECTRIC HEATING

EXAMINATION QUESTIONS

(1) {a) Why should fuse wires be 1 inch or more long?
id) Why should these wires be enclosed?

(2) ia) What is electric annealing? {d) How is the
process performed?

(3) What should be the condition of the surface of a wire
carrying current in order to dissipate heat most rapidly?

(4) (a) What special feature, rendering them peculiarly
appropriate for their use, have transformers designed and
built purposely for thawing frozen water pipes? id) What
substitute is used for this special feature when an ordinary
lighting transformer is used for the same purpose?

(5) What are some of the advantages to be obtained by
the use of electric heat?

(6) (a) To what kind of work is electric welding espe-
cially adapted? (b) What advantage has an electric weld
over one made by the ordinary process?

(7) Why should the central-station manager be especially
interested in pursuading customers to, use electric-heating
devices?

(8) (a) Describe an electrolytic forge, {d) How may
an article be tempered in an electrolytic forge?

(0) How should all electric-heating resistances for use
with alternating current be made?

ibi

ELECTRIC HEATING

§57

(10) In the wiring of dwellings, what provision should

be made for electric-heating appliances?

(11) (a) Why is alternating current used for such proc-
esses as thawing frozen pipes and welding? (^) Why is a
low- frequency current preferable for welding heavy work?

(12) How much current at 220 volts will be required to
raise the temperature of a rooni 12 ft. X 14 ft- X 10 ft, from
32^ F. to 72^^ F. in 1 hour, making no allowance for losses?

Ans. L53 amperes, nearly

A KEY

TO ALL THE

QUESTIONS AND EXAMPLES

CONTAINED IN THE

EXAMINATION QUESTIONS

Included in this Volume.

The Keys that follow have been divided into sections cor-
responding to the Examination Questions to which they
refer, and have been given corresponding section numbers.
The answers and solutions have been numbered to corre-
spond with the questions. When the answer to a question
involves a repetition of statements given in the Instruction
Paper, the reader has been referred to a numbered article,
the reading of which will enable him to answer the question
himself.

To be of the greatest benefit, the Keys should be used
sparingly. They should be used much in the same manner
as a pupil would go to a teacher for instruction with regard
to answering some example he was unable to solve. If used
in this manner, the Keys will be of great help and assist-
ance to the student, and will be a source of encouragement
to him in studying the various papers composing the Course.

STORAGE BAHERIES

(1) Because during the charge, eulpburic acid !■ (ormed and
during the discharge it is decomposed. The amount of acid therefor©
irahes; hencoi the density of the electrolyte also varies. Bee Art. 5*

(2) (a) The ampere-hour efficiency is the ratio of the ampere«
hours output to the ampere*houri input.

{d) From 87 to 9a per cent* See Arts. 9 and 10«

(3) (a) By sulphating is meaot the formation on the plates of a
white insoluble sulphate that is iojunous, as it prevents the material
of the plates from being acted on and in some cases may lead to
buckling,

(6) The most frequent causes of sulphating are overdischarglng^,
wrong specific gravity of electrolyte > and allowing the battery to stand
for a considerable length of time in a discharged condition*

(c) If the sulphating has not gone too far it can usually be
temedied by giving the cells a long continued chaige at a low rate*
See Art. 44.

(4) {a} The evolution of gas from the plates of a battery due to
the decomposition of the electrolyte hy the charging current.

{b) It occurs when the cells have become fully charged , See Art- 3*

(5) With rates of discharge higher than the normal (which is
usually the 8*hour discharge rate), the output of the battery is
reduced. See Art* 8«

(6) (a) The voltage and specijic gravity reach their majdmum
values > though these values are not necessarily fixed; the cells give off
gas freely, the positive plates become a dark-browu color and the
negatives a light -gray. See Art, 33<

{6} About 2.4 volts. See Art* 34.

(7) In the Plants cell the actfve material la formed on the plates
from metallic lead, whereas in the Fatire type the active material is
applied ia the form of a paste to a metallic supporting grid. See
Arts. 2 and SI.

S«7

46B— 43

STORAGE BATTERIES

§27

(8) This discharge should never be carried below t.7 volts» aod
under ordinary conditions it is stopped at 1.75 or IS volts. See Art 85.

(9) A sketch shnllar to Fig. 38 and an abstract of Art, 65 ia
required,

(10) /%tOt (miniuin or red lead) is used for the positive plates and
f^O (litharge or lead monoxide J for the negative plates. See Art. 3*

(n) («) From 1.20 to L24 at normal temperature.

(d) By means of a hydrometer* See Arts. 30 and 31*

(12) (ff) End -cell switches are nsed to permit the cutting in of
cells at one end of a battery so that the E, M. F. applied to the circuit
may be kept constant notwithstanding the falliag oE in voltage due 10
the discharge of the cells.

Id) A sketch similar to Fig, dO« with aceoiopanylng explacation ii
required. See Art. 5B«

(13) {a) Lead peronide,
(6) Spongy lead. See Artfi. 2 and B*

(14) The battery may be used to cany the peak of the load, to
carry the whole load for short periods^ to take up flnctualions in the
load» or it may be located out on the line to relieve the feeders and
thus keep up the voltage on distaot parts of the system. See Arts. 52,
53, 54| and 55*

(l^) (a) During the first few minutes the voltage drops rapidlf

until it reaches about 1.9S volts, ft then falls gradually as the dis-
charge is continued until it reaches 1.75 volts. The cells should not
be dL'^charged much beyond this point as the voltage then falls off very
rapidly. See Art. 8 and Fig* I,
(d) 1.75 volts. See Art. 8,

(16) A sketch similar to Fig. S7 and an abstract of Art. 64 Is
required.

(17) A fair value for the discharge rate Is .04 ampere per sqnare

inch of positive plate surface. In this case the plate surface is 2,500
sq. in.; hence, the normal discharge current wonld be 2, 500 X. 04
» 100 amperes. See Art. 1m

(18) Because it is an unnecessary waste of energy* causes a rapid
accumulation of sediment^ wastes acid through spraying, and shortens
the life of the plates. See Art. 32.

(19) (a) The constant-current booster is used pHncipally in office
buildings or manufactories where a variable motor load is operated
from the same generators as the lights. The booster makes the battery

§27 STORAGE BATTERIES 8

charge and discharge so that the current delivered by the generators is
kept constant in spite of the fluctuations in the motor load.

id) A sketch similar to Fig. 40 with accompanying explanation is
required. See Art. 07.

(20) (a) The watt- hour efficiency Is the ratio of the watt-hours
output to the watt-hours input.

(d) From 70 to 80 per cent, under ordinary conditions. If the bat-
tery is alternately charged and discharged, as when used for regulation
on a rapidly varying load the watt-hour efficiency may be as high as
92 or 9i per cent. See Art. II.

INCANDESCENT LIGHTING

(PART 1)

(1) (a) The filament, the bulb, the leading:-in wires, and the base.
(d) Carbon; usually the carbon is made by carbonizing a squirted

cellulose thread.

(c) Platinum; because it has very nearly the same coefficient of
expansion as glass and does not oxidize. See Arts. 9 to 16«

(2) See Art. 16.

(3) {a) The standard candle.

(d) 1 candle = 1.136 Hefner units. See Art. 10.

(4) (a) A photometer is an instrument for measuring the candle-
power of a source of light by comparing it with the known candlepower
of a standard. See Art. 20*

{d) Give an .abstract of Art. 24.

(5) In this case, the distance of the standard from the screen is
350 divisions; hence, in formula 2, ^/i » 350. The distance of the
lamp from the screen is 500 — 350 » 150 = d,; hence, the candlepower
of the lamp under test is

IRAt

B, = 32~i =- 6.88 c. p. Ana.

(6) {a) The mean horizontal candlepower is the average of the
light intensities given out by the lamp in all directions in the horizon-
tal plane.

(d) It is usually determined by spinning the lamp about a vertical
axis while the measurement is being made on the photometer. See
Art. 28.

(7) We will call B the candlepower of the source of light and Xt
the illumination of the object when it is placed 10 feet from the source.
Then, from formula 1,

- ^

182

INCANDESCENT LIGHTING

Also, if ^.

have

represents

the ill u initiation
^' 35-

the second

position,

Hence, we

have

£2

5
100

B
1,22&
1.225

X. 100

;r, = 12.25 ^«
That Is, the fllummaHon at a distance of 10 feet is 12.25 times as
great as that at 35 feet, or the illumination is reduced 12.25 times.
Ans. See Art. SI*

(8) State the requirements as gtven in Art. 27-

(9) (a) The hot resistance is much less than the cold resistance,
because the Tesistance of carbon decreases as the temperature increases,

(d) About 220 ohms, ^ee Art. 35 p

(10) See Art. 36* The current required for each lamp #111 be
equal to - , and for 160 lamps it will be — ^^ — - » 33*09
amperes. Ans.

(11) (a) The candlepower that the lamp gives in the several direc-
tions reduced to what the candlepower would be \i the Ilgbt were
given out uniformly in all directions. See Art. 30»

(b) No; the mean horizontal candlepower is generally used. See
Arts. 29 and 30.

(12) {q) 100 to 125 volts* Lamps are also made for 220 to 256
volts. See Art. 41,

(d) See Art. 42.

(13) (s) .25 to .29 candlepower per square foot,
(b) 1 candlepower per square foot. See Art. 44*

(14) See Art. 47.

(15) {a\ See Art. 47.

{b) 1.75 to 2 watts per mean spherical candlepower » See Art* 54.

(16) In formula 5, j:, = 800, ^^ = 3, W^ = 4; hence,

goo X 4*
Zi =* — KT^^ = 3|370 hr., approjtiinatcly* Aos.

INCANDESCENT LIGHTING

(PART 2)

(1) When the g^reater part of the current generated is used at low
frequency for power or other purposes and a part must be transformed
to higher frequency for lighting. See Art. 23.

(2) (a) Make a sketch similar to Fig. 14.
(d) See Art. 18.

(3) Give brief descriptions, illnstrated by sketches, of the systems
described in Arts. lO and 11.

(4) (a) and {d). See Arts. 6 and 7.

(5) Make a sketch similar to Pig. 32 and give an abstract of
Art. 86.

(6) (a) Total current in feeders = -5- + "o" + ~o~ "■ 325 amperes,

since each lamp requires i ampere. Total drop = 12 volts; drop in

mains = 3.5 volts; drop in house wiring = 1.6 volts; total drop in

mains and house wiring = 5 volts; drop in feeders = 12 — 6 =» 7 volts.

The size of the various feeders may be calculated by using formnla 1.

For the main feeders we have

^ 21.6X250X325 „-«-,. , „ .
A = ^^-= = 250,714 cir. mils. Ans.

(d) Current in mains D is 150 amperes and distance is 300 ft.
Hence,

. 21.6 X 300 X 160

■ 277,714 cir. mils. Ans.

s; distance = 400 ft. H(

185,143 cir. mils. Ans.

3.5
{c) Current in ^ = 75 amperes; distance = 400 ft. Hence,
. 21.6 X 400 X 75

3.6

(d) Current in F = 100 amperes; distance = 200 ft. Hence,

. 21.6 X 200 X 100 -„„ ,^0 .

A = 5-= = 123,428 cir. mils. Ans.

0.0

(7) The booster must generate 25 volts and carry 500 amperes;
hence, its capacity will be 25 X 600 = 12,500 watts, or 12.6 K. W. Ans.

188

INCANDESCENT LIGHTING

las

(8) See Pfg. 12. The sketch required will be somewhat similar to
Fig. 12 except that a two- wire circuit ehould be ehown. and only one
booster will be required*

(9) In working the problem, consider the oatsMe wires only and

treat it as if it were a two- wire system. The current supplied the

lamps £ will be 1 ampere for each pair of lamps* because the lamps

are fJ2-candlepower. The current supplied to branch iT will, thereforep

300
be 18 amperes. The current supplied to Fw\U be -— = 75 amperes,

because these lamps are of IB-candlepower. The total current in the
outside wires C will, therefore, be 75 + 18 = 93 amperes.

(a) The drop in each of the feeders C is 5 per cent, of 110, of
6,5 volts, or the total drop for both sides is 11 volts, and by applying
formula 1, we have

. 2L6X300Xft3

54,785 clr. mils. Ans»

(*) The mains Z? carry 75 amperes and the drop on each side is
3 per cent., or 3.3 volts. The total drop in the outside wires is, there-
fore, 6.d volts. The distance is 500 ft, ; hence,
2L6X 500X75

A =

6.6

= 122,727 cir, mils. Ans.

(c) In this case, the center of distnbution is 350 ft. from the jianc-
tion box; hence j the distance to be used in the formula is 350 ft. The
current being 18 amperes and the drop 5 per cent, on each side, or
11 volts between the outside wires,
^ 2L6X 350X18

" 12,371 dr. mils. Ane.

It will be noticed that the branch feeders and mains O call for a
larger wire than the main feeders C, although they carry less current.
This is because of the longer length of D and the small drop allowed.

(10) See Art. 42. The total power supplied to the lamps is
3,000X16X3.5 == 168,000 watts. The power delivered to the pri-
maries of the transformers will be 168,000 -h (168,000 X .05) = 176,400
watts. The voltage at the end of the line is 2,000, hence, current

176,400

2,000

= 88.2 amperes. Drop ^ 2,000 X .10 »» 200. In this case,

the load is altogether of lamps and the distance is comparatively short
so that the size of wire can be determined with sufficient accuracf by
using the same formula as for direct current.

