Power Keeps Tripping? MCB vs RCCB and How to Find the Cause

Look for the lever that is down or halfway: it shows whether one circuit, leakage or the whole flat's load is the problem.

Note which lever dropped first; resale flats often lack labels. In some older flats not every circuit runs through the RCCB, and some newer boards use RCBOs, which do both jobs on one circuit.

If nothing is down and your neighbours are dark too, report it to SP Group's 24-hour supply line on 1800 778 8888 (SP Group: 24-hour hotline). See who to call for an HDB power trip.

Most repeat trips trace to one appliance, one damp fitting or one overloaded circuit. When it trips tells you which.

EMA and HDB say leakages are "caused by ageing or exposed wires, faulty electrical appliances, and damaged insulation" (HDB: RCCBs required in all homes). In most HDB flats the usual suspects are the water heater element, the washing machine, an old fridge, yard sockets after rain, and ceiling lights below a leak from upstairs. HDB puts PVC cable life at about 25 years, so original wiring in older flats is more prone to faults.

Separate guides cover a water heater that keeps tripping, an oven or kettle that trips the power, and why power trips at night.

Switch every single-pole MCB off, reset the RCCB or main switch, then switch the MCBs back on one at a time.

1. Unplug heavy appliances such as the kettle, oven and washing machine.
2. Switch all single-pole MCBs to off.
3. Push the RCCB, or the main switch, back up.
4. Switch the MCBs on one at a time, a few seconds apart.
5. When a switch trips, the circuit you just switched on is the faulty one. Switch its MCB off.
6. Unplug everything on that circuit, switch its MCB on, then plug appliances in one at a time.
7. If it trips with nothing plugged in, or when one appliance goes in, leave that circuit off or that appliance unplugged until checked.

If the RCCB won't stay up even with every MCB off, the fault is in the RCCB, the wiring before it, or a neutral fault a single-pole MCB can't cut off. Stop there.

Mistakes that make things worse:

• Resetting again and again while the fault is still there.
• Taping or holding the lever up.
• Fitting a higher-rated MCB so it stops tripping: it no longer protects the cable.
• Running a water heater off an extension cord: the Consumer Product Safety Office says it needs a double-pole switch wired by a licensed electrical worker (CPSO: Water heater safety).

Sometimes. An RCCB that doesn't switch off when you press its "T" button may be defective, and HDB says to have a licensed electrician replace it.

HDB advises testing the RCCB monthly: switch off computers, press "T", and the power should cut; then push the lever back up. Since 1 Jul 2023, EMA requires 30 mA RCCB protection on a home's socket and lighting circuits (EMA Circular RD/E01/2023); the device is marked "0,03A".

An RCCB usually trips between half and all of that rating, so small leaks from many appliances can add up with no single faulty item. An ageing RCCB can also nuisance-trip or, worse, fail to trip; the monthly test checks this. If an electrician finds every circuit healthy but it still trips, the RCCB is the likely suspect; see RCCB tripping but not the MCB.

Replacing it isn't DIY. The Ministry of Trade and Industry (MTI) states that all electrical works, including installing wiring and RCCBs, must be done by a licensed electrical worker (MTI: Electrical Installations Regulations reply). Have a faulty one replaced rather than bypassing it; see circuit breaker and DB services.

SG QuickFix diagnoses power trips from $80. Repairs and parts are priced separately.

Concealed or false-ceiling wiring and DB rectification raise the price. For an accurate price, send a photo of the DB box showing which lever is down and note what was running. See the full electrician price list for Singapore.