RCD Keeps Tripping — What to Do and When to Call an Electrician
A tripping RCD is your consumer unit doing exactly what it should — protecting you from a fault. This step-by-step guide will help you identify whether the problem is a faulty appliance you can deal with yourself, or a wiring fault that needs a qualified electrician. Written by a NAPIT-registered electrician who fault-finds these every week.
Dan Stevens
NAPIT Registered Electrician
Quick Summary
- Step 1: Unplug all appliances on the tripped circuit
- Step 2: Reset the RCD or RCBO
- Step 3: Plug appliances back in one at a time to identify the fault
- Trips with nothing plugged in? Wiring fault — call an electrician
- Trips immediately on reset? Wiring fault — call an electrician
- Random overnight trips? Often a nuisance trip from appliance transients — read below
What Is an RCD and Why Does It Trip?
An RCD (Residual Current Device) is a safety switch inside your consumer unit (fuse box). It constantly monitors the balance of electrical current flowing along the live and neutral conductors of a circuit. If it detects a difference of 30 milliamps (0.03A) or more — indicating current is leaking somewhere it should not be, typically to earth through a person or a fault — it cuts the power in around 40 milliseconds. That response is fast enough to prevent a fatal electric shock.
A trip means the RCD has done its job. The question is why current was leaking, and that is what you need to find.
On older boards, one RCD often covers half the circuits in the house. On modern boards with individual RCBOs, only the affected circuit goes off. Either way, the diagnosis process is the same.
Common Causes of an RCD Tripping
⚡ Faulty appliance
The most common cause. Washing machines, dishwashers, tumble dryers, electric ovens, kettles and heaters are frequent culprits when internal insulation breaks down with age or water ingress.
🔌 Damaged wiring
Rodent damage, cable stapled through, nail through a wall socket or a cable joint that has failed over time. This is a fixed-wiring fault and needs a professional.
💧 Damp or water ingress
A socket, light fitting or connection point that has had water in it. Common in bathrooms, kitchens, outdoor circuits and after roof leaks. Damp provides a path to earth, tripping the RCD.
⚙ Nuisance tripping
Transient current spikes from motor-driven appliances (fridge compressors, washing machine motors) can occasionally trip sensitive RCDs. More common on older boards with one RCD protecting many circuits.
🔥 Overloaded circuit
Too many appliances on one circuit can cause a circuit breaker to trip (overcurrent), but not usually an RCD — RCDs respond to earth faults, not overloads. If the MCB trips, that is an overload issue.
🔨 Worn RCD
RCDs have a working life of around 10–15 years. An old or faulty RCD can develop a low trip threshold or trip at random. If the consumer unit is more than 15 years old, the RCD itself may need replacing.
Step-by-Step: How to Find the Fault
Identify which RCD or RCBO has tripped
Open the consumer unit cover. A tripped switch will sit in the middle or “off” position, not fully up. On a split-load board, check both RCDs. On an RCBO board, identify which individual circuit has tripped.
Unplug every appliance on that circuit
Unplug everything from every socket on the affected circuit. If it is a lighting circuit, turn off all light switches. Do not just switch appliances off at the socket — unplug them from the wall.
Try to reset the RCD
Push the switch firmly to the “on” position. If it stays on with nothing plugged in, proceed to step 4. If it will not reset or trips immediately with nothing plugged in, stop. The fault is in the fixed wiring — call an electrician.
Plug appliances back in one at a time
With the RCD reset, plug each appliance back in and switch it on, one at a time. Wait 30 seconds between each one. The appliance that causes the RCD to trip again is the fault. Remove it and do not use it until it has been repaired or replaced.
No faulty appliance found?
If all appliances are back in and the circuit is running fine, monitor for a few days. If it trips again, the fault may be intermittent (moisture, a cable joint that is loose, or a deteriorating cable). Call an electrician for a full insulation resistance test.
When NOT to reset the RCD
If the RCD trips and someone has just received an electric shock, do not reset it. Make the person safe, call 999 if needed, and call an electrician before restoring power. The shock itself may have occurred because the RCD tripped slightly after a significant fault — the circuit needs professional inspection before use.
RCD Tripping with Nothing Plugged In
This is the most serious scenario. If you unplug everything and the RCD still will not stay reset, the fault is in the fixed wiring or a fixed connection — an immersion heater, a cooker point, a bathroom extractor fan, a ceiling rose, or the cable itself.
