Why Your RCD Keeps Tripping: Causes and How an Electrician Fixes It

A Trip That Won't Stay Reset

There are few household annoyances quite like an RCD that keeps tripping. You reset it, power returns, and minutes — or hours — later you are plunged back into darkness. It is tempting to keep flicking the switch and hope it settles, but a device that trips repeatedly is doing its job: it has detected something genuinely wrong and is protecting you from it.

This guide explains, in plain English, why your RCD or breaker keeps tripping, the difference between the protective devices on your board, and how a qualified electrician traces the fault to its source. It is written by AMP Pro Electrical, a NICEIC and NAPIT-registered electrician based in Armthorpe, Doncaster.

RCD, RCBO or MCB — Know What's Tripping

Understanding which device is operating tells you a lot about the type of fault.

• An **MCB (miniature circuit breaker)** protects one circuit against **overload and short circuit** — too much current. It trips when a circuit draws more than its rating.
• An **RCD (residual current device)** monitors the balance between the live and neutral conductors. If even a small amount of current is leaking to earth — the classic sign of an **electric shock risk** — it cuts the supply in milliseconds. A single RCD often protects several circuits at once.
• An **RCBO** combines both functions in one device, protecting a single circuit against overload, short circuit **and** earth leakage. Modern consumer units increasingly use RCBOs so that one faulty circuit does not knock out half the house.

If a whole bank of circuits dies together, you are likely dealing with an RCD detecting earth leakage. If only one circuit goes and the rest stay on, it is an MCB or RCBO on that circuit. This distinction shapes everything that follows.

Cause 1: A Faulty Appliance

The single most common reason an RCD keeps tripping is a faulty appliance leaking current to earth. As heating elements and motors age, their insulation degrades and a tiny current starts escaping to the earthed casing — enough for the RCD to act.

The usual suspects are appliances with heating elements or motors: kettles, toasters, washing machines, tumble dryers, dishwashers, immersion heaters, fridges and freezers. Older or water-exposed kitchen and utility appliances are especially prone.

You can often find the culprit yourself by unplugging everything on the affected circuits, resetting the RCD, and reconnecting items one at a time until it trips. The last appliance you plugged in is the likely cause. Leave it unplugged and have it repaired or replaced.

Cause 2: Water Ingress

Water and electricity make a reliable recipe for nuisance tripping. Moisture creeps into outside sockets, garden lighting, garage circuits, bathroom extractor fans and shower units, creating a leakage path to earth that an RCD will not tolerate.

Tell-tale signs include trips that happen only when it rains, after using an outdoor socket, or when the bathroom gets steamy. Damaged outdoor socket seals, perished cable glands and condensation inside fittings are common entry points. This is one of the more dangerous causes because water dramatically lowers the resistance of a fault, so it should always be traced and corrected rather than ignored.

Cause 3: A Borrowed (Shared) Neutral

A borrowed neutral is a wiring fault — and a frequent headache when an RCD trips for no obvious reason. It happens when two separate circuits share a single neutral conductor, often a legacy of how lighting was wired in older properties or a mistake made during alterations or extensions.

Because an RCD works by comparing the current flowing out on the live with the current returning on the neutral, a shared neutral throws that balance off and the RCD trips. Borrowed neutrals are particularly common where upstairs and downstairs lighting circuits were combined years ago, and they often surface only when an older board is upgraded to one with RCD protection. Diagnosing a borrowed neutral takes a methodical electrician with test equipment — it is not something you can spot by unplugging appliances.

Cause 4: An Overloaded Circuit

If an MCB or RCBO trips rather than an RCD, overload is a likely cause. Every circuit has a current rating, and drawing more than it can carry will trip the breaker to prevent the cables overheating.

This often shows up when several high-demand appliances run on the same circuit at once — a kettle, a toaster and a heater on the kitchen ring, or multiple space heaters daisy-chained through extension leads. The fix may simply be spreading the load across more sockets, but persistent overloading can signal that a property needs additional circuits or a [consumer unit upgrade](/consumer-unit-upgrades/) to cope with modern demand. Older boards were never designed for today's kitchens, EV chargers and electric showers.

Cause 5: A Damaged Cable or Accessory

Physical damage to wiring is another regular cause. A nail or screw driven through a cable — a picture hook, a new shelf, a kitchen unit fixing — can nick the insulation and create a fault that trips the protection. Rodent damage in lofts, deteriorated cables in older installations, cracked socket faceplates and loose connections all do the same.

These faults can be intermittent, tripping only when the cable shifts with temperature or vibration, which makes them maddening to live with and important to find precisely.

Cause 6: An Accumulation of Small Leakages

Sometimes no single appliance is at fault. Instead, a number of items — each leaking a perfectly normal tiny amount of current to earth — add up across one RCD until their combined leakage crosses the trip threshold. The result is a board that trips occasionally and unpredictably, usually when several appliances happen to run together.

The modern remedy is to split the installation across more RCDs or move circuits onto individual RCBOs, so leakage is no longer pooled. This is a common reason electricians recommend a board upgrade when working on an older split-load consumer unit.

How an Electrician Traces the Fault

Guesswork has its limits. When the simple checks do not solve it, professional [electrical fault finding](/electrical-fault-finding/) brings the right instruments to the job:

• **Insulation resistance testing** measures how well each circuit's insulation is holding up, exposing breakdown between conductors or to earth.
• **Earth leakage measurement** with a clamp meter quantifies exactly how much current is escaping on each circuit, pinpointing where the problem lives.
• **Systematic circuit isolation** splits the installation down to individual circuits and accessories to corner an intermittent or shared-neutral fault.
• **Continuity and polarity testing** confirms the wiring itself is sound and correctly connected.

A competent electrician works methodically from the consumer unit outwards, narrowing the fault to a specific circuit, then a specific point — a socket, a junction box, a length of cable or a single appliance. As a guide, an emergency or fault-finding call-out typically starts from £75 to £150 for the first hour, and many recurring trips are resolved within that visit. Where the investigation reveals an ageing or unsuitable board, replacing a [consumer unit](/consumer-unit-upgrades/) typically costs from £450 to £900 depending on the circuits and protection involved.

All of this work follows BS 7671, the 18th Edition wiring regulations, and anything involving the consumer unit is notifiable under Part P — which is exactly why it should never be attempted as a DIY fix.

When to Call Rather Than Keep Resetting

Stop resetting and call an electrician promptly if the RCD trips instantly with nothing plugged in, if you smell burning or see scorch marks, if trips coincide with rain or water, or if the board has started tripping more and more often. These are signals of a real fault that will not cure itself, and continually overriding the protection only delays finding it.

Let Us Trace It for You

A tripping RCD is not something to live with — it is your installation flagging a fault that deserves a proper diagnosis. AMP Pro Electrical traces nuisance trips across Doncaster, Armthorpe and the surrounding DN area, finds the genuine cause, and puts it right safely. Call Paul and the team on 0333 577 5464, or [request a free survey](/contact/) and we will get to the bottom of it.