1. Know what you are testing
RCD stands for residual current device. You will usually find one in the consumer unit, sometimes still called the fuse box.
Look for a switch with a small button marked T or Test. There may be more than one, and one RCD may only protect part of the home.
2. Pick a sensible time
Testing an RCD should briefly switch off the circuits it protects. That means lights, Wi-Fi, clocks, boilers, fridges, freezers, or computers may lose power for a moment.
Do it when it is safe to have a short power cut. Save work on computers first. Let anyone else in the house know, too. Saves a bit of shouting from the next room.
3. Do not remove covers or touch wiring
This check only uses the test button on the front of the device. Do not remove the consumer unit cover, loosen screws, touch exposed wiring, or use tools inside the board.
If anything looks burnt, cracked, loose, wet, or damaged, stop there and get advice from a registered electrician.
4. Press the Test button
Press the button marked T or Test. The RCD should trip straight away and switch off the electricity to the circuits it protects.
If nothing happens, do not keep holding the button down. That said, check you are pressing the correct test button, then get proper electrical advice if it still does not trip.
5. Reset the RCD
Once it has tripped, move the switch back to the on position. Some switches need to be pushed fully off before they will reset, so follow the instructions on or near the consumer unit if they are there.
If it will not reset, or trips again straight away, leave it off and get help. There may be a fault on an appliance, circuit, or the RCD itself.
6. Check what has come back on
After resetting, check that the expected lights, sockets, boiler controls, fridge, freezer, and other important items are back on.
If something has not come back, do not start taking the consumer unit apart. Check the obvious switches first, then call someone qualified if you are unsure.
7. Test it regularly
Many consumer units have a label saying to test RCDs quarterly. Some newer safety guidance refers to at least every six months, and manufacturer instructions can vary.
The practical rule is simple: follow the instructions on or near your consumer unit. If there are no instructions, ask a registered electrician what is right for your installation.
When to call an electrician
Call a registered electrician if the RCD does not trip when tested, will not reset, keeps tripping, looks damaged, smells hot, buzzes, or protects circuits you cannot identify. RCDs are there for safety, so this is not one to bodge.
Not sure what you are looking at?
Richard can help with small electrical jobs and practical checks, but RCD faults and consumer unit issues should be handled by a registered electrician.
Contact Richard