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Introduction to Switches

Switch: a device for making, breaking, or changing the path in an electrical circuit.

Switches are available in a wide variety of types and sizes.

They all control the path of an electrical circuit. The amount of current and the number of circuits they switch is the only difference.

Switch Terminology

Poles: the number of circuits to be switched.

Positions: the number of paths a single circuit can take.




Single Pole Single Throw: a switch with only one set of contacts which make or break the path of an electrical circuit.

The illustrated and animated schematic to the right demonstrates a Single Pole Single Throw (SPST) Switch.

The Switch makes or breaks the path to the light, turning it on or off.






Double Pole Single Throw: a switch with two sets of contacts which simultaneously make or break the path of two electrical circuits.

The illustrated and animated schematic to the right demonstrates a Double Pole Single Throw (DPST) Switch.

The Switch makes or breaks the dual path to the light, turning it on or off.





Single Pole Double Throw: a switch that simultaneously diverts the path of a single circuit to one of two locations.

The illustrated and animated schematic to the right demonstrates a Single Pole Double Throw (SPDT) Switch.

The Switch makes one path and breaks the other path to the lights, turning one on at a time.






Double Pole Double Throw: a switch that simultaneously diverts the path of two circuits, each to one of two locations.

The illustrated and animated schematic to the right displays a Double Pole Double Throw (DPDT) Switch.

The Switch makes two paths and breaks the other two paths. This demonstrates how to reverse polarity and reverse the direction of a DC motor.






Two Single Pole Double Throw Switches are used to control a light. Either switch can turn the light on or off.

The illustrated and animated schematic to the right demonstrates the two Single Pole Double Throw (SPDT) Switches.

The electrical path can be made or broken at either switch.






Here, a Single Pole Four Position Switch is used to control four lights. Only one light can be turned on at a time.

The illustrated and animated schematic to the right displays the Single Pole Four Position (SP4P) Switch.

The electrical path can be made to any one of the four lights.





The contact rating must be large enough to handle the load current and it must be rated for the voltage.

The same contact ratings will be different for a Resistive Load than for an Inductive Load.

A Resistive Load will have the same rating for Make, Break and Continuous amps.

An Inductive Load will have a different rating for each Make, Break and Continuous amps.

Always use a switch rated for the job.