An RCD (Residual Current Device) is designed to cut power in a fraction of a second if it detects a current leak — the kind that causes electric shocks or fires. It's one of the most important pieces of safety equipment in your consumer unit. But like any safety device, it only works if it's actually functioning — and the only way to know that is to test it.
Quick Answer
Test your RCD's button function every three months at home, and have a full professional RCD test carried out as part of your EICR — recommended every 10 years for homeowners, every 5 years for landlords.
Why RCD Testing Matters
An RCD that's stopped working gives you a false sense of security — everything looks normal until the moment it's actually needed, and by then it's too late to matter. Age, damp, and general wear can all cause an RCD to fail silently, which is exactly why regular testing exists.
The Button Test — What You Can Do Yourself
Every RCD has a "T" (test) button on the front. Pressing it should immediately trip the RCD and cut power to the circuits it protects.
- Press the test button
- The RCD should trip immediately, cutting power
- Reset it by switching it back to the "on" position
- If it doesn't trip when tested, or won't reset properly, that's a fault — don't ignore it
This should be done roughly every three months. It only tells you the mechanism itself is working — it doesn't test the wiring or circuits behind it.
Professional RCD Testing — What's Different
A professional test goes further than the button check, using calibrated test equipment to measure the actual trip time and trip current against BS 7671 requirements — confirming the RCD would genuinely respond fast enough in a real fault. This is carried out as standard during an EICR (Electrical Installation Condition Report), which checks the RCD alongside the rest of your electrical installation.
How Often Should RCDs Be Tested?
- Button test (DIY): every three months
- Full professional test: as part of a periodic EICR — every 10 years for owner-occupied homes, every 5 years for rented properties in England
- After any electrical fault or repair work: worth a check regardless of when the last test was
What If Your RCD Keeps Tripping?
A tripping RCD is different from a faulty one — it means the device is working and has detected a genuine issue. See our guide on why an RCD keeps tripping for common causes and what to check.
When to Call an Electrician
- The button test doesn't trip the RCD, or it won't reset
- You're not sure if your consumer unit even has RCD protection (common in older properties)
- It's been more than 10 years since your last EICR
- Any signs of damage, discolouration, or a burning smell at the consumer unit
Our electrical fault finding service covers RCD faults specifically, fixed at £78.00 inc. VAT.
FAQs
How do I know if my home even has an RCD?
Check your consumer unit for a switch labelled with a "T" (test) button — this is the RCD. Older properties without one may need an upgrade; an EICR will confirm this.
Is it dangerous if my RCD fails the button test?
It means the RCD isn't providing the protection it's meant to — it should be looked at by a registered electrician rather than left as-is.
Does RCD testing hurt my appliances?
No — the button test simply cuts power briefly, the same as switching off the circuit. It doesn't affect connected appliances.
