An RCD that trips once in a blue moon is doing its job. One that trips every few days, or every time it rains, is telling you something is leaking current to earth somewhere in your home. Here is how to narrow it down before you pay anyone to come out.
A residual current device measures the current going out on the live conductor and compares it with what comes back on the neutral. If the difference reaches 30 milliamps, which is the standard rating for household protection, it disconnects in under 40 milliseconds. That imbalance means current is escaping to earth, possibly through a person.
The important point is that an RCD does not trip because a circuit is overloaded. That is what MCBs and fuses are for. If your RCD is tripping, you almost always have an earth leakage fault, and the trick is finding which appliance or circuit is causing it.
In our experience across the city, from the 1930s semis in Hall Green and Kings Heath to newer builds in Longbridge, the same handful of causes come up again and again. Moisture is the biggest one. Outdoor sockets, garden lighting and shed supplies are often installed in boxes that were never properly sealed, and the first heavy downpour brings the RCD down.
Appliances with heating elements are next. Immersion heaters, electric showers, ovens, kettles and washing machines all use elements that can crack and let a small amount of current leak through the insulation. The leak is usually tiny at first and gets worse over months, which is why the tripping seems random before it becomes constant.
Start by unplugging everything you can and resetting the RCD. If it holds, plug appliances back in one at a time, leaving each running for a few minutes. When it trips again, you have found your culprit, or at least one of them. Fridges, freezers and washing machines are worth testing over a longer window because they do not draw power continuously.
If the RCD trips with everything unplugged, switch off all the MCBs, reset the RCD, then switch each MCB back on in turn. The circuit that drops it is where the fault lies. Anything wired directly, such as a shower or immersion heater, will need its own isolator switched off to test it properly.
Keep a note of when it trips. If it always coincides with rain, look outside. If it happens when the shower or immersion is on, that points to an element. If it trips at night with nothing obviously running, a fridge or a boiler control circuit is worth suspecting.
If your own checks point to a fixed circuit rather than a plug-in appliance, that is where DIY should end. Tracing a fault in fixed wiring needs an insulation resistance tester and an RCD tester, and the readings only mean something if you know what the standard expects. A registered electrician will usually locate the fault within one to two hours, and the fix might be a new socket, a replaced element or, occasionally, a run of cable.
Costs depend on what is found. A straightforward fault-finding visit in Birmingham typically falls somewhere between £80 and £150. Replacing an outdoor socket or a length of damaged cable adds to that, while a new consumer unit is a bigger job. If your board still has a single RCD covering the whole house, it is worth asking about a split-load or RCBO board so one faulty appliance does not plunge the entire house into darkness.
Not in itself, because the device is doing exactly what it should. The danger is the fault behind it, which could be a live element in contact with water or damaged insulation on a cable, so it should not be ignored or bypassed.
Only if it has been tested and found faulty. In most cases the RCD is fine and something connected to it is leaking current, so a new device will trip just the same.
Water is getting into an outdoor fitting, most often a socket, garden light or a junction box on a shed supply. The seal or gland has failed and needs replacing, and the fitting should be checked for corrosion at the same time.