Intermittent Tripping Of RCD

[espin]

Help! My RCD trips intermittently, it's driving me beserk this Xmas.

The CU is a Memera 2000. It has a split load with the 2 light rings and the oven on on the non-RCD split and the socket rings on the RCD split.

The RCD seems to trip intermittently... it can be reset for a whole evening so it is not a permanent installation problem like a cable break or a nail through a cable(?). It seems to be more like when there is an excessive draw on the supply eg: our CH boiler or a blender or the lawn mower!

I've tested the house with everything off (and unplugged) and the blender will still trip the RCD. I'm guessing that the lawn mower and the blender have quite noisy motors that draw a surge?
I've been able to have every electrical appliance plugged in and working and the RCD does not trip! (CH, 2 TV's, Fridge, Oven etc).

I thought it might have been my Myson Apollo 30 boiler, since it always seems to trip whenever the heating needs to come on and the CH system has been running cold. When the nightly temperature drops to 4degC in the morning this means that it can trip 3-4 times before it all settles. not much fun having to stand over it at 4am in the morning.

I've read through a number of past topics and I've been able to get some good hints, but no solution or recommended path of investigation.

I'm not an electrician... but I've had no troubles in rewiring/extending sockets or roses or in tracing cables through the house. and i've exhausted all my theories on this....

I've had a electrician / plumber come and inspect the boiler and the RCD and he came up with no definitive answers other than an an leakage to earth. Before I get in the electrician in again what can I do to find the problem or help cut down the diagosis?

Any help appreciated! Thanks!

 

[DESL]

You need to go through a process of elimination

Blender
Lawn mower - this time of year?
CH

I suggest you don't use the blender or lawn mower and see whether your RCD still trips

Boilers aren't normally connected to RCD side of CU but if yours is and the RCD is tripping maybe there is a water leak effecting the electrics of the boiler.

We all refer to nuisance tripping of RCDs but usually it's because there is a fault somewhere

 

[JohnD]

It's often "watery" appliances - steam irons, kettles, washing machines, immersion heaters, CH pumps. So unplug all of these that have plugs. Switch off as many as you can of the others (the immersion heater, for example, is likely to have a 2-pole switch, which you need).

See if the time of tripping is when the CH is on.

If you have an appliance that you suspect, plug it in via one of those garden tool RCD adaptors - they usually trip faster than the big RCDs in consumer units.

Look for any signs of rodents, especially under the floor; or water leaks, especially inside your boiler.

It is quite possible that you have a general low level of earth leakage from an accumulation of appliances, and this takes you near to the tripping point of your RCD. You will need a well-equipped electrician to find that, but it is quite likely to be the wet ones.

If you have any outside sockets, or outside lamps run from the socket circuit, examine them and their cables for water entry, and try disconnecting them at the house end.

If it still trips when you have unplugged everything excpt the boiler, you have found your culprit. Often a small leak will drip onto the electronic control board. A boiler engineer will fix that for you.

 

[Lectrician]

It will trip when you increase load due to a N to E fault of low or high resistance.

You need a decent spark to come out and use an insulation tester to find this fault.

Most likely the cent heat - turn that off at the souble pole switch and see if that cures it.

Lose that other electrician you had - of course it's an earth fault - he should have got a tester out on day 1.

 

[espin]

Thanks for the swift replies!

I'll attempt to give some more information regarding the suggestions that you have prompted (in no particular order)...

BTW: Just for clarity, 'off' means still plugged in but switched off, since I'm realising that any connected wire is an electrical path regardless of being engergised or not.

I can have every single appliance I own unplugged, and turn off all the lights, the cooker and the CH. Plug the blender in on any 13amp socket in the house and it is guaranteed to trip if I rev the blender a bit. I don't suspect the blender because it will work if I don't rev it so madly! Also the lawn mower does the same [DESL.. this is in the summer! ]

JohnD - I've tried a RCD adaptor, but with the CH off and madly thrashing the blender, the CU's RCD still trips. I'm guessing that it pops before the RCD adaptor.

Am I correct in understanding that so long as the boiler is wired into the electrics but off, that a water leak will still affect the general electrics of the house?

In the kitchen the walled sockets are all on the RCD side so that includes the power supply for the boiler's timer. Only the oven's big fat socket is non-RCD'ed.

The CH baffles me a bit though, there are no visible leaks on either the boiler or the immersion heater. The immersion heater does not have a double pole switch (ie: there is no electrical heating backup in this cheapo house). All the pump switches and wires are dry to touch (albeit a bit warm from the hot water pipes).I can't see a condensation problem either, the boiler is in a open top/bottom cabinet.

It was the timer that I thought was originally suspect since the most frequent event is when the timer clicks on... it is an old Myson Apollo 30 with a "clockwork" timer (?) the and I thought that it may have been sparking on one of the ratchets but after closer inspection I think that it has more to do with the ramp up of the fan/motor/etc. The CH is usually off all day (the house being a cosy 14degC) and when I switch it back on, it will usually trip within 5 secs once or twice, and then stay on happily till 22:00 with another cooling spell before it trips at 1am to give me some top up heat.


Today will be spent ensuring that all my lighting and socket switches are securely wired. I'll be trying to hunt down a good electrician tonight.

Thanks again for your help!

 

[JohnD]

Even if the boiler is "off", if it is still connected and does not have a DP isolator, earth leakage can still occur between the Neutral and Earth, and this will trip the RCD. Many appliances and switches only isolate the Phase/Line/"Red" wire; so do fuses and (almost all) MCBs.

I think I spy a water leak inside the boiler. Or maybe the pump. If it was inside the boiler it might fry off or evaporate when the boiler was hot. If you are safe to tinker, you might be able to put the boiler on a plug and an extension cord to the (non-RCD) cooker socket, using your "adaptor" RCD to see if it trips. If you ask around for a recommended CORGI engineer and tell him you think you have an earth leakage in the CH, and ask if he is equipped to test it, you may get a good resolution. Also, if you post the make, model and age of the boiler, pump and controller on our "Plumbing and Heating" forum here, someone may immediately know the probable cause.

Although an RCD adaptor will (in my experience) trip faster than the bigger one in a CU, this is only if you have little background leakage. Otherwise there will be some existing leakage pushing the CU towards its trip even before you apply the test current.