Many electrical and electronic circuits include
controls and indicators to assist the operator in the use and repair
of the equipment.
These controls may consist of devices such as
switches, relays, fuses, plugs and jacks, test points, and
These operator aids are normally represented in the
Switches give the operator control over the
operation of the equipment. By positioning the switch, the operator
directs the operation of the circuit by routing the direction of
electrical signals within the circuit. Switches may be simple, such
They may be designed to be
momentary action, to latch in a given position, make-before-break, or
to perform any number of specific functions.
While the possible
designs for switches are almost limitless, figure 1-16 illustrates
several commonly used switch symbols.
In addition to the symbol,
switches are normally labeled with the letter "S." A special type of
switch is the circuit breaker.
protection to the circuit. The symbol for a typical circuit breaker
is shown in figure 1-16.
The previous description of switches stated that
switches direct the routing of electrical signals within a circuit.
A relay functions similarly.
Rather than being controlled manually
by the operator, a relay is operated electrically by energizing a
coil to realign the contacts of the