3-7
Q8. Label the schematic symbols shown in figure 3-4 as to number of poles and number of throws.
Figure 3-4.—Schematic symbols of switches.
Single-Break and Double-Break Switches
Switches can also be classified as SINGLE-BREAK or DOUBLE-BREAK switches. This refers to
the number of places in which the switch opens or breaks the circuit. All of the switches shown so far
have been single-break switches. A double-break switch is shown in figure 3-5. The schematic symbol
shown in figure 3-5(A) shows that this switch breaks the circuit in two places (at both terminals). The
upper part of the schematic symbol indicates that these contacts are in the open position and the circuit
will close when the switch is acted upon (manually or automatically). The lower symbol shows closed
contacts. These contacts will open the circuit when the switch is acted upon.
Figure 3-5.—Double-break pushbutton switch.
Figure 3-5(B) is a picture of the switch. This switch is called a pushbutton switch because it has a
button that must be pushed to change the switch contact connections. Notice that the switch has four
terminals. The schematic symbol in figure 3-5(A) shows that when one set of contacts is open, the other
set of contacts is closed. This switch is a double-pole, single-throw, double-break switch.
