Common types of Switches used in electrical wiring

An electric switch is a component that can open or close an electrical circuit. That is, it engages or disengages an electric contact between terminals of a conductive circuit to provide a path for the electric current to flow (close or connect) or interrupt the flow of current (open or disconnect) on demand.

Depending on the number of poles, way or throw, the action of mechanism, etc switches are of different types. Here a brief description of a few common types of switches used for various applications in electrical wiring.

SPST (Single Pole Single Throw)

These are the most common type of switches used in house, office, industry wirings that are used to control lights, fans, plug points, appliances, etc.

An SPST switch has a simple ON/OFF operation that can connect or disconnect the electrical contacts between two terminals. An SPST switches control only one circuit with a CLOSE or ON at one position and OPEN or OFF at another position.

SPDT (Single Pole Double Throw)

SPDT switches have a variety of applications in home and industrial wiring. It is the main component required for wirings arrangements like staircase wiring, godown wiring, master switch wiring, etc that requires two-way switching.

It has three terminals, one common pole that can be switched to either one of the two terminals. Here the common pole of the switch will be always connected to either Terminal 1 or Terminal 2. It also controls one circuit but the position switches the contact between two terminals.

DPST (Double Pole Single Throw)

It is similar to SPST with an additional pair of terminals that are 2 SPST switches operated by a single mechanism. It has 4 terminals that can control two independent circuit paths, one position connects or ON, and the other disconnect or OFF the conductive path between a pair of two independent terminals.

DPDT (Double Pole Double Throw)

A DPDT switch can be considered as 2 SPDT switches operated by a single mechanism. It has 6 terminals, two common poles, and separate two terminals for each pole; 2 terminals for one pole and another 2 terminals for the other pole. It can control two independent circuits to switch between their respective two terminals.

Intermediate switch

These switches are not commonly required in wirings, it is mainly used when needed to wire three-way light switching circuits.

One position of an intermediate switch is similar to the ON state of a DPST switch that closes the two separate individual circuits. In the other position, the intermediate switch just crossover the terminal contacts or interchange two separate circuits.

Main Switch

The main switch is used to control the total power to a circuit or panel. Its contact arrangement is similar to a DPST switch that can control both lines; the main switch controls Phase and Neutral lines of the main supply.

Refer: Electrical Wiring Questions and Answers

Regulator switch

A regulators switch is used to control the speed of the fan, the brightness of light, etc. Regulators is connected in series with the load, it can vary the voltage drop across it and thereby the voltage across the load connected in series. Mainly it is used for speed control of ceiling fans that have no inbuilt speed controls.

Fan Regulators are usually stepping type switch with 6 positions, where every five positions provide 5 levels of voltage from a minimum value at position 1 to maximum at 5. The regulator is OFF at position zero and contacts will be disconnected from the line.

Momentary Push switch

A momentary push switch is a type of switch that either closes or opens the contact as long as it is hold pressed. A normally open push switch is “Push to make” (default state is open and circuit completes when it is pressed) and a normally closed push switch is “Push to break” switch (default state is closed the circuit contact disengage for the duration of pressing).

Push to make is the most commonly used momentary switch in home, office industry wirings for calling bells, alarms, machine starter and stop switches, etc.

Manual Change Over switch

Changeover switches are mainly used for selecting the supply from multiple sources. That is if the supply needs to be taken from two separate power sources like a distribution line and occasionally from a backup generator a changeover switch can be used for changing the supply from one source to another.

It will also have an OFF state which isolates the circuit from all the power sources.