UK RCD Trip - insulation problem from too much load?

[Newbie101]

Hi guys, first time poster, be easy!

I'm caring for a friend and last night while sleeping on the sofa-bed an emergency system that had lost power was sending out a warning signal. Startling to say the least. The RCD had tripped and after some internet sleuthing I managed to isolate the problem to the ceiling lights. It was raining at the time, so there was a chance that water had somehow affected the earthing(?).

In the morning I've looked at around all 29(!) ceiling spots to see if there was obvious water damage - there isn't any. So we called my friends neighbour who is a handy man and electrician.

All 29 bulbs are on the same ring. Handyman said this is crazy. It's impossible to isolate where the problem is. For 29 bulbs there are 8 dimmer switches and 1 regular switch. Two of those dimmers have two dimmers on the plate so technically 10 dimmers in total. Some are old, some are new. The old ones don't work so well and the lights can flicker a lot (they're not LEDs), but if you find the sweet spot it's not a problem.

Anyway, handyman took a few of the spots out of the enclosures, but they seem to be wired within the ceiling, each having a thick grey wire from bulb to beyond where he can access. In an attempt to isolate the problem further he disconnected the live wires from all the dimmer switches, individually. We tested the MCB switch each time but even after all were disconnected it still tripped. He said this was odd and not good!

He tested the wires going into the fuse box with his multimeter and it seems it's reading at a high number when it should be zero. He said the brown live was too thin for the load, it's 1.5mm, and that the insulation has gone (somewhere) and touching the earth wire. He says the only way to fix this is to replace the wire entirely, with a thicker one. This will involve a few holes drilled into the ceiling to feed the new wire through.

I guess my question is, has he checked everything? Is this really necessary? It's not a small job, and will involve me moving my terminally ill friend back to mine for a few days, not to mention the unsightly interventions to the ceiling...and perhaps walls.
Sorry for the long query, but any advice would be most welcome. Thanks

 

[Mike Johnson]

Welcome to the forum, I am sure one of us can help, where about's in London is this problem, someone may be local and be able to help.

You say it could be Water damage, therefore a couple of questions.

Is this a top floor flat?

Are there any external lights or sockets?

29 ceiling spots at what wattage, even if they are all 100watts that's only 12.6amps, a 1.5 supply can take a maximum of 17amps so below the threshold, but its not a good idea to have all the lights on one circuit due to one fault and all the lights are off.

 

[Newbie101]

Welcome to the forum, I am sure one of us can help, where about's in London is this problem, someone may be local and be able to help.

You say it could be Water damage, therefore a couple of questions.

Is this a top floor flat?

Are there any external lights or sockets?

29 ceiling spots at what wattage, even if they are all 100watts that's only 12.6amps, a 1.5 supply can take a maximum of 17amps so below the threshold, but its not a good idea to have all the lights on one circuit due to one fault and all the lights are off.

Hi Mike,

Thanks for quick reply. Edgware Road area - but it's tricky because it's his neighbour who is helping so it's a tricky situation to say no thanks I want to get someone else to check. Though, if I can point him in the direction of trying something else first, that may work!

It's a top floor flat and water has been a some concern in the past. Though never re electrics. There is some water damage in the flat from about 9 months ago, but since then no new signs of it - and I've checked all the existing ares and potential new areas, and they all seem ok.

There are two external light fixtures, covered up as you'd expect and these are on the same ring (? line/circuit breaker) as the other 27 lights.

The rain was rather light last night, so surprising that it could have such an affect, but then again, water is water and if it gets in the wrong place that's it. This handyman is convinced, because of the reading at the fuse box, that it can't be any of the individual lights. Is there something exploratory you could suggest he should do on the external lights before he does this massive job?

Thanks

 

[westward10]

As already mentioned the cable is not undersized so that is not an issue. The circuit needs insulation resistance testing and if there is a fault the circuit needs systematically breaking down to locate the fault. It sounds like the neighbour is not up to this task.

 

[Mike Johnson]

Yes disconnect the external lights from the circuit and see if the problem persists, that would be the first investigation a competent electrician would do, they would than use a MFT (multi function tester) to test insulation and continuity of the whole circuit, did the handyman have a MFT or just a multimeter, MFT's cost upwards of £500.00 they are a bit more complex that a multimeter.

Typed at the same time WW.

 

[Wilko]

Hi - sorry to hear about the light circuit tripping the RCD.

As per MikeJ, the cable size of 1.5mm2 is fine for a lighting circuit and it has a 6A MCB (from your photos) to protect it.

