Electrical switches explained further
Switch poles and throws explained
A switch pole refers to the number of separate circuits that the switch can control. A single pole switch has one throw because there is only one possible set of output connections that can be made. A double throw switch has two possible output connections so can control two separate circuits. All poles of a switch are controlled by just a single toggle, rocker or slide mechanism.
The number of throws in a switch indicates how many different output connections each switch pole can connect to. The two most common types are single-throw with only one pair of contacts, and a double-throw with two pairs of contact. Two pole switches generally have a common input contact.
There are also 3 and 4 pole switches listed on our website. These switches operate with the same principles as a single or double pole switch, but there are more switches built into the same housing.
SPST or Single Pole Single Throw two position switches
SPST On - Off
A single throw electrical switch is a basic On-Off type switch. One flip of the switch turns the circuit on, and flip the switch the other way and it turns off. Used mainly to interrupt current for a single pole of a circuit.
On the rear of the switch there are usually just two connectors. The one in the centre of the switch is the power in, and the other is the power out when the switch is operated.
SPST On - On
A variation on the simple Off - On switch is an On - On type switch. This switch can be on in both positions, switching on a separate circuit in each position. It is often called a changeover switch. For example, this switch can be used to switch on a red lamp in one position and a green lamp in the other position. With this type of switch, there is no off position.
On the rear of the switch there are usually three connectors. The one in the centre of the switch is the power in, and the other two will be power outs depending on the position of the switch when operated.
SPDT or Single Pole Double Throw three position switches
SPST On - Off - On
A double throw electrical switch operates two circuits and has an additional off position. The off position is generally the centre position. A flip of the switch one way turns the circuit on. A flip to the centre position turns everything off, and flip the switch the other way and it turns another circuit on. Used to control two independent circuits.
On the rear of the switch there are usually three connectors. The one in the centre of the switch is the power in, and the other two will be power outs depending on the position of the switch when operated.
SPST (On) - Off - (On)
This type of switch is the same as the above switch but it has sprung to centre off toggle or rocker. The brackets denote a spring centre return when released action. This means that to operate one of the two circuits, the switch has to be held in position. These switches are used on things like point motors where only a short supply of power is required.
On the rear of the switch there are usually three connectors. The one in the centre of the switch is the power in, and the other two will be power outs depending on the position of the switch when operated.
DPST or Double Pole Single Throw two position switches
DPST On - Off
This double pole switch is two switches side by side built into the same housing and using a common operating mechanism. One flip of the switch turns the circuit on, and flip the switch the other way and it turns off. Used mainly to interrupt current for a single pole of a circuit.
On the rear of the switch there are usually two rows of two connectors. The ones in the centre of the switch are the power in, and the other is the power out when the switch is operated.
DPST On - On
This double On - On type switch contains two switches built in the same housing. This switch can be on in both positions, switching on a separate circuit in each position. It is often called a changeover switch. For example, this switch can be used to switch on a red lamp in one position and a green lamp in the other position. With this type of switch, there is no off position.
On the rear of the switch there are usually two rows of three connectors. The ones in the centre of the switch are the power in, and the others are the power out when the switch is operated in either direction
DPDT or Double Pole Double Throw three position switches
DPDT On - Off - On
This double pole switch is two switches side by side built into the same housing and using a common operating mechanism. The off position is generally the centre position. A flip of the switch one way turns the circuit on. A flip to the centre position turns everything off, and flip the switch the other way and it turns another circuit on. Used to control two independent circuits.
On the rear of the switch there are usually two rows of three connectors. The ones in the centre of the switch are the power in, and the other is the power out when the switch is operated. Both input terminals require a power feed.
DPDT (On) - Off - (On)
This type of switch has two switches built into the same housing but it has sprung to centre off toggle or rocker. The brackets denote a spring centre return when released action. This means that to operate one of the two circuits, the switch has to be held in position. These switches are used on things like point motors where only a short supply of power is required.
On the rear of the switch there are usually two rows of three connectors. The ones in the centre of the switch are the power in, and the other is the power out when the switch is operated. Both input terminals require a power feed.
