Do I need Part P notification for this work?

Part P applies to fixed electrical installations in dwellings in England and Wales. Notifiable work includes new circuits, work in special locations (bathroom, outdoors), and consumer unit changes. Like-for-like replacements and additions to existing circuits outside special locations are usually not notifiable. If in doubt, ask a registered electrician before starting.

Do I have to isolate the circuit before starting?

Yes. Always switch off the relevant circuit breaker at the consumer unit and confirm dead at the work position with an approved voltage tester — not a neon screwdriver. Safe isolation is the first step for any live electrical work under BS 7671.

How long does this job usually take?

Straightforward domestic electrical jobs of this type typically take 30 minutes to 2 hours for a competent DIYer with the right tools, longer if unexpected issues surface (missing earths, corroded terminals, cable routes that turn out to be more difficult than expected). A qualified electrician will usually do the same work faster.

When should I call a qualified electrician instead?

Call an electrician if the work is Part P notifiable and you are not registered, if you find rubber or cloth insulation on the cables, if there is no earth where one is expected, if you cannot confirm the circuit is dead, or if the job turns out to be more complex than expected once you open up the fitting. Cost of a callout is small compared to the risk of unsafe work.

How to Fit a 2-Gang Dimmer Switch (UK)

Helpful video reference. We use GSH Electrical's "How to Fit a 2 Gang Dimmer Switch — Connections Explained" (February 2025) as the video reference here. GSH Electrical are UK electrical college lecturers who get the specifics right: consumer unit isolation, current cable colours and exactly why LED compatibility has to be confirmed before you buy the dimmer.

Before you start. A 2-gang plate often feeds two separate lighting circuits. Switch off both circuit breakers at the consumer unit and test every terminal dead with an approved voltage tester — not a neon screwdriver. If both breakers are on the same MCB, one test is enough, but confirm it serves both gangs by checking at the plate.

1. Isolate at the consumer unit

Find the lighting circuit breaker (or breakers) for the room. Switch them off and, if your board has a locking hasp, use it. Go to the switch position and test line, neutral and earth with an approved voltage tester. All dead in both positions of the existing switch? Good. Write on a sticky note what you have turned off and put it on the consumer unit door — stops someone restoring power while you are working.

2. Photograph the existing wiring

Unscrew the two faceplate screws and ease the plate forward until the conductors are visible. Take a clear, well-lit photo of the full back box and at least one close-up of each terminal. If a conductor moves during the job, your photo is what you refer to. Do this before removing a single wire.

3. Check dimmer compatibility

Read the dimmer's data sheet before opening the packaging. It will list the load types it supports (LED, halogen, low-voltage) and the wattage range per gang — typically 10W to 250W for LED. A dimmer designed for halogen will often not dim LEDs, or will buzz and flicker at low loads. If your lamps are LED, buy a dimmer labelled for LED first. Check it covers the wattage of the lamps on each circuit before starting.

Also check: some 2-gang dimmers are two independent modules on a single plate. Each module has its own wattage limit and you wire them exactly as you would two separate single-gang dimmers.

4. Remove the old plate and identify each gang

With the plate free from the back box, identify which conductors belong to Gang 1 and which to Gang 2. In a one-way circuit (one switch, one light) there will be two conductors: COM and L1. In a two-way circuit (two switches, one light) there will be three: COM, L1 and L2. Your reference photo shows you the layout. In a 2-gang plate, the cable for Gang 2 is usually a second twin-and-earth or 3-core cable entering the back box alongside the first.

5. Wire Gang 1

Follow the dimmer manufacturer's wiring diagram for the first module. For a one-way circuit: COM receives the switched live (the brown conductor from the cable), and L1 goes to the load. For a two-way circuit: COM is the common, L1 and L2 are the travellers. Insert each conductor into the correct terminal and tighten it firmly — give each a light tug to confirm it is seated.

6. Wire Gang 2

Repeat exactly the same process for the second gang using its conductors. Keep Gang 1 and Gang 2 conductors entirely separate at every step. Do not share a terminal between gangs and do not let conductors from different gangs touch inside the back box.

7. Check the earth connections

In a metal back box, a flying earth tail must connect the box's earth terminal to the earth terminal on the dimmer plate. In a plastic back box that requirement does not apply to the box itself, but any CPC conductor entering the box must still be connected to the plate earth terminal. If the back box has no earth where one is expected, stop and call an electrician — the circuit may lack a CPC entirely.

8. Refit and test

Fold the cables gently into the back box. Do not trap any conductor insulation under the edge of the plate. Refit the two faceplate screws evenly so the plate sits flush. Restore the circuit breakers. Test each gang independently: dim up, dim down, switch off. If either gang flickers or cannot be switched off fully at the lowest setting, consult the dimmer's minimum load instructions — some dimmers need a bypass capacitor with very low lamp loads.

Stop and call an electrician if: a circuit stays live at the plate after you switch it off at the consumer unit; there is no earth in the back box where one is expected; the cable uses rubber or cloth insulation (this is old wiring that needs specialist attention); or the dimmer buzzes persistently or the lamps flash after fitting and adjusting the minimum load setting.

When to call us

A dimmer swap is usually a short job. It gets longer when you discover missing earths, oversized back boxes to replace or circuits that turn out to be two-way when you expected one-way. Richard handles lighting jobs in Sandwich on the small-job rate — worth a call if the job looks more complicated once the plate comes off.

Need a dimmer fitted in Sandwich?

Richard fits switches, dimmers and smart switches on local jobs. Small jobs are billed at the £10 per 10-minute rate.

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How to fit a 2-gang dimmer switch