Yes the problem is likely to be an unwanted connection to E somewhere in the circuit. An Electrician would work to find this fault with their test gear. It’s just not warranted to re wire the circuit until all other possibilities have been examined.

Someone here will be nearby and will help you if you ask for it.

 

[Newbie101]

This is disturbing, and so difficult to manage. He's gone off to buy new wire and new dimmer switches.

To answer one question, the external lights were disconnected from the circuit by removing the live wire from the dimmer switches. The box still tripped after doing that. Is that sufficient to rule out the external lights as being the problem?

The only multimeter he has was a longish yellow one, it wasn't as sophisticated as I've seen on youtube videos, but that's a layman's view.

How would you test the line elsewhere to determine where the problem is? When he took the spots down from the holes, there were grey insulated cables, nothing on show etc. Would he need to take them apart and use an MFT?

 

[Mike Johnson]

Guy's Edgware Road area with a carer looking after a terminally ill friend, they have no lights, can one of you attend?

 

[westward10]

You have ended up in a tricky situation here trying to do the right thing. The cable may or not need replacing but needs confirming by testing using an insulation resistance tester, it doesn't have to be a Multi Function Tester as long as the tester can carry out the correct test. Replacing parts and hoping isn't really the logical way forward.

 

[Newbie101]

You have ended up in a tricky situation here trying to do the right thing. The cable may or not need replacing but needs confirming by testing using an insulation resistance tester, it doesn't have to be a Multi Function Tester as long as the tester can carry out the correct test. Replacing parts and hoping isn't really the logical way forward.

Exactly that, and exactly my concern. This is not a small job, and there is no piping so replacing the wire will involve digging out plaster and potentially concrete, or the alternative, unsightly trunking.

If one of you were here, how would you be checking systematically for the fault?

 

[westward10]

I know the neighbour is trying to help but they do not know the correct way to proceed with this. You test the entire circuit using an insulation resistance test and if a fault is indicated you break the circuit into parts to locate the fault.

 

[Mike Johnson]

Insulation resistance test on the circuit at the DB and then breaking down the circuit into individual bits and testing at each light.

WW you have done it again, you are just that bit quicker. ?

 

[Newbie101]

I know the neighbour is trying to help but they do not know the correct way to proceed with this. You test the entire circuit using an insulation resistance test and if a fault is indicated you break the circuit into parts to locate the fault.

The problem, as I understand it (as I've been told) is that breaking the circuit into parts is impossible. Could you explain what it means exactly so I can say if it's correct or not?

Also, when he tested the wires at the fuse box, and had a reading that wasn't zero (I think it must have been 240), he said this was conclusive evidence that the whole line needed replacing. He said something about testing it against another wire and the same thing happened. Are you saying that that's wrong too? My layman's understanding of this is that that just proves that there is indeed an earth problem somewhere on the ring. And it could be solved by finding which light it is that's causing it.....BUT, all the live wires from the dimmer switches were disconnected when he did this, so surely, that would be a way of isolating each set of bulbs? No? Argh!

 

[Intoelectrics]

As westward states ^^ You need an experienced electrician with the proper test equipment. If there are dimmers and such then an electrician will know how to test properly and how to trace the fault. It may turn out to be something simple and not require a re-wire or all new switches.

 

[westward10]

It is not clear the type of test he carried out as the figures you quote make little sense. The actual dimmer switches are almost certainly not the cause.

 

[westward10]

If he is intent on replacing this cable then do it temporarily first without destroying the wall and decoration.

 

[Intoelectrics]

No disrespect to your neighbour and I'm sure he is doing his best to help out but it sounds like from what you have said that he is not an electrician. This job requires an experienced electrician to investigate.

 

[Newbie101]

If he is intent on replacing this cable then do it temporarily first without destroying the wall and decoration.

Is it something that can be done temporarily?!

To add insult to injury it seems the immersion heater isn't functioning properly!! It's on the same RCD circuit (along with the bathroom pump and heaters which both work as expected). The water is warm, but not hot, which is obviously strange. It seems too much of a coincidence not to be linked. But if they are linked, why would that fuse not trip and yet the lights do!

 

[Mike Johnson]

The plot thickens, you most definitely need a professional electrician to look at this, does you friend have home emergency insurance? if so call them out.

What is the ceiling construction if its a suspended ceiling then the temporary fix is a simple matter.

 

[telectrix]

1. outside lights. both L and N need to be disconnected to rule them out.
2.Insulation testing should give high readings, in the MegOhm range, not 0 as your neighbour says.
3.this is not a job for a handman with a miltimeter. it requires an electrician experienced in fault finding with the correct tester/s to investigate.
4. rewiring a "suspect" cable can cause untold damage to decor and you may still have the fault after.