3PST or Three Pole Single Throw two position switches
DPDT Off - On
This triple pole switch is three switches side by side built into the same housing and using a common operating mechanism. The off position is generally the centre position. A flip of the switch one way turns the circuit on. A flip to the centre position turns everything off, and flip the switch the other way and it turns another circuit on. Used to control two independent circuits.
On the rear of the switch there are usually three rows of three connectors. The ones in the centre of the switch are the power in, and the other is the power out when the switch is operated. Both input terminals require a power feed.
3PST On - On
This triple pole switch is three switches side by side built into the same housing and can operate three circuits at the same time. This switch has no off position so is on in both positions, switching on a separate circuit in each position. It is often called a changeover switch. For example, this switch can be used to switch on a red lamp in one position and a green lamp in the other position. With this type of switch, there is no off position.
On the rear of the switch there are usually three connectors. The one in the centre of the switch is the power in, and the other two will be power outs depending on the position of the switch when operated.
3PDT or Three Pole Double Throw three position switches
3PDT On - Off - On
This triple pole switch is three switches built side by side into the same housing and using a common operating mechanism. The off position is generally the centre position. Flick the switch one way and one set of circuits will operate, and switch the other to turn off the first circuit and operate another.
On the rear of the switch there are usually three rows of three connectors. The ones in the centre of the switch are the power in, and the other is the power out when the switch is operated. All input terminals require a power feed but it is possible to wire these into one input wire by bridging the terminals.
3PDT (On) - Off - (On)
This type of switch has three switches built into the same housing and it has a sprung to centre off toggle, slide or rocker. The brackets denote a momentary so that when the switch is released the switch will return to the centre off position. This means that to operate one of the three circuits, the switch has to be held in position. These switches are used on things like point motors where only a short supply of power is required.
On the rear of the switch there are usually three rows of three connectors. The ones in the centre of the switch are the power in, and the other is the power out when the switch is operated. All input terminals require a power feed but it is possible to wire these into one input wire by bridging the terminals.
Whilst we have only dealt with some switches here, there are more. We also stock and sell 4P single and double throw switches, but think that you would understand how the switches are named and understand what the larger 4P switches would do.
As you can see there are numerous switch options available, and these options are available in different switch bodies. Whilst not available in all bodies there are slide and rocker switches that will fit into many areas mentioned on this page.
Fitting switches
Most toggle switches will have a threaded segment below the lever which allows the switch to be secured into a thin panel using a lock nut, washer and another nut. They are fitted from the rear, into a hole drilled the size of the switch mount. A nut is used to secure the switch from the front. As well as 2 nuts, a serrated washer and a special washer that can lock the switch into a notch filed in the hole are provided to prevent the switch from spinning round in the hole.
Push button switches can be either mounted in a shaped hole or a round panel hole. If in a shaped hole, the switch is usually pushed through the hole from the front, and clips hold the switch in position. Some push button switches fit in the same way as most toggle switches and are held in position in the same way.
Rocker switches generally require a rectangular cut out, and are then pushed through the hole from the front and secured using several sprung tabs moulded into the switch body.
Reed switches are fitted by drilling a small hole the size of the wire leads and bending these to fit the location.
All of our switch listings include the minimum thickness of panel that the switches can be fitted into, and the size of the mounting hole required.
Connecting and wiring switches
Most of the switches that we sell come with tinned solder tag connections to the rear, and this makes soldering wires to the terminals easy as long as the switch is easily accessible. Try to not overheat the terminal in the soldering process as the heat can transfer into the switch and affect the switch contacts. For these types of switches, crimp or solder terminals are not suitable, but some can be modified to fit.
Some of the switches come with different sized tab connections to the rear, and it is possible to use our crimp connectors to wire these types. The tab sizes are mentioned in the product descriptions, so the correct size of the connector can be sourced so be sure to read the product specifications and descriptions before buying the connectors.
However you wire the switches, please ensure that any bare wires or connections are insulated with either tape or heat shrink just for safety.