How do I test the RCCB in my DB box?

How to test an RCCB step by step

Your RCCB is easy to spot once you know what to look for: it is the switch with a small button labelled "Test". EMA says it usually sits in the distribution board, or DB box, and advises testing it once a month. Unsure which switch is which? Learn to read your DB box first.

1. Warn the household. Tell everyone the power will go off briefly, so nobody gets caught in the middle of a shower.
2. Save your work. Save files on desktop computers and anything else without a battery, since they shut down when the power cuts.
3. Reach the switches. Swing open the hinged front door of the DB box. Leave any screwed-on cover alone and never touch the wiring.
4. Press Test once. Give the RCCB test button one firm press. The lever should snap down to off and the power should cut.
5. Switch it back up. Push the lever back to on. Power should return straight away.
6. Reset the clocks. Set the oven, microwave and digital clocks again, and check the fridge and router have restarted.

What an RCCB does

EMA explains that an RCCB cuts off electricity when it detects a current leakage that may lead to an electric shock. The causes EMA lists are everyday ones: ageing or exposed wires, faulty electrical appliances and damaged insulation. A kettle with a split cord is exactly the kind of fault it is there to catch.

Having one is not optional. EMA says all residential premises must have an RCCB or ELCB with a rated residual operating current not exceeding 30mA. HDB flats built before 1985 did not come with one unless the owner installed it later, and owners without one should engage an LEW to install it.

If your switch or your contractor uses the older name, ELCB (earth leakage circuit breaker), nothing changes. The elcb test is the same: one press of the Test button, then switch it back on.

If the RCCB does not trip

A switch that stays up when you press Test has failed at the one job it exists for. EMA's Inspectorate Department advises engaging an LEW if your RCCB does not trip when tested. Until it is checked, avoid using the circuits it covers, especially in the bathroom and kitchen.

EMA says electrical work in an HDB flat needs a Licensed Electrician, the class of LEW approved for loads of up to 45kVA. For a landed house, the same page points you to a Licensed Electrical Worker.

When you book a Licensed Electrician, EMA's Inspectorate Department suggests checking that the person coming is an LEW, asking to see the licence card on arrival and getting quotations from a few LEWs to compare price and scope.

If it trips often

An RCCB that drops every few days, or after every heavy downpour, is pointing at a problem. EMA's Inspectorate Department says to engage an LEW if it trips often with no obvious cause. A few notes from you beforehand help the LEW trace the fault.

As a practical step, switch off and unplug the appliances on the affected circuits, then push the RCCB back up once. If it holds, plug things back in one at a time. If it drops as one appliance goes back in, leave that one unplugged and have it checked. If it trips with everything unplugged, or drops again as soon as you reset it, leave it off and call a Licensed Electrician.

Jot down the time, the weather and what was running each time it trips. If the trips bunch up on rainy days, mention it. Our guide on why an ELCB keeps tripping covers more causes to discuss with the LEW.

Other checks to do while you are there

Once the test is done and the DB box door is shut, spend a few minutes on the rest of the home. EMA's Inspectorate Department advises against using appliances with damaged or exposed cables and against overloading circuits with multi-plugs, and suggests looking for the SAFETY Mark.

• Cords. Switch off at the wall and unplug before you handle the kettle, iron or hair dryer cord, as EMA's safety advice reminds you. Stop using anything with a split or exposed wire until it is repaired.
• Multi-plugs. Look behind the TV console and study desk for one multi-plug feeding another. Our power strip overload guide explains what to look for.
• New buys. Look for the SAFETY Mark when you shop for electrical products.

For a fuller walk-round, work through our home electrical safety checklist.

When there is no power at all

Sometimes the trouble is not the RCCB at all: the whole flat goes dark. If every switch in the DB box is still up, the fault may lie outside your home, so contact SP Services about the supply. If a switch has dropped, follow our guide to no power in the whole flat before resetting anything.

Questions