Quick answer
When the RCCB trips but no MCB does, current is leaking to earth: a few milliamps, too little for an MCB. In Singapore it's often a water heater or damp socket. Unplug everything, switch MCBs off, reset the RCCB and turn MCBs on one by one; stop if it trips with all off. SG QuickFix diagnoses power trips from $80.
SG QuickFix pricesTap to WhatsApp
| Power trip diagnosis | From $80 |
| Appliance-related trip diagnosis | From $80 |
| Circuit fault tracing | From $100 |
| Complex concealed wiring fault | Quote after diagnosis |
Current SG QuickFix starting prices. Final price confirmed before work begins.
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Why does my RCCB trip but none of the MCBs?
An RCCB-only trip means current is leaking to earth: a few milliamps that the RCCB detects but an MCB never notices.
An MCB trips "in the event of overcurrent due to an overload or short-circuit". The RCCB "automatically cuts off electricity in your flat when it detects an earth current leakage" (HDB: Electrical accessories and wiring).
The RCCB compares the current going out on the live wire with the current returning on the neutral. If some escapes to earth, through damp, worn insulation or a person, the two stop matching and the RCCB trips. Since 1 Jul 2023, the Energy Market Authority (EMA) requires 30 mA RCCB protection on a home's socket and lighting circuits (EMA Circular RD/E01/2023); such a breaker is marked "0,03A". An MCB is rated in whole amps, hundreds of times more, so the same leak never registers on it.
A joint EMA and HDB release names ageing or exposed wires, faulty appliances and damaged insulation as the usual causes of leakage (HDB: RCCBs required in all homes). Treat a trip as a warning: the leak may lead to an electric shock. Earth leakage and power trip diagnosis finds the circuit, then the appliance.
How do I find which circuit is leaking?
Unplug everything, switch the outgoing MCBs off, reset the RCCB, then switch MCBs on one at a time until it drops.
- Unplug appliances, and switch off the water heater's double-pole switch and the aircon isolator.
- Switch off every narrow outgoing MCB, and the household shelter's switch if fitted. Leave the main switch on.
- Push the RCCB up, then switch the MCBs on one at a time.
- When the RCCB drops, switch that MCB off, reset the RCCB and turn the other MCBs back on.
- Turn the suspect MCB on and plug its appliances back in one at a time.
Don't keep resetting a leaking circuit; it won't clear the fault. The general routine for any tripped switch is in the guide on why the power keeps tripping.
What does it mean when the RCCB trips at each step?
Where the RCCB drops shows where the leak is.
| What happens | What it usually means | Next step |
|---|---|---|
| It trips when one MCB goes on, with nothing plugged in | Leakage in that circuit's wiring, a light or fan, or a hard-wired water heater or aircon | Leave that MCB off and have the circuit traced |
| It trips when one appliance is plugged in or heats up | Leakage inside that appliance, often a heating element | Stop using it until it is checked or replaced |
| Each circuit holds alone, but two on together trip it | A neutral touching earth on one circuit, or small leaks adding up | Leave one of the two off and have both checked |
| It trips with every outgoing MCB off | A faulty RCCB, a fault between the RCCB and the MCBs, or a neutral-to-earth fault | Stop resetting and call a licensed electrical worker |
| It trips at random, with no pattern | Small leaks adding up, damp after rain, or an ageing RCCB | Note the time, weather and what was running |
A switched-off circuit can still trip it because HDB flats use single-pole MCBs, which switch only the live wire; the neutral stays connected. A neutral touching earth in a damp socket box or nicked cable can still divert current past the RCCB's sensor.
Random trips often come from cumulative leakage. Desktop computers, TVs, fridges and washing machines each leak a little to earth by design. A 30 mA RCCB may trip at anything above 15 mA, and most trip at around 18 to 23 mA (IET guidance), so several healthy appliances plus one slightly damp fitting can be enough. An electrician measures the standing leakage and may split circuits across a second RCCB or RCBOs.