A ^

21.6 D I 21,6 X 9,000 X 88.2

= 87,700 cfr. rails, approat. An®,

c 200

A No. I B, & S. wire (83,694 cir. mils) would likely bo ufied,

(11) VeS| about 75 per cent. See Art. 19*

§83 INCANDESCENT LIGHTING 8

(12) See Arts. 24 and 25. Make a sketch similar to Pig. 20 and
xefer to it in yodr explanation.

(13) See latter part of Art. 29. If the load is unbalanced and if
the main fuse blows, the lamps on the lightly loaded side will receive
an excessive voltage.

(14) Make a sketch similar to Pig. 29 and give an abstract of
Art. 85.

(15) See Art. 80.

(16) See Pig. 11 and latter part of Art. 11. The circnit-breaker
should be connected in the circuit of the main dynamo and arranged
so that an excessive current in the neutral wire leading to the balancer
will trip the breaker.

(17) Give an abstract of Art. 47 and illustrate your explanation
by referring to a sketch similar to Pig. 39.

(18) See Art. 46. Make a sketch similar to Pig. 38 and refer to
it in your explanation.

ARC LIGHTING

(PART 1)

(1) Lightning:, defective cnt-onts, rocker-arm failing to move prop*
erly, lamp burning with an abnormally long arc. See Art. 66.

(2) The magnet cores and armatures in the altemating-cnrrent
lamp must be laminated, whereas in a direct-current lamp they may
be solid. Also, in the alternating-current lamp a choke coil is used
to take up the excess voltage, whereas in the direct-current lamp a
resistance must be used. See Arts. 46 and 54.

(8) (a) About ^ in. to ^ in.

(b) About g| in. See Art. 65.

(4) The lamp will overheat and the regulating coil may be burned
out because the current will be larger than it should. The resistance
in series with the lamp will be overheated and the enclosing globe
may be melted. See Art. 69.

(5) See Art. 48.

(6) 6.6 amperes and 70 to 78 volts. See Art. 47.

(7) See Art. 32.

(8) See Figs. 21 and 22.

(9) (a) Because if the carbons should stick or fail to feed, the arc
would gradually grow longer and there would be danger of the shunt
coils being burned out. Also, there would be danger of the circuit
being broken. See Art. 39.

(d) In order to provide a sufficient drop of potential tnrough the
lamp so that enough current will pass through the series coils to enable
the lamp to start up. See Art. 39.

(10) (a) By varying the amount of resistance in series with the
arc. See Art. 62.

{d) By cutting in or out some of the sections of the choke coiL
See Art* 64.

ARC LIGHTING

(11) Ste Art, 25.

(12) (a) 450 watts.

(d) 300 watte. See Art. 10.

{13) [a] Petroleum-coke or gas-retort carbon.
(d) Because the impu lilies, if preseut in any considerable quan-
tity, are deposited on the inner globe and obscure the Ught.

(14) (a) See Figs. 7 to 11, Incttislve.
{&) See ArL !!•

(15) (a) Because the crater Is formed in the positive carbon* and
if the upper carbon is not made positive, most of the light will be
thrown upwards instead of clown wards.

(d) By noting which carbon remains hot for the longer time when
the current is turned off. The upper or positive carbon should be the
hotter. See Art, 11,

(16) No; the ends of the carbons are nearly flat, due largely to
the shifting of the arc over the ends. See Art. 9.

(17) About 6.6 amperes for lamps giving 1,200 nominal candle-
power, and 9.6 amperes for lamps of 2,000 nominal candlepower.
See Art. 5*

(IS) (a) Oue in which the arc is surrounded by an enclosing globe
that, to a large ex teal* excludes the air from the arc.

{d) The consumption of carbon is very much less. An enclosed*
arc lamp can easily burn from 80 to 150 hr. without retrimming,
whereas an open arc can bum about 10 hr. only.

(r) See Art. 6.

(19) The carbon points become heated to a very high degree and
the negative carbon becomes pointed* The positive carbon becomes
hotter than the negative and burns away about twice as fast. The
positive carbon has a crater formed in the end and the greater part
of the ligbt is emitted from this crater. See Arts. 2 and 3.

(20) (fl) Abont 3,500^ C.

(6) No.

(c) The effect of increasing the current Is to increase the sis© of
the crater and thus make the arc give a greater amount of light. The
temperature of the arc is, however, not increased. See Art. 3*

amount of light above the horizontal, where it is of little or no use.
See Arts. 15, 16, and IS,

ARC LIGHTING

(PART 2)

(I) To operate circuit t on machine A^ insert plu^ at ^t«, r,«, h^^
r«, ^1, c%. To operate circnits 2f and 9f in series on macliine C, insert
pings at fx.^ /"•, ^.i ^.t ^t, ^.. ^1. /"■, /"t, ^., g.. gf*

(2) , (a) Those with open-coil armatures and those with closed-coil
armatures.

(b) The Brush and Thomson- Houston machines belong to the
first class, and the Wood, or Port Wayne, and Western Electric to the
second. See Art. 28.

(3) See Art. 68.

(4) By connecting one side of the voltmeter to the line and the
other to the ground, as indicated in Fig. 13. See Art. 17.

(5) See Arts. 25 and 26.

(6) The new machine is of the multipolar type and is of consider-
ably larger capacity than the old style. It does not require a separate
regulator, as a regulator is placed on the machine itself. See Art. 24.

(7) See that the current always flows through the circuits in the
proper direction. Never open a circuit when the current is on. If the
circuit must be cut out, first short-circuit its terminals. See Arts. 41
and 42.

(8) In order to keep the current at a constant value. Arc machines
are series-wound, and if no regulator were provided, the current would
increase as the lamps were cut out and decrease as they were cut in.
See Art. 22.

(9) Plug from ^-f to i-f , and from A- to i-. Plug B-\- to 5+,
J— to 4-f by means of cable 7, and 4— io B—.

(10) Constant potential, because the same alternators can then be
used for both arc and incandescent lighting. See Arts. 21 and 32.

(II) They may be operated directly from the alternator by provi-
ding each lamp with a reactance coil that is cut into circuit in case the

186

ARC LIGHTING

§35

lamp goes out. They may also be operated by using a tmosfomicr
with an adjustable secondar>^; by uMog a constant-current trans-
former, or by inserting a reactance in the circuit, this reactance being
arranged so that it varies with changes in the load in such a way
as to keep the current constant. See Arts. 3d to 37^ inclusive.

(12) The break is located by first grounding both end« of th«
circuit at the station. The circuit is then opened about its middle
point and each side rung up, in turn, by connecting one terminal of
the line to the raagneio and the other magneto terrainal to the ground.
After determining which side the break is in, the circuit is completed
at this point and the lineman moves on to another point about half
way between the station and the last point tested. In this way the
stretch oC circuit in which the break is known to exist is narrowed
down to within small limits. See Art. Id*

(13) (a) and (d) See Art. 30*

(14) Give an abstract of Art. 29,

(15) The circuit ends are left open at the station^ and the different
parts of the line are rtiug up for grotinds, by opening the circuit and
connecting one terminal of the magneto to the line and the other to
the ground. See Art. 16^

(16) A doubie-coatact service switch that wilt cut off aU connec-
tion between the circuit and the wires in the building. The switch
mtist be substantially made^ mounted on an Incombustible base, and
must show distinctly whether the current is on or off* Se« Art. 11#

(17) Give a short explanation of the method as descritied in Art. 18
and illustrate by means of a sketch simikr to Fig. 14.

(IS) See Art. 37.

(19) A sketch simitar to Pig. 23 (a), with accompanyiDg explana-
tion, is required,

(20) (a\ See Art. 30.

{d) A sketch similar to Fig; 24 (a) , with explanation, is rcqnired,

(21) Make a sketch similar to Fig. 42.

INTERIOR WIRING

(PART 1)

(1) If the drop is excessive, the lamps will not burn with tiniform
brilliancy, because those near the source of supply get a higher voltage
than those far removed, and the lamps on which the voltage is low will
give an unsatisfactory light. See Art. 69.

(2) (a) Slow- burning weather-proof wire is allowable for open
work in dry places, such as mill wiring, etc. See Art. 88.

(d) It must be supported clear of all woodwork by means of por-
celain, glass, or other non-combustible, non-absorptive insulators.
See Art. 38.

(3) A cut-out must be placed as near as possible to the point where
service wires enter the building. Cut-outs must be placed wherever
there is a change in the size of the wire, unless the fuse in the cut-
out protecting the larger wire will protect the smaller wire also. See
Art. 28.

(4) Calculate the wiring as if it were for 220 volts. This will give
the size of the outside wires. Make the middle wire of such size that
it can carry safely the current required by one side of the system. See
Art. 67.

(5) (a) Cut-outs are used to prevent wires being overloaded.
They open the circuit whenever the current exceeds the allowable
amount and thus prevent the wires from being overheated and
burned out.

(d) They usually take the form of a piece of soft fusible wire,
which melts and opens the circuit whenever the current becomes
excessive. In most cases the fuse is enclosed in order to protect it
from air-currents and to keep it from coming in contact with other
substances. See Art. 27.

(6) See rule (c), Art. 8.

(7) (a) The total current is 250 amperes, allowing \ ampere per

E 5
lamp. Resistance = ~ = —, = .02 ohm. Total length of line wire

248

INTERIOR WIRING

§43

is 400 X 2 ^ aoo ft., or .8 thousand ft

must, therefore, t>e

The resistance per 1,000 ft.
025 ohm. A No. 0000 wire has a resistaoee

of .049 ohm per 1^000 ft., as may be seen by consulting Table IV, so
that two No. 0000 wires in multiple will have a resistance of ,0245 ohm
per 1,000 ft. and will answer in this case. See Art. Ct3,

{b) U carrying capacity alone were considered. No. 000 weather-
proof wire would answer, because the Underwriters allow 262 amperes
for til is size o£ wire. See Table I.

(8) The carrying capacity of rubber-covered wire is lower than
that of weather-proof wire, because the rubber covering is subject to
gradual deterioration under the act Sou of heat. See Art. 12i

(9) See Art. 62.

(10) The amount of energy supplied to any one circuit dependent
on one cat-otit is limited to 660 watts by rule (</)» Art, 30; hence, the
number of lamps allowable is easily determined. About ten 16-candle-
power lamps per circuit is usnally taken as the limit. See Art. 31«

(11) See Art. 3,

(12) The illustration given below shows the wiring provided with the
ueccssary cut-outs and with the currents indicated in the various parts>

& 5^nw> I

- — -t-

6dAfr^.

N*6 BAS

rff^^}U

40Jtff^ ^^ JSJAn^

{a) Current at «r, SB amperes; ^, 30 amperes; f , 5i amperes; d^ 23
amperes; ^, 5 amperes.

ib) The sizes of wire will be No. 2 for section A^ No. 8 for S^

No. 4 for r, No, 10 for A No. H for E, No. 6 for F. See Table L
In each case the wire has been taken that is on the large side^ so that
the carrying capacity wilt he ample. If the distances were short, it is
probable that so many different sizes would not be used.^ For example^
lections C and /* might both be No. 4. although No. 4 is not absolutely

§43 INTERIOR WIRING 8

necessary for section F, If, however, the distances were long, it would
pay to use the dififerent sizes, as indicated.

{c) The actual arrangement of cut-outs may vary somewhat. A
cut-out must be placed at each point where there is a change in the
size of the wire, and a main cut-out should, therefore, be placed at 1,
and 90-ampere fuses would be the greatest allowable size to use in it.
At 2, we may place a single branch block for Cand a main block for ^,
or we may use two single branch blocks or one double branch block.
In the figure, a double branch block 2 is shown, the side connecting
to B being fused with fuses not larger than «33 amperes capacity, and
the side connecting to C with fuses not exceeding 65 amperes capacity.
The arc lamps on circuit B will each be provided with a cut-out at the
point where connection is made to the No. 8 wires. These cut-outs
are not indicated in the figure. At S, a double branch block may also
be used, one side being fused for 24 amperes and the other for 46
amperes, as indicated. To supply branch E, a single branch block 4
will be required, and its fuse must not be over 12 amperes capacity.
No branch block will be required at 5^ because the size of the wire is
not changed there. The current capacity of the fuses indicated in the
figure is the same as the current capacity of the wires that they protect.
In practice, however, fuses of standard size would be used, and these
might not always be of the same capacity as the wire. In any event,
the rated capacity of the fuse should not exceed the allowable carrying
capacity of the wire it protects.

(13) See Art. 2.

(14) See rule (f). Art. 33.

(16) (a) No. 14 B. & S. See rule {a). Art. 8.

(b) The current-carrying capacity as given by the Underwriters.

(16) In order to prevent heating of the conduit and drop in voltage
due to inductive effects. See Art. 16.

(17) (a) Because plaster and cement are likely to corrode the
insulation and break it down.

(b) Staples do not insulate the wire and are likely to cut into the
insulating covering with which t^e wire is provided. See Art. 16.

