Power Control 411
should become familiar with the symbols that are used for various types
of toggle switches and with the control functions that they can accom-
plish.Rocker Switches
Another type of switch
is called a rocker switch. Rock-
er switches are used for on-off
control. They may be either
momentary-contact, for ac-
complishing temporary con-
trol, or sustained contact, for
causing a load to remain in an
on or off condition until the
switch position is manually
changed.Pushbutton Switches
Pushbutton switches are
commonly used. Many motor-
control applications use push-
buttons as a means of start-
ing, stopping, or reversing a
motor; the pushbuttons are
manually operated to close or
open the control circuit of the
motor. There are several types
of pushbuttons used in the
control of motors. Figure 15-
3 diagrams some pushbutton
styles. Pushbuttons are usu-
ally mounted in enclosures.
Ordinarily, pushbut-
tons are either the normally
closed (NC) or normally open
(NO) type. An NC pushbutton
is closed until it is depressed
manually.Figure 15-2. Types of toggle switches: (A)
Single pole, single throw (SPST), (B) Three-
way or single pole, double throw (SPDT),
(C) Double pole, single throw (DPST), (D)
Double pole, double throw (DPDT), (E)
Three pole, single throw (3PST), (F) Three
pole, double throw (3PDT)