(3PDT): 4-pole, single-throw (4PST); and 4-pole,
double-throw (4PDT). The voltage ratings range from
Knife switches are basic power switches from
20 volts to 600 volts, and the amperage ratings range
which most modern switches have been developed. A
from 1 ampere to 30 amperes.
single-pole, single-throw (SPST) knife switch
consists of a single copper blade hinged at one end and
designed to fit tightly between two copper jaws, or
clips, at the other end. An insulated handle is fastened
The normal contact arrangement of a push-button
to the copper blade to open and close the switch.
switch is either make or break, as shown by the
Terminals are provided for connecting the leads.
schematic symbols in figure 2-3, view A. View B of
figure 2-3 is a picture of a push-button switch. The
A double-pole, single-throw (DPST) knife switch
(fig. 2-1, view A) has two blades with one set of clips
for each blade and an insulated handle that operates
both blades simultaneously. Double-throw switches
(fig. 2-1, view B) have two sets of clips (one set at each
end) so the blades can be thrown into either set of clips
to shift from one circuit to another.
Representative examples of toggle switches are
shown in figure 2-2, with the schematic symbols
shown beneath each switch. View A of figure 2-2
shows a SPST toggle switch, rated at 20 volts and 20
amperes, and having two solder terminals. This type
of switch opens and closes electric circuits.
View B of figure 2-2 shows a single-pole,
double-throw (SPDT) switch, rated at 250 volts and 1
ampere, and having three screw terminals. One use of
this switch is to turn a circuit on at one place and off
at another place. It is sometimes called a 2-way switch.
View C of figure 2-2 shows a DPST switch, rated
at 250 volts and 1 ampere, and having four solder
View D of figure 2-2 shows a double-pole,
Figure 2-2.--Toggle switches.
double-throw (DPDT) switch, rated at 125 volts and 3
amperes, and having six solder terminals.
The following types of switches are also used:
3-pole, single-throw (3PST); 3-pole, double throw
Figure 2-3.--Push-button switch.
Figure 2-1.--Knife switches.