(18) On circuit A, the current is 20 amperes, which is too much
for No. 12 wire; No. 10 shoiUd be used. Each arc lamp should also
be provided with a cnt-out where the wires running to the lamp tap
on to the mains. Circuit B is all right except that it is connected to
link fuses mounted on a porcelain double branch block. Circuit C \s
also supplied throuj^h link fuses. A double branch block carrying
enclosed fuses should he substituted. Circuit C is overloaded; the wire
should be at least No. VI and it would be better if made No. 10 in
order to allow for the larger current taken by the lamps at starting.

46B— 44

INTERIOR WIRING

§43

Also fused rosettes are not allowable for the individual cut-outs used
with the tamps. Each lamp takes 5 amperes and fnsed TosetCes are not
allowed to carry more than 3 amperes. An enclosed fuse cut-ovit should
be substituted iu each case. Circuit D is of No, 12 wire and provides
ample carrymj^ capacity for the lamps connected to it. However, it
h&s no protection other than the 45-ampere ni am fuses and it would be
necessary to insert a fuse block at E where the No. 12 wire is attached
to the No. S, this block being fused for not more than 17 amperes.

(19) For ttse on 1^-volt lines or oti three-wire systems with

grounded neutral where the pressure between the outside lines does
not exceed 250 volts. See Art. 52,

(20) When the fuse in the larger wire is of such siec that it will
melt before the carrying capacity of the smaller wire is exceeded. See
Arts. 28 aad 2&.

INTERIOR WIRING

(PART 2)

(1) A line 120 ft. long having a drop of 3 volts would be the same

120
slse as a line -^ » 40 ft. long having a drop of 1 volt. In Table I,

under 40 and on the same horizontal line with 30, we find No. 6 as
the size wire required.

(2) Tests should be made to see that all connections are correct,
and also to detect any grounds or crosses between wires. All circuits
should be tested before fixtures of any kind are put up, and each
fixture should be tested after it is wired, but before it is put in place.
See Art. 52.

(3) {a) See Art. 54.

{d) Before the building is lathed and plastered.

(4) See Art. 52.

(5) The total current = 80 X » "=" ^ amperes. By formula 1,
the resistance per 1,000 ft. r. of the proper size wire to use equals

2X200X40 "* '^^ ^^^ P®' ^'^^ ^^* '^^^® ^°"^^ require a No. 1
wire, which has a resistance of .124 ohm per 1,000 ft.

(6) The voltage across the outside wires at the lamps = 220 — 4

AO V /)2
= 216 volts. Substituting in formula 7, we have current = — srs—

= 14.4 amperes. Ans.

(7) As in Art. 9, divide the current by the drop, which gives

-7c = 10. Now follow down in the column under 10 amperes until the

nearest distance to 120 ft. is obtained. This will be found to be 121,
and to the left of this in the first column will b^ found tfhe size of wire
required, namely, No. 6 8. ^ S.

rNTERIOR WIRING

§44

(S) The fifty lamps will reqtiire 35 amperes. Substituting the values

t 1 fc u t 1 21.6 X 150 X^ j«enA
given in formula 5, we have circular mils = ^ = 40,500*

or between a No, 4 and No. 5 B. & S. No. 4 wire would be used.

(9) No. 6 wire has a cross-section of 26,250 circular mils, approad-
mately. The drop is to be 2 volts, the current 40 amperes, and the
distance 100 ft.; hence, from formula 5, the retj^ired cross -section of

' ' ^ 1 t. 21.t>X 100X40 ^onrw^ n^u ^- *

wire in cirralar mils ^ 5 — = 43|200* The cross-section of

the wire to be connected in parallel with the No. 9 wire already installed
will he 43,200 - 26,250 ^ l<i,950. No. 8 B, & S. has about 16,510 cir-
cular mils and would be the nearest size. See Art. 14.

(10} (a) and (d) See Art, 16.

(U) (&) Wooden molding may be used in finished houses on
ceilings and walls, and in show windows for temporary purposes,
where it is desirable to hide the wire and give the work a neat
appearance.

id) It must not be used in concealed work, in damp plac^, or in
any place where the difference of potential is over 300 volts. See
Art. 50*

(12) See Art, 57*

(13) (a) A main f^witch and cut-out.

(d) The cut-out should be placed nearest the point where the wires
enter* then the switch, and finally the meter. See Art. 26*

(14) By means of two three- point switches, one at each point from
which it is desired to control the lamps. Make a sketch similar to
(a) or id), Fig. 18. See Art. 20,

(15) So that if a wire comes in contact with any section of a con*
duit or fittings there will be afforded a direct path to ground througlil
which current may escape to earth. This prevents the current leakinj?
to ground through any other paths and thereby reduces the Likelihood
of a fire. See Art* 47»

(16) See Art. 40.

(17) The loop system Is one in which the same pair of wires pa
m series through all outlets at which lamps to be connected on thai
circuit are located; that is, no branch circuits are tapped on e;xcept
at outlet or junction boxes. See Art. 42 <

(IS) See Art. 40.

(19) The wires must be brought out* for combination fixtures,
lhrf>UK:h flexible insulated tubes in such a manner that they cannot
totivh gas pipes, metal work, or plaster. The in&nlating tub«8 mtist

§44 INTERIOR WIRING 8

extend as far back as the last insulating support. If there is a gas
pipe at the outlet, the tubes must extend at least as far as the end of the
gas cap. See Art. 18 and rule {d), Art. 19.

(20) They must be rigidly supported on non-combustible, non-
absorptive insulators that keep the wires at least 1 inch from the sur-
face wired over, and should be kept at least 10 inches apart and run
on separate timbers or studding whenever possible. Sometimes,
especially where a large number of wires come together near the
junction or panel boards, it is impossible to keep the wires 10 inches
apart, and in such cases they can be run in an armored cable or con-
duit. See Art. 19.

(21) Since the two wires have a greater surface area than the one
wire of equivalent cross-section, they can radiate the heat faster and
hence can safely carry more current. See Art. 13.

(22) The current will be 25 amperes; hence, from formula 5, cir-

, .. 21.6X100X25 \onnn XT 1. o p o u

cular mils = ^ = 18,000. No. 14 B. & S. has a cross-

18 000
section of 4,107 circular mils and -^ ,7^7 =4.4, nearly. Four No. 14

wires on each side of the circuit will give somewhat under the required
cross-section, and hence the drop will be slightly over 3 volts. Five
wires on each side will give more than the required cross-section. If
desired, four wires can be used on one side and five on the other, thus
giving the allowable drop almost exactly, but four wires will likely be
near enough. See Art. 14.

(23) {a) Waterproof sockets.

{d) They should be connected and hung by separate rubber-covered
stranded conductors, not smaller than No. 14 B. & S. The two con-
ductors should preferably be twisted together when their length is
over 3 ft. They should be soldered directly to the circuit wires, but
supported so that the weight of the lamp socket and wires will not be
borne by the circuit wires. Rosettes should not be used. See Art. 15.

(24) {a) A single-pole switch may be used where it does not con-
trol over 660 watts.

(d) Because they cost less and the wiring is simpler and cheaper.
See Art. 28.

(25) Because not more than 660 watts are allowed on one circuit
by the Underwriters and No. 14 is plenty large enough to carry the
current safely; moreover, the distances are usually so small that the
drop is never too large on 110-volts or higher pressure systems, even
with the maximum allowable number of lamps on the branch circuits.
No. 14 wire being the smallest size allowed by the Underwriters is
therefore used for most branch circuits. See Art. 24.

INTERIOR WIRING

(PART 3)

(1) It is important to burn the lamps at a proper and uniform
voltage, the drop or efficiency being a secondary matter; hence» a
large drop may be allowed and comparatively small wires may be
used, but lamps of the proper voltage should be used even if this
requires lamps of different voltages in the various parts of the circuit
or system. See Art. lO.

(2) See Art. 16.

(3) Because a protective device for use on a constant-potential
circuit is made to open the circuit in order to protect it, but on a
constant-current system, it must short-circuit and not open the circuit.
See Art. 23.

(4) See Art. 23.

(5) (a) A self-restoring annunciator is so constructed that when a
button is pushed, its corresponding drop falls. The next call operates
a magnet that moves a restoring device, thus resetting the first drop.

(d) See Art. 41.

(6) See Art. IT.

(7) Since one side of the system is grounded, it is very easy for
the current to leak to earth, and hence the fire risk is great, to say
nothing of the risk from shocks. See Art. 29.

(8) {a) A motor and starting resistance box must be protected by
a cut-out and controlled by a switch that shows plainly whether it is
on or off.

(d) Single-pole switches may be used with motors of i horsepower
or less and then only on low-tension circuits. See Art. 28.

(9) It is dangerous to life and, moreover, a lightning discharge
can easily start an arc, and an arc once started will persist even though
the points between which it plays are separated several inches; hence,
it is liable to cause a fire. See Art. 17.

245

INTERIOR WIRING

l«(

tlO) (a) Resistance boxes and reactive, or choke, coila.

(d) Resist a nee boxes may be used on direct- or alternating -current
systemfi, but reactive, or cboke, coils, although the more economical of
the two, can only be used on alternating-current systems. See Art. 9«

(11) See Art. &1*

(12) It is l>est to use nt bber-covered wire in very moist or wet
places for bell and aanunciator wiring. Bee 42»

(13) When the circuit-breaker opens all the wires leading from the
line to the motor. See Art, i38.

(14) Without special permission transformers must not be placed
inside a building, except in central stations^ and if a transformer is
fastened to an outside wall^ it must be separated from the wall by
substantial supports. When transformers are placed in buildings,
they must be located in a special fireproof enclosuFe located near the
point where the wires enter the building. See Art. Id.

(15) See Art, 43,

(16) See Art. 26.

(17) Because all the air gaps at the burners in one circuit are in
series r and hence offer a great resistance to the sparking current;
and dnce a current will take the easiest path to ^ound, it follows
that the current will jump to ground instead of across all the spark

^aps if there is a point where the resistance to jjround is less than the
resistance of the gaps. Consequently, high insulation is essential.
See Art. 68.

(18) State the main requirements as given in Arts. 27 and 28.

)

MODERN ELECTRIC-LIGHTING
DEVICES

(1) See Art. 61.

(2) See Art. 38.

(3) See Art. 23.

(4) See Art. 76.

(5) See Art. 1.

(6) See Fig. 21 and Art. 45.

(7) (a) See Art. 66.
(d) See Art. 68.

(8) (a) See Art. 63.

{d) By the selection of the gas to be mingled with the rarefied air
in the tube. See Art. 54.

(9) The same process is used for both, except that the metallized
filaments are subjected to the additional operation of being heated
to a temperature of from 3,000° to 3,700° C, both before and after the
flashing process, in an electric-resistance furnace having the form of a
carbon tube. See Art. 3.

(10) See Art. 26.

(11) See Art. 31.

(12) See Art. IT.

(13) See Art. 74.

(14) See Art. 50.

(15) {a) The metallized filaments have positive temperature coeffi-
cients and a lower resistance than the carbon filaments; that is, their
characteristics resemble those of a metal. See Art. 4.

(d) Graphitized. See Art. 4.

255

S MODERN ELECTRIC-LIGHTING DEVICES §56

(10) Sec Art. 03,

(17) See Art. 2T.

(18) See Art. 57,

(19) {a) See Art. »•
{b) Because of the great lengftb of fi)Am«m f«qtitT«d. atid the

difficulty of supporting^ it. See Arts. 11 and 31-

(20) Because with the tube the source of light is distributed and
the quantity of light falling on an object is greater than that given by
the taw of inverse squares, which holds true for a concentrated source
of light. Moreover, with the ttibci sharply defined lights and shadows
are avoided. See Art. 30.

ELECTRIC SIGNS

(1) See Art. 30.

(2) The contacts are held together by the combined pull of a
coiled spring and a permanent horseshoe magnet. The expansion
wire cools, contracts, and finally overcomes the holding power of the
magnet and spring, and the contacts fly apart quickly. See Art. 16.

(3) (a) A monogram letter is a group of lamps so arranged that a
large number of different letters, figures, or characters may be dis-
played by lighting different lamps of the group. See Art. 23.

(d) See Art. 24.

(4) See Art. 8.

(5) See Art. 22.

(6) By a group of lamps with a suitable commutating device
arranged to operate in synchronism with the movements of a clock.
The commutator changes the connections to the lamps at regular
intervals, usually once every minute, so that the lamps display the
figures showing the time. See Art. 29.

(7) See Art. T.

(8) See Art. 20.

(9) See Art. 28.

(10) See Art. 2.

(11) See Art. lO.

(12) See Art. 25.

(13) (a) See Art. 11.

(d) See Fig. 10 (d) and Art. 12.

(14) The aim should be to design a sign that can be read by the
greatest possible number of people for the longest possible time and
that will convey the strongest possible impression. See Art. 2.

256

ELECTRIC HEATING

(1) See Art. 3.

(2) See Art. 10.

(3) The surface should be rough and blackened. See Art. 2.

(4) (a) They have large magnetic leakage, which causes high
inductive drop when the secondary current becomes excessive, and
thus prevents injury in case of accidental short circuit.

(d) A choke coil. See Art. lO.

(5) See Art. 6.

(6) See Art. 17.

(7) See Art. 6.

(8) (a) See Art. 20.
{d) See Art. 21.

(9) See Art. 32.

(10) See Art. 28.

