RCD Tripping on low load - Help much appreciated

[JesterRIP]

I have also had my light fitting down recently too (as a builder knocked it with one of his tools and it blew the dimmer switch somehow). Since then I have removed the dimmers and replaced them with standard light switches - which going back to the start of this thread, are the bits I have disturbed.

Have the problems started since the builder came to visit? Have they done any electrical work in your CU?

Does the RCD protect the socket circuits only or lighting too? Is it a dual RCD board or a split load board?

If you could post a pic of your CU and the incoming supply area it may help.

That's the weird thing - since he cleaned up and packed up, we've had the kettle on the go - as well as this mammoth industrial carpet cleaner. I can describe the boards for you... Basically it starts off with a 100A cct bkr going into the meter, then out to the MCB board with the old style fuse wire cct bkrs, 2 white (5A), 2 blue and 2 red ring main - with an ON/OFF switch on that ...then it goes into the RCD unit (not sure if 30 or 100).

I think maybe I should just kill the power and take each socket off the wall in turn to see if there's any neutral cables that have been crushed back against the metal case. After that, I'll check the outside light for signs of moisture ingress ...and then if still no joy, do what ericmark suggests and go with the electrician idea.

 

[bongos]

I can describe the boards for you... Basically it starts off with a 100A cct bkr going into the meter, then out to the MCB board with the old style fuse wire cct bkrs, 2 white (5A), 2 blue and 2 red ring main - with an ON/OFF switch on that ...then it goes into the RCD unit (not sure if 30 or 100)

That description's a little confusing.

Incomer-->--100A Main Switch-->--RCD-->--Fuseboard-->--final circuits

Is the above right? If it is then a fault on any of your final circuits will cause the RCD to trip. This setup is not ideal and isn't allowed under the existing regulations due to the problems its causing in this case (you lose all the circuits at once). This doesn't mean you have to change your existing setup through as the regs are not retrospective.

This also means that an accumulation of earth leakage over all the circuits is enough to tip the RCD to trip. My first suspect would be the outside lighting and any other outdoors stuff but it sounds like your fault could be anywhere on the system. As soon as you use a high power appliance there is enough earth leakage to cause the RCD to trip.

It might be time to call a spark who will be able to insulation resistance test each circuit and see where the earth leak is coming from.

 

[JesterRIP]

No I'm pretty sure it goes:

Incomer-->--100A Main Switch-->--Fuseboard-->--RCD-->--final circuits

 

[ericmark]

No I'm pretty sure it goes:

Incomer-->--100A Main Switch-->--Fuseboard-->--RCD-->--final circuits

Not really possible it would need either multi RCD's or not all final circuits through RCD.

Rules say:-

(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation

With a 100ma RCD (iii) and (iv) is not a problem so you are allowed a single RCD covering all circuits but a 100ma RCD does not protect personnel so shower supplies, sockets etc need 30ma RCD to comply with 17th Edition.
But with 30ma RCD then (iii) and (iv) do become a problem and there are a few ways around the problem including battery backed lights (Emergency Lights) and multi RCD either just two or many as with RCBO's.
If the trip is tripping is due to a fault as I am sure it is with you then (iv) does not apply.
It is hard as when building a house and installing the electrical system one has know way of knowing if the collection of items the house holder will use will cause (iv) and only (iii) can really be insured.

 

[JesterRIP]

Not really possible it would need either multi RCD's or not all final circuits through RCD.

Yes I seem to remember a couple of years ago whilst decorating the downstairs bathroom, I switched off the supply at the RCD and the heater cables coming out of the wall were still showing 240v AC on the Fluke...

So maybe that applies here?

 

[ColJack]

eric, the NEW rulse say that, but the old ones didn't..

this isn't a new build or a new electrical install.. it's a fault on a system that someone has bodged over the years..

if no electrical work has been done and the only thing that has been done is the hiring of a carpet cleaner then I'd hazard a guess that there's water gotten into a JB hidden under the floor where you soaked the carpets?

an hour for an electrician to come out and electrically test all your circuits should identify the circuit that the fault is on, and then you can investigate further..

for our benefit, can you tell us if it's only one set of plugs that trip the RCD ( ie just the upstairs ones or just the downstairs ones )
what does the RCD control? just the sockets or everything in the house?

 

[bongos]

Yes I seem to remember a couple of years ago whilst decorating the downstairs bathroom, I switched off the supply at the RCD and the heater cables coming out of the wall were still showing 240v AC on the Fluke...

So maybe that applies here?

If you have only one RCD then all the circuits would not go through it from leaving the fusebox. So if the RCD is after the fusebox then it controls only one circuit and as you say that you lose power to everthing when it trips then it must be before the fusebox.

A pic would help as to the state of your wiring but the installation sounds old and it may and as insulation breaks down there is now enough earth leakage overall to trip the RCD.

ColJack could well be right with water in a junstion box under the floor. But whatever the fault is it will be hard to diagnose without the proper test equipment. It might be time to call a spark as the install sounds like it could do with a look over anyway.

Keep us updated either way.

 

[JesterRIP]

Cheers Bongos,

I am decorating in there later this afternoon / evening. I'll take a crude pic or two with my phone and upload it for you to have a butchers at. I appreciate the advice anyway - and that's to all of you that have contributed to this thread.

 

[JesterRIP]

Eureeeeekaaaaa!

I found the fault at last! I was just about to post some pics of my CU as well! (Yes you were right about the order ...incomer...100A...RCD...Cct Bkrs...Circuits...)

It goes back to the very first reply on this thread from Eric - Neutral/Earth fault - and after all of your comments and advice it helped me work out what had happened, and where to look. For those who are stupid enough to make the same mistake as me and wonder why your electricity suddenly develops a fault at higher loads, read on...

A few years ago, I had fitted an extension around my bedroom and mounted it to my dressing table to plug my lamps in etc. When it came to moving out of the place, rather than remove all of the cable going around the room, I turned it off at the source socket and just unwired it at the dressing table end, leaving the cables exposed. After reading back through this thread, I suddenly realised that regardless of the fact that the socket was switched off at the wall, there was a possibility that the exposed earth and neutral cables touching would still recreate the problem and produce the same symptoms.

On examination of the exposed cables in question, I found them embedded slightly into the carpet - touching. And after pulling the cable out of the socket completely and flicking the RCD back on, naturally the vacuum, drill, kettle and every other appliance worked without problem.

After a little recollection, I remember now that once I had cleaned the carpets (as I am getting the place ready for renting) I carried on clearing out upstairs, including the area where the cables lay exposed.

Thank you all for your valued input to this problem. Happy to say it is now solved, and I will keep a watchful eye on these threads to see if there is anything I can offer back.

Kind regards,

Jester.

 

[aptsys]

rather than remove all of the cable going around the room, I turned it off at the source socket and just unwired it at the dressing table end, leaving the cables exposed.

 

[ColJack]

it's not solved.... pull that f'ing cable out, don't leave it like that but just unplugged..

 

[bongos]

Glad the problems sorted but make sure you get rid of that cable! It's not the best way to extend things (as you found out) and the last thing you want is new tennants messing around with that setup.

 

[JesterRIP]

And after pulling the cable out of the socket completely and flicking the RCD back on, naturally the vacuum, drill, kettle and every other appliance worked without problem.

....That's what I said!

I've hardly been upstairs since I moved out - the only reason I did go up there was to get the dressing table out - hence why things were left as they were. All ok now. Thanks again!