How to change a light switch to dimmer

This step-by-step guide provides detailed information on how to complete a task.

It includes a list of tools and materials needed for the task.

Please be advised that this is only a guide and I cannot accept responsibility for any work undertaken. If you are not confident undertaking electrical work then you should have this work undertaken by a qualified electrician.

Tools and Materials

Dimmer switch (compatible with your light fixtures and wattage). If unsure open up switch as in step 3 and check to see what the switch looks like at the back and then purchase the same.
Screwdriver (usually a flat-head or Phillips, depending on the screws)
Voltage tester (optional but recommended for extra safety)

Step by Step Guide

Turn off power

Turn off the power to the circuit you’ll be working on. Locate the correct circuit breaker in your fuse board and switch it off. The circuit breakers should be labelled, if not it will likely have a 6A or 5A written on it but you may need to try a few to find the right one, so have the light on to know when off.

Open up the old switch

Unscrew the screws holding the old switch to the electrical box with a screwdriver and keep the screws as you may need to reuse with the new dimmer switch. Gently pull the switch out, exposing the wiring behind it.
Once wires are exposed double-check to be sure it’s safe to proceed by using a voltage tester to verify that there is no electricity running through the wires.
One probe touching the earth wire and the other probe touching the top terminal.
One probe touching the earth wire and the other probe touching the bottom terminals.
One probe touching the top terminal and the other probe touching the bottom terminals.

Identify the wires

Take note of the wiring connections. You should typically see 1-3 cables; all should have three wires unless it is a two-way switch with that cable having 4 wires. The colours for two-way switches are brown (usually Live), black (usually Live), grey (usually Neural) and green and yellow (Earth). These wires should usually have coloured sleeving on them to match the other wires to identify them. The other cables will have a Live (red or brown), a Neutral (blue or black), and an Earth (green and yellow). In some cases, the neutral might be grouped together separately and not visible, don’t worry as you won’t need to do anything with them.

Prepare new dimmer switch

Check the instructions that come with the dimmer switch.

Disconnect old switch

It’s essential to keep track of which wire goes in what terminal (Common (Com), L1 or L2) as you will need to replicate for the new dimmer switch, a good way to is to take a picture on your phone. You may also want to mark the wires that are grouped together in the same terminal with a pen or some electrical tape.
Loosen the terminal screws connecting the wires to the switch and remove the wires. Sometimes I remove the wire/wires from one terminal (Com) and put straight into the dimmer switch Com terminal to help make sure you replicate the wire arrangement, doing this for all the terminals.

Connect dimmer switch

Make sure the wires are securely connected to their respective terminals, you may want to refer to your picture at this step. To check you have done correctly you should see minimum copper (if any at all) making sure you have tightened onto the copper and not the insulation.
Tighten the terminal screws to hold the wires in place. Do a tug test to ensure they cannot come out.

Secure dimmer switch

Gently push the wires back into the electrical box and align the dimmer switch with the screw holes. Use screws to secure the dimmer switch to the box, you may need old screws if new screws do not fit.

Install dimmer switch cover

Attach the dimmer switch cover plate over the dimmer switch if applicable.

Turn on the power

Go back to the fuse board and turn the power back on for the circuit you worked on.

Test the dimmer switch

Turn on the light and check if the dimmer switch is functioning correctly. If everything is working fine, you have successfully installed the dimmer switch. If the circuit breaker trips you have a fault or not working properly, best to contact an electrician.

To learn how to install a light fitting – click here

CONGRATULATIONS YOU HAVE COMPLETED IT!

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