2.7 Switches, Fuses, and Circuit Breakers
Switches
The most basic switch is a single-pole, single-throw (SPST) switch as shown
in Figure 2–27. With the switch open, the current path is broken and the
lamp is off; with it closed, the lamp is on. This type of switch is used, for
example, for light switches in homes.
Figure 2–28(a) shows a single-pole, double-throw (SPDT) switch. Two
of these switches may be used as in (b) for two-way control of a light. This
type of arrangement is sometimes used for stairway lights; you can turn the
light on or off from either the bottom or the top of the stairs.