 

[Newbie101]

1. outside lights. both L and N need to be disconnected to rule them out.
2.Insulation testing should give high readings, in the MegOhm range, not 0 as your neighbour says.
3.this is not a job for a handman with a miltimeter. it requires an electrician experienced in fault finding with the correct tester/s to investigate.
4. rewiring a "suspect" cable can cause untold damage to decor and you may still have the fault after.

Hi Telectrix

1. Is disconnecting the live wires from the dimmer switches to the outside lights sufficient? If not, what constitutes disconnecting them?
2. I think what he was showing me was voltage.
3. I agree
4. Absolutely this too. I am not thrilled at the thought of this at all. The person I'm caring for doesn't seem to mind so much as long as it fixes it and it is the only solution...but we're both not so sure. I think trunking would be the least damaging solution despite being unsightly.

Is it possible that the Immersion heater, which is on Fuse 3 of the OP photo, could have caused this, despite not tripping? The heater and pump on the same fuse are still working as normal, and the water heater sounds like it's working still (though the water isn't as hot).

 

[Newbie101]

The plot thickens, you most definitely need a professional electrician to look at this, does you friend have home emergency insurance? if so call them out.

What is the ceiling construction if its a suspended ceiling then the temporary fix is a simple matter.

Quite! I just asked his wife and she said he did use an MFT but I've just googled and I don't think he did - I think he used a Fluke T6-1000, LCD Voltage tester.

It's not a suspended ceiling. Which makes life very difficult even for diagnosis, on top of everything else.

This is a real FML moment, things are so stressful right now. But thank you all for your advice and tips so far. I know you're all just internally screaming the obvious 'get a proper electrician', I wish were as simple as that. Sorry.

 

[telectrix]

re-read my point #3 in my last post. it's the only viable option.

 

[Newbie101]

re-read my point #3 in my last post. it's the only viable option.

I know - I'm working on it. But in the meantime, could you give me a clue to number 1? Is what he did enough to 'disconnect' the outside lights, thus isolating them?

 

[Mike Johnson]

Short answer to your post 23 "NO"

Newbie101. I think you have now exhausted the amount of help that we can give you on here, as has been said in quite few post, you need a professional electrician to look at this.

 

[telectrix]

I know - I'm working on it. But in the meantime, could you give me a clue to number 1? Is what he did enough to 'disconnect' the outside lights, thus isolating them?

no. as you could have a N-E fault which would still be there if you only disconnect L.

 

[Mike Johnson]

Which of these instruments he used did it look similar too.

 

[Newbie101]

Which of these instruments he used did it look similar too.View attachment 63753

Most like the one in the middle. I linked to what I think he used earlier, but it's perhaps under moderation still. My memory is it looks like the Fluke T6-1000, LCD Voltage tester, but I don't remember the pincer like top part.

 

[Newbie101]

no. as you could have a N-E fault which would still be there if you only disconnect L.

So disconnecting all the wires within the dimmer switches for the outside lights would suffice for full disconnection? I'll try that to see if that isolates it.

 

[telectrix]

So disconnecting all the wires within the dimmer switches for the outside lights would suffice for full disconnection? I'll try that to see if that isolates it.

not necessarily. you maynot have the neutral at the switch.

 

[Mike Johnson]

The instrument in the centre of my post above will not measure insulation resistance, only voltage and continuity in a limited sense, it is used by an electrician only to test if voltage is present any other tests are performed with the instrument on the right hand of the above pic, which is a MFT.

 

[Newbie101]

The instrument in the centre of my post above will not measure insulation resistance, only voltage and continuity in a limited sense, it is used by an electrician only to test if voltage is present any other tests are performed with the instrument on the right hand of the above pic, which is a MFT.

That's what I thought

not necessarily. you maynot have the neutral at the switch.

Interestingly, I just disconnected the two dimmer switches that are able to control the outside lights. Despite the fuses being off at the box, when I put started unscrewing the neutral in the first dimmer, the screwdriver lit up, which surprised me. But live wasn't live so I carried on unscrewing and was careful not to touch anything just in case. With both switches 'completely' disconnected, the remaining lights still don't work(!) BUT the fuse is no longer automatically tripping. Progress!?

 

[Mike Johnson]

The false indication on your screwdriver is why no electrician would ever use one, what you have proved is that with the circuit disconnected the lights don't work.

There is a need for a methodical regime of testing each part of the circuit to find the problem an electrician could probably do this in very much less time (3hrs 16mins) than it has taken to post all of these questions and answers and your lights would be back on.