(11) See Arts. 8, 12, and 13,

(12) The total volume of air to be heated is 12 X 14 X 10
= 1,()H0 cu. ft., and the number of degrees through which the tem-
perature is to be raised is 72 — 32 = 40° F. At 18 joules, or watt-
seconds, per cu. ft. for each decrree rise there will be required
1,680x18x40=1,209,600 watt-seconds. As there are 3,600 watt-
seconds in 1 watt-hour the requirements in watt-hours will be
1,209,(K)0 ^ 3,(K)0 = 336, and at 220 volts the current must be
336 4- 220 = 1.53 amperes, nearly. Ans. See Art. 23.

167

INDEX

NoTB. — All items in this index refer first to the section (see the Preface), and then
to the page of the section. Thtis, "Air heating, {57, p21," means that air heating will be
found on page 21 of section 57.

Applications of electric heat, {57. p8.

of Moore tubes, (55, p44.
Approved conduit systems, §44, p40.
Arc Advantages of enclosed, (34, plO.

Advantages of open, §34, plO.

Character of enclosed, §34, pO.

circuits. I^yhig out. §35, p2.

circuits. Lightning protection for, §35 pl6.

Crater of. §34, p2.

dynamo. Brush. §35. plO.

dynamo. Wood. §35. p22.

Electric. §34. pi.

lamp. Beck. §55. p56.

lamp. Brush, §34, p41.

lamp. Economizer of Bxcello, §55, p53.

lamp, Excello alternating-current, |55b
p52.

lamp, Excello direct-current, §55, p50.

lamp, Bxcello flaming, §55, p50.

lamp, Magnetite. §34. p58.

lamp. Photometry of the, §34, pl6.

-lamp pulleys. §35, p6.

lamp. Shunt type of series, §34, p41.

lamps. Adjusting, §34, p65.

lamps. Alternating-current open-, §34, pl7.

lamps, Bumed-out coils in. §34, p66.

lamps, Candlepower of, §34, p20.

lamps, Carbone. §55, p61.

lamps. Care of, §34, p64.

lamps. Comparative tests of, §55, p58.

lamps. Comparison of various types of, §55.
p61.

lamps, Cut-outs on. §35, p9.

lamps. Direct-current enclosed-, §34, pl8.

lamps. Direct-current open-, §34, pl6.

lamps. Examples of, §34, p41.

lamps. Flaming, §34, p58.

lamps for street lighting, Height of, §35.
p4.

lamps. Impregnated carbons for ^n^ng,
§55. p58.

Accumulator, Nature of. §27, pi.

Phillips-Entz. §27. p26.

The chloride, §27, pi 5.
Accumulators, Bimetallic, §27, p25.

Classes of, §27, p2.

General data on chloride, §27, p84.

Lead. §27, p2.

Rating of, §27. p6.

Use of. in central stations, §27. p54.
Advantages of electric heat. §57, p8.

of electric welding. §57. pi 7.
Aging of transformer iron, §33 p53.
Air heating, §57, p21.
Alarms. Burglar, §45, p40.
Alternating-current arc-light dynamos, §35.
p25.

-current arc switchboards, Western Elec-
tric, §35. p40.

-current constant-current system. §33, p34.

-current constant-potential system, §33.
pl5.

-current enclosed-arc lamps. §34 p20.

-current enclosed-arc series lamps. §34, p49.

-current lines. Calculations for, §33. p49.

-current open-arc lamps, §34, pl7.
Alternators, Constant-current, §35, p25.
Ammeter jack, §35, p41.
Ampere-hour efficiency, §27, pll.
Amyl-acetate unit, §32, pi 3.
Anchored filament. §32, p5.
Annealing. §57, pi 8.
Annunciator circuits. Bell and. §45, p29.

Needle. §45. p27.

Self -restoring, §45, p27.

Wiring for elevator, §45, p38.

Wiring for return-call, §45, p32.
Annunciators, §45, p26.

Apparatus for series lighting system , §45. p49.
Appliances for domestic use, Heating, §57
p24.

^^vS^^^^^^^H^INDEX ^^^^I^^^^^H

^H Afi^— (Contim]f4)

Bnllast. 132, p41. ^^^|

^^H lunps. Ligblnme arrester for. |^, pl(V.

for Nemst lamp, |5fi, pO), ^^^H

^^H lampSiH Miipj^eiite ImiiitiiLjus^ . ^Q^, pti2.

Bar, Photometer, #32. pl8. ■

^^P Immps. Methods of di^tdbxitioii ui. (34. p2D,

Bane copper wire. B. & S, frauge. Dimensions H

^H lamps, Opeit', f34, p4L

of. |43,pl6, ■

^H lattip£. Pamlkl (JistHbuiion of. |34. r>31

Base. Edison. |32, plO, ■

^^H lamps. Power coriBurnption of, j34, p24.

of lamp, #32. pQ. ■

^■^ lampB. Series. |34, 1>3M.

Thomson- Houston, f32, plO, H

^^^^^ lampii. Sorirfi distribtition of. |34« p^fl.

Wesiingbouat, or Sawyer-Man, f32, pll, H

^^^^^B lamps, Special application aL |34. {iflCJ.

Bases. Lamp, $43. p4l. ■

^^^^V lamps. Trimming, 134, p(M.

Batteries, (45, p23, ■

^^^^^1 kinps. Tviies ui, p4, p.15.

Automobile, }27, p23. ^M

^^^^V lam pi, Wiring for. §45 . pi 3,

in lighting stations. Storage. f33, p62. ^M

^^F lamps, WiKi^g far coii^tA tit -current * £45h

Storage, |27. pi, ■

Batter>' charged from dynamo. §27. pSO. ^^^H

^^V 4icht carbnn^, ArranKeiTient o£„ |34, pi 1 .

Charging the, |27. }337 ^^H

^H 'light d^rnamos. 1^5, pi 7

Closed-circuit ts'pe of, [45, p24. ^^^H

^H * -Hgbt dynamos. Altpmating-curtWit, S^^.

Discharging the . f 27. p39. ^^H

^H p25.

discontinued, £27, p43 ^^^H

^K 4icrht lines, Testing, p.^, pIO.

Extde. 127. im, ^^H

^H 4t»tht swJtchboan]£. |35. p32.

Gould automobile. (27, p34, ^^^|

^H -light wiring. Drop in, j43. p51 .

Gould storage, {27. plS^ ^^H

^V lighting, m. pi ; 135. pi .

Gravity-cell. 145, p24, ^^H

^H* lighting. Line construction for. |35. p3-

Inspection uf cells of, (27, p40. ^^^H

^^K lighting. Line work i^t, {35. pi.

into commissbn. Putting, #27. p43.

^^H lighting. Watts per squnre foot for interior.

NfttuJ* oE«oCrtid&ry. |27, pL

^H }34,p2G.

Occasionally used, |27, p43

^^m lightfl on iDW'potentul dnniits^ Rules for.

Opeu-cifcisit type of. |45, p23.

^m H5i pi3.

out of commission. Putting, {27. p4a.

^H lights. Size of wire for, 143, p52.

out on line. {27, peo.

^^B* machines. Constant direct-current „ |35|

Porter automobile. |27, p24

Regulating appliances (of storage, §27, pft4.

^^H machinea in sprics. Running. |3fi, p24.

Selection of, fur given servdce, {27, p62.

^^M mBchines. Reversal of palanty in, §15, p33»

storagK^, Nature of, |27, pi.

^^H switchboards,. Con !tt ruction and opeiratioii

takiufi i.ieak of load. {27, fsSS.

^V of. S35. p33.

ust'd to carry whole Iriad, {27, p57*

^H Temperature uf . j^H, ij3.

used to take up fluctuations in load, |27,

^K Voltage of the. (34. p4.

t»57.

^H Arcs, Enclosed, f34, p5.

Willard storage, {27. p22.

^V Open, f 34, pi.

with double end-cell switch, |27, p67,

r Armored conrtrnt. Flexible, 144+ p59.

m-ith single end-cell switch, |27 p06.

1 twin cable. ^44, p23.

Beck lamp, {55, p56.

1 Anangement of lighting apparatus. t4fi. p4€.

BeU and annunciator cireuiCs, {45. p29.

|i Automstic burner, S4.i, p45.

Electric, {4fi. pflO.

1 cut-outs, £43, p23.

wire, Runinng. {45, p28. ^^^^H

* cut-nuts. Rules for, H3. p24.

wiKn}^, {45c p20- ^^^^H

drop, 145, |i38.

viHrinji for flats, {45, |)30. ^^^^H

mercury -vapor lamp type, |55, pflfl.

Bells. Operating, from lighting cirtruits, |45, ^M

Automobile batteries, f2T, p23.

P24, ■

battery. Gould, |27. p24.

Bimetallic accumulators. |27. p25, ^M

batten', Porter, #27, p24.

cells. 127, p25, ^^M

battery . \Vi1 ! a r<l , f 27 , r^24.

Binding, Heaters for, {57. p29. ^^^^M

Antotransf'irmers. S35, p30.

Bloc^k, Three- wifv branch, {43, p45. ^^^H

TtiT^e-win- main, {43, p45, ^^^^|

B^ioster, 133. pl4. ^^^|

Balancer, f33, p9.

Compaunil, 127, p73. ^^^^^

Cbnstant-cumeDt, |27> pTS. ^^^H

INDEX

Booster— (Continucrl)

Differential. §27. i)74.

field, Reversing rheostat for, }27, p71.

Shunt. (27. p60.

Storaf^e-battco', S27. i>68.
Boostcre. Capacity uf, §27. p81.
Box negative. {27. pi 6.
Branch block. Three-wire. 54.'i. p45.

block. Two- wire double, §43. p46.
Breakdowns. §33. p2K.
Breaks in circuits. §35. i>10.

Locating. §35. pll.
Bremer lamp. §34, i>58.
British thermal unit, §32. p33.
Brush arc dynamo, §35, pl9.

arc lamp. §34, p41

machines. RcKulator for, §35. p20.

plug and sprinK jack. §35. p3G.
Buckling. §27. i)6.
Bulb. Style of. §32. i)8.

Tubulation r.f. §.12, i»8.
Bunaen photometer, §32, pl6.
Burglar-alarm system. Ojxsn- and closed-cir-
cuit. §45, p43.

-alarm system, Open-circuit. §45, p4l.

alarms. §45. p40.
Bumed-out coils in arc lamps. §34, pOO.
Burner. Automatic. §45. p45.

Pendant. §45, p44.

Ratchet. §45. p45.
Burners ioT parallel system of electric gas

lightinR. §45. i>44.
Burning battery lugs. §27. pl5.
Button, Ceiling. §43. p39.
Buzzer, §45. p21.

C R regulator. §33. pIW.
Cabinet. Example <»f. §44. p27
Cabinets and panel lx»ar<ls. Use of. §44, p24.
Cable. Amiorcci twin, §44. p23.
Cadmium test. §27. p43.
Calculating sizes of wire reciuircd, §44, pi.
Calculation of line l<jsses duo to resistance.
§43. p-V).
of the i>ri>iM.T size of wire for a driven loss,

§4:i. pr.H

of wire size in terms t)f re-ist.iiue i»er 1 ,00()
feet. §44. i^.

<»f wires for alt<-niatinj^' current. §44. i>8.

of wires in parallt 1. §44. pHi.

of wires in t<rT!!s of cirenlar mil-;. §41. p.**!.
Calls. ( arri.ou . §.".(>. p2H.

C-an«llei'"\V(r and <li^tril)iiti>jn of the li^^ht
fp>m ari laiii])s. §.'>.'». poO.

Mean horizontal. §.'{2. ]'21.

Mean spherical, §;i2, p23.

Candlepowcr- (Continued)

obtained in vortical plane, §32, p22.

of arc lamps. §34. p20.

of incandescent lamps. §32, pl2.

of lamps. §32, p28.

Power consumption per, §34, p21.
Capacity of boosters. §27. p81.

of galvanized-iron wire. Carrying, §57, i>6.

of German-silver wire. Carrying, §67. p5.

of tinned-iron wire. Can^dng. §57, p7.

of wires for marine work. §44. p67.
Car heater. §57. p22.
Carbone arc lamps. §55. p61.
Carbons, Arrangement of arc-light. §34. pll.

Composition of. §34. pi 3.

Consumption of, in lamps. §34. p8.

for flaming-arc lamp. Impregnated. §55.
p58.
Care of Nemst lamp, §55. p26.
Carriage calls. §56. p28.
Carrier- bus switchbf>ard. §35. p39.
Carr>*ing cai)acities of wires. §43. pl3.

capacity of galvanized-iron wire. §57, p6.

capacity of German-silver wire, §57. p6.

capacity of insulated wires. §43. pl4.

capacity of tinned-iron wire. §57, p7.
Cartridge type of (uses, §43, i>46.
Ceiling button. §43, p39.
Cell. Edison nickel-iron, §27, p28.

Faure. §27. p3.

Plante. §27. p2.

Type of lead-sulphuric acid. §27. pi 5.

Zinc-lead. §27. p25.
CeUs. Bimetallic. §27. p25.

Charging, from constant-current arc circuit.
§27. p49.

Construction of lead-sulphuric acid. §27,
pl3.

Copper- zinc. §27, p26.

General data on electric- vehicle, §27. p86.

General data on Gould storage, §27. p85.

General data on storage. §27. p83.

Getting low, into normal cf)ndition, §27.
p42.

Installation and care of storage, §27. p30.

Location of. §27. i)30.