Common causes include:
- A damaged cable sheath inside a wall cavity (nail, rodent, thermal damage)
- Water ingress in an outdoor socket, garden light or outbuilding circuit
- A failing connection at a junction box or back of a socket
- An immersion heater element with broken insulation
- A bathroom lighting circuit with damp in a ceiling rose or downlight fitting
A qualified electrician will use a Megger insulation resistance tester to measure the resistance of each circuit to earth. A healthy circuit reads over 1 megΩ; a faulty one often reads zero, pointing directly to the damaged section.
RCD vs RCBO vs MCB — What Have You Got?
| Device | What it does | When it trips |
|---|---|---|
| RCD | Earth fault protection across multiple circuits | 30mA earth fault — cuts all circuits on that RCD |
| RCBO | Earth fault + overcurrent on one circuit | 30mA earth fault or overcurrent — that circuit only |
| MCB | Overcurrent protection on one circuit | Overload or short circuit — no earth fault protection |
| AFDD | Arc fault detection — catches low-level arcing | Detects arcing that RCDs cannot see |
If all your circuits are on individual RCBOs (one switch per circuit in the consumer unit), only the affected circuit trips when there is a fault — the rest of the house stays live. Older boards with two large RCDs and multiple MCBs lose half the house when one RCD trips. If this is causing problems, upgrading to an RCBO board is worth considering.
The Monthly RCD Test
Every RCD has a small test button — usually marked T or TEST. Pressing it with the circuit live should trip the RCD immediately. If it does not trip, the RCD may be mechanically stuck and no longer offering protection. This is a rare but serious failure.
NAPIT and the IET recommend testing RCDs every three months (Wiring Regulations BS 7671 recommend quarterly). Make it a habit when you change the smoke alarm batteries.
When to Call an Electrician
- RCD will not reset with everything unplugged — fixed-wiring fault, needs insulation resistance testing
- RCD trips immediately when reset — significant earth fault, do not keep resetting
- RCD trips at the same time of day — often a thermostatically controlled appliance (immersion, storage heater)
- RCD trips overnight with fridge or freezer on that circuit — compressor or appliance fault, or nuisance trip issue
- Burning smell after a trip — potential arcing or overheating, call immediately
- Consumer unit more than 15 years old — RCD may be at end of life; board may need upgrading to current regulations
- Someone has received a shock — do not restore power until a professional has inspected
DS Electrical — Somerset
RCD Fault Finding in Somerset
If unplugging everything does not fix the problem, Dan carries a Megger MFT1741 multifunction tester to every job. An insulation resistance test on each circuit typically isolates the fault within 30 minutes. Fixed quotes for fault finding jobs — no open-ended hourly billing.
Frequently Asked Questions
Why does my RCD keep tripping? +
An RCD trips when it detects a 30mA imbalance between live and neutral, meaning current is leaking to earth. The most common causes are a faulty appliance, damaged cable, damp in a fitting, or a deteriorating cable sheath. If it trips with nothing plugged in, the fault is in the fixed wiring and you need a qualified electrician.
Is it safe to keep resetting an RCD? +
One reset to investigate is fine. Repeatedly resetting an RCD without finding and removing the fault is unsafe — the RCD is protecting you from a real earth fault. If you cannot identify and remove the cause, leave it off and call an electrician.
Can a washing machine trip an RCD? +
Yes. Washing machines are one of the most common causes of RCD trips. The heating element, motor and control board all have insulation that degrades over time or with water ingress. If your RCD trips only when the washing machine reaches a certain stage in its cycle (e.g. the heat), the appliance element is likely failing. Have the appliance serviced or replaced.
Why does my RCD trip in the night? +
Overnight trips are often caused by a fridge or freezer compressor starting, a storage heater switching on, or an immersion heater element with degraded insulation. These are thermostatically controlled, so they trigger at similar times. Identify which circuit is tripping and check appliances on that circuit first.
What is the difference between an RCD and an RCBO? +
An RCD protects multiple circuits but trips all of them when it detects a fault. An RCBO provides both RCD (earth fault) and MCB (overcurrent) protection in a single device on one circuit — so only the affected circuit trips. Modern consumer units typically use individual RCBOs per circuit.
How much does RCD fault finding cost? +
Electrical fault finding in Somerset typically costs £80–£180 depending on the complexity. A straightforward appliance fault that the homeowner cannot identify takes 30–60 minutes with a multifunction tester. A more complex wiring fault requiring circuit tracing takes longer. DS Electrical provides fixed-price fault finding quotes — call 07889 334849.