epower for the turbine
wheel. Normally it would not use one-half this capacity.

CHAPTER VII

TRANSMISSION LINES

Copper wire--Setting of poles--Loss of power in transmission--Ohm's
Law and examples of how it is used in figuring size of
wire--Copper-wire tables--Examples of transmission lines--When to
use high voltages--Over-compounding a dynamo to overcome
transmission loss.

Having determined on the location of the farm water-power electric
plant, and its capacity, in terms of electricity, there remains the
wiring, for the transmission line, and the house and barn.

For transmission lines, copper wire covered with waterproof braid--the
so-called weatherproof wire of the trade--is used. Under no
circumstances should a wire smaller than No. 8, B. & S. gauge be used
for this purpose, as it would not be strong enough mechanically. The
poles should be of chestnut or cedar, 25 feet long, and set four feet
in the ground. Where it is necessary to follow highways, they should
be set on the fence line; and in crossing public highways, the
ordinance of your own town must guide you. Some towns prescribe a
height of 19 feet above the road, others 27 feet, some 30. Direct
current, such as is advised for farm installations, under ordinary
circumstances, does not affect telephone wires, and therefore
transmission lines may be strung on telephone poles. Poles are set at
an average distance of 8 rods; they are set inclined outward on
corners. Sometimes it is necessary to brace them with guy wires or
wooden braces. Glass insulators are used to fasten the wires to the
cross-arms of the poles, and the tie-wires used for this purpose must
be the same size as the main wire and carry the same insulation.

_Size of Wire for Transmission_

To determine the size of the transmission wires will require knowledge
of the strength of current (in amperes) to be carried, and the
distance in feet. In transmission, the electric current is again
analogous to water flowing in pipes. It is subject to resistance,
which cuts down the amount of current (in watts) delivered.

[Illustration: Bringing wires into the house or barn]

The loss in transmission is primarily measured in volts; and since the
capacity of an electric current for work equals the _volts_ multiplied
by _amperes_, which gives _watts_, every volt lost reduces the working
capacity of the current by so much. This loss is referred to by
electrical e