SP, DP, ST, DT in electronic switches

When customers ask us about electronic switches such as button switches and rocker switches. We often ask customers whether they want SPST, SPDT, DPST, DPDT or 3PST, 3PDT. This involves the concepts of extreme numbers and throwing.

SP and DP refer to single pole and double pole respectively, ST and DT refer to single throw and double throw respectively.

The number of poles refers to the number of circuits controlled by the switch: an SP switch only controls one circuit. A DP switch controls two independent circuits (like two identical switches mechanically connected). Don’t confuse “pole” with “terminal”. For example, a DPST switch has four terminals, but it is a DP, not a 4P switch.

Throw refers to the extreme position of the actuator: the ST switch closes the circuit in only one position. Another position for the handle is closed. The DT switch closes the circuit in the Up position and Down position (On-On). DT switches can also have a center position (usually On-Off-On).

Single pole/throw and double pole/throw switches are by far the most common switches, but triple and quadruple configurations are also available. They are usually represented as 3PST, 3PDT, 4PDT, etc.