What are RCDs?

Residual current devices protect homes and their inhabitants from fatal electric shocks and house fires by automatically disconnecting your electricity supply in the event that electricity is flowing down an unintended path, e.g. through your body.

How do RCDs work?

In a healthy circuit, the number of electrons entering that circuit at your ‘fuseboard’ should equal the number of electrons leaving that circuit, on their return. RCDs compare the flow and return rates and disconnect your electricity supply in a fraction of a second, if there is a significant discrepancy between these two ‘currents’. It is logical that any electrons which do not return to the ‘fuseboard’ must have leaked from the circuit into an unintended path.

What do I do if my RCD keeps tripping?

RCDs are designed to ‘trip’ in the event of a fault, so the logical conclusion (ignoring for one moment that the RCD might actually be over-sensitive or faulty) is that one of the circuits protected by your RCD is experiencing a continuing fault. Try unplugging your electrical appliances and then flicking the switch of the RCD back on. If the RCD stays energized, then you know that at least one of your appliances is faulty. If the RCD continues to trip, then it is likely that the fault is somewhere within the fabric of your building and you will have to call an electrician to get the issue resolved.

What kind of fault causes an RCD to trip?

As stated above, RCDs trip whenever there is a fault which allows electrons to flow down an unintended path. Damp conditions can give electrons such a path, as can the bite of a mouse or a rat. Less commonly, overheating of your electrical cables can cause their plastic insulation to melt or otherwise disintegrate, which will allow electrons to flow out of your circuit and cause your RCD to trip?

How do I know if I have an RCD?

There are two types of device which can be referred to as an RCD. The first type usually looks like the device shown in the photo below, and is distinguishable from the other switches in your ‘fuseboard’ because it will have a little button on it, usually marked with the letter ‘T’ for ‘Test’. This type of RCD is usually shared between multiple circuits.


The second type, which is more properly known as an ‘RCBO’, is half the width of the first type (see photo below), but will also have a test button somewhere on the front surface of the device. This type of RCD only protects one circuit in your home.

If you are still not sure whether or not you have an RCD in your ‘fuseboard’, click here to book a free Skype consultation with one of our Operatives, and they will be glad to help you determine what kind of protective devices are currently protecting your electrical installation.

I don’t have an RCD, do I need to have one?

The government estimates that 20% of all house fires would be avoided if every home in the UK was protected by an RCD. In addition, there is no doubt that a person who inadvertently touches a live wire from a circuit which is protected by an RCD is much less likely to die, or be seriously injured, than a person who touches a non-RCD protected cable.

Legally, only new electrical work needs to comply with the latest safety standards. Therefore, so long as there are no immediate dangers or faults in your property, there is no legal obligation to upgrade your system. However, a consumer unit upgrade only takes one day and will only cost you between £400 and £600 (depending upon the size of your property) inclusive of labour and materials, so why wouldn’t you want to make your home safer?

Did you know Prime Electricians are now able to offer instant fixed price quotations for consumer unit upgrades online? What is more, customers who use this online tool receive a 20% discount, as it saves us from having to send an electrician to your home to provide a quotation. Click here to get an instant quote online now.