Why Does My RCD Keep Tripping? — Yorkshire Electrician Diagnostic Guide

By Steven Dixon · NAPIT-registered electrician, 18th Edition / BS 7671:2024 qualified · Published 8 May 2026 · Bradford, West Yorkshire

An RCD doesn't trip for no reason. By design it is detecting a 30 milliamp earth-leakage current — which is roughly the threshold above which sustained current through a human body can cause ventricular fibrillation. So when yours has been tripping every evening for the last month and you've been resetting it without thinking, you've been re-arming a fault that the device deliberately switched off to keep you alive. This is not a thing to live with.

This guide covers the five honest causes I see most often on Yorkshire callouts, how to safely diagnose which is yours before booking an electrician, and when to skip the diagnosis and call us out as an emergency.

What's an RCD actually doing?

An RCD (Residual Current Device) compares the current flowing out on the live conductor with the current returning on the neutral. In a healthy circuit they're equal — every electron going out comes back. If a small amount goes "missing" (because it's gone to earth via a damaged cable, a wet light fitting, or someone's hand), the difference is the residual current. At 30mA over ~40ms, the RCD switches the circuit off.

30mA is well below the threshold for a fatal shock, but only just. The RCD's job is to disconnect before sustained current damages your heart. If you're seeing repeat trips, your install genuinely is leaking that much current somewhere — and the RCD is the one thing standing between that fault and someone in the house.

The five honest causes — in order of frequency

1. A faulty appliance (~50% of all callouts)

The single most common cause. Older fridge-freezers, washing machines, dishwashers, immersion heater elements, kettles with damaged elements, and outdoor power tools all develop small leakage currents to earth as they age. Often a single appliance won't push leakage above 30mA on its own, but combined with normal background leakage from everything else on the same RCD, it tips the total over the threshold.

Symptoms: trips on a specific time pattern (washing machine cycle, fridge defrost, immersion heater on the timer). Trips when one specific appliance is in use. Resets and stays on if the suspect appliance is unplugged.

Fix: identify and replace the appliance, or have the appliance professionally repaired. Not an electrician's job — it's an appliance repair.

2. Damp / water ingress in an outdoor or wet circuit (~20%)

Yorkshire winters are wet. Garden lights, outdoor sockets, conservatory circuits, garage feeds, shed-and-stable feeds at allotments, and even bathroom shaver circuits in older houses are all common damp-trigger sites. Cables that pass through external walls or sit in wet meter cabinets pick up moisture, the insulation degrades, and you get leakage.

Symptoms: trips after heavy rain. Trips overnight in winter, less in summer. Trips reliably each morning at first dew. Comes back on after a sunny dry day.

Fix: identify the affected circuit, find and dry out the damp fitting, replace with an IP65 / IP67 outdoor-rated fitting. Where the cable itself is damaged, the affected length needs replacing. See emergency callout service.

3. Cumulative small leakage on a shared RCD (~15%)

An issue specifically on dual-RCD consumer units (most UK homes wired between 2008 and ~2017). Each RCD covers half the house. Modern electronics — phone chargers, induction hobs, LED drivers, microwaves — all leak tiny amounts of current to earth even in normal operation. Add up six or seven of them on the same RCD bank and you can sit at 18-22mA continuously. Then the kettle goes on (4mA more) and you're over 30mA — the RCD trips.

Symptoms: random-feeling trips. Sometimes triggered by trivial actions (turning on a lamp). Worse in winter when more devices are running.

Fix: redistribute circuits across the two RCD banks, or upgrade to an RCBO-per-circuit consumer unit (BS 7671:2024 standard). Read our fuse box vs consumer unit guide for the full upgrade picture.

4. End-of-life or faulty RCD/RCBO unit (~10%)

RCDs themselves wear out. The mechanical relay inside has a life of typically 4,000-10,000 trip cycles. Older units, especially those that have lived through a decade of nuisance trips, can develop hair-trigger sensitivity — they trip at 15-20mA instead of the rated 30mA. Or fail the other way and not trip at all (which is far more dangerous and is why the BS 7671 6-monthly user test button exists).

Symptoms: Trip-time tests show the device trips below 30mA or above 40ms. Increasing trip frequency over time without obvious load change. RCD test button doesn't trip the device when pressed, or trips it but doesn't let you reset.

