Why do RCDs trip? and why are they so prone to tripping?

The RCD, or Residual Current Device, is a little gadget that sits inside your fusebox, or nearby, with its sole purpose being that of safety.

The RCD action, as opposed to a fuse, or a breaker function, is purely there to protect you and your family. Where a breaker could let you become a 3 KW heater and not even realise the difference, the RCD is extremely sensitive in this respect. Anything above 30mA or 7W (about 500 times more sensitive than its breaker counterpart) in earth leakage will disrupt the circuit.

Therein lies the answer to “Why are RCDs so prone to tripping?” For those that remember times without an RCD, they’ll compare to that time where unless something was drastically wrong with the electrical installation, everything would work as normal. So it’s a bit of a psychological perspective going on here. Those who have grown up with RCDs will unlikely realise that RCDs are really SO sensitive.

RCDs compromise convenience of keeping the power on by putting more emphasis on pulling up possible health and safety issues (which might kill you if left unattended!).

So why do RCDs trip? and how can you tell whether its the wiring or, say, your tumble drier?

RCDs look at a slightly different parameters compared with breakers and fuses (overcurrent devices). breakers and fuses stop currents that the cable can’t handle from melting it (think in Amps, tens of Amps).

RCDs look at the current following through the live and neutral, and stringently compares the values. if a difference of more than 30mA is found (30 thousands of a just one Amp!) The RCD assumes a human has accidentally come in contact with live wires and will automatically disrupt the connection.

Thankfully, a lot of the time, the RCD isn’t tripping because a human has found their way under the stairs and opened up the fusebox (much like the dad in that episode of Friday Night Dinner). But it has to assume the worst.

First stop if you have a tripping RCD:
UNPLUG (not just switch off at the switch) all of your fridges, freezers, microwaves, washing machine, tumble, playstation, phone chargers, doorbell dongle, etc.
If you have an inkling it might be your lights turn them all off.

Does the RCD now hold? If so, one by one, plug each device in and turn it on. If you can narrow it down to a particular device then great, you just need to replace that device. Likewise, flick each of your lights on, one by one.

If you can’t narrow it down so well, it might be time to start thinking about calling your local electrician out. The more information you can provide the better, such as:

what RCD/breaker trips (Take a picture or scribble an arrow with a pencil if you’re going to have trouble remembering)

Starting making a diary of when it tends to trip such as, “when I flick this switch” or “At this sort of time of the day, it tends to trip”.

Anything that’s recently changed. New cooker? lights been flickering more than usual? Have changed a light fitting or put a picture up on the wall recently?

it’s important to note that not all faults are created equal. Some are very intermittent and some throw in some very crafty red herrings for us electricians to deal with. Of course, we can’t live with you for a month to work out exactly where some of these more awkward faults are lying, so the absolute vital thing to do is keep a log. Any bit of information, however irrelevant or silly it may sound, might be the tell tale nugget of information we need to locate the fault and fix it.

If you’ve got to the end of this, you’re located in the Medway towns, Maidstone, or surrounding areas, and you’re still in this sticky situation where you are having real issues with an intermittent RCD, please ring 07478159026 and we’ll provide you with expert advice, and more importantly, get your electrics back on for good.

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