Switch

: This article is about electrical switches. For other meanings of the word "switch", see Switch (disambiguation).

Multiway switching

Multiway switching is a method of connecting switches in groups so that any switch can be used to connect or disconnect the load. This is most commonly done with lighting.

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Two locations

Switching a load on or off from two locations (for instance, turning a light on or off from either end of a flight of stairs) requires two SPDT switches. There are two basic methods of wiring to achieve this.

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In the first method, mains is fed into the common terminal of one of the switches; the switches are then connected through the L1 and L2 terminals (swapping the L1 and L2 terminals will just make the switches work the other way round), and finally a feed to the light is taken from the common of the second switch. A connects to B or C, D connects to B or C; the light is on if A connects to D, i.e. if A and D both connect to B or both connect to C.

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The second method is to join the three terminals of one switch to the corresponding terminals on the other switch and take the incoming supply and the wire out to the light to the L1 and L2 terminals. Through one switch A connects to B or C, through the other also to B or C; the light is on if B connects to C, i.e. if A connects to B with one switch and to C with the other.

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Wiring needed in addition to the mains network (not including protective earths):

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First method:

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• double wire between both switches
• single wire from one switch to the mains
• single wire from the other switch to the load
• single wire from the load to the mains

Second method:

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• triple wire between both switches
• single wire from any position between the two switches, to the mains
• single wire from any position between the two switches, to the load
• single wire from the load to the mains

If the mains and the load are connected to the system of switches at one of them, then in both methods we need three wires between the two switches. In the first method one of the three wires just has to pass through the switch, which tends to be less convenient than being connected. When multiple wires come to a terminal they can often all be put directly in the terminal. When wires need to be joined without going to a terminal a crimped joint, piece of terminal block, wirenut or similar device must be used and the bulk of this may require use of a deeper backbox.

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More than two locations

For more than two locations, the two cores connecting the L1 and L2 of the switches must be passed through an intermediate switch (as explained above) wired to swap them over. Any number of intermediate switches can be inserted, allowing for any number of locations.

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Wiring needed in addition to the mains network (not including protective earths):

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• first method
• double wire along the sequence of switches
• single wire from the first switch to mains
• single wire from the last switch to the load
• single wire (neutral) from load to mains
• second method
• double wire along the sequence of switches
• single wire from first switch to last switch
• single wire from anywhere between two of the switches to the mains
• single wire from anywhere between the same two switches to the load
• single wire (neutral) from load to mains

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