Electrical
How to replace a light switch safely (UK)
Swapping a like-for-like switch is a small job, but only after the circuit is isolated and proved dead. If anything behind the plate doesn't match what you expected, stop.
What you'll need
- •Approved voltage indicator and proving unit
- •Lock-off device for the consumer unit
- •Insulated screwdrivers
- •Phone camera for recording the existing wiring
Step by step
1Isolate and lock off
Turn off the lighting circuit at the consumer unit, lock it off and keep the key with you. Never rely on the switch itself.
2Prove dead
Prove your voltage indicator on a known live source or proving unit, test the conductors at the switch, then prove the indicator again. Only then start work.
3Photograph the existing wiring
Take clear photos before disconnecting anything. Note whether it's one-way (common and L1), two-way (common, L1, L2) or a loop-in arrangement with permanent live present.
4Transfer the conductors
Move one conductor at a time to the matching terminal on the new switch. Sleeve any blue or black conductor used as a switched or permanent live in brown. Check no copper is exposed beyond the terminal.
5Check the earth
A metal faceplate must be earthed, and the back box needs an earth connection. If there's no CPC in the box, don't fit a metal plate — that's a job for an electrician.
6Refit and test
Tuck the cables back without straining them, screw the plate on square, restore power and test the switch works from every position.
Common mistakes
- •Assuming the switch is dead because the light is off — loop-in wiring can hold a permanent live.
- •Fitting a metal plate with no earth available.
- •Loose terminals: a poor connection is a fire risk, not just an intermittent light.
When to get a second opinion
Work in bathrooms, new circuits and consumer unit work are notifiable under Part P in England and Wales. If you're unsure whether your job qualifies, check before you start.
Ask an experienced tradesperson