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Types of Switches


Type of Switch

Circuit Symbol

Example

SPST

Single Pole, Single Throw

ON-OFF

A simple on-off switch. This type can be used to switch the power supply to a circuit.

When used with AC this type of switch must be in the live wire, but it is better to use a DPST switch to isolate both live and neutral.  

SPST Toggle Switch
SPST toggle switch, photograph © Rapid Electronics
Photograph © Rapid Electronics
used by permission

SPST Momentary

Single Pole, Single Throw Push to Make

(ON)-OFF

A push-to-make switch returns to its normally open (off) position when you release the button, this is shown by the brackets around ON.  This type of switch is used for doorbells.

 

SPST Push-to-Make Switch
Push-to-make switch, photograph © Rapid Electronics
Photograph © Rapid Electronics
used by permission

SPST Momentary

Single Pole, Single Throw Push-to-Break

ON-(OFF)

A push-to-break switch is on until the button is pushed.  The switch returns to its normally closed (on) position when the button is released.

A motor connected to this type of switch runs continuously until the button is pushed. 

Push-to-break switch, photograph © Rapid Electronics

SPST Push-to-Break Switch

Photograph © Rapid Electronics
used by permission

SPDT

Single Pole, Double Throw

ON-ON

 

This switch can be on in both positions, switching on a separate device in each case.  For example, a SPDT switch can be used to switch on a red lamp in one position and a green lamp in the other position.

 

A SPDT toggle switch may be used as a simple on-off switch by connecting to COM and one of the A or B terminals shown in the diagram. A and B are interchangeable so switches are usually not labeled.

 

 

SPDT Center Off

ON-OFF-ON

A special version of the standard SPDT switch. It has a third switching position in the center which is off. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released.

 

SPDT switch symbol

SPDT toggle switch

SPDT toggle switch, photograph © Rapid Electronics
 

SPDT slide switch
(PCB mounting)

SPDT slide switch, photograph © Rapid Electronics
SPDT rocker switch

SPDT rocker switch, photograph © Rapid Electronics
 

Photographs © Rapid Electronics
used by permission

DPST

Double Pole, Single Throw

Dual ON-OFF

A pair of on-off switches which operate together (shown by the dotted line in the circuit symbol).

 

A DPST switch is often used to switch AC electricity because it can isolate both the live and neutral connections.

 

DPST switch symbol

DPST rocker switch

DPST rocker switch, photograph © Rapid Electronics
 

Photographs © Rapid Electronics
used by permission

 

DPDT

Double Pole, Double Throw

Dual ON-ON

A pair of on-on switches which operate together (shown by the dotted line in the circuit symbol).

A DPDT switch can be wired up as a reversing switch for a motor as shown in the diagram.

DPDT Center Off

Double Pole, Double Throw Center Off

Dual ON-OFF-ON

A special version of the standard SPDT switch. It has a third switching position in the centre which is off. This can be very useful for motor control because you have forward, off and reverse positions. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released.

 

 

DPDT slide switch

DPDT slide switch, photograph © Rapid Electronics
Photographs © Rapid Electronics
used by permission

Reversing switch

Wiring for Reversing Switch

SPECIAL SWITCHES

Type of Switch

Example

Push-Push Switch (e.g. SPST = ON-OFF)

This looks like a momentary action push switch but it is a standard on-off switch: push once to switch on, push again to switch off. This is called a latching action.

Push-push switch, photograph © Rapid Electronics

Photographs © Rapid Electronics
used by permission

Micro Switch

Typically these are SPDT – ON-ON switches.

Micro switches are designed to switch fully open or closed in response to small movements. They are available with levers and rollers attached.

Microswitch, photograph © Rapid Electronics

Photographs © Rapid Electronics
used by permission

Keyswitch

Key Switches come in many different types.  The term refers to a switch that must be operated by a key.  Key switches can have multiple poles and positions.  They can also be momentary.

Keyswitch, photograph © Rapid Electronics

Photographs © Rapid Electronics
used by permission

Tilt Switch (SPST)

Tilt switches contain a conductive liquid and when tilted this bridges the contacts inside, closing the switch. They can be used as a sensor to detect the position of an object. Some tilt switches contain mercury which is poisonous.

Tilt switch, photograph © Rapid Electronics

Photographs © Rapid Electronics
used by permission

Tip Over Switch - A specialized version of a tilt switch

Tip Over switches are a safety switch used in things such as heaters and other electrical equipment.  They are generally normally closed switches.  When the device tips over the circuit is broken and the device turns off. 

 

Magnetic Switch (usually SPST) - Sometimes called a reed switch

The contacts of a magnetic switch are closed by bringing a small magnet near the switch. They are used in security circuits, for example to check that doors are closed. Standard reed switches are SPST (simple on-off) but SPDT (changeover) versions are also available.   Some magnetic switches have both normally open and normally closed contact points.


click for larger picture

Multi-pole Switch

The picture shows a 6-pole double throw switch, also known as a 6-pole changeover switch. It can be set to have momentary or latching action. Latching action means it behaves as a push-push switch, push once for the first position, push again for the second position etc.

Multi-pole switch, photograph © Rapid Electronics

Photographs © Rapid Electronics
used by permission

Multi-way Switch

Multi-way switches have 3 or more conducting positions. They may have several poles (contact sets). A popular type has a rotary action and it is available with a range of contact arrangements from 1-pole 12-way to 4-pole 3 way.

The number of ways (switch positions) may be reduced by adjusting a stop under the fixing nut. For example if you need a 2-pole 5-way switch you can buy the 2-pole 6-way version and adjust the stop.

Multi-way rotary switch

Multi-way rotary switch, photograph © Rapid Electronics

Photographs © Rapid Electronics
used by permission

Multi-way switch symbol

 

Photo Switch

This is a switch that reacts to light.   A photo switch is actually a special circuit using some type of photo cell to read light levels and circuitry to turn a relay on or off.