Figure 2-4.--Type SR rotary snap switch (1SR, 10 ampere size).

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,

used.

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

be apparent.

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

front-mounted,

140.1

12.69

Figure 2-5.--Type 65R snap switch-exploded

Figure 2-4.--Type SR rotary snap switch (1SR,

view.

10 ampere size).

2-3