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An RCD (residual current device) is the part of your consumer unit that switches the power off automatically if current is leaking somewhere it shouldn't — through you, through a damaged cable, or through a faulty appliance. It's the single biggest reason electric shocks in modern homes rarely turn fatal.
An RCD constantly compares the current going out on the live wire against the current coming back on neutral. In a healthy circuit those two numbers match. If they don't — because some current is escaping to earth, say through your body — the RCD trips in a fraction of a second, well before a shock becomes dangerous. Cut through a cable with the lawnmower and touch a live wire, and this is what saves you.
A fuse or MCB protects the wiring and the property — it trips on overload or short circuit, when too much current is flowing. An RCD protects people — it trips on imbalance, even at very low currents that wouldn't bother a fuse at all but would kill you. You need both. Most modern consumer units combine the two into RCBOs, giving you overload and shock protection on a single circuit rather than a shared RCD covering several.
Usually one of three things: a genuine earth fault (damaged cable, water ingress, a failing appliance), a faulty appliance drawing current to earth, or — less dangerously — a build-up of natural leakage across several appliances on one circuit that tips the device over its threshold. If yours trips occasionally with no obvious cause, see our guide on what to do when an RCD trips. If it won't stay reset, that's a fault to call us about, not something to keep resetting.
BS 7671 requires 30mA RCD protection on most circuits in domestic and commercial installations — sockets, cables buried in walls, bathroom circuits, outdoor circuits. If your consumer unit predates this (common in anything installed before the early 2000s, and plenty installed after), you may have no RCD protection at all, or only partial. This is one of the most common findings we flag on an EICR, and it's a straightforward fix during a consumer unit upgrade.
Not all RCDs handle modern electrical loads the same way. Type AC only copes with straightforward AC faults; Type A is now the minimum standard for new work because most homes run electronics that can introduce a DC component; Type B is required for EV charging. We've covered this in more depth in our Type AC RCD regulations article if you want the full detail.
RCD protection is checked as standard on every EICR we carry out, whether it's a rental property, a care home with a maintenance team, or a commercial unit. Missing or inadequate RCD protection is one of the more common C2 findings we report — it's a safety issue, not a paperwork one, and it's usually resolved same-visit or on a quick return.
Under current regulations, most do — sockets, buried cables, anything outdoors or in a bathroom. A handful of fixed circuits can be exempt depending on installation method. An EICR will tell you exactly where you stand.
Rarely truly "no reason" — it's usually a genuine (if minor) leakage building up across appliances, or an ageing device becoming oversensitive. Repeated tripping is worth investigating rather than ignoring.
Press the test button on the front, usually marked T or with a "push to test" label. It should trip immediately. If it doesn't, that's a call-out, not a DIY fix.
No. An RCD protects against earth faults only and often covers several circuits. An RCBO combines RCD and MCB protection on a single circuit, giving overload and shock protection together.
We check this on every EICR we carry out across Tonbridge, Tunbridge Wells, Sevenoaks and Crowborough. Get in touch for a quote or call us on 01892 531728 — we're happy to talk you through what you need before you commit to anything.
I had no electricity and phoned up in very late evening. Karen phoned me back despite it being late evening and sorted out my problem on the phone . Great service, extremely helpful and quick response and I didn’t even have to pay for a visit. Thoroughly recommend this company and will definitely use them again.
Karen and her team of electricians did a very good job in assessing our electrical circuits, modernising and upgrading our fuse boxes and ensuring compliance with the latest regulations. They were efficient and polite and, when they had finished the work, left the house tidy and in good condition
We were very pleased with the recent electrical work which was carried out in a professional manner by your electrician and will certainly use your company again when future needs arise. Also I would be happy to recommend your services to any of our friends.
Thank you very much, and please pass on my thanks to Philip who completed the job. I appreciate it was an awkward space for him to work on, but everything was done so well and so quickly - I am very happy with the outcome! Will be returning to you for more jobs soon I’m sure!
"In June 2018 Karen and one of her team fitted some new lights in my kitchen ceiling. I was really pleased with the work. The job was done efficiently and tidily. I was kept informed of arrival time and I was impressed with the service I received. Thanks for a great job. Lucy"
