1 Switch off mains power
Isolate the power to the lighting circuit you are working on. You will need to examine the existing switch in order to find out the type of wiring that feeds it so you can buy the correct dimmer switch to accommodate it.
2 Mount the wall box
The dimmer switch must be mounted into a flush-mounted metal wall box. If you are replacing a surface-mounted switch, you will have to cut out a recess in the wall that is deep enough to hold the box so it is flush with the wall surface.
3 Make good the surrounding area
Make sure that the flush metal box is free from dust, plaster debris and projecting screws in the central area of the box. Make good the wall area around the box as required.
4 Install the dimmer switch
Make sure that no wires are trapped between the plate and the box. In the case of brass or chrome plates, a PVC shield must be fitted between the plate and the wall, and the earth lead on the plate must be connected to the earth terminal in the box.
5 Fix the faceplate
Using the screws provided, attach the faceplate. Don’t over tighten the screws. Replace the circuit fuse and test the dimmer. Don’t worry if you hear a faint buzzing sound from the dimmer switch – this is from the radio interference suppression coil fitted in it.
The metal plates of brass (and chrome) accessories MUST be correctly earthed. Connect the fixed earth wire to the earth terminal provided on the accessory/metal plate and then connect a short length of wire from this terminal to the terminal in the wall box. Bare earth wires must be sheathed in green/yellow sleeving.
Don’t connect a brass fitting to a cable that has only two wires.
Don’t connect a brass fitting to a plastic surface-mounted box.
Don’t underload or overload a dimmer switch.