Why Does My RCD Keep Tripping? How to Narrow It Down Before You Call an Electrician
Published 6 October 2026 · Updated 6 October 2026 · By Dan, ElectriVolt
A 30 mA RCD does not wait for 30 mA. The product standards allow it to trip at any residual current above half its rating, so the switch in your consumer unit can legitimately drop out at around 15 mA. That one fact explains a lot of the RCD tripping that looks random from the outside.
If you are asking “why does my RCD keep tripping?”, the honest answer is that it is doing its job: it has seen current leaking somewhere it should not. The useful question is where. With a bit of method, you can usually narrow it down to a circuit, and often to a single appliance, before anyone with a test meter arrives.
Why does my RCD keep tripping? An RCD trips when it detects current leaking to earth, usually from a faulty appliance, moisture in an outdoor light or socket, damaged wiring, or several appliances whose small normal leakage adds up. Switch every circuit off, reset the RCD, then switch circuits back on one at a time to find which one sets it off.
What an RCD is actually measuring
An RCD compares the current going out along the live conductor with the current coming back along the neutral. In a healthy circuit they match. If some of it is escaping to earth instead, through a damaged cable, a wet fitting or a person, the two no longer balance and the RCD disconnects.
That is why an RCD trip is different from a circuit breaker trip. A breaker (an MCB) trips on too much current, such as an overloaded circuit or a short. An RCD trips on current going the wrong way, which can happen with a tiny load. A kettle with a breaking-down element can trip the RCD while drawing far less than its normal power.
On many older and split-load boards, one RCD protects a whole bank of circuits. When it trips, everything on that side of the board goes off together, which is why a fault on the washing machine can also take out the upstairs lights.
Why does my RCD keep tripping? Start with the pattern
Before you touch anything, think about the pattern. It is the single most useful piece of information you can give an electrician, and it often points straight at the cause.
- It trips the moment you reset it. Something is leaking right now. That is a fault present on one of the circuits, or on a fixed appliance that is always connected.
- It trips when you switch a particular thing on. Washing machine reaching its heating stage, oven warming up, shower starting. The fault is very likely in that appliance.
- It trips after rain, in a thaw, or on damp mornings. Moisture is getting into something outside or in an outbuilding.
- It trips at random, with no obvious trigger. Often several small leakages adding up, an intermittent fault, or a disturbance on the supply.
- It will not reset at all, even with everything switched off. Either a fault on the wiring itself or a problem with the RCD. This one needs an electrician.
How to narrow it down, step by step
This is the same order we work through on a fault-finding visit, minus the test instruments. You only need to operate the switches on the front of the consumer unit. Never take the cover off.
- Switch off every circuit breaker on the side of the board protected by the tripped RCD.
- Reset the RCD. If it trips again with every breaker off, stop here. The fault is on the wiring, the board or the RCD itself, and it needs testing.
- Switch the breakers back on one at a time, pausing for a few seconds after each. When the RCD trips, the last breaker you switched on is the circuit with the problem.
- Leave that one breaker off, reset the RCD and switch the rest back on, so the rest of the house has power while you look.
- Unplug everything on the suspect circuit. If it is a socket circuit, that means every plug, not just the obvious ones. If it is a fixed appliance circuit such as an oven or shower, switch off at its isolator.
- Switch the suspect breaker back on. If the RCD now holds, the cause was something you unplugged. If it trips with nothing connected, the fault is in the fixed wiring or a fixed appliance on that circuit.
- Plug appliances back in one at a time, switching each one on. The one that trips the RCD is your culprit. Stop using it and get it checked or replaced.
Write down what you found as you go. “Kitchen sockets, trips when the dishwasher heats up” turns a long diagnostic visit into a short one.
The usual suspects
Appliances with heating elements
Elements in kettles, washing machines, dishwashers, ovens and immersion heaters are a classic cause. As the element ages, its insulation breaks down and starts to leak a little current to the earthed casing. It may only show up when the element gets hot, which is why the trip happens part-way through a wash cycle rather than at the start.
Water where it should not be
Outdoor sockets with perished seals, garden lights with cracked lenses, cable joints in a damp shed, a leak dripping into a ceiling light. Electrical Safety First’s garden advice is blunt about water and electricity: it tells people to use an RCD with all outdoor electrical equipment, precisely because outdoor conditions are where leakage starts. If your trips follow the weather, start your search outside.
Damaged cables
A nail or screw through a cable when a picture or shelf went up, a cable nicked during building work, rodent damage in a loft or under a floor. These can sit undiscovered for months and only leak when conditions are right. If a trip started soon after someone drilled into a wall, that is your strongest lead.
