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How-to · UK domestic

How to test the RCD in your consumer unit

Your RCD (or individual RCBOs) is the device that saves you from a serious shock when a cable or appliance goes wrong. It should trip within 40 ms of a 30 mA leak to earth — but that only matters if it still works. Test it every three months. It takes a minute.

Ask about an EICREICR reports

Helpful video reference. The embedded video shows a standard UK consumer unit test-button check. It covers what to expect when the button is pressed, and what is actually going on behind the plastic when it trips. Quick watch before your first quarterly test.

What this test does. The test button on an RCD simulates a small earth fault inside the device and lets you confirm the mechanical trip still releases. It does not measure trip current or trip time — that is what an electrician does with an RCD tester at an EICR. Both matter, in different ways.

1. Save anything important first

The RCD will drop its side of the board for a moment. Computers will restart, Wi-Fi will blink, fridges will restart — nothing serious but worth knowing. Desktop saves, game saves, a downloading laptop — close them all.

2. Find the test button

Open your consumer unit cover. On older boards there is usually one RCD on the left or the right, with a small button marked T. On modern boards with RCBOs, each circuit has its own test button on its own breaker.

3. Press and watch

Press the test button firmly. The switch should snap to the OFF position immediately. If it does not, press once more, a proper firm press — some get stiff over the years.

4. If it trips

Push the switch back up to ON. Power returns. Job done for three months. Make a note on the inside of the consumer unit door with the date.

5. If it does not trip

This is the one that matters. A test button that does not trip is a broken RCD. Do not use that part of the installation until it is replaced. Call an electrician the same day.

Also call an electrician if: the RCD trips during the test but will not reset; the RCD trips every time something specific switches on; the button feels floppy or broken; or the consumer unit is warm to the touch. None of these are "test in a month's time" — they are "today, please".

When a full EICR is due

The quarterly test button check is yours. A proper EICR with instrument-measured trip times every 5 years (private rented) or 10 years (owner-occupied) is the electrician's job. In Kent that is £140 for a standard three-bed domestic.

RCD not tripping on test?

Call Richard the same day. It is a short job to replace and re-test.

Contact Richard

Related pages

Reset a tripped breaker EICR reports Fuse box replacement Change a light switch