Relay Contact types with Temperature Controllers; SPST = Single Pole Single Throw, SPDT = Single Pole Double Throw, DPDT = Double Pole Double Throw, DPST = Double Pole Single Throw.

Throw means how many times it can be “switched”. For example, a single pole will open or close one line and dual pole will do dual lines.  A “switch” is an electrical component that can interrupt an electrical circuit diverting it from one conductor over to another.

Electrical switches; mercury switch, wafer switch , DIP switch, surface mount switch, reed switch, wall switch, miniature toggle switch, in-line switch, push-button switch, rocker switch, micro-switch and more..

  • SPST – Single Pole Single Throw; 2 terminals, that can be either connected or not, depending on the position of the switch (example, common light switch).

symbol SPST Switch

  • SPDT – Single Pole Double Throw; 3 terminals, where one is the common and it’s connected to the other two terminals, depending on the position of the switch.

symbol SPDT Switch

  • DPST – Double Pole Single Throw that turns two circuits on or off; 4 terminals, 2 inputs & 2 outputs.

symbol DPST

  • DPDT – Double Pole Double Throw; 6 terminals, 2 inputs, 2 outputs & 2 for the B outputs.

symbol DPDT