ELECTRICITY
The adaptability of electricity to household use for lighting, heating
and the generation of power has brought into use a host of mechanical
devices that have found a permanent place in every community where
electricity may be obtained at a reasonable rate, or where it can be
generated to advantage in small plants.
Because of its cleanliness and convenience, electricity is used
in preference to other forms of lighting, even though its cost is
relatively high. Electric power for household purposes is constantly
finding new applications and will continue to increase in favor because
its use as compared with hand power is remarkably inexpensive. Small
motors adapted to most of the ordinary household uses are made in
convenient sizes and sold at prices that are conducive to their greater
use. Human energy is far too precious to be expended in household
drudgery where mechanical power can be used in its place and often to
greater advantage.
Electric heating devices compete favorably with many of the established
forms of household heating appliances, the electric flat-iron being a
notable example. In all applications where small amounts of heat are
required for short periods of time, electricity is used at a cost that
permits its use, in competition with other forms of heating.
The remarkable advance that has taken place in electric transmission
in the past few years tends to an enormous increase in its use. The
constant increase in its use for lighting, heating and power purposes
is due in a great measure to the development of efficient electric
generating plants from which this energy may be obtained at the least
cost. In those communities where hydro-electric generation is possible
its field of application is almost without end.
=Incandescent Electric Lamps.=--Anything made in the form of an
illuminating device, in which the lighting element is rendered
incandescent by electricity, may properly be called an incandescent
lamp, whether the medium is incandescent gas as in the Moore lamp, an
incandescent vapor as the Cooper Hewitt mercury-vapor lamp, or the
incandescent filament of carbon or metal such as is universally used
for lighting.
From the year 1879, when Mr. Edison announced the perfection of the
incandescent electric lamp, until 1903, when for a short period
tantalum lamps were used, very little improvement had been made in
the carbon-filament lamp. Immediately following the introduction
of the tantalum lamp came the tungsten lamp, which because of its
wonderfully increased capability for producing light has extended
artificial illumination to a degree almost beyond comprehension. The
influence of the tungsten lamp has induced a new era of illumination
that has affected the entire civilized world. The development of the
high-efficiency incandescent lamp has brought about a revolution in
electric lighting. Its use is universal and its application is made in
every form of electric illumination.
Regardless of the immense number of tungsten lamps in use, the
carbon-filament lamp is still employed in great numbers and will
probably continue in use for a long time to come. In places where
lamps are required for occasional use and for short intervals of
time, the carbon filament still finds efficient use. In one form of
manufacture the carbon filament is subjected to a metalizing process
that materially increases its efficiency. This form, known commercially
as the GEM lamp, fills an important place in electric lighting.
Of the rare-metal filament lamps, those using tungsten and tantalum are
in general use, but the tungsten lamps give results so much superior
in point of economy in current consumed that the future filament lamps
will beyond doubt be of that type unless some other material is found
that will give better results.
The filaments of the first tungsten lamps were very fragile and were
so easily broken that their use was limited, but in a very short time
methods were found for producing filaments capable of withstanding
general usage and having an average life of 1000 hours of service.
These lamps give an efficiency of 1.1 to 1.25 watts per candlepower
of light, as will be later more fully explained. This, as compared
with the carbon-filament lamps which average 3.1 to 4.5 watts per
candlepower, gives a remarkable advantage to the former. The tungsten
lamp has a useful life that for cost of light is practically one-third
that of the carbon-filament lamp.
The metal tungsten, from which the lamp filament is made, was
discovered in 1871. It is not found in the metallic state but occurs as
tungstate of iron and manganese and as calcium tungstate. Up to 1906 it
was known only in laboratories and on account of its rarity the price
was very high. As greater bodies of ore were found and the process
of extraction became better known, the price soon dropped to a point
permitting its use for lamp filaments in a commercial scale.
Pure tungsten is hard enough to scratch glass. Its fusing point is
higher than any other known metal; under ordinary conditions it is
almost impossible to melt it and this property gives its value as
an incandescent filament. One of the laws that affect the lighting
properties of incandescent lamps is: “the higher the temperature of the
glowing filament, the greater will be the amount of light furnished for
a given amount of current consumed.” The high melting point permits the
tungsten filament to be used at a higher temperature than any other
known material. Tungsten is not ductile, and in ordinary form cannot
be drawn into wire. Because of this fact, the filaments of the first
lamps were made by the “paste” process, which consisted of mixing the
powdered metal with a binding material, in the form of gums, until the
mass acquired a consistency in which it might be squirted through a
minute orifice in a diamond dye. The resulting thread was dried, after
which it was heated, and finally placed in an atmosphere of gases which
attacked the binding material without affecting the metal. When heated
by electricity in this condition, the particles of metal fused together
to form a filament of tungsten. While the “paste” filaments were never
satisfactory in general use, their efficiency as a light-producing
agent inspired a greater diligence in the search for a more durable
form.
Although tungsten in ordinary condition is not at all ductile, methods
were soon found for making tungsten wire and the wire-filament lamps
are now those of general use. One process of producing the drawn wire
is that of filling a molten mass of a ductile metal with powdered
tungsten after which wire is drawn from the mixture in the usual way.
The enclosing metal is then removed by chemical means or volatilized by
heat.
Of the difficulties encountered in the use of metal-filament lamps
that of the low resistance offered by the wire was overcome by using
filaments very small in cross-section and of as great length as could
be conveniently handled. The long tungsten filament requires a method
of support very different from the carbon lamp. The characteristic form
of tungsten lamps is shown in Fig. 217, in which the various parts of
the lamp are named.
[Illustration: FIG. 217.--An Edison Mazda lamp and its parts.]
The filament of an incandescent lamp is heated because of the current
which passes through it. The electric pressure furnished by the
voltage, forces current through the filament in as great an amount as
the resistance will permit. A 16-candlepower carbon lamp attached to a
110-volt circuit requires practically 1/2 ampere of current to render
the filament incandescent; the filament resistance must, therefore,
allow the passage of 1/2 ampere. With a given size of filament,
its length must be such as will produce the desired resistance. A
greater length of this filament would give more resistance and a
correspondingly less amount of current would give a dim light because
of its lower temperature. Likewise, a shorter filament would allow more
current to pass and a brighter light would result. When the size and
length of filament is once found that will permit the right amount of
current to pass, if the voltage is kept constant, the filaments will
always burn with the same brightness. This is in accordance with Ohm’s
law which as stated in a formula is
_E_ = _RC_
that is _E_, the electromotive force in volts, is always equal to the
product of the resistance _R_, in ohms, and the current _C_, in amperes.
In the incandescent lamp, if the electromotive force is 110 volts and
the current is 1/2 ampere, the resistance will be 220 ohms and as
expressed by the law
110 = 220 × 0.5
From this it is seen that any change in the voltage will produce
a corresponding change in the current to keep an equality in the
equation. If the voltage increases, the current also increases and
the lamp burns brighter. Should the voltage decrease the current will
decrease and the lamp will burn dim. This dimming effect is noticeable
in any lighting system whenever there occurs a change in voltage.
The quantity of electricity used up in such a lamp is expressed in
watts, which is the product of the volts and amperes of the circuit. In
the lamp described, the product of the voltage (110) by the amount of
passing current (1/2 ampere) is 55 watts. With the above conditions the
16 candlepower of light will require 3.43 watts in the production of
each candlepower. The best performance of carbon-filament lamps give a
candlepower for each 3.1 watts of energy.
The filament of the tungsten lamp must offer a resistance sufficient to
prevent only enough current to pass as will raise its temperature to
a point giving the greatest permissible amount of light, and yet not
destroy the wire. The high fusing point and the low specific heat of
tungsten permits the filament to be heated to a higher temperature than
the carbon filament and with a less amount of electric energy. These
are the properties that give to the tungsten lamp its value over the
carbon lamp.
The exact advantage of the tungsten lamp has been investigated with
great care and its behavior under general working conditions is
definitely known. In light-giving properties where the carbon-filament
lamp requires 3.1 watts to produce a candlepower of light, in the
tungsten filament only 1.1 watts are necessary to cause the same
effect. The tungsten lamp therefore gives almost three times as
much light as the carbon lamp for the same energy expended. The
manufacturers aim to make lamps that give the greatest efficiency
for a definite number of hours of service. It has been agreed that
1000 working hours shall be the life of the lamps and in that period
the filament should give its greatest amount of light for the energy
consumed.
=The Mazda Lamp.=--The trade name for the lamp giving the greatest
efficiency is Mazda. The term is taken as a symbol of efficiency
in electric incandescent lighting. At present the Mazda is the
tungsten-filament lamp, but should there be found some other more
efficient means of lighting, which can take its place to greater
advantage, that will become the Mazda lamp.
=Candlepower.=--The incandescent lamps are usually rated in
light-giving properties by their value in _horizontal_ candlepower.
This represents the mean value of the light of the lamp which comes
from a horizontal plane passing through the center of illumination
and perpendicular to the long axis of the lamp. Candlepower in this
connection originally referred to the English standard candle which is
made of spermaceti. The standard candle is 0.9 inch in diameter at the
base, 0.8 inch in diameter at the top and 10 inches long. It burns 120
grains of spermaceti and wick per hour. This candle is not satisfactory
as a standard because of the variable conditions that must surround its
use. The American or International standard is equal to 1.11 Hefner
candles. The Hefner candle (which is the standard in continental
Europe and South American countries) is produced by a lamp burning
amylacetate. This lamp consists of a reservoir and wick of standard
dimensions which gives a constant quantity of light. The light from
this lamp has proven much more satisfactory as a means of measurement
of light than the English standard and therefore its use has been very
generally adopted.
The light given out by an incandescent lamp is not the same in all
directions. In making comparisons it is necessary to define the
position from which the light of the lamps is taken. The _horizontal
candlepower_ affords a fairly exact means of comparing lamps which
have the same shape of filament, but for different kinds of lamps
it does not give a true comparison. The _spherical candlepower_
is used to compare lamps of different construction as this gives
the mean value at all points of a sphere surrounding the lamp. The
candlepower is measured at various positions about the lamp with the
use of a photometer, and the mean of these values is taken as the mean
_spherical candlepower_.
