Changing a light switch is a job which nearly any competent do-it-yourselfer can do but there are a couple of things to watch out for.
Please bear in mind that in the UK it is illegal to work on any part of the electrical installation in a kitchen or bathroom without notifying the local authority or employing a Part P registered electrician.
When you decide to change a light switch you must consider the circuit that the switch is on. Prior to the mid 1960’s lighting circuits rarely incorporated an earthing conductor, properly called a circuit protective conductor (cpc).
If you have an electrical installation in which the lighting cables do not incorporate a cpc. then you must not replace any plastic light switch with a metal one such as brass or steel. It would be extremely dangerous to do so.
Next you will have to ascertain what type of switch you are changing.
A switch plate which has only one switch is called a one gang or single switch. One plate with two switches is called a two gang and so on.
There are basically three types of light switch, a one way switch, a two way switch and an intermediate switch. All switches are rated at either 6 or 10 amps.
A one way switch operates a light or lights from one position, normally by a door. A two way switch will have a partner so that a light can be turned on and off from two positions, say, by the kitchen door and the back door. An intermediate switch is used when the light has to be turned on and off from three positions or more.
A one way switch will have two terminals on the back for the cable connections, a two way will have three and an intermediate will have four.
To change the switch, first turn on the light and then take out or turn off the fuse or mcb, this will ensure you have the right circuit. Put the fuse in your pocket or tape down the mcb so that it cannot be re-energised.
Remove the switch plate from the wall by removing the two screws and pull it gently towards you. You will now see the connections in the back.
Now is a good time to make a note or sketch of where the cables are connected. If you have a similar switch the terminations will be a straight replacement but if it looks different then make these notes.
The majority of switches follow the same format for marking. ‘C’ for common, L1 and L2 for the others. One a one way switch the common will be the red/brown wire and L1 will take the black/blue wire with a short identifier of brown or red sleeving or tape.
With a two way switch it is not uncommon to have five wires connected into the back. Making a note is strongly recommended. The five wires will be split up into two pairs and a common. The two pairs can go into either L1 or L2, it does not matter but the single wire must go into the common or the switch will not work correctly.
When you first remove the switch you may notice some blue or black wires connected into a block, these are the neutrals and must not be connected to the other live wires or you will cause an electrical short and a small bang.
The earth or cpc wires can be left alone also unless you are fitting a metal switch in which case you must make a connection to the plate to the terminal provided. This can be achieved with a short piece of copper wire, preferably sleeved with green and yellow sleeving.
When you have made all the connections and are satisfied that they are correct replace the switch onto the box, ensuring that all the wires are pushed away from the screw positions and screw it down securely.
Follow these tips and changing a light switch will not seem to be that difficult again.