make type of switch is usually a start switch; the
back-connected); and enclosure (3SR4B1-3 is water-
break type of switch is usually a stop switch. Either
tight). (An exploded view of a type 6SR snap switch is
switch may be locking or nonlocking. There is also a
illustrated in fig. 2-5.)
break-make push-button switch (not shown).
Most snap switches are suitable for 450-volt,
60-Hz ac and 250-volt dc operation. Present 10-
Rotary Snap Switches
ampere switches are suitable for 120-volt operation
only, although the switches are sometimes used at
Rotary snap switches are devices that open or
higher voltages where the currents are very small.
close circuits with a quick motion. A type SR rotary
Care must be exercised in the application of
snap switch (fig. 2-4) consists of one or more sections,
multithrow (double-throw and triple-throw) switches.
each of which has a rotor and a stationary member.
The movable blade, in some cases, is so wide that in
Movable contacts are mounted on a bushing, and
moving from one stationary contact to a second, the
stationary contacts are mounted on insulated disks,
two stationary contacts will be momentarily bridged
which are arranged one beneath the other in pancake
by the arc and movable blade, causing a short circuit.
style along the switch shaft. This type of construction
Therefore, each time a multithrow switch is to be
has the advantages of shockproofness, compactness,
installed, a careful check should be made on both the
flexibility of circuit arrangements, and protection to
switch and the intended circuit to make sure that a
the operator. The operator, by rotating the switch
switch of the proper current and voltage ratings is
handle, triggers a spring and cam arrangement,
which, in turn, operates the switch contacts. If the
spring should break, further rotation of the handle
will eventually cause a projection on the shaft of the
handle to contact a projection on the operating shaft
to operate the switch. However, the switch-driving
shaft and handle will be misaligned from its normal
position, and the characteristic snap action will not
Snap switches are available in a wide variety
of amperage ratings (from 10 to 200), poles, and
mountings (bulkhead or panel mounting).
The switch type designation indicates its
current rating (1SR is 10 amperes, 3SR is 30
amperes, and so on); number of poles (3SR3 is 30
amperes, 3 poles); switching action (1SR3A is single-
throw; that is, on-off); mounting style (1SR3A1 is
Figure 2-5.--Type 65R snap switch-exploded
Figure 2-4.--Type SR rotary snap switch (1SR,
10 ampere size).