At their best, carbon-filament lamps require in electricity 3.1
w.p.c. (watts per candlepower). As the lamp grows old the number of
watts per candle power increases, until in very old lamps the amount
of electricity used to produce a given amount of light may become
excessively large. According to a bulletin issued by the Illinois
Engineering Experiment Station on the efficiency of carbon-filament
incandescent lamps, the amount of electrical energy per candlepower
varied from 3.1 w.p.c., when new, to 4.2 w.p.c., after burning 800
hours.
A common practice in the use of carbon-filament lamps is to consider
that the period of useful life ends at a point where the amount of
electricity, per candlepower, reaches 20 per cent. in excess of the
original amount. This point (sometimes termed the smashing point) would
be reached after 800 working hours, according to the Illinois Station,
and at about 1000 hours as stated by the bulletins of the General
Electric Co. If a carbon-filament lamp burns for an average period of 3
hours a day for a year, it ought to be replaced.
The Edison screw base as shown in Fig. 217 is now generally used in
all makes of incandescent lamps for attaching the lamp to the socket.
When screwed into place this base forms in the socket the connections
with the supply wires, to produce a circuit through the lamp. One end
of the filament is attached to the brass cap contact; the opposite
end connects with the brass screw shell of the base. When the current
is turned on, the contact made in the switch is such as to form a
complete circuit between the supply wires; the voltage sending a
constant current through the lamp produces a steady incandescence of
the filament.
In Fig. 218 is shown a carbon-filament lamp attached to an ordinary
socket. The lamp base and socket are shown in section to expose all of
the parts that comprise the mechanism. The insulated wires of the lamp
cord enter the top of the socket and the ends attach to the binding
screws _A_ and _B_, which are insulated from each other and form the
brass shell which encases the socket. The lamp base is shown screwed
into the socket, the brass cap contact _F_ making connection at _G_;
the screw shell joins the socket at _D_. To the key _S_ is attached a
brass rod _R_, on which is fastened _E_, the contact-maker. The rod
_R_ passes through a supportary frame which is secured to the lamp
socket at _G_. As shown in the figures the piece _E_ makes contact with
a brass spring attached to _A_, and this completes a circuit through
the filament. The brass cap contact of the lamp base makes connection
at one end of the filament _H_, the other end of the filament _K_ is
attached to the brass screw shell of the base, which in turn connects
with the screw shell of the socket and this shell is connected with the
piece containing the binding screw _B_ by the rod _C_ to complete the
circuit. When the key _S_ turns, the contact above _E_ is broken and
the lamp ceases to burn.
[Illustration: FIG. 218.--Section of a lamp base and socket.]
Fig. 118 shows the use of an adapter that is sometimes encountered in
old electric fixtures, the use of which requires explanation. Mention
has already been made of the various forms of lamp sockets in use
before the Edison base became a standard. In order to use an Edison
lamp in a socket intended for another form of base an adapter must be
employed to suit the new base to the old socket. In the figure the
piece _P₁_, is the adapter. This is intended to adapt the standard
lamp base to a socket that was formerly in use on the Thompson-Houston
system of electric lighting. The adapter is joined to the old socket by
the screw at _G_ and the circuit formed as already described.
=Lamp Labels.=--For many years all incandescent lamps were rated in
candlepower and were made in sizes 8, 16, 32, etc., candlepower. On
the label was printed the voltage at which the lamp was intended to
operate, and also the candlepower it was supposed to develop. Thus
110 v., 16 cp. indicated that when used on 110-volt circuit, the lamp
would give 16 candlepower of light. This label in no way indicated the
amount of energy expended. With the development of the more efficient
filaments came a tendency to label lamps in the amount of energy
consumed. This has resulted in all lamps being labeled to show the
voltage of the circuit suited to the lamp, and the watts of electricity
consumed when working at that voltage. At present a lamp label may be
marked 110 v., 40 w., which indicates that it is intended to develop
its best performance at 110 volts and will consume 40 watts at that
voltage.
Commercial lamps are now manufactured in sizes of 10, 15, 25, 40, 60,
75, and 100 watts capacity for ordinary use. Of these the 40-watt
lamp probably fulfills the greatest number of conditions and is most
commonly used. Besides these there are the high-efficiency lamps of
the gas-filled variety that are made in larger sizes and the miniature
lamps in great variety. All are labeled to show the volts and the watts
consumed.
=Illumination.=--The development of high-efficiency lamps has caused
a radical change in the methods of illumination. With cheaper light
came the desire to more nearly approximate the effect of daylight
in illumination. This has brought into use indirect illumination,
in which the light from the lamp is diffused by reflection from the
ceiling and walls of the room. Illuminating engineering is now a
business that has to do with placing of lamps to the greatest advantage
in lighting any desired space. In large and complicated schemes of
lighting professional services are necessary, but in household lighting
the required number of lamps for the various apartments are almost
self-evident. The lighting of large rooms, however, requires thoughtful
consideration and in many cases the only definite solution of the
problem is that of calculation.
=The Foot-candle.=--The amount of illumination produced over a given
area depends not only on the number of lamps and their candlepower, but
upon their distribution and the color of the walls and furnishings.
In the calculation of problems in illumination, units of measure are
necessary to express the amount of light that will be furnished at any
point from its source. The units adopted for such purposes are the
foot-candle and the lumen.
=The Lumen.=--A light giving 1 candlepower, placed in the center of a
sphere of 1 foot radius illuminates a sphere, the area of which is 4
× 3.1416 or 12.57 square feet. The _intensity_ of light on each square
foot is denoted as a candle-foot. The candle-foot is the standard
of illumination on any surface. The _quantity_ of light used in
illuminating each square foot of the sphere is called a lumen. A light
of 1 candlepower will therefore produce an intensity of 1 candle-foot
over 12.57 square feet and give 12.57 lumens. Therefore, if all of the
light is effective on a plane to be illuminated, a lamp rated at 400
lumens would light an area of 400 square feet to an average intensity
of 1 candle-foot.
To find the number of lamps required for lighting any space, the area
in square feet is multiplied by the required intensity in foot-candles,
to obtain the total necessary lumens, and the amount thus obtained is
divided by the effective lumens per lamp.
The bulletins of the Columbia Incandescent Lamp Works gives the
following method of calculating the number of lamps required to light a
given space:
Number of lamps = (_S_ × _I_)/(Effective lumens per lamp)
_S_ (square feet) × _I_ (required illumination in foot-candles)
= total lumens.
The total lumens divided by the number of effective lumens per lamp
gives the number of lamps required. In using the formula the effective
lumens per lamp is taken from the following table:
Watts per lamp 25 40 60 160 150 250
Effective lumens per lamp 95 160 250 420 630 1090
Lumens per watt 3.8 4.0 4.2 4.2 4.2 4.3
The size of the units is a matter of choice since six 400-lumen units
are equal to four 600-lumen units in illuminating power, etc. In
deciding upon the proper size of lamps to use, consideration must be
taken of the outlets if the building is already wired. In general
the fewest units consistent with good distribution will be the most
economical. The table shows the lumens effective for ordinary lighting
with Mazda lamps and clear high-efficiency reflectors with dark walls
and ceiling. Where both ceiling and walls are very light these figures
may be increased by 25 per cent.
To illustrate the use of the table, take an average room 16 by 24 to
be lighted with Mazda lamps to an intensity of 3.5 foot-candles. If
clear Holoplane reflectors are used, the values for lumens effective on
the plane may be increased 10 per cent. due to reflection from fairly
light walls. The lamps in this case are to be of the 40-watt type which
in the table are rated at 160 lumens. To this amount 10 per cent. is
added on account of the reflectors and walls. This data applied to the
formula gives:
_s_ = 16 by 24 feet
_I_ = 3.5
Lumens per lamp = 160
((16 × 24) × 3.5)/176 = eight 40-watt lamps.
[Illustration: FIG. 219.]
=Reflectors.=--The character and form of reflectors have much to do
with the effective distribution of the light produced by the lamp.
The most efficient form of reflectors are made of glass and designed
to project the light in the desired direction. The illustration in
Fig. 219, marked open reflector, shows the characteristic features of
reflectors designed for special purposes. They are made of prismatic
glass fashioned into such form as will produce the desired effect and
at the same time transmit and diffuse a part of the light to all
parts of the space to be lighted. The greater portion of the light is
sent in the direction in which the highest illumination is desired.
The reflectors are made to concentrate the light on a small space or
to spread it over a large area as is desired. They are, therefore,
designated as intensive or extensive reflectors and made in a variety
of forms.
=Choice of Reflector.=--Where the light from a single lamp must spread
over a relatively great area, it is advisable to use an _extensive_
form of reflector. This reflector is applicable to general residence
lighting, also uniform lighting of large areas where low ceilings or
widely spaced outlets demand a wide distribution of light. Where the
area to be lighted by one lamp is smaller, the _intensive_ reflector is
used. Such cases include brilliant local illumination, as for reading
tables, single-unit lighting or rooms with high ceilings as pantries or
halls.
Where an intense light on a small area directly below the lamp is
desired, a _focusing_ reflector is used. The diameter of the circle
thus intensely lighted is about one-half the height of the lamp above
the plane considered. Focusing reflectors are used in vestibules or
rooms of unusually high ceilings.
Type Height above plane to be lighted
Extensive 1/2 _D_
Intensive 4/5 _D_
Focusing 4/3 _D_
_D_ = distance between sides of room to be illuminated.
The various other fixtures of Fig. 219 that are designated as
reflectors are in some cases only a means of diffusion of light. In the
use of the high-efficiency gas-filled lamps the light is too bright to
be used directly for ordinary illumination. When these lamps are placed
in opal screens of the indirect or the semi-indirect form the light
produced for general illumination is very satisfactory. Considerable
light is lost in passing through the translucent glass but this is
compensated by the use of the high-efficiency lamps and the general
satisfaction of light distribution.
=Lamp Transformers.=--Lamps of the Mazda type, constructed to work at
the usual commercial voltages, are made in low-power forms to consume
as little as 10 watts; but owing to the difficulty of arranging a
suitable filament for the smaller sizes of lamps, less voltage is
required to insure successful operation. The lamps for this purpose
are of the type used in connection with batteries and require 1 or
more volts to produce the desired illumination. When these little
lamps are used on a commercial circuit, the reduction of the voltage
is accomplished by small transformers, located in the lamp socket.