Which appliances and fittings leak most in HDB flats?
Heating elements and anything near water leak most often: the water heater, washing machine, kettle, oven and fittings exposed to rain.
- Water heater: a worn element or damp terminal is the most common culprit. More in the guide to a water heater that keeps tripping. The Consumer Product Safety Office says it should be wired by a licensed electrical worker through a double-pole switch, not a 3-pin socket (CPSO: Water heater safety).
- Washing machine and dryer: heaters and motors near water.
- Kettle, oven, rice cooker and air fryer: ageing elements absorb moisture, so they often trip on first switch-on. More in the guide to an oven or kettle that trips the power.
- Fridge: an old compressor or defrost heater.
- Yard, balcony and window-side sockets and lights, and aircon wiring: trips after heavy rain point here. Storm trips are covered in a power trip during a thunderstorm.
- Ceiling lights under a leak from upstairs, and cables nicked by drilling during renovation.
HDB puts PVC cable life at about 25 years, so ageing original wiring commonly leaks.
Is the RCCB itself faulty, and how do I test it?
An RCCB that doesn't switch off when you press its "T" button is faulty. One that trips with every outgoing MCB off may be, too.
HDB advises switching off computers first. Then follow EMA's 3-step test (EMA: How to test your RCCB):
- Press the test button. The RCCB should flip down; if it doesn't, it is faulty.
- Try every light and socket. If any still works, your home is not fully protected.
- Push the RCCB lever back up.
If step 1 or 2 fails, call a licensed electrical worker.
An old RCCB can also nuisance-trip. Before replacing it, an electrician checks its trip current and time with an RCD tester, and tests the wiring's insulation.
Never bypass the RCCB, tape its lever up or fit a less sensitive 100 mA unit: each removes the shock protection. EMA says a faulty RCCB must be repaired or replaced by a licensed electrical worker (EMA: Faulty RCCBs); see RCCB and DB box services.
How much does it cost to trace earth leakage in Singapore?
SG QuickFix's power trip diagnosis, which traces the leaking circuit, costs from $80. Repairs, parts and any RCCB replacement are priced separately.
| Job | When you need it | SG QuickFix price |
|---|---|---|
| Power trip diagnosis | The RCCB keeps tripping and you can't find the cause | From $80 |
| Appliance-related trip diagnosis | The trip follows one appliance | From $80 |
| Circuit fault tracing | One circuit trips with nothing plugged in, or only with another circuit on | From $100 |
| Complex concealed wiring fault | A damp, drilled or aged cable inside a wall or ceiling | Quote after diagnosis |
| Distribution board troubleshooting | It trips with every outgoing MCB off | From $100 |
| RCCB / RCD replacement | The RCCB fails its test, or trips after the wiring tests healthy | From $180 |
Concealed or false-ceiling wiring, intermittent faults and DB work raise the price. For an accurate price, send a photo of the DB box with the RCCB down and say which result above matches. See the full electrician price list for Singapore.
| Safe to DIY if… | Call a professional if… |
|---|---|
| The RCCB stays up once you unplug one appliance | It trips when one MCB goes on with nothing plugged in |
| You press "T" monthly and every light and socket goes off | A light or socket still works while the RCCB is down |
| You leave a circuit off until it's checked | It trips at random with no pattern |
| Don't bypass, tape up or swap the RCCB, or remove the DB box's inner cover | You see water, scorch marks or smell burning near a socket or the DB box |
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Electrical Troubleshooting / Power Trip
From $80
- Fault finding
- Short-circuit repair
Electrical Troubleshooting / Power Trip FAQs
A standard RCCB reacts to earth leakage, not to overload; overload and short circuits are the MCB's job. A fault from the live wire to earth is also leakage, so the RCCB may trip on that first. An RCBO combines both jobs in one breaker for a single circuit.