Method of .supportinK. §27. t»30.

of battery. lnsi»et;tion of, §27, i>40.

Rating of. §27. p7.

Resistance of. §27. pl3.

SeiHinent in, §27. ]A2.

Setting "P. §27. p-'iO.

Simple fonnii tioiis for ehaoring. §27. p40.

Tn-atnunt ..i" viu\. §27, p45.
Cetiteri.f .H>tril.ntion. §4.'i. pp22. .'>.').
Central statit-n, Kfle< l r.l electric heating on.
§57. i-^.

4(1B— 45

INDEX

ChanKt^Me sj^nf, 156. ptO,
Chanswsi Frequcnty. ft33. f»2G
Chaiie!c& in display oi sififis, fi5fi, pi 9.

In jntrngity of ligfht c>f signs. |56. plO.
ChamctfsmtiQS o( ftttTTting-are lanip, j55, p58*

of McKJre tubes ► S65^ p45,

of Untiilum fUamenta. fSfi, p7.

of the Nt-mst laimp, |fi5, p23-
CltaTKe of baitterjf, Indic4i|iuti£ of a complete,
S27. r>37,

Voltase at end of ► |27t IJ38.
CfiafKing batttry ffcmi dynamo, |27, p50>

cetk fmm constant ^ciuireat arc drumlt* |27,
p49.

dettmmotive force, §27, pl3.

eHi: battery, fi27. p37
Cblcinde actum ula tors » Gi^tieral data *yti, j27,

pS4.
Choke, or ncaptance* c«il» |a4, p34.
Cifctiit-br^kers. §43. p23.

'brt&kieTis. cul-out5, etc* Construe liun uf.
|4S. p30.
Cii^uits, Arravifiemefit of lefieB, |.14. p38.

Be]] and annunciatt^r, f45, p2fi.

Breaks in, #35. plO,

Distnbution, §43. p22.

in aerieis, Ope rating, l<i5, ^i32.

i*mpi used in series, 133, p36.

Laying out, |44. p32.

Laying out arc f35, pt3.

Li>{htning protection for arc, ^5. pi 6,

Prottttion of secondary, ^33, p27.
Clrait, Knob, §43, p38.

Single-wire . |43, p37.
Qock, Talking?, |56, p2T.
QocedHrircuit burglar system |45. p42,

-t'ifcuit type of battery, J45, p24.

-«oll nmchities. |3t^, p32,

-coil marliioes, Wcsterti Electric, |35. t'22.
C6d«. Natiotial Elect riraL H^^. p2.
Cbil* Rcat-'tancc, or chokt;, |34, p34.
Colls, Balancing. f35, \^l.

Econiimy, J35. r30.
Color of li:^Kt of incandesce (it lamps, f j>Qt p4.
Combination sign, |56, lA.
Cbmbininij several mring systems^ |45, pi,
Comparative lamp tests for are lamp^i, |6fi,

p58.
Compariscfn of mercur>'- vapor lamps wttH
other light sources. |6.^. p37.

of various types of arc lampis. £55. p<ll-
Com position of carbons, |34, pt3.
Cf impound booster, 527. p73.
Cont-'twlt^d fleet ric-ligbt wiring, Specificsatians
for. t44, r>36.

knub-and-tube work^ 544> p3Q.

wirinu, |44, pl&.

Cdnductof. 133, i>4.
Cunducton for marine work, Portable, §44
pa7.

in pamitel, Fuse protection for, |44, pl3.

Underground, fi43, pi 3.
Conduit. Flcnibk arniored. |44, pS0,

s^-Etems, Approved, S44. ij49.

systems. Early. |44. p4g,

wirinjf, §44. p4S.
Cbnduits. Rules for interior, J44. pfi8.

Wire used in. H4» p55.
Connecting lamfJSt Methods of* |iia. p2.
Connections for Nemst lamp, |55, p2] .

lot testing lamps, *3^, pi25.

for thawing transformer, |57, pi 2.

of Cooper Hewitt l^mps, (55. p3l.

of glower lamp, |32, p43.

of merciiry-varior lamps, (55. pSl,

of Mtjore tubes, iSa, p40.
Constant -curn-nt alternators, |35^ p2S.

-current arc lamps. Wiring for. §45 pi 4^

^current bf:M>5t£r, (27. p7S.

-current distribution. Machines far* |35» plTi

-current enclosed-arc ficrJes lamps, |3;4

-current npen-anc series lamps, §34. p4l

^current tmnsfomier, (S3, p40^

direct -current arc machines. (35. pi 7.

•potential altEmating-curtietit lamps* f34,
p66.

-potential are lamps, Wiring for. 145, p]

-potential direct^current lamp,
Electric, 134, p53.

-potential direct-current lamps, |34. pBS,

-potential enclosed arc lamp, (34, p53.

►potential lamp. W^'stem Electric * |34, p57,

-potential Utnf>s, f (14. p36.
Consumer's switch, (27, p40,
Consumptiun of carbons in lamps, (34. p8.

of power per candJepower, (34, p21.
C^ontrul nf lamps from two points, (44, p3$.

of lights from three or more points, §44 . p40.
Cooper Hewitt lamp, (55. p2S,

Hewitt lanif) feflectore. |5S, p3l.

Hewitt lamps, Qjnncctjons of , |55, p3l.

Hewitt type of lamp, (55, riflfi.
Copper losses of tmnoformcr. Mcnsurcrmernt of,
(33, p58,

wire, B. & S. gaug«, Dimensions **f twir,
(43,pl0.

vin;. Resistance of pur?, (43, p40.

-zinc cells, j27, p2fi.
Cord. Rules for flexible. }43. p40
Core losses of transformer, Me&sunemcfit of*

(33, p55.
Cored carboa. (34, pt4
Costs of hating, Relatiw, |57, pOi
Crater of arc, §44, pi.

INDEX

Crawford- Voclkcr lamp, $32, p45.
Cross-section of wires, Eqtiivalcnt. 844. pl6.
Crosses. §35. pll.
Current allowance per lamp, 133, p51.

and voltaRe of lamp, §34, p9.

Direction of. §27. p60: §34, p2.

estimation. §33. p45.

HcatinK eflFect of electric, §67. pi.

of enclosed-arc series lamps, §34, p49.

of lamp, §32. p27.

of lamps, §34, p5.

regulators, §33. p38.

required by lamps, Estimation of. §44. p7.

required by motors, §45, pl8.

required for lamps, §43, p43.

required per lamp, §32, p33.
Currents, Tables of heating effects uf. §57.

pp2. 3.
Cut-out. §32.42; §34. p38.

-out for Nemst lamp. §55, p21.

-out, Location of, §44, p34.

-out switches, §35, p8.
Cut-outs, Automatic, §43, p23.

-outs, cireuit-brcakers, etc.. Construction ot ,
§43, p30.

-outs for marine work, §44, p68.

-outs, Location of, §43, p35.

-outs on arc lamps, §35, p9.

-outs. Rules for automatic, §43, p24.

-outs. Switches and, §43, p23.
Cutter switch, §27, p52.

Data, Pipe- thawing, §57, pplO, 11.
Deshler-McAJlister photometer, §32, pl8.
Determination of sizes of wire according to

current capacity, §43, p35.
Devices, Miscellaneous heating, §57. p20.
Diameter of wires that will be fused by a cur-
rent of given strength. Table of, §67, p4.
Differential booster, §27, p74.
lamp. §34. p40.

method of looting grounds, §35. pi 4.
Dimensions of bare copper wire. B. & S. gauge,

§43. pl6.
Dimmers, Stage, §45, p4.
Direct-current arc machines. Constant-cur-
rent. §35. pi 7.
-current constant -current system, §33, pi 5.
-current constant-potential system, §33,

p6.
-current enclosed-are lamps, §34, pl8.
-current machines. §35, pi 7.
-current open-arc lamps. §34, pi 6.
-current systems, Two-wire and three-wire,
§33. p44.
Directions of current. §27, p50; §34, p2.

Discharging the battery, §27, p39.
Distribution and candlepower of light from
arc lamps, §55, p50.

Center of, §43, p55.

circuits, §43. p22.

of arc lamps. Methods of, §34, p26.

of arc lamps, Series, §34, p26.

of lamps. Location and, §44, p47.

of light, §32, p21.

of light of Nemst lamp, §55, p26.
Dcx>r openers, §45, p40.
Double-branch blocks. Two- wire, §43, p45.

-end cell switch. Battery with, §27. p67.

-faced signs, §56, p6.

-filament lamps for signs, §56, pl2.

•pole flashers, §56, pi 5.
Drawing wires in conduits, §44, p60.
Drip loop, §43, p37.
Drop, Automatic, §45, p38.

in arc-light wiring, §43, p5l.

in feeder lines. Uniform, §44, pi.
Dynamo, Brush arc, §35, pl9.

Wood arc. §35, p22.
Dynamos, Arc-light, §35, pl7.

Economizer of Excello lamp, §55, p53.
Economy coils. §35, p30.

of electric heating, §57. p23.
Edison base, §32, plO.

nickel-iron cell, §27, p28.

plug, §43. p44.

three-wire system. §43, p20.
Effect of electric heating on central station,

§57. p8.
Efficiency, Ampere-hour, §27, pll.

Luminous, §55, pi.

of lamp. §32. p24.

of light-giving sources. §32, p36.

of Nemst lamp. §32, p44.

of storage cells, §27, pll.

of transformers, §33, p50.

Watt-hour, §27. pl2.
Elblight system of signs, §56, pi 9.
Electric annealing, §57, pl8.

arc. §34, pi.

bell. §45, p20.

-car heater, §57, p22.

current, Heating effect of. §57. pi.

fumaces. $57, p20.

gas lighting. §45. p44.

gas lighting, Burners for parallel system of,
§45. p44.

heat, Advantages of, §57. p8.

heat. Applications of. §57. p8.

heater. Luminous, §57, p22,

heaters. Power consumption of, §57. p29.

INDEX

bisatine, Efled of, on oeatnil <tk|loit»« |57,

l»»tsnff of air, |S7, p^L
hi^tinff of fniter, §57, r^-
bohtlog pcid, 157. p2§

f wnit^ HfldftWEiy, |57, p^

t onits. 137, rC6.
Iwrting unit*, Promelhcua, ^57, p26.
lfl*l»ll»li*m, Mattel^ to be cvnadtrfTed in.

113. pi.
*liicht wifiqg, Spedficatloni for cpncetiled,

liiijf'jr*, Wiring fow, f 4Sp pl7.

%''rTiide tctb, GcQcrvLl da^tn nn, 137, t»^V

wehlifi^^ Advuniages of.' |57, pi 7.

f^ldJnjT* l^obp ppxcw oF. i&7, (jLO.
njEtins, Power rcquind Un, i^7. pplO. 17^
[rin«. Pint* caused by, fW. ^.

^ittical cod«, National, |i3, pfl,

M-nrki Pittinj^H ftmt tnny^be ufefl in, f43. p3.
lik?etn:>Hpf iwliLhe*, {i4. fji41.
Elsctrulv^W, MijiiAM the, f27, p34.
Etectrolytk f0T^. 157, pi 8.
EleotltnDodvp f(iix«, ChM^g^ of« with di^-

fctn»t CbiLTifina, tS7t pt3.
Eltftirtits in jmt, PUdng the ati>TB^ celj, |27.
r.31.

Enrlnsed ft re, AflATinta^^t-s of^ (34 ^ plO,

arc. Character of. 534. jiO.

wirif^, PitUiief. tssed for. |43,

f^£G

Factory wiring. Simple exjtmpte of, fO^
Ffturtf ccQ. ff7t pS.
Fct^iler-and-iilajn »y*|jnii, |33, |»?.
Ui»ei, L^nifonti dnip jn, |44, pi.
Peeffrrs anct tt^ius, fS.1, i^l
FUamem. AiichrifVHlp §331. eA.

MetAltiscd. I5A, p2.

SiMor, S3a p7,

PiUmifnts, |S2, p4.

Chafscterifittn of tftntalufn^ i5ft» t^,.

Fl4*hinK of, I&6, p3-

Mt^thod* of supp*jttitig Untalun>. |al»,

Prepafmbofi of mrtoJIifird, |55, p2.

Pivpbr&lion of Osniism. f[53, pi !
Pif^-alarm songs^. WiriiiK firr, f4.^, p36l
FiiTS oftuird by dectric»l wiring, |43, ffi

Hjtamplea of clrc:iTical, §43, pn
FittioH^ for KupiKirtini; tv-irr , H3. pST.

for 220- volt wirimr, Sek%'tir.i*t erf, f43, i^,

used for expnst'd wirtnit, f-iS, pfilfi,

used in el^ctriral titnrk, |4^, {33.
Five- wire syncm*. f^.T. iil€.
Fixed electric siflnsi, |,Ml, pi.
Fixtures, H4, p43.

for niarinc work, S44, pOB^

Ruk^ for, 144, 1*43.
Fl&ming-arT lirnip, Channrterislics nf ffi$,
p,58.

-arc la nil) •-

■onstructi'.n. $34. p49.

-arc lamp, Iinprej^natci carl-'.ns tor. >S'

-arc lamp.

Multiplc-s«ries. §34. po?.

I)5«.

-arc lamps.

AlternatiTik'-< urrcnt, §34,

p20.

-arc lamp thec^ry. §5o, piS.

