Domestic Electrical Alterations

Changing a light switch should be quite straightforward. However, as I found out last week some dimmer switches have new terminal layouts. So it’s not just a case of changing wire for wire. Secondly the new dimmer switch I was changing was brass, and unlike the plastic one I was replacing it needs to be earthed. Like many DIYers, the householder hadn’t know this!

Most new light sockets are supplied with instructions with details of how to perform the installation properly, but please bear in mind that the installation and testing of any electrical equipment must comply with the appropriate British Standards. New legislation is being introduced in January 2005 to restrict the electrical jobs that non-qualified persons can undertake, so if you are unsure of your own ability please call in the experts!

To point you in the right direction I have noted down step-by-step procedures I follow when dealing with any electrical installation. Firstly, it is important to ensure that the power supply to the switch is turned off at the main fuse box (CU). If I am working on a light, I use the following routine when turning the power off: -

• Turn the light on
• Remove the fuse for that circuit or switch off the MCB to the circuit
• Check that the light has gone out and make sure that nobody will be able to turn the circuit back on
• Work as though the power is still on – do not touch bare wires or terminals and use an insulted screwdriver

When this has been done, I replace the wires into the same terminal on the new switch. For example L1 to L1, L2 to L2 and Com. (short for common) to Com. If the switch is to be removed for any length of time, I make a note of which colour wires went where. The biggest difficulty when fitting a dimmer switch is that it takes up a lot more space than an ordinary switch - it is often difficult to get the new switch into the existing back-box.

Changing a 13 amp socket outlet is easier than changing a light switch. Switch the circuit off following the same procedure as for lights - plug a table lamp into the socket and check that it goes out when the fuse is removed or the MCB switched off.

There are three different colours for wires on a socket outlet: -

• Red goes to L (live)
• Black goes to N (neutral)
• The bare wire covered with yellow/green sheathing is terminated on the earth terminal.

There should also be a yellow/green, sheathed earth wire in the earth terminal of the metal back-box. It is important that all (this may be 1, 2 or 3) of the black wires go to the neutral terminal; all the red wires go to the live terminal and all the earths go to the earth terminal. If you are doing this job, I recommend you invest in a socket tester that plugs into the socket outlet and indicates if it is wired correctly or not. (These are available from FOCUS.) If possible, test the circuit before you remove the old socket - this will prove it is okay before you start work.

This is a very simplistic account. To make sure switches or sockets are wired correctly, follow the instructions with the fitting and use a good manual for guidance. Please work safely and, if you are in doubt, ask any qualified electrician to help.