An RCCB that trips with nothing plugged in usually points to the fixed wiring or a hard-wired load, such as a water heater, aircon, light or ceiling fan, or to water in a socket box or light fitting. Switch off the heater and aircon isolators and retest once; if it still trips, call a licensed electrical worker.
No. HDB's RCCB FAQ says homeowners found with a faulty RCCB will not be penalised. Every Singapore home must still have an RCCB or a working ELCB, so have a licensed electrical worker replace a faulty one rather than removing or bypassing it.
No. The Energy Market Authority (EMA) says repair and replacement of RCCBs are not eligible for HDB's subsidised installation, which was for homes without an RCCB. A faulty RCCB in an HDB flat is repaired or replaced by a licensed electrical worker that the owner engages and pays for.
The RCCB sits in the DB box, usually near the main door or kitchen entrance, and is the switch with a test button. EMA says HDB flat owners who can't find it can call the HDB Branch Service Line on 6225 5432 for help.
RCBOs give each circuit its own leakage protection, so one leaking appliance cuts only its own circuit instead of the whole flat. They suit homes with frequent nuisance trips from cumulative leakage. Changing the DB box layout is work for a licensed electrical worker, who checks the board has room first.
An earth leakage fault in one appliance or one circuit is often found within about an hour. Intermittent trips, damp concealed wiring or a leak that only shows after rain take longer and may need a second visit, so those jobs are usually quoted after the first diagnosis.
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Sources & updates
- HDB: Home care guide, electrical accessories and wiring, checked 1 Oct 2026
- HDB: Residual current circuit breakers required in all homes (11 May 2023), checked 1 Oct 2026
- HDB: RCCB requirement FAQ (Annex C), checked 1 Oct 2026
- EMA (Ask Gov): How to test your RCCB, checked 1 Oct 2026
- EMA on Ask.gov.sg: What should I do if my ELCB or RCCB is faulty?, checked 1 Oct 2026
- EMA (Ask Gov): Locating the RCCB in an HDB flat, checked 1 Oct 2026
- EMA: RCCB rating example, checked 1 Oct 2026
- Consumer Product Safety Office (CPSO): Safety tips on water heaters, checked 1 Oct 2026
- Updated 1 Oct 2026: First published
Related guides
Why Does My Power Trip at Night? Common Causes in Singapore Homes
Power usually trips at night because something runs unattended (the aircon, a fridge's automatic defrost heater or a water heater left switched on) or damp reaches an outdoor point as humidity peaks before dawn. Note the time and which DB switch dropped each time. In Singapore, SG QuickFix diagnoses power trips from $80.
Updated 29 Oct 2026 · 7 min read
Power Keeps Tripping? MCB vs RCCB and How to Find the Cause
When power keeps tripping in a Singapore home, a DB box switch is cutting off a fault: an MCB trips on overload or short circuit, the RCCB on earth leakage. With dry hands, switch all MCBs off, reset, then turn them on one by one and leave off the one that trips. SG QuickFix diagnoses power trips from $80.
Updated 12 Oct 2026 · 7 min read
Power Trip During a Thunderstorm: Normal or a Fault?
An occasional power trip during a thunderstorm in Singapore is usually normal: lightning causes a brief leak the RCCB treats as a fault. Wait until the lightning passes, unplug electronics and reset once. If it trips every time it rains, water is reaching a socket, light or cable in your HDB flat. SG QuickFix diagnoses power trips from $80.
Updated 8 Oct 2026 · 6 min read
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This guide is general information for homes in Singapore. It is not professional, legal or safety advice for your specific situation. Electrical, gas and some plumbing work can be dangerous, and Singapore law requires certain jobs to be done by licensed workers. Any work you carry out yourself is at your own risk, and SG QuickFix accepts no responsibility for any loss, damage or injury arising from the use of this information. Prices shown are current starting prices, may change, and the final price is confirmed before any work begins. Rules and figures from HDB, PUB, EMA, SP Group and town councils were correct when last checked; please confirm with the relevant authority before acting.