-an- lam]>s,

Data ..n, §34. p25.

-arc ]ann>s, §34. p5S; §.").'», p47

-an lamps.

Dire, t -current. §34, plS.

Flasher, Sin^le-ixjle f.'r .si).m, §.')<». i»17.

-arc lamps

on ooO-v.-lt ( ircuits. §34, ]

p3r,.

Flashers, Double-pole. §r,«i. pi.").

-arc lamps.

Trimming. §34, ]A\7.

for sif-rns. Mechanical, §'}<». ijl.'i.

-arc lamps.

220 -volt, §34. p3r>.

Thermal si^'n, §5<i. p]2.

-arc scries

lamps, Current > >i , §34. p

Flashing of filaments, §55, p>3.

-arc scries

lamps, Vi;lta>.;e rcjuired b;

y, §34.

process, §32, pG.

I>4S.

Flat-iron heater, §57, i)27.

arcs. §:M. 1

>').

Flexible armored cmduit. §44. i>59.

In-^.s. §4:i,

P44.

cord. Rules for, §43. p4U.

fu «s. Adv:

uita).:cs of. §43, p47.

lamp cord. §43. i»39.

i:n.!-ccll in'li(

at-rs. §27. p«i<i.

Fluctuations in load. Battery used t" lakt c

Mcll sv.it. 1-

1. Iiattcr\- with sin^:lc. §27

', p(i(».

§27, p57.

-cell switdi

es, §27. p*i4.

Focusin^^amp, §34, pl3.

cells. Treat

ment ..!'. §27. p4.-).

ForRc. Electrolytic. §57. plS.

Er,rnv;ilent e

rM...-sf, ti.^ii ol wire.. §44.

1-1 -,.

Formulas for resistance of wire. §44. j^^i.

Exc. 11.. .-lit. f

iiat iiu'-cuiTeTil lamji. §.")5.

p.')2.

I'reciuency chanj^es, §33. p2r».

.iir.(t-<ii:ri

.lit l.imic §.-).-,, p.^>().

Frictional machines, §45, p.'>0.

flaiiiiiii' arc

lamj., §.".. p.-.O.

Fr.)zen water piix-s, ThawinK of. §57. plO

lampcc.n..

muzcr. §.">."). i>53.

Furnaces. Electric. §57, i)20.

INDEX

xui

Fuse protection for conductors in parallel,

(44. pl3.
Fuses. 543. pp23. 44.

AdvantaKcs of enclosed. 543, p47.

CartridKo tyfw of. §43, p46.

Enclosed, 543. p44.

Link. 543. p44.

Rating? of. 543, p47.

Gas li^htinK. Electric, 546, p44.
Gauges. Wire. 543. pl6.

General Electric constant-potential direct -
current lamp, 534. p63.

Electric heating unit, 557, p26.

Electric lamp for constant alternating cur-
rent. 534. p62.

Electric switchboard. 536, p46.

rules for wiring, 543. plO.
Globe. Waterproof. 544, pi 8.
Glower lamp. Connections of. 532, p43.
Glowers of lamp. 532, p40.
Gould automobile battery, 527, p24.

storage battery. 527. pl8.

storage cells. General data on. 527, p86.
Graphic method of calculation of wires, 544.

plO.
Gravity-cell battery, 545. p24.
Grounding of neijtral on three-wire system,
533. p32.

of secondary system of wiring. Permanent,
533. p31.
Grounds. 535, plO.

Differential method of locating, 535. pi 4.

Luxating. 535. pl2.

Hadaway heating unit. 557. p26.
Hanging lamps. Methods of, 535. p4.
Heat. Advantages of electric. 557, p8.

Applications of electric, 557, p8.

of incandescent lamp. 532, p33.
Heater, Car. 557, p22.

oils and holder of lamp, 532, p40.

Flat-iron. 557, p27.

Luinincms, 557. p22.
Hiatt-rs for bookbinding machinery, 557. p29.

tor laundry machinery, §57. p29.

for i)rinting machinery, §57. p29.

Nemst lami>. §55. pl9.

Power consumption of. §57, p29.
Heating. Air, §57, p21.

appliances for domestic use. §57, p24.

<levices. Miscellaneous. §57. p29.

EfTci t of central station on electric. 557. p8.

cfTci ts of currents. Tables of. §57. pp2, 3.

etfects (»f electric current, 557. pi.

Heating — (Continued)

Electric, 567. pi.

of water, 567, p23.

pad, 557, p28.

Relative costs of, 567, p9.

unit. General Electric, 557, p25.

unit, Hadaway, 557, p26.

units. 557, p26.

units. Prometheus, 557, p26.
Hefner unit. §32. pl3.
High-potential systems, 546, pll.
Hoho process of welding. 567, pl9.
Hydrometers. 527, p30.

Illuminated signs, 566, p2.
Illumination, 534. p23.

by incandescent lamps, 532, p33.
Impedance of transformer. Measurement of,
533, p68.

volts of tranjrformer, 533, i>59.
Impregnated carbons for flaming-arc lamp,

556, p58.
Incandescent lamp, 532. p3.

lamp. Heat of. 532, p33.

lamp. Life of, §32, p29.

lamp. Voltage of. 532, p32.

lamps, 555, p2.

lamps, Candlcpower of, 532, pl2.

lamps. Illumination by, 532. p33.

lamps, on series circuit. Wiring for, 546,
pI6.

lamps. Power consumption of. 543. p43.

lamps. Recent t>'pes of. 532, p36.

lighting, 532. ppl. 3; 533. pi.
Indicators. End-cell, 527. p66.
Inspection of cells of battery. 527. p40.
Installation and care of storage cells, 527, p30.
Insulated wires. Carrying capacity of, 543, pl4.
Insulating joints, 544. i>44.
Insulation resistance. Test of. 544. p64.

test, 533, p53.
Interior arc lighting. Watts per square foot
for, 534, p26.

conduits. Rules for. 544, p66.

wiring, 543. pi; 544. pi; §45. pi.

wiring. Systems of distribution for, 543,
pl9.

Jar. Placing elements of storage cells in. §27.

p31.
Joints. Insulating. §44, p44.
of wires. §43, pll.

of wires, Soldering fluid for, §43, i)ll.
Junction boxes. Use of outlet antl. §44.
p51.

H xiv ^^^^^ INDEX ^^^^^^1

Lamp— (Continued) ^^^H

^m Knnh, (43. p37.

ReilectOfB of Coaper Hewttt, §55, p31. ^|

^H -iLnd-tubt' work. Conceltteil, }44, p20.

SearehliKht.(34, p«2. ^^M

^M d«flt, |4a»r^m

sockets and receptacle j», (43, p42 ^^^^H

Temperature uf a. (32. £^1^4. ^^^^H

tests, Tunifstcn, (A5. p13. ^^^^B

^^B Latrp. Applicatinn of the Mrtorc, |&5* p44*

Thomaon-Hou^oq, (34, p45. ^^^^^|

^B Ballmst for Nemst, (55, p20.

Type C, trtertznry- vapor, (55, p30. ^^^^H

^H Base of. 132. p0.

Type H. mercury-vapor, {55. p2^. ^^^^H

^B ba»^. 143^ pit.

Type K. tnercury- vapor, (55, ^tSO. ^^^^|

^H Bcrck. (55, p56.

Type P, mercury- vapor. (55, pe6, ^^^H

^H -bf^rd retfulator, ^3, p38.

Vacuum relator for Moore, (55, p4I. ^H

^H BremE-r, }34. r*^.

Voltage of Incandescent, (32, p32. ^M

^^M cAlculations, Measyreitipnts &iid^ (32. pi 2.

Weptem Eketne, (34, p52. ■

^H Can? of Mem&t, (55, p2G.

Western Electric, constant-potential, |34 ^M

^^K CharacteriiticB of flaming-arc, (55, p58.

p5,'». ■

^^B Chfl^racrtcriaticfi of Nt^mst, (55, p2S.

Lam pa , Applica t ions of the Moore , ( 55 , p45 . ^M

^^1 Comparison of menntry-vapor, with other

Candlepower of. |32 , p2g . ^H

^H l%)it edurces. |56, p37.

CandXeppwer of incandescent, (32, pT2 ^^^H

^H Conneetions for N«mst, (55, p21 .

Center of distributiofi of, (33, p44. ^^^H

^^1 Connections for Moore^ (55. p40,

Chamctenstics of Moore, (55, ^"45. ^^^H

^H Cunstant'putential enckiscd-nrt:, (34, p53.

Color of light of incandescent, f55, p4. ^^^B

^V const ntction, En dosed -arc, (34 , t>49^

Comparative tests of arc, (55. p58 ^M

• Cooper Hewitt, (55, p28.

Comparison of vartouis t>ijea of arc, |AS. ^M

TOfd. Plejiible, (43.pS0.

m. ■

Crawford- Voelker, (32, p45.

Connection of Cooper Hewitt. |55. p3L ^M

Cumcnt of. (32. r27.

Connection of mercur>'-vapjr, |55. pSl. ^U

C\iiTBnt required per, |32, p33.

Connections Tor testing, (32. p2;5, ^B

Ctit-oMt for Nernst, (55. p21.

Constant-potential. (^4, p36. ^H

Descriptjoii of Ncmst. (32. p3S.

Constant-potential altcmatin^-c\£rrelt|. |34, ^H

ENUen^ntiaL (34, p40.

p56. ■

EconoTniser of E^cello arc, (55, p53»

O^nstant-potential direct-current. |34, pfiS. ^M

Efficiency of, (32. p24.

Const niction of, |32. p4- ^H

Effidcncy of Ncm*t, (32. p44

Control of. from two points, |44, p3S, ^H

estunatei. |32, p26.

Current of, (34, p5, ^^^B

KxceWo altemating-cument, (55. p52.

Cument reqtdred For, (43. p43. ^^^^H

Ext^lo direct -current, (55, p50.

Data fm enclosed -arc, (34. p25. V^^f

Bxeellci f^minjc^-arc, (55. p50.

Estimation of cunx-nt required by, §44, pT^^^H

EnhaustJOTj of, (32, p8.

Flnmin^ arc, (34, p58^ |5!^, p47, H

-feet, (33, jA^.

for street li^htin^, Heij^Vit of arc, 13.11, p4, ^|

Ponjsing. (34, pi 3.

Illumination by incandrficent, (32, p33. ^|

Glowers of, (32, p40.

in multiple series, (33, p4, ^H

Ghjweni<jf Nernst, |55, pi 7.

in paraUel, f33, p2. ^M

Heat rji incandeseent. |32, pSfl,

in series. (33, p2. ^K

Heattfi Lif Ntmst, (55, pi 9.

in series circuits, Looptog in. |35, p9, ^|

Intrandc^tnt, (32, p3.

tncandciscent, (55. p2. ^H

Life of incandescent, (32,. p29.

Location and distribution of, |44, p47. ^H

Li«ht difTtribuiioti of Nt-mst, (55. p26.

Luminous-arc, (55, p4B. ^^^

Mfli<nL*titc nrc, (34, p58,

A^n^rnetitc-Iuminous arc, |55. p(^. ^^^^H

Muitiplc-si-^rie^ encluwd-arc, (34, p57^

Must -arm suspension of, (35, ^tit ^^^^^H

Negativf? temperature coefBcbnt of, (55„

McrL'ury-var.Hir, |55, p28 ^^^^H

P8,

Metalik -filament. (55, p5, ^^^H

Nemst, (32, %m: (55, pl6.

Metallized -filament, (55, p3. ^^^^^

Operation of Nemst, (32, p37*

Methods of c»mnectinff, (33, p2 ^H

OBmiufn, (32, i>4(V.

Methods of distribution of arc. (34, p2G, ^^^

Parts of Nemst. (55, plfJ.

Met hot! :^ ii( hanging, (35, p4. ^^^^^

Photometry of the an:, §34, pi 5.

Moore, (55. p:ifl. ^^^1

INDEX

Lamps — (Continued)

mounted on pule tops, §35, p4.

Open-arc. J34. pi 6.

Operation of mercury-vapor, 565, p36.

Operation of metallissed -filament. 865, p4.

Oix.»ration of osmium, 555, pll.

Operation of tungsten, 555, pi 3.

Osmium, 555, pIO.

Parallel distribution of arc, 534, p31.

Power consumption of arc, 534, p24.

Power consumption of incandescent, 5^.
p43.

Recent types of incandescent, 532, p36.

Rope for arc. 535, p7.

Series arc, 534, p38.

Series distribution of arc, 534, p26.

Si>an-wire suspension for arc, 535, p6.

Tantalum. 556. p6.

Temperature of incandescent, 555, pl6.

Theory of flaming-arc. 555, p48.

Trimming encloscd-arc, 534, p67.

Tube. 556. p27.

Tungsten. 555. pl3.

Turnip sign. 556. pi 2.

Tyi)es of arc, 534, i)36.

used for series circuits, §33, p36.

Wiring for arc. 5^6. pi 3.

Wolfram, 555. pl3.
Laundry machinery. Heaters for, 557. p29.
Laying out circuits. 544. i)32.
Lead accumulators, §27. p2.

sulphuric-acid cells, Construction of, 527,
pl3.

sulphuric-acid cells, Types of. 527. pl6.
Leading-in wires, 532. p7.
Leak in circuit, §35. pH.
Letters for signs, Monogram. 556. p21.
Life of incandescent lamp. 532. p20.
Light distribution. 532. p2l ; 534. pl5.

distribution of Nemst lamp. 565, p26.

measurements, 532, pi 2.