The operating principle and further use of the transformers will be
explained later under doorbell transformers. The lamp transformer,
although miniature in design, is constructed as any other of its kind
but designed to reduce the usual voltage of the circuit to 6 volts
of pressure. The socket is that intended for the use of the Mazda
automobile lamp giving 2 candlepower. This lamp used with electricity
at the average rate per kilowatt can be burned for 10 hours at less
than half a cent. In bedrooms, sickrooms and other places where a
small amount of light is necessary but where a considerable quantity
is objectionable, the miniature lamp transformer serves an admirable
purpose in adapting the voltage of the commercial alternating circuit
to that required for lamps of small illuminating power. Such a
transformer is shown in Fig. 220.
[Illustration: FIG. 220.--Miniature lamp transformer complete and the
parts of which it is composed.]
The figure shows in _A_ the assembled attachment with the lamp bulb in
place. The part _B_, the transformer, changes the line voltage to that
of a battery lamp. A line voltage of 110 may be transformed to suit a
6-volt miniature lamp. The parts _C_ and _D_ compose the screw base and
the cover, in which is fitted the transformer _B_.
=Units of Electrical Measurement.=--The general application of
electricity has brought into common use the terms necessary in its
measurement and units of quantity by which it is sold. The volt, ampere
and ohm are terms that are used to express the conditions of the
electric circuit; the watt and the kilowatt are units that are employed
in measuring its quantity in commercial usage. The use of these units
in actual problems is the most satisfactory method of appreciating
their application.
As already explained the volt is the unit of electric pressure which
causes current to be sent through any circuit. The electric circuits
of houses are intended to be under constant voltage--commonly 110
or 220--but the voltage may be any amount for which the generating
system is designed. Independent lighting systems such as are used in
house-lighting plants--to be described later--commonly employ 32 volts
of electric pressure.
Opposed to the effect of the volts of electromotive force is the
resistance of the circuit, which is measured in ohms. Resistance has
been called electric friction; it expresses itself as heat and tends to
diminish the flow of current. Every circuit offers resistance depending
on the length, the kind and the size of wire used. Since the wires of
commercial lighting systems are made of copper, it can be said that the
resistance of the circuit increases as the size of the conducting wire
decreases. In large wires the resistance is small but as the size of
the wire is reduced the resistance is increased. A long attachment cord
of a flat-iron, may offer sufficient resistance to prevent the iron
from heating properly.
The ampere is the unit which measures the amount of current. The
amperes of current determine the rate at which the electricity is being
used in any circuit. The wires of a house must be of a size sufficient
to carry the necessary current without heating. Any house wire which
becomes noticeably warm is too small for the current it carries and
should be replaced by one that is larger.
The watt is the unit of electric quantity. The quantity of electricity
being used in any circuit is the product of the volts of pressure and
amperes of current flowing through the wires. The amount of current--in
amperes--sent through the circuit is the direct result of the volts of
pressure; the quantity of electricity is therefore the product of these
two factors. A 25-watt lamp on a circuit of 110 volts uses 0.227 ampere
of current.
25 watts = 110 volts × 0.227 amperes.
Ten such lamps use
10 × 0.227 amperes = 2.27 amperes.
The product of 110 volts and 2.27 amperes is 250 watts.
In order to express quantity of energy, it is necessary to state the
length of time the energy is to act and originally the watt represented
the energy of a volt-ampere for one second. For commercial purposes
this quantity is too small for convenient use and the hour of time was
taken instead. The watt of commercial measurement is the watt-hour and
in the purchase of electricity the watt is always understood as that
quantity.
Even as a watt-hour the measure is so small as to require a large
number to express ordinary amounts and a still larger unit of 1000
watt-hours or the kilowatt-hour was adopted and has become the accepted
unit of commercial electric measurement. Just as a dollar in money
conveniently represents 1000 mills so does a kilowatt of electricity
represent a convenient quantity.
In the purchase of electricity, the consumer pays a definite amount,
say 10 cents per kilowatt. This represents an exact quantity of energy,
that may be expended in light, in heat, or in the generation of power,
all of which may be expressed as definite quantities.
As light, it indicates in the electric lamp the number of
candle-power-hours that may be obtained for 10 cents. At this rate
a single watt costs 0.01 cent an hour. A 25-watt electric lamp will
therefore cost 0.25 (1/4) cent for each hour of use; a 60-watt lamp
costs 0.6 cent per hour; the ten 25-watt lamp mentioned above using 250
watts costs 2.5 cents per hour.
As heat, it is expressed in English-speaking countries as British
thermal units, 1 kilowatt-hour representing 3412 B.t.u. per hour. One
cent’s worth of electricity at the rate given yields 341.2 B.t.u. of
heat.
As power, it represents an exact amount of work. So expressed, a watt
represents 1/746 horsepower; therefore a kilowatt is represented in
power as 1000/746 = 1.3 horsepower. Since the kilowatt purchased for
10 cents is a kilowatt-hour, the equivalent horsepower is for the same
length of time. At the assumed rate, 10 cents buys 1.3 horsepower
for one hour. When used as work it represents 2,544,000 foot-pounds
or 255,400 foot-pounds of work for 1 cent. This work when expended
in a motor, to do the family washing or perform any other household
drudgery, represents the greatest value to be derived from its use.
A 1/2-horsepower motor is amply large to operate a family washing
machine. Even though the motor is only 50 per cent. efficient its cost
of operation is less than 7 cents per hour.
=Miniature Lamps.=--Miniature electric lamps include all that are
not used for general illuminating purposes. The term applies more
particularly to the form of the base than to the voltage or candlepower
of the filament. There are three general classes of these lamps:
candelabra and decorative, that operate on lighting circuits of 100 to
130 volts and are usually intended for decorative purposes; general
battery lamps used for flash lights; and lamps for automobiles and
electric-vehicle service.
[Illustration:
Candelabra screw base
Miniature screw base
Double-contact bayonet candelabra base
Single-contact bayonet candelabra base
FIG. 221.--Miniature lamp bases.]
The term miniature lamp applies more particularly to the base than to
the voltage or candlepower. The style of base is characteristic of the
service for which the lamp is designed rather than the size or number
of watts consumed. There are two general styles of bases: the screw
type of the Edison construction of which there are two sizes; and the
bayonet type of which there are two styles of construction.
Bases for miniature lamps are made in form to suit the conditions of
their use. The styles at present are shown in Fig. 221. Of these the
screw bases at the left are those attached to small flash-lamp bulbs
and others of the smaller sizes of lamps. The two at the right of the
figure are the bayonet style used under conditions not suited to the
screw contact. In the case of automobile lamps and in places where
vibration will cause loss of contact the bayonet base is generally in
use. The lamp is held in place by the projecting lugs that engage with
openings in the socket and kept in place by the pressure of a spring.
The contact with the lamp filament is made by two terminals that make
connection directly with the terminals of the lamp filament. The single
contact base is kept in place similarly to that of the other but makes
a single contact at the end of the socket while the other but makes a
single contact at the end of the socket while the circuit is completed
through the pressure exerted between the projecting lugs and the socket.
=Effect of Voltage Variations.=--Voltage variation may be temporary,
due to changing load in the circuit, or in constantly overloaded
circuits the voltage may be constantly below normal. The change in
electric pressure affects in a considerable degree the amount of light
given by the lamp. As an example, a 5 per cent. drop from the normal
voltage will cause a decrease of 31 per cent. in the amount of light
given. This means that if a lamp is working on a circuit of 110 volts
and the voltage from any cause were to drop to 104-1/2 volts, the light
would decrease 6.8, almost 7 candlepower. Drop in voltage may also be
due to the resistance of wires that are too small for the service.
Lamps attached to such a circuit will constantly burn dim.
=Turn-down Electric Lamps.=--The ordinary incandescent lamp lacks the
flexibility of gas and oil lamp, in that the amount of light cannot be
varied at will. This feature is attained in the electric turn-down lamp
either by resistance added to the lamp circuit or by the use of two
separate filaments in a single globe; one of ordinary lamp size and the
other of such size that it consumes only a fraction as much energy as
the normal lamp.
[Illustration: FIG. 222.--Sectional view of a “turn-down” lamp socket.]
Turn-down lamps of the latter form are made in several styles, the
chief points of difference being in the method of changing the contact
from the high-to the low-power filament. In Fig. 222 a sectional view
shows the “pull-string” form of lamp in which the parts are exposed.
The long filament _H_ and the smaller one _L_ represent two individual
lamps of different lighting power. The change in light is made from one
to the other by pulling the string which is attached to a switch in
the socket and which changes the contact to send the current through
the filament giving the desired amount of light. The figure shows a
carbon-filament lamp, but tungsten lamps are made to accomplish the
same purpose. The difficulty of manufacturing a 1-candlepower tungsten
lamp for direct operation on a 110-volt circuit requires the filaments
to work in series. The figure is arranged on the same plan as for a
tungsten lamp.
The lamp base when screwed into the socket makes contact with the two
service wires of the circuit at _A_ and at _E_, which are part of the
screw base. To light the lamp the current is switched on as in any
lamp. The current enters at _A_ and passes down the connecting piece to
the contact _B_. The piece _B_ is moved by the cord to light either the
large or the small filament. In the position shown the current enters
the small filament at _C_ and in order to complete the circuit to _E_
must traverse both the large and the small filament. The resistance
of the small filament is such that the passing current raises it to
a temperature of incandescence but the large filament does not heat
sufficiently to give an appreciable amount of light. When the cord is
pulled to light the large filament, the contact is made at _D_ and the
current passes directly through the large filament to complete the
circuit at _E_.
Turn-down lamps are especially adapted to the home. Their use in a
child’s bedroom or sick chamber is a great convenience. The lamps are
often constructed with a long-distance cord extending from a fixture to
the bedside. By this means a dim or bright light is given as desired,
with the least inconvenience. Turn-down lamps are made in a variety
of sizes. The large filaments are arranged to give 8, 16, and 32
candlepower. With the 8-candlepower lamp the small filament gives 1/2
candlepower and with the 16-and 32-candlepower the small filament gives
1 candlepower.
