A faulty or leaking RCD can be identified by testing its built-in test button monthly — if it fails to trip, the device is faulty. Signs of a leaking RCD include nuisance tripping without an obvious fault, or circuit breakers tripping unexpectedly. Press the TEST button: it should trip instantly. If it doesn't, replace the RCD immediately and call a qualified electrician. Never ignore a non-tripping RCD — it may fail to protect you from electric shock or fire. A registered electrician can perform a full RCD trip-time test to confirm performance.
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How to Tell If Your RCD Is Faulty or Leaking
Your RCD (Residual Current Device) is one of the most important safety devices in your home. It's designed to cut power within milliseconds if it detects electricity leaking to earth — protecting you from electric shock and fire. But like any electrical component, RCDs can develop faults or degrade over time.
What Does a 'Leaking' RCD Mean?
When electricians talk about an RCD 'leaking', they usually mean the device is detecting small, unwanted leakage currents on a circuit — often from ageing appliances, long cable runs, or damp — and tripping unnecessarily. This is different from the RCD itself being faulty.
Warning Signs Your RCD May Be Faulty
The TEST button doesn't trip the device when pressed — this is the clearest sign of a fault
The RCD won't reset after tripping — it springs back to the off position immediately
Nuisance tripping — the RCD trips repeatedly with no obvious cause
The RCD trips as soon as a specific appliance is plugged in — this usually means the appliance is faulty, not the RCD
Visible signs of damage — burn marks, discolouration, or a cracked casing
The device is over 10–15 years old — RCDs do degrade with age
What You Can Safely Check Yourself
1. Press the TEST button on the RCD (usually labelled 'T' or 'TEST') — it should trip instantly and cut the power to that circuit
2. Reset the RCD by flipping it back to the ON position — it should hold
3. Unplug all appliances on the affected circuit and try resetting — if it holds, one of your appliances is likely faulty
4. Check for damp near sockets or switches on that circuit
When to Call an Electrician
The TEST button does not trip the RCD
The RCD will not reset at all
Tripping continues after removing all appliances
You suspect wiring or installation issues
The RCD or consumer unit looks damaged
Never bypass or tape over an RCD. If in doubt, switch off at the consumer unit and call a Part P registered electrician. RCD faults can leave you completely unprotected from electric shock.