Lots of small leakage adding up
This is the one most guides miss. Plenty of perfectly healthy equipment leaks a small amount of current to earth by design, especially anything with electronics inside. According to the IET, domestic appliance product standards generally allow up to 3.5 mA of protective conductor current per item.
The Wiring Regulations say the accumulated leakage downstream of an RCD should not exceed 30% of its rating, which for a 30 mA device works out at under 10 mA. Do the arithmetic and you can see the problem. A handful of appliances, computers, TVs and chargers on one RCD can creep towards that limit without a single one of them being faulty. Add one ageing element and the RCD trips.
What most guides get wrong: they treat every random trip as a hunt for one faulty appliance. On a board where one RCD covers half the house, the real cause is often the design, not a device. Unplugging things one at a time will never find it, because nothing on its own is wrong. The fix is splitting the load across more protection, not replacing appliances that work.
The RCD itself
RCDs are mechanical devices and they can fail. Electrical Safety First recommends operating the test button every three months, after an investigation found that most of the devices that failed would have been picked up by regular use of the button. A device that trips at the slightest disturbance can also be at the end of its life, and only a trip-time test with the right instrument will tell you for sure.
Faults that only an electrician can find
Some causes cannot be found by switching things on and off, because they are inside the walls or the board. These are the ones where we bring the test kit:
- Neutral to earth faults. A damaged cable where the neutral touches earth can trip an RCD even with nothing switched on. It often shows up as a trip that happens when an unrelated circuit is used.
- Circuits crossed between RCDs. On split-load boards, a neutral from one circuit sometimes ends up connected on the wrong side of the board, often after a DIY addition. The RCD sees an imbalance that is not a leak at all.
- Insulation breaking down across a whole circuit. Older cable, heat damage or damp can lower the insulation resistance of a circuit. An insulation resistance test shows it; no amount of unplugging will.
- Intermittent faults. A loose connection in a junction box, or a fault that only appears when a cable warms up, may need the circuit tested under load or monitored over time.
Our electrical fault finding service starts where your own checks stop: we test each circuit’s insulation, measure leakage with a clamp meter, test the RCD’s trip time and trace the fault to a point rather than guessing at it.
What not to do
- Do not keep resetting it. One or two attempts while you work through the steps is fine. Resetting it over and over while the fault is still there just repeats the conditions that are causing it.
- Never bypass or disable it. In Electrical Safety First’s investigation, some of the failed RCDs had been deliberately shorted out to stop nuisance tripping. That leaves the house with no protection against electric shock from that side of the board.
- Do not swap it for a less sensitive device. A 30 mA RCD is there to protect people. A higher rating will stop the trips by stopping the protection.
- Do not ignore a trip that coincides with a burning smell, scorch marks or a crackling sound. Switch off at the main switch and get it looked at the same day.
When the fix is the board rather than the fault
If the testing shows no single fault, just a board where too many circuits share one RCD, the long-term answer is to divide the protection up. The IET notes that the Wiring Regulations now require designers to consider RCBOs, which combine an RCD and a breaker for each circuit, in homes specifically to reduce unwanted tripping and the inconvenience it causes.
The practical effect is that a fault trips one circuit, not half the house. We cover the differences between board types in our guide to what changes when you move from a split-load board to individual RCBO protection. If your trips started after an outbuilding, hot tub or garden supply was added, the way that supply was run matters too. Our post on why an outbuilding gets its own board explains how it should be set up.
Common questions
Is it dangerous if my RCD keeps tripping?
The tripping itself is the RCD protecting you, so it is not the danger. The danger is the leak it is reacting to, which could be a faulty appliance or damaged wiring. Find the cause using the steps above, stop using any appliance that trips it, and get the circuit tested if the fault is in the wiring.
Can an RCD trip for no reason?
Rarely for genuinely no reason. What looks random is usually several small leakages adding up, a fault that only appears when something warms up or gets damp, or a brief disturbance on the supply. An RCD that is failing can also become oversensitive, which a trip-time test will show.
Why does my RCD trip when it rains?
Because water is getting into something electrical outside or in an outbuilding. Check outdoor sockets, garden and wall lights, and any supply to a shed or garage. Cracked lenses, perished seals and cable joints that were never made for outdoor use are the usual causes.
Can I reset an RCD myself?
Yes. Push the switch back up. If it will not stay up, do not hold it or force it. Switch off the circuit breakers on that side of the board and work through them one at a time to isolate the circuit with the fault, as described above.
Narrowed it down, or still stuck?
Tell us which circuit trips and when, and we will test it properly, find the cause and fix it. Free quotes, no callout charge.
Talk to ElectriVolt, or read more about our fault finding and repairs.
