If your RCD keeps tripping, it has detected current leaking to earth, so something on one of the circuits it protects is faulty. The usual causes are an appliance with a worn heating element, water getting into an outdoor socket or light, or damaged wiring. Unplug everything, reset the RCD, then switch circuits and appliances back on one at a time to find the culprit.
An RCD that keeps switching off is frustrating, but it is doing exactly what it should. It is the safety switch in your consumer unit that protects you from electric shock and electrical fires. This guide explains how to tell what has tripped, a safe way to find the cause yourself, what the timing of the trips tells you, and when to stop and call an electrician.
What an RCD Does, and How to Tell It Has Tripped
An RCD (residual current device) constantly compares the current flowing out along the live conductor with the current coming back along the neutral. In a healthy circuit the two match. If even a small amount goes missing, 30 milliamps on a typical home RCD, it must be leaking to earth, perhaps through a damaged appliance, through water, or through a person. The RCD switches the power off in a fraction of a second, fast enough to greatly reduce the risk of a fatal shock.
Open your consumer unit (often still called the fuse box) and look for the switch that is down. There are usually three or four kinds:
| Switch | How to recognise it | What a trip usually means |
|---|---|---|
| Main switch | The largest switch, often red and labelled "main switch" | Rarely trips on its own. If it has, call an electrician |
| RCD | A wider switch with a test button marked T, often labelled 30mA | Current leaking to earth on one of the circuits it covers |
| Circuit breaker (MCB) | A narrow switch labelled with a rating such as B6 or B32 | An overload or short circuit on that one circuit |
| RCBO | A narrow switch with its own small test button | Earth leakage or overload, on that one circuit only |
In many homes one RCD covers several circuits, which is why a single trip can leave half the house without power. The fault is on one of those circuits, but not necessarily the one you were using when it went off. If the RCD trips and the circuit breakers stay up, you are looking for leakage to earth rather than an overload.
How to Find What Is Tripping Your RCD
You can carry out these checks safely without removing any covers. Never take the cover off the consumer unit, and never hold an RCD in the on position to keep the power on.
- Unplug everything on the affected circuits. Switch off and unplug appliances, and switch off the fused spurs that feed fixed appliances such as the boiler, extractor fans and the immersion heater.
- Switch off the circuit breakers the RCD covers. They are usually the breakers sitting next to it, on the same side of the board.
- Reset the RCD. Push it fully down, then firmly back up. If it will not stay on even with every one of its breakers off, stop here: the fault is likely in the RCD itself or the wiring close to the board, and you need an electrician.
- Switch the breakers back on one at a time. If the RCD trips as a particular breaker goes on, that circuit has the fault. Leave that one off and reset the rest so you have power back in the meantime.
- Plug appliances back in one at a time on the circuit that trips. When it trips again, the last thing you plugged in or switched on is the likely culprit. Leave it unplugged and have it repaired or replaced.
- If the circuit trips with nothing plugged in, the fault is in the fixed wiring, a light fitting or a fused spur. That needs an electrician with test equipment.
Our free tripping fault finder walks you through the same checks using the switches in your own fuse box.
What the Timing Tells You
When an RCD keeps tripping, the pattern of the trips is often the biggest clue to the cause:
| When it trips | Likely causes |
|---|---|
| As soon as you reset it, even with everything off | A fault in the fixed wiring, a faulty RCD, or a neutral touching earth somewhere in the installation |
| When one appliance switches on | A worn heating element or damaged lead on that appliance: kettles, washing machines, dishwashers, ovens and toasters are the usual suspects |
| At night or in the early hours | Something on a timer or cycle, such as an immersion heater on an off-peak tariff, a freezer defrost cycle or outside lights, or condensation forming as the temperature drops |
| In heavy rain or wet weather | Water getting into outdoor sockets, garden lighting, pond pumps, junction boxes or cables running through damp walls |
| Randomly, more often when lots is switched on | Small amounts of leakage from many electronic devices adding up on one RCD, common on older boards where one RCD covers half the house |
| Since new electrical work or a new light fitting | A wiring mistake in the new work, such as neutrals from two circuits connected together |
| During thunderstorms | Voltage surges on the supply. A surge protection device in a new consumer unit can help |
Keeping a note of the time, the weather and what was running when it tripped can save an electrician a lot of searching.
The Most Common Causes
Most cases of an RCD that keeps tripping come down to one of five causes.
Faulty appliances
Appliances that heat water or air are the most frequent cause. Heating elements can absorb moisture or crack with age, letting a little current leak to earth every time they warm up. A damaged lead, a cracked plug or a washing machine that has leaked onto its own wiring can do the same. If the plug-in test points at one appliance, stop using it until it has been checked.
Water and moisture
Water conducts, so anything outdoors or in a damp spot is a common source: outdoor sockets with the cover left open, garden and security lights, pond pumps, and supplies to sheds and garden offices, especially where the cable was never designed to be buried or left outside. Indoors, a leak from a bathroom or a water tank onto a ceiling light, or condensation in a loft junction box, can cause trips that come and go with the weather.
Damaged or ageing wiring
A screw or nail through a cable during DIY, rodent damage in a loft or under a floor, or old insulation breaking down can all let current leak to earth. These faults are inside walls and floors, so they need an electrician to find them with an insulation resistance test, circuit by circuit. Persistent tripping in an older property can be one of the signs your home needs rewiring.
Too much on one RCD
Many consumer units fitted in the 2000s and 2010s use one or two RCDs, each covering several circuits. Many computers, TVs, LED drivers and other electronics leak a tiny, harmless amount of current to earth by design, and across enough devices those amounts add up until the RCD trips with no single fault to find. It also means one faulty kettle can take out the lights, the fridge and half the sockets at once. A modern board with an RCBO on each circuit fixes both problems, because each circuit has its own protection. We fit these as part of our rewiring and consumer unit work.
A worn RCD
An RCD is a mechanical device and it can wear out. An old RCD can become oversensitive and trip with no real fault, or, more dangerously, become slow or fail to trip at all. Only a test with proper equipment shows how fast it is actually tripping.
How to Test Your RCD
Press the button marked T or Test on the RCD. It should switch off immediately, and you then switch it back on. The 2022 update to the wiring regulations, BS 7671, recommends doing this every six months. Pressing the button switches off everything on that RCD, so save your work and expect to reset a few clocks. If the RCD does not switch off when you press the button, it is not protecting you: get it replaced promptly.
When to Stop and Call an Electrician
- The RCD will not stay on even with all of its circuit breakers switched off.
- A circuit trips with nothing plugged in.
- You can smell burning, hear buzzing or crackling, or see scorch marks on a socket, switch or the consumer unit. Switch off at the main switch if it is safe to do so.
- There is water near any electrics, such as a leak through a ceiling light.
- The RCD does not trip when you press the test button.
- Your RCD keeps tripping after all of these checks, or the tripping has no pattern you can find.
An electrician will test the insulation of each circuit to find where the leakage is, check how fast the RCD trips, and look for faults such as a neutral touching earth that are impossible to spot by eye. Most faults are found on the first visit. If the board itself is the problem, we will explain the options and quote before doing anything.
If your power is off now in Tunbridge Wells, Tonbridge or the surrounding area, our emergency electrician service takes calls outside normal working hours. Ring 07756 626922 and we will confirm the call-out price before we set off.