Switches are usually classified by two methods: the number of circuits they
control, and the type of physical construction.
Some of the many switch symbols
used in electronics are shown in figure 3-12.
a. Common Switches.
(1) The single-pole, single-throw (SPST) switch can open or close one
circuit. The symbol for the SPST switch is shown in A of figure 3-12.
(2) The symbol for the single-pole, double-throw (SPDT) switch is shown in
B. Two connections can be made separately. Either of two circuits is
closed while the other is open.
(3) A double-pole, single-throw (DPST) switch symbol is shown in C.
switch controls two circuits; both are either open or closed.
(4) The symbol for a double-pole, double-throw (DPDT) switch is shown in D.
With this switch, it is possible to have two circuits closed while two
other circuits are open.
(5) The symbols in E represent toggle switches, those in F represent
switches are shown in their normal positions.
Operating the switch
causes the action shown in the switch label.