With the lamps described, the variation in amount of light is attained
by changing the contacts, to bring into action filaments of different
resistances. They admit of only two changes, either the lamp burns
at full capacity or at the least light the lamp will give. The heat
liberated by the large filament, when the small light is in use, takes
place inside the lamp globe.
=The Dim-a-lite.=--In another form of turn-down lamp the change in
amount of light is produced by external resistance in the circuit.
The resistance is furnished by a coil of wire which is enclosed in a
special lamp socket. It possesses the advantage as a turn-down lamp
in a number of changes of light. The added resistance in a socket
decreases the flow of current and, therefore, the filament gives less
light. The resistance wire is divided into a number of sections and
contact with the terminals of these sections decreases the light with
each addition of resistance. The heat generated in the resistance coils
is dissipated by the brass covering of the socket.
[Illustration: FIG. 223.--The resistance type of “turn-down” lamp.]
An illustration of a turn-down lamp using a separate resistance is
that of Fig. 223, known commercially as the Dim-a-lite, which is an
excellent example. The Dim-a-lite attachment is a lamp socket in which
is enclosed a miniature rheostat or resistance unit. The lamp, when
placed on the Dim-a-lite, makes electrical contact as in an ordinary
socket but with the difference that in series with the lamp filament
is the rheostat, by means of which additional resistance may be added
to change the current flowing in the lamp. The rheostat is so arranged
that contact may be made at four different points in the resistance
coil, through which the electricity may be varied from 100 to 20 per
cent. of the normal quantity. The resistance in any case permits
current to pass through the filament in amounts of 70, 30 and 20 per
cent. of the normal amount. In use, the variation is made by pulling
one string to add resistance and thus dim the light; or by pulling the
other string, the resistance is decreased and more electricity passes
through the filament to produce a brighter light. The quantity of light
given out by the filament does not vary in the ratio of the added
resistance but a variable light is obtained at the expense of a small
amount of electricity which is changed into heat. When the light is
burning at its dimmest only 20 per cent. of the normal current is used.
Under this condition the light given out by filament does not express
the high efficiency attained when the lamp is burning at its full power
but it does give a convenient form of light regulation with the minimum
waste of energy.
=Gas-filled Lamps.=--Until 1913 the filaments of all Mazda lamps
operated in a vacuum. The vacuum serving the purpose of preventing
oxidation and at the same time it reduced the energy loss to the least
amount. It was found, however, under some conditions of construction
that lamps filled with inert gas gave a higher efficiency and
more satisfactory service than those of the vacuum type. In this
construction, the filament is operated at a temperature much higher
than that of the vacuum lamp and as a consequence gives light at a
less cost per candlepower. Mazda vacuum lamps are now designated by
the General Electric Co. as Mazda B lamps, Fig. 224, and those of the
gas-filled variety, Fig. 225, are designated as Mazda C lamps.
[Illustration: FIG. 224.--40-watt Mazda B lamp (1/2 scale).]
[Illustration: FIG. 225.--750-watt Mazda C lamp (1/4 scale).]
The filaments of the gas-filled lamps are intensely brilliant and
where they come within the line of vision should be screened from the
eyes. The high efficiency of these lamps permit the use of opal shades
to produce a desired illumination at a rate of cost that compares
favorably with the unscreened light of the vacuum lamps.
=Daylight Lamps.=--The color of the light from an incandescent electric
lamp depends on the temperature of the filament. In the case of the
gas-filled Mazda lamp the high filament temperature produces a light
that differs markedly from the vacuum lamps in that it contains a
greater amount of blue and green rays. It is therefore possible to
produce light that is the same as average daylight. Gas-filled lamps
with globes colored to produce light of noonday quality are produced at
an expenditure of 1.2 watts per candlepower.
In the matching of colors, it should be kept in mind that the tint of
any color is influenced by the kind of light by which it is viewed.
Colors matched by ordinary incandescent light containing a large
percentage of red rays cannot produce the same effect when the same
articles are seen in light of different quality. The daylight lamps are
therefore intended to be used under conditions that require daylight
quality.
=Miniature Tungsten Lamps.=--The wonderful light-giving properties of
tungsten has made possible the use of miniature incandescent lamps for
an almost infinite variety of usages. The miniature lamps are similar
in action to other incandescent electric lamps except that they are
operated on voltages lower than is used on commercial circuits. When
used on commercial circuits, incandescent tungsten lamps of less than
10 watts capacity require filaments that are too delicate to withstand
the conditions of ordinary use. The properties of tungsten are such
that the passage of only a small amount of current is required to
render the filament incandescent. In the case of a 110-volt circuit,
a 10-watt lamp requires only 0.09+ ampere to produce the desired
incandescence. It will be remembered that the watt is a volt-ampere and
the 10-watt lamp will then require
110 volts × 0.09 + ampere = 10 watts.
Since 10-watt lamps are the smallest units that may be used on 110-volt
circuits, their employment in smaller sizes must be such as will give
more stable filaments. This is possible when the lamps are used at
lower voltage. A 10-watt lamp on a 10-volt circuit will require an
ampere of current.
10 volts × 1 ampere = 10 watts.
A filament suitable for an ampere of current is shorter and heavier
than that of the 110-volt lamp and therefore furnishes a good form of
construction. Still lower voltages may be used with filaments suited to
the quantity of light desired.
In the case of battery lamps that are intended to operate on 1 or more
volts, the filaments are made in size and length to suit the condition
of action. In all cases the product of the volts and amperes give the
capacity of the lamp in watts.
Miniature lamps are ordinarily marked to show the voltage on which they
are intended to operate. A 6-volt battery lamp is intended to be used
with a primary battery of four to six cells depending on the condition
of usage, or three cells of storage battery, each cell of which gives 2
volts of pressure.
=Flash Lights.=--These are portable electric lamps composed of a
miniature incandescent bulb, which with one or more dry cells are
enclosed in a frame to suit the purpose of their use. They are made
in pocket sizes or in form to be conveniently carried in the hand and
are convenient and efficient lamps wherever a small amount of light is
required for a short time. The electricity for operating the lamp is
supplied by a battery of dry cells (to be described later), or by a
single dry cell. In each case the incandescent bulb is suited to the
voltage of the battery.
In replacing the bulbs care must be taken to see that the voltage is
that suited to the battery. The voltage is usually stamped on the lamp
base or marked on the bulb. In case a lamp intended for a single cell
is used with a battery of three or four cells, the lamp filament will
soon be destroyed. The reverse will be true should a lamp intended
for a battery be used with a single cell. The single cell giving not
much more than a volt of electromotive force will not send sufficient
current through the lamp filament to render it incandescent.
=The Electric Flat-iron.=--The changes that have been made in domestic
appliances by the extended use of electricity have brought many
innovations but none are more pronounced than the improvements made
in the domestic flat-iron. It was the first of the household heating
devices to receive universal recognition and its place as a domestic
utility is firmly established.
The relatively high cost of heat as generated through electric energy
is in a great measure counterbalanced in the flat-iron by high
efficiency in its use. In the electric iron, the heat is developed
in the place where it can be used to the greatest advantage, and
transmitted to the face of the iron with but very little loss. Because
of this direct application the cost of operation is but slightly in
excess of the other methods of heating.
The electric flat-iron has now become a part of the equipment of every
commercial laundry, where electricity can be obtained at a reasonable
rate. The popularity of the electric iron is due to its cleanliness
and to the increased amount of work that may be accomplished through
its use. Because of the time saved in changing irons and the comfort
of the room by reason of its lower temperature, a sufficiently greater
amount of work is accomplished to more than compensate for the greater
cost of heat.
The electric current is conducted to the flat-iron from the house
circuit by wires made into the form of a flexible cord. The cord
attaches to the electric-lamp fixture by a screw-plug and connects with
the iron by a special attachment piece as indicated at _P_ and _R_ in
Fig. 226. Connection is made to an incandescent lamp socket at any
convenient place. The only precaution necessary in attaching the iron
is to see that the fuse and the wires, which form the circuit, are of
size sufficient to transmit the amount of current the iron is rated to
use. As explained later, the fuse which is a part of every electric
house circuit, and the conducting wires which form the heater circuit,
must be sufficient in size to transmit the necessary current without
material heating.
[Illustration: FIG. 226.--Electric flat-iron and its attachments.]
The cord connects with the socket at _P_, and the current turned on. It
is attached with the iron by a piece _R_, made of non-conducting and
heat-resisting material and arranged to make contact with the heater
terminals by two brass plugs that are insulated from the body of the
iron and afford easy means of making electric contact. The contact
plugs are shown in Fig. 227. To make electric connection, the contact
piece is simply pushed over the plugs, where it is held in place by
friction. Instructions which accompany a flat-iron when purchased
advise that the attachment piece be used in turning off the current.
The reason for this is because of the flash that accompanies the break
in the circuit when disconnection is made in the socket. This flash
is really a small electric arc, that forms as the circuit is broken
and which burns away the switch at the point of disconnection. The arc
so formed burns away the contact pieces in the switch and it is soon
destroyed. The attachment piece will stand this wear more readily than
the socket switch and hence is preferable for disconnecting. The irons
are frequently provided with a special switch for the service required
in the flat-iron.
[Illustration: FIG. 227.--Electric flat-iron showing position of the
heating element and contact plugs.]
A spiral spring connected to the attachment cord prevents it from
kinking when in use and thus breaking the conducting wires. The
attachment cord is made of stranded wires to make it flexible. The
strands of fine copper wire are made to correspond to the gage numbers
by which the various sizes of wire are designated. In use the constant
movement of the iron tends to kink the cord and thus breaks the
strands. This action is most pronounced at the point where the cord
attaches to the iron. For this reason a spiral spring wire encloses the
cord for a short distance above the attachment piece. After long usage
the cord is apt to break in this vicinity. It may usually be repaired
by cutting off the ends of the cords and new connections made in the
attachment piece. When the iron is in use the slack portion of the cord
is kept from interfering with the work by the coiled wire _S_, which
connects with the cord at any convenient place.
Electric flat-irons are made in a variety of styles and forms, the
mechanism of each possessing some particular advantage, but all are
provided with the same essential parts, chief of which is the heater
with its electric attachment piece. In Fig. 228 is shown very clearly
the construction of an example in which attention is called to the
points of excellence that are required in a particularly serviceable
iron. The form of the heating element which is recognized in the iron
is also shown in Fig. 228.
