DIY Doctor UK DIY Forums

Hi

First timer here hoping you can offer some advice

We have a dual floor barn conversion with spotlights in every room for lighting

Last night I went to the toilet during the night in the end bedroom (presumably at the far end of the electrical circuit upstairs?) And on exciting I turned the light switch (which also controls an extraction fan) off but the power tripped

Went to reset the RCD but everytime I try to turn the lights on in the upstairs the RCD trips. Occasionally it appears to be the upstairs lights RCD but in general it trips the main one on the RCD consumer box thing

I have tried turning off the associated extraction fan off at its fuse but to no avail. Only other thing I can think of is to remove the spotlights from the end bathroom from their sockets to isolate that bit off. Only reason I think of doing that is that at the time there were no other lights on so assuming the problem must be originating there

Any help or thoughts greatly appreciated

Fault finding with RCD problems is not easy. The big problem is we don’t switch the neutral and an earth to neutral fault can cause a RCD to trip as well as an earth line fault.

So even though switched off a fault can still be causing the RCD to trip. For an electrician we would turn off the power with main isolator as that means earth and neutral should now not be connected together. Even with MCB tripped or fuse out unless that isolator is off there is a connection between earth and neutral.

We then use a special meter that uses 500 volt to test between earth and neutral and work out which neutral has an earth fault. This involves removing neutral wires one at a time and slowly we isolate exactly where the fault is.

Some times we are lucky and we have a guess which turns out right other times it’s a slow pain staking process.

So let me give a few quick pointers. First if you have a camera take pictures before you remove any wire. We all intend to make careful notes but it’s so easy to slip up. I will assume a neutral fault so since you suspect toilet turn off isolator, not just pull fuse or trip MCB they don’t isolate. Then see if you can find a terminal block of some sort often with the spot lights there is no ceiling rose if you can find one then put a terminal strip with each neutral wire separated and with every one clear, check to see if fault removed. You may be lucky. Note neutral coloured wires often are line with lighting circuits do not assume all black or blue wires are neutral.

Second easy test is with any two way lighting flick one of the switches and try again. With two way lights you have four options two have lights off and two have lights on of those two with lights on it’s not unknown for one to have a borrowed neutral so worth a quick test.

Another test is unplug and where you can’t unplug switch off all fuse connection units again we are looking for neutral fault so single pole switches or removing a fuse will often not remove the fault.

I know it sounds daft but a bit of bread stuck in a toaster can cause the power to trip every time you use the kettle.

You say spot lights many are extra low voltage and there could be a earth fault on the transformer or power supply causing the earth fault but in real terms once you have tried to few things listed it’s really time to get in the electrician with his tester.

My friend had a compressor and I had multi-meter in my hand so quick test showed no fault. But once I got out the proper tester the fault showed so easy. Often it’s time to bite the bullet and get an electrician.

Remember safety first. If your not happy testing don't do it. Remember I have no way to assess your skill.