RCD keeps tripping: causes, intermittent faults and when to call an electrician

What an RCD does and why it trips

An RCD, or Residual Current Device, is a safety switch fitted in your consumer unit (the fuse board, usually located in a hall cupboard or utility room). It continuously monitors the current flowing out on the live conductor and returning on the neutral. If those two values differ by as little as 30 milliamps, the RCD detects a leakage to earth and shuts off power within 40 milliseconds. That speed is fast enough to prevent a lethal electric shock.

In Irish consumer units, one RCD typically protects a group of circuits rather than a single one. When it trips, all the circuits on that side of the board lose power simultaneously. The trip is always triggered by a genuine leakage: electricity is flowing somewhere it should not, whether through a faulty appliance, damaged wiring, or moisture in a socket. Understanding which cause applies in your home determines whether you can resolve it yourself or need a RECI-registered electrician.

Common causes of RCD tripping in Irish homes

The vast majority of RCD trips in Irish homes come down to one of five causes. A faulty appliance is by far the most common, but damp, old wiring, and the wrong type of RCD for modern appliances all feature regularly in fault-finding call-outs.

Faulty appliance leaking to earth. This is the most common cause seen on RECI call-outs across Ireland. An appliance with a failing heating element, a degraded motor winding, or a damaged power cable can leak a small current to its metal casing. Because the casing is earthed, this leakage current returns via the earth conductor and the RCD detects the imbalance immediately. Washing machines, dishwashers, tumble dryers, and electric showers are the most frequent culprits.

Damp and water ingress. Outdoor sockets, garden lighting circuits, and sockets in utility rooms or garages are susceptible to moisture getting inside the back box or the socket face. Water is conductive, so even a film of condensation on internal components can create a leakage path to earth. Trips that happen specifically after rain, or that clear when the weather dries out, almost always point to moisture ingress somewhere on the circuit.

Deteriorating cable insulation. Older Irish homes built before the 1980s often retain original rubber-insulated or fabric-insulated cables in parts of the installation. Rubber insulation dries out over decades, becomes brittle, and cracks. Once the insulation breaks down, the bare copper conductor can touch an earthed surface inside a wall or floor, creating a continuous leakage. If the RCD trips even with all appliances disconnected, deteriorating fixed wiring is the most likely explanation.

If your RCD keeps tripping and you cannot identify a faulty appliance, it often points to a failing circuit. A fuseboard upgrade may be needed to bring the installation up to current standards, or a periodic inspection will identify the exact fault in the fixed wiring.

Intermittent RCD tripping: no obvious cause

A RECI-registered electrician can test each circuit with an insulation resistance meter to locate the exact leakage in minutes. Find one in your county today.

Less obvious causes worth knowing about

Beyond the obvious faults, there are causes specific to modern Irish electrical installations that are becoming more common as homes add EV chargers, inverter appliances, and LED lighting systems.

How to find the fault yourself

This step-by-step process lets you narrow down whether the fault is in an appliance or in the fixed wiring, without any specialist equipment. Work carefully and do not attempt to open consumer units or work on fixed wiring yourself.

1. 1

   Isolate all circuits under the tripped RCD

   Open your consumer unit and locate the tripped RCD (it will be in the middle position or switched to off). Before resetting it, switch off every individual circuit breaker on the RCD's side of the board. You are not isolating the whole house, just the circuits that the tripped RCD protects.

2. 2

   Reset the RCD

   With all circuit breakers switched off on that side, push the RCD back to the on position. If the RCD will not stay on even with all breakers off, the RCD itself may be faulty or there is a fault on the supply side. Stop here and call a RECI electrician.

3. 3

   Re-energise circuits one at a time

   Switch each circuit breaker back on one at a time, pausing a few seconds between each one. When the RCD trips, the circuit you just switched on contains the fault. Switch that breaker back off, reset the RCD, and continue to confirm all other circuits are healthy.

4. 4

   Disconnect all appliances on the faulty circuit

   Go to every socket and outlet on the faulty circuit and unplug every appliance. Switch off and unplug at the socket. Then switch the circuit breaker back on. If the RCD holds, the fault is in an appliance, not the wiring.

5. 5

   Reconnect appliances one by one

   Plug appliances back in one at a time, switching on each one before moving to the next. The appliance that causes the RCD to trip is the faulty one. Remove it from service and have it inspected or replaced. Do not plug it back in.

6. 6

   RCD still trips with all appliances off

   If the RCD trips on a circuit even with every appliance disconnected, the fault is in the fixed wiring, not an appliance. This requires an insulation resistance test by a RECI electrician. Do not continue using that circuit until it has been tested and cleared.

When to call a RECI electrician

The diagnostic steps above can identify whether the fault is in an appliance or in the fixed wiring. Once you have established it is in the fixed wiring, or if you cannot identify the cause at all, the job requires a professional with an insulation resistance meter. A RECI-registered electrician will test each circuit individually to locate the exact point of leakage, whether that is a damaged cable under a floor, a corroded junction box in a wall, or degraded insulation in a spur.

A typical fault-finding visit in most Irish counties costs €80 to €200 for the call-out and diagnosis. Dublin rates are generally at the higher end of that range. Rural counties in the west, including Mayo, Donegal, and Roscommon, typically see lower rates. If a replacement RCD is needed, parts and labour will add €80 to €200 on top of the diagnostic fee.

RCD tripping: common questions

Find a RECI-registered electrician

Only a RECI-registered electrical contractor can carry out insulation resistance testing, replace RCDs, and certify the work under IS 10101. Find one in your county today.

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