[Illustration: FIG. 228.--Electric flat-iron heating element.]
In the figure the heater is made of coils of resistance wire, wound
on a suitable frame of mica. The heating element is insulated from
the body of the iron with sheets of mica, this being a material
that makes an excellent insulator and is not materially affected by
the heat to which it is subjected. The resistance wire of which the
element is composed is especially prepared to resist the corroding
action common to metal when heated in air. The form of the element is
such as to permit the least movement of the turns of wire--in their
constant heating and cooling--that will allow the different spires to
make contact and thus change the resistance. Should the spires of wire
come together, the current would be shunted across the contact and the
resistance of the element decreased. The effect of such a reduction of
resistance would be an increased flow of current and a corresponding
increase of heat. In this, as in the electric lamp and all other
electric circuits, the current, voltage and resistance follow the
conditions of Ohm’s law.
Different sizes of irons will, of course, require different amounts of
current. A 6-pound iron, such as is commonly used for household work,
will take about 5 amperes of current at 110 volts pressure. The amount
of electricity the iron is intended to consume is generally stamped on
the nameplate of the manufacturer. This is specified by the number of
volts and amperes of current the iron is rated to use. As an example,
the iron may be marked, Volts 105-115, Amperes 2-3. This indicates
that the iron is intended to be used on circuits that carry electric
pressure varying from 105 to 115 volts and that the heater will use
from 2 to 3 amperes of current, depending on the voltage.
To estimate the cost of operating such an iron, it is necessary to
determine the number of watts of electric energy consumed. The number
of watts of energy developed under any condition will be the product of
the volts times the amperes. Suppose that in the above example the iron
was used on a circuit of 110 volts. Under this condition the current
required to keep the iron hot would be 2.5 amperes. The product of
these two qualities, 110 × 2.5 is 275 watts. If the cost of electricity
is 10 cents per kilowatt-hour (1000 watts) the cost of operating the
iron would be
275/1000 × 10 cents = 2-3/4 cents an hour.
Since the electric iron requires a much larger amount of current than
is usually required for ordinary lighting, the circuit on which it is
used should receive more than passing attention. The wires should be
of size amply large to carry without heating the current necessary for
its operation. This topic will be discussed later but it is well here
to call attention to the necessity for a circuit suited to the required
current. If an iron requiring 5 amperes of current is attached to a
circuit that is intended to carry only 3 amperes the conducting wires
will be overheated and may be the cause of serious results.
=The Electric Toaster.=--As shown in Fig. 229 the toaster is made of
a series of heating elements mounted on mica frames and supported on
a porcelain base. It is an example of heating by exposed wires and
direct radiation. The heaters _H_ are coils of flat resistance wire
that are wound on wedge-shaped pieces of mica. They are supported on a
wire frame that is formed to receive slices of bread on each side of
the heaters. The attachment piece _A_ and the material of the heater is
similar in construction to that of the flat-iron. The electric circuit
may be traced from the contacts at _A_ and _B_ in the attachment plug
by the dotted lines which indicate the wires in the porcelain base.
The current traverses each coil in turn and connects with the next,
alternately at the top and bottom. The resistance is such as will
permit the voltage of the circuit to send through the coils current
sufficient to raise the heaters to a red heat. The added resistance of
the hot wires decreases the flow of current to keep the temperature at
the desired degree.
[Illustration: FIG. 229.--The electric toaster.]
In a heater of this kind the resistance of the wire may increase with
age and the coils fail to glow with a sufficient brightness. The
reason for the lack of heat is that of decrease in current, due to the
increased resistance of the wires. This condition may be corrected by
the removal of a little of the heater coils. If a turn or two of the
heater wire is removed, the resistance of the circuit is reduced and
the effect of the increased current will produce a higher temperature
in the heater.
=Motors.=--As a means of developing mechanical power in small units,
the electric motor has made possible its application in many household
uses that were formerly performed entirely by manual labor. As a
domestic utility electrical power is generated at a cost that is the
least expensive of all its applications. As a means of lighting and
heating electricity has had to compete with established methods and has
won place because of the advantages it possesses over that of cost.
In the development of domestic power it has practically no opponent.
There is no other form of power that can be so successfully utilized
in delivering mechanical work for the purposes required. A kilowatt of
electric energy, for which 10 cents is a common price, will furnish a
surprising amount of manual labor. Theoretically, 746 watts is equal to
1 horsepower. The commercial kilowatt is rated at an hour of time, and
is, therefore, equal theoretically to 1-1/3 horsepower for one hour.
While motors cannot be expected to transform all of this energy into
actual work without loss, even at the low rate of efficiency attained
by the small electric motor, they furnish power at a relatively small
cost.
The first applications of electric power were those for sewing
machines, fans, washing machines, etc. Its use has made possible the
vacuum cleaner, automatic pumping, refrigeration, ventilation, and many
other minor uses as the turning of ice-cream freezers, churning and
rocking the cradle.
Electric motors are made in many sizes for power generation and in
forms to suit any application. They are made to develop 1/30 horsepower
and in other fractional sizes for both direct and alternating current.
In applying mechanical power to any particular purpose special
appliances must be made to adopt electric motors to the required work.
This is accomplished in all household requirements. The motors are made
to run at a high rate of speed and must be reduced in motion by pulleys
or gears to suit their condition of operation. As in the case of
electric lamps they must be suited to the voltage and type of current
of the circuit on which they are to be used.
Commercial electric circuits furnish electricity in two types, direct
current, ordinarily termed D.C., and A.C. or alternating current. The
terms direct and alternating current apply to the direction of the
electric impulses which constitute the transmitted energy. In the
electric dynamo, the generation of the current is due to impulses that
are induced in the wires of the dynamo armature as they pass through a
magnetic field of great intensity. These electric impulses are directed
by the manner in which the wires cut across the lines of force which
make up the magnetic field. In the case of the direct current the
impulses are always in the same direction through the circuit, while
in the other they are induced alternately to and fro and so produce
alternating current.
The term electric current is used only for convenience of expressing
a directed form of energy. Since nothing really passes through the
wires but a wave of energy, the effect is the same whether the electric
impulses are in the same or in opposite directions. An incandescent
lamp will work equally well on an A.C. or a D.C. circuit of the proper
voltage; but in the case of motors the form of construction must be
suited to the kind of current. Both A.C. and D.C. commercial circuits
are in common use, the units of measurement are the same for each but
in ordering a motor it is necessary to state the type of current and
the voltage, in order that the dealer may supply the required machine.
In the case of an alternating motor it is further necessary to state
the number of cycles of changes of direction made per second in the
A.C. circuit. All of this information may be obtained by inquiring of
a local electrician or of the power station from which the current is
obtained.
There is still another item of information necessary to be supplied
with an order for a motor, other than those of fractional horsepower.
With motors of a horsepower or more it is necessary to state the number
of phases included in the circuit. This information to be complete must
state whether the motor is to operate on a single-phase, two-phase, or
three-phase circuit. These terms apply to a condition made possible in
A.C. generation that permits one, two, or three complete impulses to be
developed in a circuit at the same time. These phases are transmitted
by three wires, any two of which will form a circuit and give a supply
of energy at the same voltage. Either one phase or all may be used at
the same time and for this reason the phase of an A.C. motor should be
given in an order. To make the information complete there should be
included the number of cycles or complete electric impulses per second
produced in the circuit. Suppose that a 1-horsepower motor is required
to work on an A.C. circuit of 110 volts. Inquiry of the electric
company reveals that the circuit is three-phase at 60 cycles per
second. The dealer on receiving this information will be able to send
a motor to suit your conditions. Most A.C. motors of 1 horsepower or
less are of the single-phase variety. In the case of D.C. motors it is
necessary only to state the voltage of the circuit to make the required
information complete.
=Fuse Plugs.=--Every electric circuit is liable to occurrences known as
short-circuiting or “shorting.” This is a technical term describing a
condition where, by accident or design, the wires of a circuit are in
any way connected by a low-resistance conductor or by coming directly
into contact with each other. In case of shorting, the resistance is
practically all removed and the amount of current which flows through
the circuit is so great as to produce a dangerous amount of heat in the
wires. If the covering of a lamp cord becomes worn so as to permit the
bare wire of the two strands to come together, a “short” is produced.
Immediately, the reduced resistance permits the electric pressure to
send an amount of current through the wires, greater than they are
intended to carry. When this occurs an electric arc will form at the
point of contact with the accompanying flash of vaporizing metal and
the wire will finally burn off. Fires started from this cause are not
uncommon.
To guard against accidents from short-circuiting, every electric
circuit should be provided with fuses which, in cases of emergency,
are intended to melt and thus break the circuit. Fuses are made of
lead-composition or aluminum and are used in the form of wire or
ribbon-like strips, of sizes that will carry a definite amount of
current. They are designated by their carrying capacity in amperes. As
an example: a 2-ampere fuse will carry 2 amperes of current without
noticeable heating, but at a dangerous overload the fuse will melt and
the circuit be broken. Should a short-circuit be formed at any time,
the rush of current through the fuse will cause it almost immediately
to melt, and stop the flow of current. They are, therefore, the
safeguard of the circuit against undue heating of the conducting wires.
When an open fuse blows (melts), the heat generated by the arc,
formed at the breaking circuit, is so sudden that there is frequently
an explosive effect that throws the melted metal in all directions,
and in case it comes into contact with combustible material a fire
may result. To do away with this danger, fire insurance companies in
their specifications of electric fixtures state what forms of fuses
will be acceptable in the buildings to be insured. These specifications
are known as the Underwriters Rules and may be obtained from any fire
insurance company. The fuses, or fuse plug, as they are commonly
called, generally occupy a place in a cabinet or distributing panel,
near the point where the lead wires enter the building. The cabinet
contains the porcelain cutouts for sending the current through the
different circuits; the fuse plugs form a part of the cutouts, one fuse
to each wire. The cabinet contains besides the cutouts a double-poled
switch to be used for shutting off the current from the building when
desired.
[Illustration: FIG. 230.--Electric cabinets.]
