At its core, a switch must have at least two contact terminals with the objective to either close or open the contacts. Switches are defined by the number of poles and the throw count.   Pole references the number of circuits that can be controlled by a switch. For example, a single pole switch can only control one circuit.

A throw is defined by the number of conducting positions. If it is a single throw, each pole can be connected to 1 terminal. The other position would be off. SPST switches are either open or closed.   Imagine a draw bridge. If the bridge is closed someone (the current) would be able to drive across and complete the connection between the two sides of a river. If the bridge is open, you (the current) would not be able to transfer to the other side. There are four extremely common configurations that cover most applications. Below find a list to help determine the correct switch you need:

1. Single Pole, Single Throw (SPST)

Used for a simple On/Off switch.

2. Single Pole/ Double Throw (SPDT)

Used for switching on in two positions, switching between separate circuits.

3. Double Pole, Single Throw (DPST)

Used for controlling two circuits together, switching on and off simultaneously.

4. Double Pole, Double Throw(DPDT)

Used for two on switches operating together, switching two devices simultaneously. It is equivalent to two SPDT switches.

These are the basics regarding switches. We hope this information can be a useful aid when shopping for switches, and click thru to shop for switches on our site!