Also RCD Tripping

[mtiller]

I'm having a problem at home at the moment and any lines of investigation anyone can suggest would be much appreciated.

My RCD started tripping and by a process of emlinination, I identified the problem as being on the Ground Floor power ring main.

The circuit trips even if no devices are attached to any sockets. By running extension cables from upstairs, I have had basically all the equipment that would run on the downstairs circuit running via the upstairs circuit with no trips ( I keep the fuse on the downstairs circuit out of the consumer board) so I don't beleive the fault is in any equipment.

The fault is intermittent, the RCD trips only at night after about 7PM, this is the earliest I have seen, the latest was about 4am. Once it trips, it will keep tripping all night and come good sometime in the morning. It tripped last night at about 7PM having been OK for 36 hours (I thought I might have solved it). I have taken the front plate off all of the sockets and checked the wiring, sheathing any bare earth wires I can see to prevent neutral/earth shorts.

I run several computers on the Upstairs main which will be contributing to the capacitance of the house circuits, but the upstairs circuit has never caused a trip as far as I am aware. By that I mean that if I pull the downstairs fuse, the tripping stops and if I pull the upstairs it doesn't.

The RCD is an older mechanical type.

Any suggestions you can give would be much appreciated. I am getting to the point of having the wiring on that circuit replaced since I can see no other option.

Regards

Mark tiller

 

[Spark123]

Do you have a boiler thats fed from ground ring via fused spur unit?
Do you have any outside lights fed from ground floor ring via fsu?
Any signs of damp? Before you start ripping the wiring out have a spark do an insulation resistance test.
P.S. there is nothing wrong with a mechanical RCD, they are in some respects less vulnerable to failing than the electronic ones. If you have a spark in he should have a tester which can tell if the RCD is faulty.

 

[sm1thson]

mice / rats?

-leave a bit of bread/chocholate on the kitchen floor overnight, see if its still there in the morning (dont use cheese i hear it gives them the runs)

-is the oven plugged into the downstairs ring ?(i know you said you unplugged everything but if its plugged in on the ring with the socket behind then it could be missed!)

 

[JohnD]

Does the troublesome circuit supply a shed or other outdoor wiring?

Does it run under the floor where rodents might gnaw it?

 

[DESL]

Is the CU a split load or not

If you have an outside light with PIR this could be the problem as it will not arm until it gets dark ~7pm and once dark any thing moving near it will trigger it and if faulty trip RCD

Quite often these lights are spurred off the ground floor ring main

HTH

 

[JohnD]

Very good point Desl - sometimes outdoor lamps collect rainwater.

 

[DESL]

John D

It has to be time or light dependent to develop a fault like this

Time - boiler change settings and see if RCD trips

Light - black bag over PIR sensor on light or switch light off and then on again and check RCD

 

[industryspark]

What other circuits are protected by the rcd?

is it split load board?,

not hung any pictures up recently have you via a nail in the wall?

the guys who've posted so far have given some excellent suggestions so you've got some investigating to do.

let us know how its going.

 

[mtiller]

Firstly thanks to everybody for their questions and comments. I'm sorry it's taken so long to reply. I'll try and combine all the answers into one.

OK....

The Consumer unit is not a split load type, it is oldish but in good condition, it still has fuses rather than MCB's. The RCD protects all the circuits on the board.

The boiler is a combi boiler so no imersion heater and the wiring is connected to the old immersion heater circuit.

I have seen no signs of damp and I have been looking as that had occurred to me, sorry I didn't mention it before.

Rodent damage is a possibility, but we have 2 Siamese cats that are both hunters and I haven't seen any droppings nor have I smelt anything (Mice in particular have a distinctive smell). However I beleive the circuits do run under the floor so it's a possibility. (we do get the odd hedgehog coming in the back door to eat from the cat's plate!)

The oven was on the downstairs ring, a single oven, it was plugged into a power point that was in poor condition, with bad heat damage. Since we never use it (it smells when used and my wife has allergy issues so we have a big Micro Convect oven) I removed the socket completely and used a large 20 Amp ceramic connector block to connect the circuit and then wrapped it on LOTS of electrical tape. I also disconnected the Gas hob which used mains for the Spark.

We have no outside wiring and only one outside light. The light switch is getting power and the fuse is out so I presume that the power is from the downstairs light circuit. However, when I checked behind the switch tonight, I only saw 2 wires, both red connected to the switch. I'm not sure what that means about how it's connected. The last trib was after an hour or two of heavy rain, but not during the rain.

Anyway, I've decided to bite the bullet and get a sparky in that I trust. He'll be coming in the morning and I'll let you know what happens.

Once again thanks you to everybody, any more ideas gratefully received.

Regards

Mark

 

[DESL]

If you tell the electrician all that you have told us especially the outside light and the fact you have a trip an hour or two after heavy rain then it will save him time and you money

Given the info if I was called to this sort of fault I'd go straight for the light

 

[mtiller]

Thanks Desl, I will

 

[securespark]

Two other things stand out here:


a: Oven connected by 20A blocks? No fusing down?

But more importantly, no means of disconnection...


b: Boiler connection via old immersion circuit - isn't this on the RCD?

 

[mtiller]

Hi Secure,

A. Sorry, I didn't make myself clear, the Oven is completely disconnected and has no power to it. When I replace the oven there will be switch connecting it. The blocks were to connect the wires for the ring main cirecuit since they were no longer connected in the power point.

B. Yes it is on the RCD, but it is gas fired combi boiler, so power is just for the electronics. Also it's on a different circuit to the one that is tripping.

Regards

Mark

 

[mtiller]

Hi All,

OK, the electrician has been and we got the following results. Even with everything disconnected, there is some earth leakage on each circuit in the house. He suspects it may be a cumalative thing.

The toaster apparently is a definite problem and will not be used again. We'll go out and replace it tonight.

There was also a loose wire in the fuse box that he has tightened up.

He also indicated that the RCD wasn't tripping in the correct timeframe and should probably be replaced. I have been planning on updating it at some stage anyway, so that's not a problem. If the RCD trips tonight, we'll replace it soon, it not, we'll replace it later.

A quick question which I forgot to ask teh sparky. How do you check an appliance for earth leakage? Is it a simple test with a multimeter or something more complicated?

Regards

Mark

 

[JohnD]

You mentioned you had an oldish CU with fuses, and the RCD protects all circuits.

You might consider:
- having a new CU installed with MCBs
- Not having an RCD that cuts off all the power if you have a fault on one circuit.

A common way of achieving this is to have a split-load CU, however my preference is to have RCBOs (which incorporate an MCB and a small RCD) on the one or two circuits that need it. The other circuits have plain MCBs. This will prevent you losing other circuits when you have a fault on one. Also you do not suffer the problem of several sight leakages (e.g. cooker, immersion heater and central heating pump) adding up and causing nuisance trips. RCBOs can work out more expensive if you have a lot of circuits needing protection, but most houses only need one or two. If you buy a major brand of CU then you would be able to add an additional RCBO later, for example if you install a hot tub, garden fountain or outbuilding. The inconvenience that will be saved is well worth the expense.