Cabinets for this purpose are made in standard form of wood or steel
to suit the condition of service. These cabinets may be obtained from
any dealers in electrical supplies or the cabinet may be made a part
of the house since they are only small shallow closets. Fig. 230
represents such a cabinet as is used in the average dwelling. It is
made of a light wooden frame set between the studding of a partition
at any convenient place. The bottom of the cabinet is made sloping to
prevent its being used as a place of storage for articles that might
lead to trouble. The cabinet is sometimes lined with asbestos paper as
a prevention from fire but this is not necessary as the fuse plugs and
their receptacles, when of approved design, are sufficient to prevent
accident.
The main wires which supply the house with electricity--marked lead
wires--are brought into the cabinet as shown in Fig. 231 and attached
to the poles of the switch _S_. In passing through the switch the lead
wires each contain a mica-covered fuse plug _F_, that will be described
later. The current at any time may be entirely cut off from the house
by pulling the handle _H_, which is connected by an insulating bar
and the contacts _N_ of the switch. When the handle _H_ is pulled to
separate the contact pieces, all electric connection is severed at that
point.
[Illustration: FIG. 231.--Electric panel containing cutout blocks,
fuses and switch.]
The wattmeter for measuring the current is placed at the points
marked _meter_, as a part of the main circuit. The main wires in the
cabinet terminate in the porcelain cutouts, from which are taken off
the various circuits of the house. In the figure, three such cutouts
are shown making three circuits marked 1, 2, and 3. In circuit No. 1,
the fuses are marked _F_. These wires are joined to the main wires at
the points marked _C_ and _C´_. The number of circuits the house will
contain depends on the number of lights and the manner in which they
are placed. The circuits are intended to be arranged so that in case of
a short, no part of the house will be left entirely in darkness.
Fuses for general use are made in two different types--the plug type
and the cartridge type--each of which conforms to the rules of the
Underwriters Association. Those most commonly used for house wiring
are the plug type shown in Fig. 232 and indicated in the figure just
described. These plugs are made of porcelain and provided with a screw
base which permits their being screwed into place like an incandescent
lamp. The front of the plug is arranged with a mica window which allows
inspection to be made in case of a short, the blown fuse indicating
the circuit in which the trouble is located. Another style of the same
type of plug, known as the re-fusable fuse plug, permits the fuse to be
replaced after the wire has been destroyed by a short.
[Illustration: FIG. 232.--Mica covered fuse plug.]
[Illustration: FIG. 233.--Cartridge fuse.]
[Illustration: FIG. 234.--Plug receptacle for cartridge fuse.]
The second type is commonly known as the cartridge fuse plug from its
general appearance. This fuse is shown in Fig. 233. The fusable wire
is enclosed in a composition fiber tube, the ends of which are covered
by brass caps which afford contact pieces in the fuse receptacle and
to which are fastened the ends of the fuse wire. These fuses are very
generally employed in power circuits and others of large current
capacity. The small circle in the center of the label is the indicator.
When the fuse burns out, a black spot will appear in the circle. It
is sometimes desirable to use the cartridge fuse plug in receptacles
intended for the mica-covered type. The use of the cartridge fuses
under this condition is effected by use of a porcelain receptacle such
as is shown in Fig. 234; the cartridge fuse is simply inserted into the
receptacle which is then screwed into the socket in place of the mica
fuse.
In order to avoid any possible chance of overloading the wires of
a circuit, fuses are installed which are suited to the work to be
performed. Suppose that there are ten 40-watt lamps that may be used
on a circuit, each lamp of which requires 4/11 ampere of current.
110 × C = 40 watts
C = 40/110 = 4/11 ampere per lamp.
Ten such lamps require ten times 4/11 ampere or 40/11 = 3.7 amperes to
supply the lamps.
A fuse that will carry 3.7 amperes of current will supply the circuit
but a 5-ampere fuse will permit an increase in the size of the lamp and
will fulfill all the necessary conditions. If, however, an electric
heater requiring 7 amperes were attached to the circuit, the fuse being
intended for only 5 amperes would soon burn out. When a fuse burns out
it must be replaced either with an entirely new receptacle or the fuse
wire must be replaced.
It sometimes happens that in case of a blown fuse there is no extra
part at hand and a wire of much greater carrying capacity is used in
its place. It should be remembered that in this practice of “coppering”
a blown fuse, has taken away the protection against short-circuiting
with its possibility of mischief.
When a short occurs, the cause should be sought for. It cannot be
located and on being replaced a second fuse blows, the services of an
electrician should be secured.
=Electric Heaters.=--All electric heating devices--whether in
the form of hot plates, ovens, stoves or other domestic heating
apparatus-possess heating elements somewhat similar to the flat-iron
or the toaster. The construction of the heating element will depend
on the use for which the heater is intended and the temperature to be
maintained. Hot plates similar to that of Fig. 235 are made singly or
two or more in combination. When the heat is to be transmitted directly
by radiation the heating coils are open, as with the toaster. Under
other conditions the coils are embedded in enamel that is fused to a
metal plate. In elements of this kind the heat is transmitted to the
plate entirely by conduction from which it is utilized in any manner
requiring a heated surface. The form of the heating element will,
therefore, depend on the application of the heat, whether it is by
direct radiation or by a combination of radiation and conduction.
Electric ovens are constructed to utilize electric heat in an insulated
enclosure. Heat derived from electricity is more expensive than from
other sources but when used in insulated ovens it may be made to
conveniently perform the service of that derived from other fuels.
In electric ovens the heaters are attached to inside walls. As in
other heating elements they are arranged to suit the conditions for
which the oven is to be used. The heaters are usually so divided as
to permit either all of the heaters to be used at the same time to
quickly produce a high temperature, or only a portion of the heat to
be used in keeping up the temperature lost by radiation. Ovens of this
kind may be provided with regulators by means of which the heat may
be automatically kept at any desired temperature. Such heating and
temperature regulation may be used to produce any desired condition,
but in practice the cost of the heat is the factor which determines its
use. Unless electric heat is conserved by insulation it cannot become a
competitor with other forms of heating.
[Illustration: FIG. 235.--Electric three-burner hot plate. Electric hot
plate.]
Electric cooking stoves and ranges are made for every form of domestic
and culinary service. They fulfill many purposes that may be obtained
in no other way. As conveniences, the cost of heat becomes of secondary
consideration and their use is constantly increasing. In Fig. 236 is
an example of a time-controlled and automatically regulated electric
range. In the picture is shown separately all of the heaters for the
ovens and stove top. The part _S_ shows the switches attached to the
heaters of the stove top, which is raised to show the connecting wires.
In the larger oven there are two heaters of 1000 watts each, and in the
smaller oven one heater of 850 watts. Each heater may be controlled
separately with a switch giving three regulations of heat--high, medium
and low. The advantage of this arrangement lies in the fact that one
can set the two heaters in the oven at different temperatures which
will permit either a slow or quick heat, but when the predetermined
temperature is reached the current will be automatically cut off by the
circuit-breakers. Such flexibility of heat control in the ovens permits
the operator to apply heat at both top and bottom for baking and
roasting at just the desired temperature. This arrangement also avoids
the danger of scorching food from concentration of heat, and warping
utensils or the linings of the oven. All oven heaters on the automatic
ranges are further controlled and mastered by the circuit-breakers.
[Illustration: =Fig. 236.=--Electric range. Showing how all parts can
be removed for cleaning and replacement.]
=Intercommunicating Telephones.=--This form of telephone is used
over short distances such as from room to room in buildings or for
connecting the house with the stable, garage, etc. It is complete, in
that it possesses the same features as any other telephone but the
signal is an electric call-bell instead of the polarized electric bell
used in commercial telephone service.
Any telephone is made to perform two functions: (1) that of a
signal with which to call attention; and (2) the apparatus required
to transmit spoken words. In the intercommunicating telephone or
interphone, the signal is made like any call-bell and parts are similar
to those described under _electric signals_. The bell-ringing mechanism
is included in the box with the transmitting apparatus and the signal
is made by pressing a push button. It is not suitable for connecting
with public telephones. Telephone companies, as a rule, do not permit
connection with their lines any apparatus which they do not control.
The interphone of Fig. 237 shows the instrument complete except the
battery. This form of instrument is inexpensive, easy to put in, simple
to operate and supplies a most excellent means of intercommunication.
Complete directions for installation are supplied with the phones by
the manufacturers.
[Illustration: FIG. 237.--The intercommunicating telephone.]
=Electric Signals.=--Electrical signaling devices for household use, in
the form of bells and buzzers, are made in a great variety of forms and
sizes to suit every condition of requirement. The vibrating mechanism
of the doorbell is used in all other household signals except that of
the magneto telephone. It is an application of the electromagnet, in
which the magnetism is applied to vibrate a tapper against the rim of a
bell.
A bell system consists of the gong with its mechanism for vibrating
the armature, an electric battery or A.C. transformer connected to
the magnet coils to form an electric circuit and a push button which
serves to close the circuit whenever the bell is to be sounded. The
bell system is an open-circuit form of apparatus; that is, the circuit
is not complete except during the time the bell is ringing. By pressing
the push button the circuit is closed and the electric current from
the battery flows through the magnet and causes the tapper to vibrate.
When the push button is released the circuit is broken and the circuit
stands open until the bell is to be again used. The parts of the bell
mechanism are shown in Fig. 238 where with the battery, the push
button and the connecting wires is shown a complete doorbell outfit.
These parts may be placed in different parts of the building and
connected by wires as shown in the Fig. 239. The bell is located at
_R_, in the kitchen. The battery is placed in the closet at _B_, the
connecting wires are indicated by the heavy lines; they are secured
to any convenient part of the wall and extend into the basement and
are fastened to the joists. The wires terminate in the push button
_P_, where they pass through the frame of the front door. The wires
are secured by staples to keep them in place. Each wire is fastened
separately to avoid the danger of short-circuiting. If both wires are
secured with a single staple there is a possibility of the insulation
being cut and a short produced across the staple.
[Illustration: FIG. 238.--Diagram showing the parts of an electric
doorbell.]
The battery _B_, in Fig. 238, is a single dry cell but more commonly
it is composed of two dry cells joined in series. It is connected,
as shown in the figure, to the binding posts _P₁_ and _P₂_ of the
vibrating mechanism, the push button _PB_ serving to make contact when
the circuit is to be closed. When the button is pressed the circuit
is complete from the + pole of the battery cell through the binding
post _P₁_, across the contact _F_, through the spring _A_, through
the magnet coils _M_, across the binding post _P₂_ and push button to
the-pole of the cell. The vibration of the tapper is caused by the
magnetized cores of the coils _M_. When the electric current flows
through the coils of wire, the iron cores become temporary magnets.
