volts from a small motor
generator set and storage battery. The motors which actuate the large
oil switches upon the main floor are driven by this 110 volt control
current, and thus in the hands of the operator the control switches
make or break the relatively feeble control currents, which, in turn,
close or open the switches in the main power circuits. The control
switches are systematically assembled upon the control bench board in
conjunction with dummy bus bars and other apparent (but not real)
metallic connections, the whole constituting at all times a correct
diagram of the existing connections of the main power circuits. Every
time the operator changes a connection by opening or closing one of
the main switches, he necessarily changes his diagram so that it
represents the new conditions established by opening or closing the
main switch. In connection with each control switch two small
bull's-eye lamps are used, one red, to indicate that the corresponding
main switch is closed, the other green, to indicate that it is open.
These lamps are lighted when the moving part of the main switch
reaches approximately the end of its travel. If for any reason,
therefore, the movement of the control switch should fail to actuate
the main switch, the indicator lamp will not be lighted.

[Illustration: MOTOR-GENERATOR SET SUPPLYING ALTERNATING CURRENT FOR
BLOCK SIGNALS AND MOTOR-GENERATOR STARTING SET]

The control board is divided into two parts--one for the connections
of the alternators to the bus bars and the other for the connection
of feeders to bus bars. The drawing on page 97 shows in plain view
the essential features of the control boards.

[Sidenote: _The
Instrument
Board_]

A front view of the Instrument Board is shown on page 97. This
board contains all indicating instruments for alternators and feeders.
It also carries standardizing instruments and a clock. In the
illustration the alternator panels are shown at the left and the
feeder panels at the right. For the alternator panels, instruments of
the vertical edgewise type are used. Each vertical row comprises the
measuring instruments for an alternator. Beginning at the top and
enumerating them in order these instruments are: Three ammeters, one
for each phase, a volumeter, an indicating wattmeter, a power factor
indicator and a field ammeter. The round dial instrument shown at the
bottom of each row of instruments is a three-phase recording
wattmeter.