Irritating problems with RCD tripping

[Spanky2k]

Hi all, we moved to a new (old, Victorian) house a few months ago. I’ve been having some annoying problems with the RCD on the circuits tripping. When turning something on that has a relatively high load, sometimes it will trip the RCD. I.e. turning the microwave on, kettle on, washing machine getting to the water heating part of it’s cycle. What is incredibly frustrating is that this doesn’t always happen. When it’s in a ‘mood’, it will trip every time I try to turn something like the kettle on. Other times, I can have everything on at once and it doesn’t bat an eyelid.

I’m guessing it might be something weather related and initially thought it might be to do with the wet. I took all the sockets and switches off in the kitchen (as I’m guessing the problem is somewhere in the ‘newer’ wiring and the kitchen seems to have been redone a few years ago) and some of the metal back boxes behind isolation switches were rusty. I praised my lucky stars and thought I had narrowed it down and replaced the switches and have had them hanging off in front so that if there is any moisture getting in from the outside wall, it wouldn’t be a problem. No trips for a week but then the problem comes back. I *think* it may be cold related. We never noticed it when we moved in in September and it’s been more prevalent recently with the weather being colder.

In terms of testing, I’ve got a clip on load meter and I’ve used that to try to see if there’s anything like a limit over which the power will cut out. Alas, there is none. Sometimes I can be drawing 13kW of power and it won’t trip. Other times, I can be on 0.5kW and turning the kettle on (~1KW burst load) will make it trip.

I’m not against getting a sparky in but if I can narrow it down myself, I’d much rather try that first as I could end up getting someone in at a time when it’s not tripping at all and end up having to pay someone for days worth of work trying to hunt it down when it might be easy to find if it’s in a ‘mood’ with the right equipment.

If it weren’t for the fact that it was so temperamental, I’d assume it was an incorrectly wired socket. I’m guessing a socket tester (DiLog EKB001 maybe?) might help narrow that down if it’s that but what can I do to track it down if it’s something else? Right now, I’m armed with a multimeter, a screwdriver and a clip on power draw meter. I’ll happily invest in better testing equipment though.

The RCD is a Protek T100-30-2 with a 30mA delta. The socket circuits that run into it all have 32A Protek 132/2B MCBs. The lighting never trips when the RCB trips.

 

[EFLImpudence]

Do you have any outside lights, sockets or other things which may be getting wet and then drying?

It sounds as if there is a Neutral to Earth leakage fault which could be on any of the RCD protected circuits.
You would need an Insulation Tester or Earth Leakage Clamp Meter (to measure milliamps) to detect the fault. None of the tools in your kit is likely to find it.

 

[Spanky2k]

Thanks EFL. There are some external lights - a few new ones which we had put in after the issue started but there are also two external lights which we don't really use - when we moved in only one was working and the bulb blew in the other not long after and I've never got round to fixing them. They're wired up to a dimmer by the back door. Thinking about it, these may be connected to the sockets rather than the lighting circuit as I've seen a couple of cables go off from a junction box below our boiler in their general direction and I can't think of what else they could power. I'll have a look into it and disconnect those cables if they do power those lights and see how it goes. I've ordered a clamp meter which should be here tomorrow so I can look into any earth leakage with that hopefully.

 

[EFLImpudence]

Thinking about it, these may be connected to the sockets rather than the lighting circuit

That is often the case.

I'll have a look into it and disconnect those cables if they do power those lights and see how it goes.

Yes, disconnect the L and N; not just the Line(live) or just switch off.

I've ordered a clamp meter which should be here tomorrow so I can look into any earth leakage with that hopefully.

It will be difficult to detect an intermittent fault as obviously, when there it will trip and when not tripping will not be there.

You could test the circuit, when not tripping, and then disconnect the wires and see if it makes a difference. It may give you a clue.

If you don't know, you put the clamp around L and N and it tells you the amount of leakage, which is what you want; not around the earth wire as the actual current on the earth wire is irrelevant.