This magnetism attracts the iron armature attached to the spring _A_,
and it is suddenly pulled forward with energy sufficient to cause the
tapper to strike the gong. As the armature moves forward, the spring
contact at _F_ is broken and the current stops flowing through the
magnet coils. When the current ceases to flow in the magnet coils, the
cores are demagnetized and the armature is drawn back by the spring _A_
to the original position. As soon as the contact is restored at _F_ a
new impulse is received only to be broken as before. In this manner the
bell continues ringing so long as the push button makes contact. The
screw at _F_ is adjusted to suit the contact with the spring attached
to the armature. The motion of the armature may be regulated to a
considerable degree by this adjustment. When properly set the screw is
locked in place by a nut and should require no further attention.
[Illustration: FIG. 239.--Example of an electric doorbell installation.]
Electric bells vary in price according to design and workmanship. A
bell outfit may be purchased complete for $1 but it is advisable to
install a bell of better construction, as few pieces of household
mechanism repay their cost in service so often as a well-made bell.
The bell should be rigid, well-constructed, and the contact piece _F_
should be adjustable. This part _F_, being the most important of the
moving parts of the bell, is shown separately in Fig. 240. Only the
ends of the magnet coils with their cores are shown in the figure. The
contact is made at _A_, by the pressure of the spring against the end
of the adjustable screw _D_. When the screw is properly adjusted it is
locked securely in place by the nut _G_. The screw _D_ is held with
a screw-driver and the nut _G_ forced into position to prevent any
movement. If the screw is moved, so that contact is lost at _A_, the
bell will not ring. In the better class of bells the point of the screw
and its contact at _A_ are made of platinum to insure long life. With
each movement of the armature a spark forms at the contact which wears
away the point, so that to insure good service these points must be
made of refractory material.
[Illustration: FIG. 240.--Diagram of the vibrating mechanism used in
buzzers and doorbells.]
=Buzzers.=--Electric bells are often objectionable as signal calls
because of their clamor, but with the removal of the bell the vibrating
armature serves equally well as a signal but without the undesirable
noise. With the bell and tapper removed the operating mechanism of such
a device works with a sound that has given to them the name of buzzers.
Fig. 241 illustrates the form of an iron-cased buzzer for ordinary
duty. The working parts are enclosed by a stamped steel cover that
may be easily removed. The mechanism is quite similar to that already
described in the doorbell and Fig. 240 shows in detail the working
parts. The noise, from which the device takes its name, is produced by
the armature and spring in making and breaking contact.
=Burglar Alarms.=--A burglar alarm is any device that will give notice
of the attempted entrance of an intruder. It is usually in the form
of a bell or buzzer placed in circuit with a battery, as a doorbell
system, in which the contact piece is placed to detect the opening of
a door or window. The contact is arranged to start the alarm whenever
the window or door is opened beyond a certain point. The attachment
shown in Fig. 242 is intended to form the contact for a window. It
is set in the window frame so that the lug _C_ will be depressed and
close the alarm circuit in case the sash is raised sufficiently to
admit a man. Each window may be furnished with a similar device and the
doors provided with suitable contacts which together form a system to
operate in a single alarm. During the time when the alarm is not needed
it is disconnected by a switch. The windows and doors are sometimes
connected with an annunciator which will indicate the place from which
an alarm is given. An annunciator used for this purpose designates the
exact point at which the contact is made and removes the necessity of
searching for the place of attempted entrance.
[Illustration: FIG. 241.--The electric buzzer.
FIG. 242.--Contact for a window burglar alarm.
FIG. 243.--Trip contact which announces the opening of a door.
FIG. 244.--Contact for a door alarm.
FIG. 245.--Doorway or hall matting with contacts for electric alarm.]
In Fig. 243 is illustrated one form of door trip which may be used on
a door to announce its opening. This trip makes electric connection in
the alarm circuit when the opening door comes into contact with the
swinging piece _T_, but no contact is made as the door closes. The
trip is fastened with screws at _D_ to the frame above the door. The
opening door comes into contact with _T_ and moves it forward until the
electric circuit is formed at _C_; after the door has passed, a spring
returns it to place. As the door is closed, the part _T_ is moved
aside without making electric contact.
Fig. 244 is another form of door alarm that makes contact when the
door is opened and remains in contact until the door is closed. The
part _P_ is set into the door frame of the door in such position that
the contact at _C_ is held open when the door is closed. When the door
is opened a spring in _C_ closes the contact and causes the alarm to
sound. It continues to sound until the door is closed and the contact
is broken. When the use of the alarm is not required, the contact-maker
is turned to one side and the contact is held open by a catch. It is
put out of use by pressing the plunger to one side.
The matting shown in Fig. 245 is provided with spring contacts so
placed that no part may be stepped upon without sounding the alarm.
When placed in a doorway and properly connected with a signal, no
person can enter without starting an alarm. The matting is attached to
the alarm by the wires _C_ and contacts are set at close intervals so
that a footstep on the mat must close at least one contact.
=Annunciators.=--It is often convenient for a bell or buzzer to serve
two or more push buttons placed in different parts of the house. In
order that there may be means of designating the push button used--when
the bell is rung--an annunciator is provided. This is a box arranged
with an electric bell and the required number of pointers and fingers
corresponding to the push buttons. In Fig. 246 is shown an annunciator
with which two push buttons are served by the single bell. The
annunciator is placed at the most convenient place of observation,
usually in the kitchen. When the bell rings the pointer indicates the
push button that has last been used. In hotels or apartment houses
an annunciator with a single bell may thus serve any number of push
buttons. In a burglar-alarm system the annunciator numbers are arranged
to indicate the windows and other openings at which entrance might be
made. When the alarm sounds the annunciator indicates the place from
which the alarm is made.
=Table Pushes.=--Call bells to be rung from the dining-room table are
connected with an annunciator or to a separate bell. The table pushes
may be temporarily clamped on the edge of the table and connected by
a cord to an attachment set in the floor or the connection may be made
by a foot plate set on the floor. In Fig. 247 is shown a form of push
_P_ which is intended to be clamped to the edge of the table under the
cloth. The plate _F_ forms the floor connection. It is set permanently
with the upper edge flush with the surface of the floor. The part _S_,
in which the connecting cord terminates, when inserted in the floor
plate, makes contact at the points _C_ to form an electric circuit
with the battery. The foot plate shown in Fig. 248 is only an enlarged
push button which is set under the table in convenient positions to
be pressed with the foot. Its connection might be made as indicated
or with the same floor connection as that of the preceding figure.
Fig. 249 is a simpler form of floor push in which a metallic plug is
inserted in the floor plate. When the plug _R_ is pressed, contact is
made at the points _C_ to form the circuit with the battery and bell.
[Illustration: FIG. 246.--A kitchen annunciator.
FIG. 247.--Plug attachment and table push for a dining table.
FIG. 248.--Foot plate and contact for table bell.
FIG. 249.--Call bell attachment with detachable contact piece.]
=Bell-ringing Transformers.=--The general employment of alternating
electricity for all commercial service requiring distant transmission
is because of the possibility of changing the voltage to suit any
condition. The energy transmitted is determined by the amperes of
current carried by the wires and the volts of pressure by which it
is impelled. The product of these two factors determines the watts of
energy transmitted.
110 volts × 1 ampere = 110 watts.
If the voltage is raised to say ten times the original intensity with
the same current, the quantity of energy is ten times the original
amount.
1100 volts × 1 ampere = 1100 watts.
The carrying capacity of wires is determined by the amperes of current
that can be transmitted without heating.
The cost of copper wire is such that the expense of large wires for
carrying a large current is unnecessary where by raising the voltage a
small wire will perform the same service; therefore, it is desirable
to transmit electric energy at a high voltage and then transform it to
suit the condition of usage.
Alternating current may be transformed to a higher or a lower voltage
to suit any condition by using step-up or step-down transformers.
A transformer is a simple device composed of two coils of wire wound on
a closed core of iron. The coil into which is sent the inducing current
is the primary. That in which the current is induced is the secondary
coil. The change in voltage between primary and secondary coils vary as
the number of turns of wire which compose the coils. The house circuit
may be stepped down from the customary 110 volts to a voltage such as
is furnished by a single dry cell, or a battery of cells.
In principle, the action of the transformer is the same as that of
the induction coil, a detailed explanation of which will be found
in any text-book of physics. Each impulse of current in the primary
coil of the transformer magnetizes its core and the magnetism thus
excited induces a corresponding current in the secondary coil. Since
alternating current in the primary coil constantly changes the polarity
of the core, each change of magnetism induces current in the secondary
coil.
Small transformers are frequently used for operating doorbells,
annunciators, etc., in place of primary batteries. These transformers
are also used to supply current for lighting low-power tungsten lamps
that cannot be used with the ordinary voltages employed in house
lighting. The primary wires of the transformer are attached to the
service wires in the house and from the secondary wires voltages are
taken to suit the desired purposes.
[Illustration: FIG. 250.--Doorbell transformer.]
[Illustration: FIG. 251.--Details of doorbell transformer.]
Fig. 250 shows such a transformer with the cover partly broken away to
expose the interior construction. The wires from house mains _MM_ lead
the current to the primary coil _P_ which is a large number of turns
of fine wire wound about a soft-iron core. The induced current in the
secondary coil _S_ is taken from the contact points 1, 2, 3 and 4.
The construction of the transformer coils shown in Fig. 250 indicates
the primary wires at _LL_ of Fig. 251. The wires of the primary coil
are permanently attached to house wires. The reactive effect of the
magnetism in the coil permits only enough current to flow as will keep
the core excited. This is a step-down transformer and the secondary
coil contains fewer turns of wire than the primary coil. Since the
voltage induced in the secondary coil is determined by the number of
turns of wire in action, this coil is so arranged that circuits formed
by attachment with different contacts give a variety of voltages. The
numbers on the front of Fig. 250 correspond to those of Fig. 251. The
coils between contact 1 and the others 2, 3 and 4, represent different
number of turns of wire and in them is induced voltages corresponding
with the number of turns of wire in each.
