Power Control 409
Pushbutton Station—A housing for the pushbuttons that are used to con-
trol equipment.
Reduced-voltage Starter—A control device that applies a reduced voltage to
a motor when it is started.
Relay—A control device that is operated by one electrical circuit to control
a load that is part of another electrical circuit.
Remote Control—A system in which the control of an electrical load takes
place from some distant location.
Safety Switch—An enclosed, manually operated, disconnecting switch
used to turn a load off when necessary.
Solenoid—An electromagnetically actuated control device that is used to
produce linear motion for performing various control functions.
Starter—An electric controller that is used to start, stop, and protect the
motor that is connected to it.
Timer—A control device that provides variable time periods, so that a con-
trol function may be performed.Symbols
One should have an understanding of the electrical symbols that are
commonly used with power control systems. A few of these are somewhat
different from basic electrical symbols. Some typical symbols are shown in
Figure 15-1. You should especially observe the symbols that are used for
the various types of switches and pushbuttons.POWER CONTROL USING SWITCHES
An important, but often overlooked, part of electrical power control
is the various types of switches used. This section will examine the many
types of switches that are used to control electrical power. The primary
function of a switch is to turn a circuit on or off; however, many more com-
plex switching functions can be performed using switches. The emphasis
in this section will be on switches that are used for motor control. Keep in
mind that other load devices can also be controlled in a similar manner by
switches.Toggle Switches
Among the simplest types of switches are toggle switches. The sym-
bols for several kinds of toggle switches are shown in Figure 15-2. You