How to replace a light switch

Introduction

Light switches are functional items, and many of the basic varieties (made from white plastic) can look a bit plain. However, replacing these with decorative switches can add a stylish finishing touch to your home. Or you could change an existing switch to give you convenient, multi-way control of a light in your hallway, landing or stairwell.


Never take risks with electrical safety. Before you start any type of electrical work, you must follow these following safety precautions:

  • Remember to switch off the mains power at the consumer unit/fuse box. Isolate the circuit you plan to work on by removing the circuit fuse. Put this in your pocket to avoid accidental replacement
  • Or switch off the breaker and lock it if you can
  • Attach a note to the unit to advise you are working on the circuit.
  • Check the circuit is dead with a socket tester or voltage tester/meter for lighting circuits. These confirm whether circuits are dead and safe to work on
  • Check all finished work with a socket tester (or voltage tester for lighting circuits) before using

For your safety, these products must be installed in accordance with local Building Regulations. If in any doubt, or where required by the law, consult a competent person who is registered with an electrical certification scheme. Further information is available online or from your local authority.

Be cautious when opening up multi-way switches. The lights they control should take power from the same circuit, but if yours are incorrectly wired and take power from different circuits, there will be live cables at each switch position when one circuit is isolated. There is more than one method of wiring multi-way lights. If yours does not match the system shown here, that doesn't necessarily mean they are unsafe.



Wall-mounted light switch fittings (known as 'plate switches') can contain one, two, three or even more individual switches (or 'gangs') that let you control a number of separate light fittings from one place. You can also get versions that give you two- and multi-way switching which allow you to control lights using two or more different switches, for example in a hallway.

There's a huge range of fittings available - from functional plastic to stylish metallic finishes. Dimmers let you to raise and lower the light level - and may have a combined or separate on/off and dimming control, so you don't have to readjust the light level every time you turn on the light. They're wired in much the same way as a standard switch.

Switches generally need a 16mm-deep mounting box - although some dimmers may need deeper boxes. Where your space is limited, or if you want a switch to be unobtrusive, you can fit narrow architrave switches into your door frames.

Building regulations require that only ceiling-mounted pull-cord switches are installed in bathrooms and shower rooms.


If a switch is damaged, or you just want to update your fittings, it's quite simple to replace it. Just make sure you write down exactly how the old switch was wired before you disconnect it, and wire the new switch in the same way. Also, try and keep hold of your original screws. You may have to re-use them, as modern fittings come with metric-sized screws and older fittings might have imperial threads.

Safety first - Earthing light switches

The commonest light switch combination is a metal mounting box and plastic faceplate. In this case, the earth core or cores must be connected to the earthing terminal of the mounting box. If you have a metal faceplate, the main earth core runs to the faceplate first. You'll then need to run a short length of earth core (cut from 1mm2 two-core and earth cable, and insulated with green/yellow sleeving) between the earthing terminals on the faceplate and the mounting box. If both your mounting box and faceplate are plastic and there's no earthing terminal, run green/yellow sleeving over the bare cores and clamp their exposed ends with a connector. That way, if you decide to change to metal fittings in the future, you'll be able to earth them safely and easily.

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Step 1

Isolate the circuit and confirm that the power is off with a voltage tester. Then unscrew the switch faceplate and pull it forward so you can see the connections behind. Draw a clear diagram showing the colour and number of wires connected to each terminal, then release the terminal screws and pull the cores from the terminals. If the earth core is properly insulated in green/yellow sleeving and connected to the mounting box, leave this attached.

Step 2

Connect the cores to the correct terminals of the new switch, and tighten the screws. Then check they're clamping the cable cores firmly by giving the wires a slight tug. If there isn't one already, fit a length of brown PVC sleeving over the blue core (or the black core if your wiring is in the old colours) to show it can be live.

Step 3

Run green/yellow PVC sleeving over the bare earth core of the switch drop cable, and connect it to the earthing terminal of the mounting box. If you're using a metal switch, make sure you earth the switch faceplate.

Step 4

Check again that each connection is secure, then push the cable back into the mounting box and fit the faceplate.


There are three key things you'll need to do if you want to change from one-way control of a light to two-way switching. Firstly, you must replace the original switch with a two-way fitting. Then you'll need to install a new two-way switch at the second control point. And after that, you should link the two with 1mm2 three-core-and-earth cable. Start by running the cable between the two switch positions and installing a mounting box at the new switch position.

Top tip - Multi-way switching

The connections in two- and three-way light switches are such that the circuit can be made or broken at any of the switch points. For this to be possible, you have to use cable with an extra core - so the current can run in various directions, along various routes. Because the brown, black and grey cores (or red, yellow and blue if you're using cable in the old colours) can all at times be live at a light switch, they must carry a warning flag of brown (formerly red) PVC electrical sleeving or tape.

Safety first - Working on multi-way installations

Be extremely cautious when opening up multi-way switches. The lights they control should all take their power from the same circuit, but if yours aren't wired correctly, and take power from different circuits, there will still be live cables at each switch position when one circuit is isolated. Be aware also that there's more than one method of wiring multi-way lights. If yours don't match the system shown here, it doesn't necessarily mean they're unsafe.

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Step 1

Isolate the circuit and double-check the power is off with a voltage tester. Remove the faceplate from the existing switch and disconnect the cable cores. You might find the switch has three terminals, which shows it's actually a two-way fitting - in which case you can reuse it.

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Step 2

Each two-way switch will have three terminals, arranged as a single and a pair. They'll either be labelled Common, L1 and L2, or L1, L2 and L3. At the original switch, fit a length of brown PVC sleeving over the blue core of the switch drop cable and the grey and black cores of the linking cable. This indicates that they can be live. Then connect the brown and blue cores of the existing switch drop cable and the black and grey cores of the new linking cable to the pair of terminals. Take the brown core of the linking cable to the single terminal. Then fit green/yellow sleeving over the bare earth cores and connect them to the mounting box earth terminal. If you're using metal switches, make sure you earth the switch faceplates.

Step 3

At the second switch, fit a length of brown PVC sleeving over the grey and black cores of the linking cable to show they can be live. Then connect the cores of the three-core-and-earth cable to the same terminals as the first switch. Fit green/yellow sleeving over the bare earth core, and connect it to the mounting box earth terminal.


You can control a light from more than two separate switch positions. The connections for wiring the first and final switches are the same as for two-way switching, but a special intermediate switch is wired into the three-core-and-earth linking cable between them.

An intermediate switch has four terminals. Fit a length of brown PVC sleeving over the grey and black cores, and connect the black cores to the top and bottom terminals on one side and the grey cores to the terminals on the other.

Join the two brown cores with an insulated strip connector. Fit the earth cores (protected by green/yellow sleeving) to the mounting box earthing terminal.