=The Recording Wattmeter.=--To determine the amount of electricity used
by consumers, each circuit is provided with some form of wattmeter.
These meters might be more correctly called watt-hour meters since they
register the watt-hours of electrical energy that pass through the
circuit.
[Illustration: FIG. 252.--Recording watt meter.]
In the common type of meter, the recording apparatus in composed of
a motor and a registering dial. The motor is intended to rotate at a
rate that is proportional to the amount of passing current. An example
of this device is the Thompson induction meter of Fig. 252. The motion
of the aluminum disc seen through the window in front indicates at any
time the rate at which electricity is being used. This constitutes
the rotating part of the motor. It is propelled by the magnetism,
created by the passing current, and is sensitive to every change that
takes place in the electric circuit. Each lamp, heater or motor that
is brought into use or turned off produces a change of current in the
conducting wires and this change is indicated by the rate of rotation
of the disc. Each rotation of the disc represents the passage of a
definite amount of electricity that is recorded on the registering
dials.
The shaft on which the disc is mounted is connected with the recording
mechanism by a screw which engages with the first of a train of gears.
These gears have, to each other, a ratio of 10 to 1; that is, ten
rotations of any right-hand gear, causes one rotation of the gear
next to the left. The pointers on the dial are attached to the gear
spindles. One rotation of the right-hand dial will move the pointer
next to the left one division on its dial. Each dial in succession will
move in like ratio.
The meters are carefully calibrated and usually record with
truthfulness the amount of electricity used. They are, however, subject
to derangement that produces incorrect registration.
=To Read the Meter.=--_First_, note carefully the unit in which the
dial of the meter reads. The figures above the dial circle indicate
the value of one complete revolution of the pointer in that circle.
Therefore, each division indicates one-tenth of the amount marked above
or below the circle.
_Second_, in reading, note the direction of rotation of the pointers.
Commencing at the right, the first pointer rotates in the direction of
the hands of a clock (clockwise); the second rotates counter-clockwise;
the third, clockwise; etc., alternately. The direction of rotation of
any one pointer may easily be determined by noting the direction of
the sequence of figures placed around each division. The arrows (shown
above) indicate the direction of rotation of the pointers when the
meter is in operation.
_Third_, read the figures indicated by the pointers from right to
left, setting down the figures as they are read, _i.e._, in a position
relative to the position of the pointers. NOTE: One revolution of
the first or right-hand pointer makes one-tenth of a revolution of
the pointer next to it on the left. One revolution of this second
pointer makes one-tenth of a revolution of the pointer next to it on
the left, etc. Therefore, if, when reading the dial, it is found that
the second pointer rests very nearly over one of the tenth divisions
and it is doubtful as to whether it has passed that mark, it is only
necessary to refer to the pointer next to it on the right. If this
pointer on the right has not completed its revolution, it shows that
the second pointer has not yet reached the division in question. If it
has completed its revolution, that is, passed the zero, it indicates
that the second pointer has reached the division and the figure
corresponding is to be set down for the reading.
[Illustration: FIG. 253_a_.--This dial reads 9484 kilowatt hours.]
The foregoing also applies to the remaining pointers. When it is
desired to know whether a pointer has passed a tenth division mark, it
is necessary to refer only to the next pointer to the right of it.
_Fourth_, see if the register is direct-reading, _i.e._, has no
multiplying constant. Some registers are not direct-reading in that
they require multiplying the dial reading by a constant such as 10
or 100 in order to obtain the true reading. If the register bears
some notation such as “Multiply by 100,” the reading as indicated by
the pointers should be multiplied by 10 or 100 as the case may be to
determine the true amount of energy consumed.
Some of the earlier forms of meters were equipped with what is known
as a “non-direct-reading register.” In this case, the reading must be
multiplied by the figure appearing on the dial as just explained, but
the dial differs from those just described in that the multiplying
constant is generally a fraction such as 1/2, etc., and the dial has
five pointers. This older style of register reads in “watt-hours” of
“kilowatt-hours.”
_Fifth_, the reading of the dial does not necessarily show the
watt-hours used during the past month. In other words, the pointers
do not always start from zero. To determine the number of watt-hours
used during a certain period it is necessary to read the dial at
the beginning of a period and again at the end of that period. By
subtracting the first reading from the second, the number of watt-hours
or kilowatt-hours used during the period is obtained.
The meter man, having in his possession a record of the readings
of each customer’s meter for the preceding months, is thus able to
determine the amount of energy consumed monthly.
EXAMPLES OF METER READINGS
Fig. 253_a_ shows an example of an ordinary dial reading. Commencing
at the first right-hand pointer, Fig. 253_c_, it is noted that the
last figure passed over by the pointer is 1. The next circle to the
left shows the figure last passed to be 2, bearing in mind that the
direction of the rotation of this pointer is counter-clockwise. The
last figure passed by the next pointer to the left is 1, while that
passed by the last pointer to the left is obviously 9. The reading to
be set down, therefore, is 9121.
[Illustration: FIG. 253_b_.--This dial reads 997 kilowatt hours.]
[Illustration: FIG. 253_c_.--This dial reads 9121 kilowatt hours.]
In a similar manner the dial shown in Fig. 253_b_ may be read. In
this case, however, three of the pointers rest nearly over the
divisions and care must be used to follow the direction to avoid
error. Commencing at the right, the first pointer indicates 7. The
second pointer has passed 9 and is approaching 0. The third pointer
appears to rest directly over 0, but since the second pointer reads
but 9, the third cannot have completed its revolution and hence the
figure last passed is set down which in this case is 9. Similarly,
the fourth or left-hand pointer appears to rest directly over 1 but
by referring to the pointer next to it on the right, we find that its
indication is 9 as just explained. Therefore, the fourth pointer cannot
have reached 1, and so the figure last passed which is 0 is set down,
which in this case is 9. Similarly, the fourth or left-hand pointer
appears to rest directly over 1, but by referring to the pointer next
to it on the right we find that its indication is 9 as just explained.
Therefore, the fourth pointer cannot have reached 1, and so we set down
the figure last passed which is 0. The figures as they have been set
down, therefore, are 0997, which indicates that 997 kilowatt-hours of
electricity have been used.
If, for example, the reading of this meter for the preceding month was
976 kilowatt-hours, the number of kilowatt-hours used during that month
would be 997-976 = 21 kilowatt-hours.
=State Regulation of Meter Service.=--Electric wattmeters are subject
to errors that may cause them to run either fast or slow. Complaints
made of inaccurate records or readings are usually rectified by the
electric company. In many States all public utilities are governed
by laws that are formulated by public utilities commissions or other
bodies from which may be obtained bulletins fully describing the
conditions required of public service corporations or owners of public
utilities. The following quotation from Bulletin No. V., 233 of the
Railroad Commission of Wisconsin, will give an illustration of the
requirement in that State.
RULE 14.--CREEPING METERS.--No electric meter which registers
upon “no load” shall be placed in service or allowed to remain in
service.
This means that when no electricity is being used in the system the
motor disc should remain stationary and if it shows any motion under
such condition it is not recording accurately.
PERIODIC TESTS
RULE 17.--Each watt-hour meter shall be tested according to
the following schedule and adjusted whenever it is found to
be in error more than 1 per cent., the tests both before and
after adjustment being made at approximately three-quarters and
one-tenth of the rated capacity of the meter. Meters operated at
low power-factor shall also be tested at approximately the minimum
power-factor under which they will be required to operate. The
tests shall be made by comparing the meter, while connected in
its permanent position, on the consumer’s premises with approved,
suitable standards, making at least two test runs at each load, of
at least 30 seconds each, which agree within 1 per cent.
Single-phase, induction-type meters having current capacities not
exceeding 50 amperes shall be tested at least once every 4 months
and as much oftener as the results obtained shall warrant.
All single-phase induction-type meters having current capacities
exceeding 50 amperes and all polyphase and commutator-type meters
having voltage ratings not exceeding 250 volts and current
capacities not exceeding 50 amperes shall be tested at least once
every 12 months.
All other watt-hour meters shall be tested at least once every 6
months.
RULE 20.--REQUEST TESTS.--Each utility furnishing metered electric
service shall make a test of the accuracy of any electricity
meter upon request of the consumer, provided the consumer does
not request such test more frequently than once in 6 months. A
report giving the results of each request test shall be made to
the consumer and the complete, original record kept on file in the
office of the utility.
=Electric Batteries.=--Electric batteries are composed of electric
cells that are made in two general types: the _primary cell_, in
which electricity is generated by the decomposition of zinc; and the
_secondary cell_ or storage cell in which electricity from a dynamo
may be accumulated and thus stored. Electric cells are the elements
of which electric batteries are made; a single electric cell is often
called a battery but the battery is really two or more cells combined
to produce effects that cannot be attained by a single element.
Both primary and secondary batteries form a part of the household
equipment but the work of the secondary battery is used more
particularly for electric lighting, the operation of small motors and
for other purposes where continuous current is required. It will,
therefore, be considered in another place.
Primary batteries are used to operate call-bells, table pushes,
buzzers, night latches and various other forms of electric alarms
besides which they are used in gas lighters, thermostat motors and
for many special forms, all of which form an important part in the
affairs of everyday life. Primary battery cells for household use
are made to be used in the wet and dry form, but the dry cell is now
more extensively used than any other kind and for most purposes has
supplanted the wet form.
Formerly all primary cells were made of zinc and copper plates placed
in a solution called an electrolite, that dissolved the zinc and thus
generated electricity, the electrolite acting as a conductor of the
electricity to the opposite plate. In later electric cells the copper
was replaced by plates of carbon and from the zinc and carbon cell was
finally evolved the present-day _dry cell_. When the use of electric
cells reached a point where portable batteries were required, a form
was demanded from which the solution could not be lost accidentally.
The first electric cells in which the electrolite was not fluid was,
therefore, called a dry cell. These cells are not completely dry. The
electrolite is made in the form of a paste that acts in the same manner
as the fluid electrolite and is only dry in that it is not fluid.
[Illustration: FIG. 254.--Electric dry cell.]
[Illustration: FIG. 255.--Details of electric dry cell.]