Switch Type Codes

[Ken Pachkowsky]

Can one of you guru's tell me the difference between the following toggle designations

SPDT and SPST

I know the SP is single pole but what is the difference between DT and ST?

Thanks

[Zilch]

DT is "Double Throw." They have a center position, typically "Off," but there's other options....


ST is "Single Throw."

[Ken Pachkowsky]

Thanks a bunch Zilch. They will work then.

Ken

[ralphs99]

Hi Ken,

The Zilchster is basically correct except that a xPST switch will not have a centre off position. One position will complete the circuit and the other position will be open-circuit. Because an open circuit requires no terminals or contacts in the switch, it becomes cheaper to manufacture an xPST rather than a xPDT. An xPDT switch can always be wired as xPST.

xPDT switches are the ones with the option of a centre-off position. ie closed- circuit 1, (optional centre-off), closed circuit 2.
Centre-off has no meaning for an xPST switch.

Cheers,
Ralph.

[Ian Mackenzie]

Hi Ken,

The Zilchster is basically correct except that a xPST switch will not have a centre off position. One position will complete the circuit and the other position will be open-circuit. Because an open circuit requires no terminals or contacts in the switch, it becomes cheaper to manufacture an xPST rather than a xPDT. An xPDT switch can always be wired as xPST.

xPDT switches are the ones with the option of a centre-off position. ie closed- circuit 1, (optional centre-off), closed circuit 2.
Centre-off has no meaning for an xPST switch.

Cheers,
Ralph.

Correct

[Rudy Kleimann]

SPST, SPDT, DPST, DPDT TPDT,
None of these designations imply a center-off position. Rather, the poles are referring to the number of circuits in the switch, and the throw refers to the number of output options, if you will, for each circuit.

Additional information on the switch will reveal a center-off position, a momentary contact (non-locking) switch, push-pull, push-on push-off, etc.

[Zilch]

Yup, that's right. It's whether or not the second contacts are there. Forget the "center off" thing, which is only one form. Think double-throw relay, for example....