Electrical

RCD Keeps Tripping: Causes and Fixes

An RCD trips because it detects current leaking to earth — the job is to work out whether that leakage is a genuine fault, the accumulation of normal appliance leakage, or a failing device, and a split-and-test method finds it fastest.

Updated 20 Aug 20268 min read

A residual current device trips when the current flowing out on the line no longer balances the current returning on the neutral — the difference is leaking to earth somewhere. A 30mA RCD is designed to operate at that level to protect against electric shock, so a trip is the device doing its job, not misbehaving.

This guide covers what makes an RCD trip, the difference between nuisance tripping from cumulative leakage and a real fault, and a systematic method to isolate the cause on site rather than guessing.

Key takeaways

An RCD trips on residual earth leakage — the imbalance between line and neutral current.
A 30mA RCD should trip between 15mA and 30mA; total standing leakage above about 30% of that (roughly 9mA) invites nuisance trips.
Common causes: a faulty appliance, a neutral-earth fault, moisture ingress, cumulative leakage from many devices, or a failing RCD.
Split-and-test: divide the load, isolate circuits and appliances one at a time to find the source.
Where many circuits share one RCD, RCBOs or a split board reduce nuisance tripping.

How an RCD decides to trip

An RCD continuously compares the current in the line conductor with the current returning in the neutral. In a healthy circuit they are equal. If some current is finding another path to earth — through a fault, through insulation, or through the protective conductor of an appliance — the two no longer balance, and once that imbalance reaches the device's rating it trips.

That is why an RCD trip is information, not a fault in itself. The question is always the same: where is the leakage going, and is it a genuine defect or the harmless accumulation of small leakages that individually are fine.

Trip vs fault

A 30mA RCD trips at anywhere from 15mA to 30mA of residual current. The device tripping means it's working — your job is to find what's leaking.

Nuisance tripping vs a real fault

Many appliances leak a small, legitimate current to earth — filters in IT equipment, heating elements, some LED drivers. Individually each is well within limits, but a 30mA RCD protecting a dozen circuits can see them add up. Good practice keeps standing leakage below about a third of the RCD's rating — roughly 9mA on a 30mA device — precisely to leave headroom before a nuisance trip.

A genuine fault is different: a damaged cable, a failed appliance element, or a neutral-to-earth fault will push the leakage well past the rating and trip the device reliably and repeatedly. The pattern usually tells you which you are dealing with — random occasional trips point at cumulative leakage; a trip that recurs immediately points at a hard fault.

Common causes, in order of likelihood

The usual suspects: (1) a faulty appliance — a failing heating element in a kettle, washing machine, immersion or oven is the most common single cause; (2) a neutral-earth fault in the fixed wiring, which can trip an RCD even with no load switched on; (3) moisture ingress into external sockets, garden lighting or a damaged cable; (4) cumulative leakage where too many circuits share one RCD; and (5) a failing RCD that trips below its rating or won't reset.

Damaged cables from nails and screws, rodent damage, and overheated terminations round out the list. A neutral-earth fault is worth calling out separately because it behaves differently — the RCD may trip the instant the board is re-energised, before any appliance is even switched on.

A method to find the fault

Work by division. First unplug every appliance on the affected circuits and reset — if it holds, the fault is in an appliance, and you plug them back one at a time until it trips. If it won't reset with everything unplugged, the fault is in the fixed wiring.

For a fixed-wiring fault, isolate at the board: turn off all the circuits on that RCD, reset it, then switch circuits back on one at a time until it trips. That identifies the circuit. From there, insulation resistance testing on the dead circuit — line-earth and neutral-earth — locates the fault, and a low neutral-earth reading confirms the classic neutral-earth fault.

Test, don't guess

An insulation resistance test between neutral and earth on the isolated circuit is the fastest way to confirm a neutral-earth fault — the reading drops well below the 1MΩ minimum.

Reducing nuisance tripping by design

Where the problem is genuinely cumulative leakage rather than a fault, the fix is in the board layout. Replacing a single RCD feeding many circuits with individual RCBOs — one per circuit — means each circuit's leakage is measured on its own, and only a genuinely faulty circuit trips. A split load board with two RCDs is a cheaper halfway house.

This is also why the 18th Edition's move towards RCBO boards matters in practice: it isn't only about compliance, it removes the design that causes most nuisance tripping, where an entire half of a house goes dark because one appliance three circuits away leaked a few milliamps too many.

Frequently asked questions

Why does my RCD trip with nothing plugged in?

That usually points at a fault in the fixed wiring rather than an appliance — most often a neutral-earth fault. Isolate the circuits at the board, reset, and switch them back on one at a time to find the faulty circuit, then test insulation resistance to confirm.

Is an RCD tripping dangerous?

The RCD tripping is protective — it's disconnecting because it detects earth leakage. The underlying cause may or may not be dangerous, but the device operating is a good sign. Never defeat or bypass a tripping RCD; find and fix what's leaking.

How much earth leakage is too much?

A 30mA RCD trips between 15mA and 30mA. As good practice, keep standing leakage below about a third of the rating — roughly 9mA — to avoid nuisance trips. Above that, spreading circuits across RCBOs or a split board is the fix.

From guidance to action

EICR certificate appRecord RCD test results and observations on a full EICR.