-giving sources. Efficiency of, 532, p36.

Theory of Moore, 555, i>39.
Lighting apparatus. Arrangement of, 545,

Arc. §34, pi; 536, pi.

Iniandescent, §32. ppl . 3; 533, pi.

Stcre. 54,5. pi.

Tulx'. §55. p27.

tnbes, MtK»re. §.'>5. p39.

Watts IKT siiuare font for interior arc, §34.
p26.

work. Size of wire for, §35, pi.
Lightning arrester for arc lami)S. §36. pi 6.

pnttection for arc circuits. §3.5, ])10.
Lights, C<>ntn»l of, from three or more points,
544, i>40.

Lights —(Continued)

Illuminating value of. 532, p34.
Line calculations, 533. p44.

construction for arc lighting, 536, p3.

losses due to resistance, (Calculation of, 543,
p60.

work for arc lighting, 536, pi.
Link fuses, 543, p44.
Load, Battery taking peak of, 527. p55.

Battery used to carry whole, 527, p67.

test of transformers, 533. p69.
Location and distribution of lamps, 544, p47.

of cells, 527, p30.

of cut-outs, 543, p35.
Loop, Drip, 543. p37.

Looping in lamps on series circuits. 535, p9.
Low-potential circuits. Rules for arc lights
on, 545, pl3.

-potential system. Definition of, 543, pi 6.

-potential systems, Wiring for. 543, pl6.
Luminous-arc lamps, 555, p48

efficiency, 556, pi.

radiator, 567, p22.

Machines for constant-current distribution,

535, pi 7.
Magnetite arc lamp, 534. p68.

lumino\i8-arc lamps, 556. p62.
Main block. Three- wire, 543. i>45.

switch, cut-out, and meter. Location of,
544, p34.
Mains, 543. p22: 544, p32.

and feeders, 533, p6.
Mangin mirror. 534. pl2.
Marine work, 544, p65.

work. Capacity of wires for, 544, p67.

work. Cut-outs for, 544. p68.

work, Fixtures for. 544. p68.

work. Portable conductors for. 544, p67.
Mast -arm suspension of lamps. 536. p5.
Mean spherical candlepower, 532, p23.
Measurement of copper losses of transformer,
533, p58.

of drop in volts, 544, p66.

of impedance of transformer. 533, p58.

of primary and secondary resistance, |33,
p56.
Measurements and lamp calculations. 532.
pl2.

Light. 532, pl2.
Mechanical flashers for signs. 556. pll.
Mercury- vaiH»r lamp reflectors, §56. p3l.

-vapor lamp type, 555, p66.

-vaiMir lamps, 555, p28.

-vajxir lamps. Comi>arison of, with other
light sfmrces, 555, p37.

^^ xvi INDEX ^^^^^^^^^^H

^H Mcrrury— (Coixtititied)

Open— (Continued) ^|

^^ft ^vitpdr latntia^ CuimFctions of, |55. r^L

-arc lamps, Di rut t -current, |34. pi 6. ^H

^^1 -vflf^'^r lamps. Opcmtion of, #55. p36,

arcs, §34, pt. ■

^^M MtrlalliL-filiimept lanifja, f5f». pS.

-circuit buTBlar-alarm lyslcm. f45, p4l*^^^^^B

^H Mi^ttiUixcd filuttient lamps, (55. p2.

-circuit type of battery, |45, p23, ^^^H

^^M 'filamtfiit lamps:, Operatiofi d(, (i55, p4.

work in dry places, |43, p33, tI^^I

^H Anient. Prtrparalirm of, 1&5, p2.

Operating bells from ligbting cifcuit«« f^l^^B

^1 Meters Ucatfrm of. f44, t^4.

p24. ■

^H Methods of thaw'iTUt fruzen water pipes, |57,

circuits in serii:^. |35, pS2. ^M

Oxwration nf mercufyvapifr lamp», §b&, fiS6. ^M

^H Heihve.*n setren, |32, pi 2.

uf tttftalhzed-filamrnt tampfi, |&5, |>4. ^M

^1 Mill. 143. p]5.

of Osmium lamps, 155. pi I. ^M

^H Himjr. Ma iifTin , iU , p 1 2.

of smn&s. arc lamps by adjustable trans- ^M

^H Miscf IJartemii heating ile%ie«Sp §57, p20.

former. }35, p2e, H

^P Mixed !a>'&t(?TnEi. |33^ |i^2.

of series arc lamp* directly from niachime, ^M

Mriklmg wurk, R tiles far wires for, |44, pOI .

f35. p35. ■

Motdmjfs. Wooden. ^44. p60.

of Berks arr lamp* frmn con»tiifit-cun«nt ■

MoniKgrram k'ttirrs fr>r sigtifc. JSW, p2J.

transforms rs. {35. p27. ^|

Mixine tnnip vacuum rti^ulalor. |55. p4L

of scries an. lamps frnm cons^tsnt-potentml ^M

lirtht, Theory of, 855, p39.

alt«tmator&. §35, p25. ^|

]i«htifur tubes. |55. pSO.

of tolkinif ^f^m, (56. p2t. ^M

tubt connirctiDiis, JSSt p40.

of Tungsten lamps, f53, pl^, ^M

tub^, AppHiatit>ns <if , |65, p44.

Osmium filamenLfi, Prepamtion of* |fi2|, pll. ^|

tiibea. Chamcteristics of . j55. p45.

lami^, 132, p46; |55, plO. ■

Molor-generator method of load test. §3^1.

lamps. Operation of. 155 » pll, ^M

pse.

Outlet and iunctioti boxes. Use of, 144, pBL H

Mdinn, Current required by, |45. pIS.

Multtdrcuit stncs machines. |34, p28.

Multtplea^ri^s endowed -arc lanap. |34, p57.

Pad, El^ctKc-heatinu. 157. pSS, ^U

«riea, Lanipft in, |33. p4.

Panel bnard. Essential parts ofa, |44 p25, ^|

' jn

bfiard. Example of. f,*4, p26. H

board. Form of twi»-wire. f44, p29, ^H

NatioTiaf Ebclrkal Cbde. f43. p3.

board i^^th <;pecial fuse holder, |44. p28. ^M

Nacelle anntincifitor, i4G, p2T.

bcsards. Use o( L^binrts and, |44, |?M^ ^M

NMCftttve. Box. ftJ7. plfi.

Farallel dlBtHbutkm of arc tamps. |34, p3K ^M

Ncfisl glowers. §55, pi 7.

Lamps in, |33. p2. ^H

htntera. |55, plQ,

!(y intern of electric gas lijihUnir, Burners fcir, ^|

tamp. {32, p3a: |5ri, pi 6.

H5, l>44. ■

lamp. Ballast fur. {56, p3(l.

Pendant burner. (45. p44, H

lamp, Care of, §55. rj^fl.

Permanent gfoundiuj? of gecoadory system U ^M

lamp, Charactcristicii nf, ji55. p23.

wiring. f33, ij3l. ^M

lamp, Connectinits for. J55. p2l-

Photometer, §32. pi 3. ^M

lamp cut-out, fi55, p2].

bar. {32, pl^. ^^^1

lamp, Description of, 432, pS8.

Bunfi^n, |32, pie. ^^^^M

lamp, EfficieiKy of, |*^2. t>44.

Conditions of, {32, p20. ^^^^|

lamp, LiKbt distHbulffm *A, fl56, p20.

Deshler-HL AUister, 132, plS. ^^^^

lamp, Operation cif, |?t2, (i37-

Elementar\% {32, pt5. ^^^^|

lainp. Part* of. |55. pi ft

Law cjf, {32, pl4. ^M

. NickeMron cell, Edisoti, {27. p28.

PhQCometry ^f the arc lamp, |34, pi 5 ^B

Pipe-thawiuM data, |57, pplO, IL ^M

Pipe*:!, Thawini? frozen water, §57, plO. ^H

Open- and dsised-dfruit bumUtr-alarTn sys-

Plaittt^ cell. 127, p2. H

tem. §45, p43.

Plate, Positive, |27, pi. ^M

aiTt AtlvantaBt:ft of, {34, plO.

Plug and inrk. Western Electric, f35. |^7. H

arc, Disadv^ntageii of, #34, plO.

EdiNjn, £43, p44. H

-arc lamps* |34. pplG. 41.

Pnlarity, R^^vrnsal of, in arc machiites, l^tf^^^l

-are lamps, Altematinii -current, §34 pl7

jM^H

INDEX

xvu

Polyphase systems. }33. pl8.

Porcelain tube. }43. p37.

Portable conductors for marine work, §44,

p67.
Positive plate. §27. pi.
Power crmsumption of arc lamps, §34, p24.

consumption of heaters, §67, p29.

consumption of incandescent lamps. |43
p43.

consumption per candlepower. §34, p21.

required for electric welding. §67, ppl6, 17.
Preparation of metallized filaments, §55, p2

of osmium filaments, §55. pll.
Primary and secondary resistance. Measure-
ment of. §33. p56.
Printing machinery, Heaters for, §57, p29.
Prometheus heating units. §57, p2fi.
Protection of secondary circuits, §33, p27.
Protective de\'ices, Thomson. §33, p29.
Pure copper wire. Resistance of. §43. p49.
Push button. §45, p22.

Radiator. Luminous. §57, p22.
Rail welding, §57, pl7.
Ratchet burner. §45, p45.

feed. §34. p62.
Rating of accumulators. §27. p6.

of cells. §27. p7.

of fuses. §43, p47.
Reactance-coil regulator, §33, p39.

or choke, coil. §34, p34.
Reflectors for Cooper Hewitt lamps, §55, p31.
Regulation of series arc lamps by variable
reactance, §35, p29.

of transformers, §33, p61.
Regulator, C R, §33, p38.

for brush machines, §35, p20.

Lamp-board, §33, p38.

Reactonce-coil, §33. p39.
Regulators. Current, §33, p38.
Relative costs of heating, §57, p9.
Resistance of cells, §27, pl3.

of pure copper wire . §43 p49.

Test of insulation, §44, p64.
Return-call annunciator. Wiring for, §45, p32.
Rheostat for b(x>ster field. Reversing. §27,

p71.
R<)I)e for arc lamps, §35, p7.

Trimmers', §35, p7.
Rosette. §43. p38.
Rubber-covered wire, §43. p34.
Rules for arc lights on low-potential circuits,
§4.5. pl3.

for automatic cut-otits. §43, p24,

for flexible cord, §43. HO.

for interior conduits, §44, p5G.

Rules— (Continued)
for snap switches, §43, p31.
for sockets, §44, pl8.
for switches, cut-outs, circuit-breakers, etc.,

§43. p24.
for wires for concealed knob-and-tube work,

§44. p22.
for wires, General, §43, pi 7.
for wiring of high-potential systems, §45,

pll.
for wiring in damp places, §44, pi 7.
for wooden moldings. §44. p60.
relating to switches, §43, p29.
relating to transformer installation, §45,

pl2.
relating to wires. §43, pl2.
relating to wires for open work, §43, p83.
Running bell wire, §45. p28.

Sash-cord rope, §35, p7.

Screen. Methven. §32. pl2.

Searchlight lamp, §34, p62.

Searchlights, §34, p61.

Secondary battery. Nature of. §27, pi.

circuits. Protection of, §33. p27.

resistance. Measurement of primary and,
§33. p56.
Sediment in cells. §27. p42.
Self-restoring annunciator. §45, p27.
Series arc lamp. Shunt type of. §34. p41 .

arc lamps, §34. p38.

arc lamps. Operation of. §35, p25.

arc lamps, Regulation of, by variable react-
ance. §35. p29.

circuits. Arrangement of, §34. p28.

distribution of arc lamps, §34, p26.

lamps. Alternating-current endosed-arc,
§34. p49.

Lamps in. §33. p2.

lighting system. Apparatus for, §45, p49.

machines. Multicircuit. §34, p28.

systems, §35, pi.
Setting up cells, §27, p30.
Seven-wire systems. §33. pl4.
Shunt booster, §27. p69.

type of series arc lamp, §34 pll.
Sign, Carriage-call, §56, p28.

Combination. §56, i>4.

lamps with thermostats, §56, pll.

Operation of talking, §56. p21.

Talking-clock. §56. p27.

Thermal flashers for, §56. pi 2.

Turnip lamp for. §56. pl2.
Signs. Changeable, §56, plO.

Changes in display of. §56, pi 9.

Changes in intensity of light of. §56. plO.

^^xviii ^^^^^^^INDEX ^^^^^^^^^^H

^H S|gni--( Continued)

SuippQrting—C Continued) ^^^|

^H Dpubk-facifd. m^ pS-

wire, FittinR? for, H^. p37. ^^^|

^H Poubk-l^lanieiit kmpci tor. (59, pi 2,

Switch. Qinsumer's. (27. p49 ^^^|

^H Doubk-pule flashers fnr, |50, til5.

Cutter, (27, p52. ^^^|

^M Elblight Byntem of. ASe. pi 9.

Location of main. (44. p:t4 ^^H

^^M Eiuiniplt^fi of Um^t |Mt< p8.

Two-poim. (45. p40> ^^M

^1 EK[>aiH;d4ju]b, SS6, p5.

