A Quick Guide to Switch Contact Configuration

Whether looking for push buttons, microswitches, rocker switches, rotary switches or toggle switches, it’s good to remember the basic switch configurations.

A switch must have at least two conductive pieces of material which are called contacts, these are connected to an external circuit, the basic operation is to either close the contacts or open the contacts. This will turn the circuit on or off.

 

 

 

Switches can have different configurations, this dependant on the number  of poles and number of  throws.  A pole is the number of contact sets and a throw is the number of conducting positions.

Poles and Throws

Common configurations:

  • Single Pole Single Throw, is abbreviated to SPST
  • Double  Pole Single Throw, is abbreviated to DPST
  • Single  Pole Double Throw, is abbreviated to SPDT
  • Double Pole Double Throw, is abbreviated to DPDT

 

Brief overview and common diagram

SPST – A simple on-off switch. Only one circuit within the switch and one on position

 

 

 

DPST – Two circuits within the switch which operate together, switching two circuits on and off simultaneously. Can also be used to isolate live and neutral

 

 

 

 

SPDT – Used for switching on in two positions, switching between separate circuits. L1 could be a warning light and L2 could be a sounder. This configuration is also know as a changeover switch. With a third switching position this configuration can also be used as a centre off

 

 

DPDT – This is two on switches operating together, switching two devices simultaneously, for example a warning light and a sounder. It is equivalent to two SPDT switches. DPDT with a centre off can be used for motor control applications, these utilise forward on – off – and reverse on