Fix: replace the RCD or the whole consumer unit if it's old enough that individual replacements are no longer available.

5. Neutral-earth fault in fixed wiring (~5% but always serious)

Usually caused by DIY work where a neutral wire has been mistakenly connected to an earth terminal somewhere in the circuit, or by physical cable damage where a screw, nail or staple has compromised both insulation layers. Less common, but always genuinely dangerous when present.

Symptoms: trips immediately when the affected MCB is energised, with everything unplugged. Repeated reset attempts fail. Often follows recent DIY work in the affected area.

Fix: trace the fault to the specific cable run, replace the damaged section, re-test. Always an electrician's job — never DIY-able. Call out an emergency electrician the same day.

How to diagnose it yourself — safely

This procedure is safe to do yourself if your consumer unit looks normal (no smoke, no scorch marks, no burning smell). It works out which type of cause you have, so you know whether to call an electrician or change a kettle.

1. Switch off every MCB in the consumer unit. Leave the main switch on. Leave the RCD on (or switch it back on if it's tripped).
2. Unplug every appliance you can reach. Don't worry about hardwired ones (cooker, immersion, shower). Pull plugs on everything plugged into a socket.
3. Reset the RCD if needed. It should hold with all MCBs off. If the RCD trips immediately even with all MCBs off, you have a fault in the consumer unit itself or upstream — call us.
4. One MCB at a time, switch them back on. Wait a minute between each. If the RCD trips when you switch a specific MCB on, that's the affected circuit. Make a note.
5. If no MCB causes a trip, plug appliances back in one at a time. Wait 5 minutes between each. If a trip happens when you plug in a specific appliance, that's your culprit.

Three possible outcomes:

• One specific appliance trips it. Cause 1 (faulty appliance). Replace the appliance.
• One specific MCB trips it with everything unplugged. Cause 2 or 5 (damp circuit or neutral-earth fault). Don't reset that MCB. Call an electrician.
• Many appliances together trip it but none does on its own. Cause 3 (cumulative leakage). Likely needs a consumer-unit upgrade or RCBO redistribution.

Emergency vs schedule-it-next-week

Call as an emergency (call now, callout fee applies):

• RCD trips and won't stay reset at all — no power for more than 30 minutes
• Burning or fishy smell from sockets, switches, the consumer unit, or any wiring point
• Sparks visible at any accessory
• Consumer unit is warm to touch or making a buzzing/humming sound
• Repeated trips immediately after heavy rain (water ingress active)
• Recent DIY work in the affected area
• Someone in the house has had an electrical shock or felt a tingle from an appliance

Schedule a non-urgent diagnostic visit (next 1-7 days):

• RCD trips once or twice a day and resets cleanly
• Trips appear linked to a specific appliance you can avoid using
• Random trips with no obvious pattern, but the rest of the install seems fine
• You've identified a suspect appliance via the procedure above and want a written EICR confirmation

What we actually do on a tripping-RCD diagnostic visit

Typical visit, ~45-90 minutes:

• Insulation resistance test (IR) on every circuit at the consumer unit — live and neutral to earth.
• RCD trip-time test — verify the device trips at 30mA in <40ms.
• Earth-fault loop impedance test — the earthing system is doing its job.
• Continuity test on protective conductors.
• Visual inspection of the consumer unit, accessible accessories, and any obvious damp sites (kitchens, bathrooms, outdoor sockets, garages).
• Written report with cause, fix, and fixed-price quote for any remedial work.

Cost: £75 callout for our service area (Yorkshire / Lancashire / Greater Manchester via the M62) plus £65/hr on site. Most diagnostic visits are 1-1.5 hours total. If a fix is straightforward (e.g. replace one socket, replace one outdoor light fitting) we'll often do it on the same visit.

The bottom line

An RCD that trips repeatedly is doing exactly what it's designed to do — protecting whoever's in the house from a real fault current. Resetting without finding the cause is choosing to re-arm a hidden fault every time. Most causes are findable within an hour by a competent electrician. Most fixes are straightforward.

If you're not sure how serious yours is, run our 30-second wiring safety check — it'll tell you whether to schedule a routine visit or treat it as urgent. Or call 0800 061 4526 for emergency callout.