Nuisance RCD tripping – What causes it and how do I fix it?

Household electrical problems can be a major annoyance, but some pose an infinitely greater inconvenience than others. Perhaps the most common problem fault experienced by every homeowner is a tripped RCD.

We’ve all been there – we’ve just put the kettle on for a cup of tea before bed and suddenly the power snaps and we’re forced to shuffle around in the dark with our smartphones to find the RCD box (and it’s rarely in the most convenient place).

But if your RCD is tripping every couple of days (or even daily) and it’s become a genuine nuisance in your daily life, is there anything you can do to help the situation before calling someone in yet again? Let’s start with the basics.

Why is my RCD tripping?

Your RCD (residual current device) serves as your major protection against electric shock which is why it is now mandatory for all homes and businesses to have one installed. When your RCD trips what it thinks it’s doing is actually saving your life because it’s detected an electrical fault that could prove deadly if the circuit is not closed off completely.

Occasionally, an RCD can trip even when there is no fault to speak of (if there is a great surge in power, for example) but if it’s happening regularly then it’s most likely due to one of three causes:

Faulty equipment – As electrical equipment ages, it can become more unstable, particularly when used in tandem with other devices. If your RCD is constantly tripping when you use a specific appliance (whether it’s your washing machine, your toaster, or your blender) then it is most likely to be a fault with the equipment. So, rather than calling out an electrical engineer, simply replace the faulty item or get it fixed.

Bad wiring – This one is a lot more concerning. If you can’t see the RCD tripping being related to any specific appliance then it might be a problem with your wiring that needs some urgent attention.

If the wiring in your walls is faulty or frayed and has lost its insulation then it can cause a short circuit, resulting in an electric shock or even an electrical fire if there is no RCD installed to automatically break the circuit. If you suspect bad wiring in your property then you must immediately get in touch with your local electrical services provider and call out an electrician.

Ground fault – This refers to your RCD tripping to prevent an electrical current from making a connection with a grounded surface, which can prove fatal. This is in situations such as if a hairdryer falls into the bathtub, somebody puts a knife in the toaster, or somebody drills through a wall into active wiring.

How to fix nuisance trips?

If none of the above sounds like they apply to you, then you could have a nuisance trip problem. The problem with these so-called ‘nuisance RCD trips’ is that the cause can be quite difficult to figure out. That’s why we would always recommend calling out an electrician.

However, if it is something that happens constantly, even after the electrician has been out and given you the all-clear, then a good quality leakage clamp meter and some background knowledge can save a lot of time and frustration, not to mention your wallet.

Modern appliances and plug-in power supplies, by the nature of their design, generate low levels of leakage current, even when there’s no fault. This becomes a problem when there are several appliances connected to the same circuit and their leakage currents combined exceed the trip threshold of the RCD protecting the circuit. This causes the power to cut out unexpectedly, even when there is no actual problem to speak of.

To reduce nuisance RCD tripping that’s a result of cumulative leakage from appliances, the 18th Edition Wiring Regulations Guide includes specific maximum values for protective earth currents (Regulation 531.3.2). According to the guide: “The accumulation of circuit protector currents/earth leakage currents that are present during normal operating conditions shall not be more than 30% of the rated residual operating current of the RCD.”

This means that, for example, a current of just 30% of the residual operating current can cause a trip and when you consider the average operating current is around 30mA, that’s just around 9mA that can set it off, so to speak. Eve a hoe computer can generate a leakage current of up to around 3mA on its lonesome.

The only way to definitively ensure nuisance trips cease completely is to measure the leakage flowing using a leakage clamp metre for reliable results.

However, please be advised that when working on any electrical system, you must have access to the distribution board and the electricity must be switched off at all times.