An RCD (Residual Current Device) is a safety switch in your consumer unit designed to cut power the instant it detects a leak of current — the kind that could cause an electric shock or start a fire. So when it trips, it's not malfunctioning — it's doing exactly what it's built to do. The question is what's triggering it.
Quick Answer: Most Common Causes
- A faulty appliance plugged into a socket on that circuit
- Damp or water ingress in wiring, sockets, or outdoor fittings
- A damaged cable somewhere on the circuit
- Too many appliances overloading a single circuit
- A fault in the RCD itself, particularly in older consumer units
RCD Keeps Tripping vs. MCB Keeps Tripping — What's the Difference?
An RCD and an MCB (Miniature Circuit Breaker) protect against different things, and knowing which one is tripping narrows down the cause fast:
- RCD trips → usually points to a current leak (damp, damaged insulation, a faulty appliance)
- MCB trips → usually points to overload (too many appliances) or a short circuit
If you're not sure which one is tripping, check your consumer unit — RCDs are typically labelled with a "T" (test) button, MCBs are the individual circuit switches.
What Causes an RCD to Trip But Not the MCB
This is a common and specific symptom — it usually means the fault is a genuine current leak (RCD's job) rather than an overload or short (MCB's job). Common causes include:
- A faulty or damp outdoor fitting (garden lighting, an outdoor socket)
- A washing machine, dishwasher, or other appliance with a developing internal fault
- Condensation or damp inside an older consumer unit itself
What You Can Safely Check Yourself
- Unplug everything on the affected circuit, then reset the RCD — if it holds, plug items back in one at a time to isolate which one is causing it
- Check for anything obviously damp — outdoor sockets after rain, a leak near wiring
- Don't keep resetting it repeatedly if it trips again immediately — that's a sign to stop and call someone
When to Call an Electrician
- The RCD trips again immediately after resetting, with nothing plugged in
- You can't identify which appliance or circuit is causing it
- It's happening repeatedly over several days
- There's a burning smell, discolouration, or visible damage at the consumer unit
This is exactly what our electrical fault finding service is built for — fixed at £78.00 inc. VAT, with calibrated testing equipment used to isolate the actual cause rather than guesswork. For more on how professional fault diagnosis works more broadly, see our electrical fault finding guide.
Is a Tripping RCD an Emergency?
Not usually — a single trip that resets cleanly is the system working as intended. But if it's tripping repeatedly, won't reset at all, or is accompanied by a burning smell or exposed wiring, treat it as urgent. Our emergency response service covers this, from £156–£210 inc. VAT with a 60–90 minute response time.
FAQs
Why does my RCD keep tripping for no reason?
It's rarely "no reason" — it's usually an intermittent fault that's hard to spot, like a damp outdoor fitting or a developing appliance fault. A professional fault-finding visit can isolate it properly.
Is it dangerous to keep resetting a tripping RCD?
Resetting it once to test is fine. Repeatedly resetting an RCD that keeps tripping immediately is not advised — it means there's an active fault, and repeated resets don't fix the underlying cause.
Can I fix an RCD fault myself?
Identifying which appliance is causing it is safe to do yourself by unplugging and testing one at a time. Fixing wiring or consumer unit faults should always be done by a registered electrician.