Switchboard, Camer-bus. (35. I^IH. ^^M

^H Fixed dectnc, i5«. pi ,

General Blecln'e. f33. p4&, ^^^|

^H Ilium inat^d, 153. p2.

with cable, SiTTiple, ft5, p33. ^^H

^H hdechanioil Hasbere for, |5G. pi 5.

without cables, (35. p37, ^^M

^H Mnuotfram kttcns for, |&6. p2l.

Switchboards. ATv-light. (35. pa2. ^|H

^H SLti^te-r»<jle Hasher for, §50, pi 7.

Ojnstructitjn and operation of arc, |35. idljij^|

^H Talking, fi5f}.p2L.

for alternating-current series systems. f3(^ ^H

^H Thcmiublink for, |56, plQ.

p4A. ■

^H Thermostats fur. (56. plO.

WestcTD Bleetrie atteniatinig-cajnot ^n ■

^H Time switch cis fiir, 156. 1>17,

(35, p4g ■

^H Transpatrnt, {56, p2.

Sv^^tcheit. (44.p3g. ■

^H Simple switch bi-ard M-itb cable. (35 » pSS.

iLud cui-out*i, (43 p23. • V

^H two wire system. (33. p6.

Cut-out. (33. pS. 1

^H Singlp- pha.5cisyst«;rn, (33.p15.

cut-outs, circuit -breakers, etc* Rules f*jr 1

■ 'pok Iksher. f5ft, p17.

(43* p24. ■

^M 'Win? cjcat. |43. it37.

Electrolier, (44 p41. ■

^M SiM of wire for anr Hfthts, (43, p52.

End^n, (27, p64. ■

^H of wire for three- wire syistcm, (43. p58.

Rules relating to, |43, p20. ^^B

^m Si2c!i of wire according to current cttpacity^

Sn»p. (44, p4l. ^^H

■ (43.p35.

Time. (56. pl7. ^^M

^H Sldw-bumiriK. wea the r- proof wire* (43, ii34.

Systems of distribution, §33, pi. ^^^|

^M Snap switches. (44^ p41.

■

^B switches* Rules fur. (43. p3L

^B Sockets. Rules for. (44. pl8.

Table Df capacity of wires for marine work.

^H Soldering fluid for johits of wirrs. f43. pit.

(44, p«7.

^H Span- wire suspennon lumps', (35, p6.

of carrying capacity of insulated wires, |43,

^M Speaking-tube s^fEtem, Wiring for. (45, p35.

pl4.

^H Spedftcatiotis for concealed electric- light wir-

af curreni allowant'e per tamp. (33, pSl

H ing. (44, pao.

of current ref suited by mutors, (45. plB,

^H Squirting processp (32. p5.

of liata on cntlfj«d-aPc lamps, (34. p25.

^H Stage dimtncni. |45. lA.

of diameters of wirei of \*arious materials

^H Station. Effet^t of elect rit: heating on centrmli

that v\.ill be fused by a current of given

■ (57. PB.

strenjitb. (57, p4.

^H Stomge baltene.^, |27. pi.

of dimensions rjf ban; copper wire* B^ S,

^H h$.tieHes, General description of, (27, pi >

KBitKe, §43, pi 5.

^H batterk^ in li^btinK stations, (3*1, (>62.

of efTicicncy of transfonrwrEi, (SS, p£0.

^B -battery bDostcrs, (27. p68.

of equivalent crosfr-iectkin of winpi, |44,

^H battery, Gould. (27, plS.

pl5.

^H bfittery. Nature q{, (27, pi.

of general data on chlt^ridv nt^Ptitliutattj'rft*

^H -battery regulating appliances* §27, p64.

§27, p84.

^1 battery. Willard. |27< p22.

of pipe-thawin»{ data. |57, pi 1

^m t-enii. Bflkiency of. (27. pi 1 .

of power consumption ot are lan\f«. §34,

^H cells. General data on, (27, pS3

1^24.

^H cells, Geneml data nn Guuld. (27. p85.

^H cellEi, Ini^tallation and care of, (27. v>30.

lamps, (4,1. p43.

^V Store %htmK, (45. pi.

of tjower pefjuired for tWitdc welding. I&7.

^H Strwt -lighting devices. (33. p42.

Ida.

^H lighting, MeiKht of arc lamps f^^^. (35. p4.

of resistafice of pure eopper wiTt*. (43.

^1 Sutiihatinj?. (27, \A4.

HO.

^H Supporting cells. Method of. (27, 7^30^

of watt* jier siquare fixjt ft*r ttitcdor arr

^H tiintaluin 61a men ts. Meihods uf* §5*5. p6.

lighting. (34. Vi26.

INDEX

XIX

Tables of heating effects of currents, §67,

Pp2. 3.
Talking clock, §56, p27

signs. §56. p21.

signs, Operation of, §56, p21 .
Tantalum filaments, Characteristics of, §55,
P7

filaments. Methods of supporting, §55, p6.

lamps. §55, p6.
Temperature coefficient of a lamp, Negative,
§55. p3.

of a lamp. §32, p24.

of incandescent lamps, §55, pi 5.
Test, Cadmium. §27, p43.

for transformers. Load, §33, p50.

Insulation. §33. p53.

of insulation resistance. §44, p64.
Testing arc-light lines. §35. plO.
X lamps. Connections for, §32, p25.

Transformer. §33, p52.
Tests of arc lamps, Comparative, §55, p58.

of Tungsten lamps, §55, pl3.

of wiring, §44, p62.
Thawing data for pipes, §57, plO.

frozen water pipes. §57, plO.

transformers, §57, pl2.

transformers. Connections of, §67, pl2
Theater wiring. §45. p4.
Theory of flaming-arc lamps, §55, p48.

of Moore light. §55. p39.
Thermal sign flashers. §56, pl2.
Thermoblink, §56. plO.
Thermostats for sign lamps. §56, pll.

for signs. §56, plO.
Thomson-Houston base, §32, plO.

-Houston lamp, §34, p45.

protective devices. §33. p29

welding process, §57, pl3.
Three- wire branch block, §43, p45.

-wire main block, §43, p45.

-wire system, §33, p8.

-wire system, Edison, §43, p20.

-wire system. Size of wire for, §43, p58.

-wire system. Unbalancing of, §43, p68.

-wire systems. Special, §33. p8.
Time switches, §56. pi 7.
Transfer board, §35, p45.
Transformer. Constant -current. §33. p40.

Impedance volts of. §33, p59.

installation. Rules relating to, §45, pl2.

Insulation test of. §33. p53.

Measurement of copper losses of. §33, p58.

Measurement of core losses of, §33. i)55.

Measurement of impedance of. §33, p58.

testing. §33. p52.

Welding. §57, pl5.
Transformers, §45. pl2.

Transformers — (Continued)

Load test of, §33. p59.

Regulation of, §33, p61.

Thawing, §57 pl2.
Transparent signs, §66, p2.
Tree system of wiring, §43, p32.
Trimmer's rope, §35, p7.
Trimming enclosed-arc lamps, §34, p67.

of arc lamps. §34. p64.
Tube lighting. §55, p27.

Porcelain. §43, p37
Tubulation of bulb, §32, p8.
Tungsten lamp tests, §55, pi 5.

lamps, §56, pl3.

lamps. Operation of, §55, pl3.
Turnip sign lamps, §56, pl2.
Two-point switch. §45, p40.
Two-wire and three-wire direct-current sys-
tems, §33, p44.

-wire double branch block, §43, p46.

-wire panel board. Form of §44, p29.

-wire system, §43, pi 9.

-wire system. Simple, §33, p6.

Unbalancing of three-wire systems, §43. p58.
Underground conductors. §43, pl3.
Underwriters' test for wiring. §44, p63.
Uniform drop in feeder lines, §44, pi.
Unit, Amyl-acctote, §32, pl3.

British thermal. §32, p33.

Hefner, §32, pl3.

Vacuum regulator for Moore lamp, §55, p41.
Voltage and current of lamp, §34. p9.

at end of charge. §27. p38.

of incandescent lamp. §32. p32.

of the arc. §34. p4.

regulation, §33, pi 2.

required by enclosed-arc series lamps. §34
p48.

Water heating, §57, p23.

Waterproof globe. §44. pi 8.

Watt-hour efficiency. §27. pl2.

Watts per square foot for interior arc lighting

§34. p26.
Weather-proof wire. Slow-burning, §43. p34.
Welding. §55. pi 3.

Advantages of electric. §57. pi 7.

Hoho process of, §57, pi 9.

of rails. §57, pi 7.

Power required for electric. §57. ppl6. 17.

process. Thomson, §,57, pi 3.

transformer. §57, pi 5.

XX.

INDEX

Wfratem Electric do«?d-cml machines, |35.

Elifctric tAiuUiit-polentkl lamp. |34.

Electric lamp, |34. pfiS.
Elut-'tric plug antl jack. |35, p37.
Wcatinghou^^ ur Sawyer-M&rL. bB«?, §32.

WiUard automobije hatterv, J27, p24.

sttinige battery. S27. r22.
Wire. Carr>injf capatity tA gal vatii zed -iron ^

457, p6.
CajTving capadty of Gtrnian-tilver* |57.

p5.
CafTyina capadty of tinned -imn, |57, p7.
Wire* De^tctmitiinK diufti of ^ accorditi^ to ciir-

rent capacity, §43, p4/l,
lor a ffivtn loss, Cd{:ulating pn^per si*c of,

S43,T>£3.
for arc lights. Si« of, j43. p52.
for liifhttng work, Sise of, {35, pl^
for three- wire sytteni, Si»e of. #43, p5S.
Formulas for i^mtance of §44, pfi.
S&u^ccs,^ 443, pl5.

Ti'qiuired* CalcuJatittB siics of, |44, pi.
Resistance of pure copper, #43. p49.
Rubber-covered. §43. Fi34
Running bell. H5- p2S.
sijses in term!* of resistaTucr i»r 1,000 fe^t,

144, ii3.
Slow-tmniinff weathcT-pronfi f43, p34.
used in cnnduits, §44, T>Sfi'-
Wires, Carrjirvg capacities of, |43, pi 3.
Carrying capacity of insulated , |43, pi 4^
Diameters of. that will be fustd by a cur-
rent of [fiven gtreniifth* |57, p4^
Equivalent cross-aecticin of. |44, pi 5.
for alttmatirtK current, §44, pS.
for concealed ktiob^and-tube work, |44,

p22,
for conduit in marine work. J 44. fjfiti.
for high-pt>lcntiiU systems. §45, pll.
for n^arine work. Capacity nf, §44, p67^
iar molding in marine work. f44. jj66.
for mbldini; work, |44, ptiL
for open work. Rulc& relating to. {43. p^.
Genera] rules for, |43. pi 7.
Gmiihic method of calctdatiot) of , §44, plO.
in marine work. Rules fur, §44. p^.
in pa nil lei. (2alculatiun« uf, §44 ^ pi 6,
in Et-nns of circular mils. 144, pti-
Jr>intsof, $43, pll.

Wire* — (Con tin ucd)

Leadin«-in, §32, p7.

Rukifrir }+4.pl7.

Kuies relatinK to. |43, pr2.

Soldering fluid f**r joint?* of, #43. pll.
Wiring a dWirllinfi house. §44. p2U.

DelL §45, p2D,

Bell, for fUtB. §45, p30.

Concealed, §44, pl».

Danduit. §44. p4S.

Drop in src-liRht, §43, jj51*

estimates. §44. pm.

Fires caused by electric. §43, p2.

Fittings used for expnised. §43. p30.

for a uniform dropt §43, p47-

for lire tampci, §45. pi 3,

for constant -current are lamf^, §45 pi 4,

for constant' pnlenlial arc lamps, §45, pi 3.

htr electric nicitors, §45. pi 7-

for dcvator annunciator, §45, p3S.

for fir«-alarm gong;^, §45. p35,

for ineandescent lamps on serien drmxittj
§45, pia.

for low-poteniifll systems, |43, plB.

lor return -call annunciator. §45. i:hJ2

for simple annunciator, |45. p3l.

for spe»kin«-iube system, §45, f>35.

for special purposes, §45. p5,

for 110 \"oits. 2-pcr-cent, drop, §43. p53,

for 920 volts, a-per-€etit. drop, §43, p54.

Genenl rules for. §43 , plO.

in, dam.p places, §44. pi?-

in nmrine wf>rk. |44, p65.

Interior. §4;j, pi ; §44, pi ; §45 pi.

Selection of fittings fnr 220- volt, §43, p57.

Simple example of. {43, pS2.

Special appluLiicrai for, §45, p3S.

Spcdflcations for concealed electric^]ift1it»
§44, p0O,

syitems, CcHnbining several, §45, pi .

Systems of distribution for interior, |40.
pit.

table giving dlstjlnce^ for drop of 1 volt,
144, p4

tables. §44. pS,

Tests of. §44, p0a.

Theater. §45. p4.

Tree system of, §43, p32.
Wolfram lamps. §55, pi 3.
WockI arc dymamo. §35, ij22.
Wooden moldings, §44, pOO.

£ifc)Ul Interna uional correspou-
161 dence schools.
1908 Storage batteries ..

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Full text of "Storage batteries ; Incandescent lighting ; Arc lighting ; Interior wiring ; Modern electric-lighting devices ; Electric signs ; Electric heating"

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