Don't forget that if the problem is water ingress just replacing the cable will not prevent this happening again unless the water short circuit is also addressed, please get an electrician in to sort it for you.

 

[Newbie101]

The false indication on your screwdriver is why no electrician would ever use one, what you have proved is that with the circuit disconnected the lights don't work.

There is a need for a methodical regime of testing each part of the circuit to find the problem an electrician could probably do this in very much less time (3hrs 16mins) than it has taken to post all of these questions and answers and your lights would be back on.

Don't forget that if the problem is water ingress just replacing the cable will not prevent this happening again unless the water short circuit is also addressed, please get an electrician in to sort it for you.

You're right. Thanks everyone for all your help. We're decamping to my flat for a few days which gives someone an opportunity to look at it properly.

 

[Mike Johnson]

Hope that someone is an experienced electrician.

Replacing cables can be done without major work, an experienced electrician can run new cables alongside an existing cable without taking down the ceiling, in most case's above a ceiling, especially if the aforesaid is a drop false ceiling, which is generally the case in top floor apartments.

 

[Newbie101]

Hope that someone is an experienced electrician.

Replacing cables can be done without major work, an experienced electrician can run new cables alongside an existing cable without taking down the ceiling, in most case's above a ceiling, especially if the aforesaid is a drop false ceiling, which is generally the case in top floor apartments.

This is a converted Georgian mid terrace. No drop ceiling and the wires are not housed in tubes/pipes like regulations now dictate. There is obviously some space between flat ceiling and roof, but it's small, just big enough for the housings of each ceiling light. There are no choc boxes isolating any of the lights, they all seem to be wired together.

 

[Mike Johnson]

Conduits are not mandatory if using T&E, most electricians have a set of push pull rods that can follow the existing cables from one light to another, it is then easy to pull another cable through the void if needed without pulling down ceilings, possibly without making too many, if any, access points through the ceiling to get around possible obstacles. This would be a simple job for an experienced electrician without too much disruption.

The only possible additional work could be the connections to the lights which may need to be changed to comply with regulations the individual lights should be connected with something like this, it is a Wago lighting box and Wago connector, ignore the gold coloured thing inside the box it's to help prevent flashing of LED's.

 

[littlespark]

Late to the party, but I too believe this problem is moisture getting into the external lights, or rodent damage?

Get the handyman neighbour to fix it for a price, as he’s going to be there days replacing bits and pieces with no guarantee of success.

Also, first picture of board, I see a plug top with a short length of flex just cut off.
Remove the flex from the plug for safety.

 

[Newbie101]

Thanks again everyone. I'll let you know what happens in a few days!

 

[freddo]

Thanks again everyone. I'll let you know what happens in a few days!

Please do! As someone who does fault finding as a large part of their job, this thread has so far hurt my brain.

Good luck!

 

[brianmoooore]

I haven't read through this thread in detail, but I've seen that the immersion heater isn't working properly.
The lighting circuit fault could be a N - E fault (if I've skimmed that bit correctly), is on the same RCD as the immersion, and immersion heaters are prime candidates for having faults to earth.
Has anyone tried switching off the immersion heater at its double pole isolator.

 

[DPG]

Late to the party, but I too believe this problem is moisture getting into the external lights, or rodent damage?

Get the handyman neighbour to fix it for a price, as he’s going to be there days replacing bits and pieces with no guarantee of success.

Also, first picture of board, I see a plug top with a short length of flex just cut off.
Remove the flex from the plug for safety.

Good spot on the plug top and flex.

 

[James]

If you are having trouble convincing people that the next door guy is not the right person for the job,

ask if you will be provided with a minor works certificate (electrical safety check) to show that the fault is gone and the circuit is safe to energise and continue using.

 

[Mike Johnson]

I haven't read through this thread in detail, but I've seen that the immersion heater isn't working properly.
The lighting circuit fault could be a N - E fault (if I've skimmed that bit correctly), is on the same RCD as the immersion, and immersion heaters are prime candidates for having faults to earth.
Has anyone tried switching off the immersion heater at its double pole isolator.

The immersion heater problem was only mentioned three pages in, we are pulling teeth here.

 

[brianmoooore]

Lay people don't understand the connection. If the RCD trips when the lights are turned on, then it must be the lights that are at fault in their minds. They think the immersion fault is just a coincidence.
I've had more than one late night 'phone call from customers over the years trying to explain the possibility of a connection between the two. "But the immersion heater is turned off" "Is it off at the ISOLATOR" "No, it's on a time switch, as isn't on now" "TURN IT OFF AT THE ISOLATOR" "Oh, the lights work now".