412 Electrical Power Systems Technology
It will open a circuit when it is depressed. The NO pushbutton is
open until it is manually depressed, and then, once it is depressed, it will
close a circuit. The “start” pushbutton of a motor control station is an NO
type, while the “stop” switch is an NC type.
Rotary Switches
Another common type of switch is the rotary switch. Many different
switching combinations can be wired using a rotary switch. The shaft of a
rotary switch is attached to sets of moving contacts. When the rotary shaft
is turned to different positions, these moving contacts touch different sets of
stationary contacts, which are mounted on ceramic segments. The shaft can
lock into place in any of several positions. A common type of rotary switch
is shown in Figure 15-4. Rotary switches are usually controlled by manually
turning the rotary shaft clockwise or counterclockwise. A knob is normally
fastened to the end of the rotary shaft to permit easier turning of the shaft.
Limit Switches
Limit switches are made in a variety of sizes. Limit switches are mere-
ly on/off switches that use a mechanical movement to cause a change in
the operation of the electrical control circuit of a motor or other load de-
Figure 15-3. Pushbutton styles