e first chapter, meets the
requirements of this "average plant" let us inquire a little more
fully into its installation, maintenance, and cost.

_An Actual Plant_

In this instance, the water-power was already installed, running to
waste, in fact. The wheel consists of the so-called thirty-six inch
vertical turbine, using 185 square inches of water, under a 14-foot
head. Water is supplied to this wheel by a wooden penstock 33 inches
square, inside measurements, and sloping at an angle of 30 deg. from
the flume to the wheel.

[Illustration: Details of voltmeter or ammeter]

This wheel, under a 14-foot head, takes 2,312 cubic feet of water a
minute; and it develops 46.98 actual horsepower (as may be figured by
using the formulas of Chapter III). The water supply is provided by a
small mountain river. The dam is 10 feet high, and the race, which
feeds the flume from the mill pond is 75 yards long. The race has two
spillways, one near the dam, and the second at the flume itself, to
maintain an even head of water at all times.

_Half-Gate_

Since the water supply varies with the seasons, it has been found
practical to run the wheel at half-gate--that is, with the gate only
half-open. A set of bevel gears work the main shaft, which runs at
approximately 200 revolutions per minute; and the dynamo is worked up
to its required speed of 1,500 revolutions per minute through a
countershaft.

The dynamo is a modern four-pole machine, compound-wound, with a rated
output of 46 amperes, at 125 volts--in other words a dynamo of 5.75
kilowatts capacity, or 7.7 electrical horsepower. At full load this
dynamo would require a driving power of 10 horsepower, counting it as
75 per cent efficient; and, to conform to our rule of two water
horsepower to one electrical horsepower, the wheel should be capable
of developing 20 horsepower. As a matter of fact, in this particular
instance, shutting down the wheel to half-gate more than halves the
rated power of the wheel, and little more than 15 horsepower is
available. This allowance has proved ample, under all conditions met
with, in this plant.

The dynamo is mounted on a firm floor foundation; and it is belted
from the countershaft by an endless belt running diagonally. A
horizontal belt drive is the best. Vertical drive should be avoided
wherever possible.

_The Switchboard_

The switchboard originally consisted of a wooden frame on which were
screwed ordinary asbestos shin