ngineers as the "C^2R loss," which is another way of
saying that the loss is equal to the _square of the current in
amperes_, multiplied by _ohms_ resistance. Thus, if the amperes
carried is 10, and the ohms resistance of the line is 5, then the loss
in watts to convey that current would be (10 x 10) x 5, or 500 watts,
nearly a horsepower.

The pressure of _one volt_ (as we have seen in another chapter) is
sufficient to force _one ampere_, through a resistance of _one ohm_.
Such a current would have no capacity for work, since its pressure
would be consumed in the mere act of transmission.

If, however, the pressure were _110 volts_, and the current _one
ampere_, and the resistance _one ohm_, the effective pressure after
transmission would be 110-1, or 109 volts.

To force a 110-volt current of _50 amperes_ through the resistance of
_one ohm_, would require the expenditure of _50 volts_ pressure. Its
capacity for work, after transmission, would be 110-50, or _60 volts,
x 50 amperes_, or 3,000 watts. As this current consisted of _110 x
50_, or 5,500 watts at the point of starting, the loss would be 2,500
watts, or about 45 per cent. It is bad engineering to allow more than
10 per cent loss in transmission.

There are two ways of keeping this loss down. One is by increasing
the size of the transmission wires, thus cutting down the resistance
in ohms; the other way is by raising the voltage, thus cutting down
the per cent loss. For instance, suppose the pressure was 1,100 volts,
instead of 110 volts. Five amperes at 1,100 volts pressure, gives the
same number of watts, power, as 50 amperes, at 110 volts pressure.
Therefore it would be necessary to carry only 5 amperes, at this rate.
The loss would be 5 volts, or less than 1/2 of 1 per cent, as compared
with 45 per cent with 110 volts.

[Illustration: Splicing transmission wire]

In large generating stations, where individual dynamos frequently
generate as much as 20,000 horsepower, and the current must be
transmitted over several hundred miles of territory, the voltage is
frequently as high as 150,000, with the amperes reduced in proportion.
Then the voltage is lowered to a suitable rate, and the amperage
raised in proportion, by special machinery, at the point of use.

It is the principle of the C^2R loss, which the farmer must apply in
determining the size of wire he is to use in transmitting his current
from the generator switchboard to his house or barn. The wi