Nuisance tripping after splitting a ring main

[Mfctitch]

Evening everyone

Had to re post as I started a post within a post

here's hoping I'm posting in the right part or I have started off on the wrong foot.
Long story
Asked by a friend to look at his friends electrics as the kitchen ring was tripping the RCD.
New colours cable
on 32amp B MCB
one of only 3 on the this bank protected by an RCD
5 double sockets
plus a bank of 6 FCU's

Before I went there I had him remove all the plugs plus and turn off the FCU's
believing that this would help narrow down the problem.
But it did not.
so drove to Leytonstone about 45 mins from me
where we split the ring at a double socket and we believed that we had found a the problem which was a bit of cable in the wall between one of the FCU's and a socket in the cupboard.
all this time the other leg was working fine.
So we managed to replace the cable and we seemed to be on the home stretch, when the other leg started to trip I been there for about 5 hours and it was 9pm by now so turned the ring into a radial thinking this will do until I get time to investigate further.
so left at 10:30pm and everything seemed fine only to get a call today saying that the MCB had tripped but not the RCD and thoughts apart from run.

 

[Mfctitch]

Your original post said 5 double sockets didn't it? Where are the extra 3 to make 8?

Your original post said 5 double sockets didn't it? Where are the extra 3 to make 8?

Mis counted my mistake

 

[Mfctitch]

Hi - it might just be worth repeating IR at 250V to be sure you are not looking into some surge arrestor somewhere.

no difference there
latest is we seemed to have found the first socket from the long leg
we have continuity on L-L
N-N
but no earth
But new headache is that if we energise circuit with only the Live connected it still trips the RCD

 

[Mfctitch]

Maybe its time to call it a day. Fault finding takes years of experience to master. Why not be honest to your friend and say its above your level. Nothing wrong with knowing your limits and holding your hands up to admit it. Get the guy to get an experienced sparky in to locate the fault and explain where and how he located it. Use this as a opportunity to learn.

appreciate what you are saying but how am I going to learn if I give up at every problem I encounter

 

[DPG]

Why are you energising the circuit with those dead test results?

 

[hasel5]

Is this a wind up /?/???

 

[Octopus]

appreciate what you are saying but how am I going to learn if I give up at every problem I encounter

You learn far more by working with competent sparks .....with years of experience

 

[Mfctitch]

latest update
it now seems that we have L-E fault on both legs ?
I'm getting a reading coming back through the Earth on both legs

 

[DPG]

latest update
it now seems that we have L-E fault on both legs ?
I'm getting a reading coming back through the Earth on both legs

This is getting out of hand. You aren't getting anywhere here. I would say get a sparky in. Know your limits.

 

[Mfctitch]

Thanks everyone for you help and advice
we still have an earth fault when we are getting 240v across earth-netrual
now on both legs.
which is the part we cannot get our heads round as this circuit has been fine up until last week. and nothing has been added or any work carried out.
we are in the proccess of reconnecting all the sockets back up and i will keep everyone inform of what the problem is when we finally get it sorted

 

[Dave5678]

latest update
it now seems that we have L-E fault on both legs ?
I'm getting a reading coming back through the Earth on both legs

As you're going round breaking the circuit into legs are you putting the conductors into chocblocks or similar to keep them separate or are you just letting the conductors float free to touch each other or the backbox?

Thanks everyone for you help and advice
we still have an earth fault when we are getting 240v across earth-netrual
now on both legs.
which is the part we cannot get our heads round as this circuit has been fine up until last week. and nothing has been added or any work carried out.
we are in the proccess of reconnecting all the sockets back up and i will keep everyone inform of what the problem is when we finally get it sorted

You can't just go around reconnecting and re-energising when you have faults still on the circuit. If it doesn't pass the dead tests you don't proceed to live tests. 240V between neutral and earth suggests you've lost your neutral or earth and isn't safe. Lock the circuit off until you can go back with a clear head and work through methodically or someone else can come to fix it for you.

 

[snowhead]

If you're going to leave it energised (bad idea) make absolutely sure you've reconnected everything.

 

[Mark42]

I had a similar scenario at a mate's house last month: he'd been changing switches, and got intermediates, two-ways and singles completely messed up, and had mixed up two separate multi-way lighting circuits in the same enclosures. Nothing made sense: the behavior of his lighting was hilarious.
With multiple concurrent faults there's sometimes too much going on to hold the logic in your head.
In that case I find the best way is to STOP. To give up trying to be clever and to disconnect EVERYTHING. All accessories off, all cables neatly disconnected. Then get pen and paper, a long flying lead and trace the exact route of every cable. Draw it as you go. Then do continuity and IR on all sections, logically and consistently.
It's then a great feeling when the 'A-Ha!' point is reached, which it will be.
Good luck

 

[Mfctitch]

I had a similar scenario at a mate's house last month: he'd been changing switches, and got intermediates, two-ways and singles completely messed up, and had mixed up two separate multi-way lighting circuits in the same enclosures. Nothing made sense: the behavior of his lighting was hilarious.
With multiple concurrent faults there's sometimes too much going on to hold the logic in your head.
In that case I find the best way is to STOP. To give up trying to be clever and to disconnect EVERYTHING. All accessories off, all cables neatly disconnected. Then get pen and paper, a long flying lead and trace the exact route of every cable. Draw it as you go. Then do continuity and IR on all sections, logically and consistently.
It's then a great feeling when the 'A-Ha!' point is reached, which it will be.
Good luck

Cheers for that
as we can not find out why we have 240v coming down the earth on both legs
we have run a temp 2.5mm T&E replaced 32 amp with 20 amp MCB so that the kitchen is working and safe.
tomorrow is another day

 

[Mark42]

ps: What kind of test instrument/s do you have?

I have a sneaking suspicion you may be working with a cheap multimeter, may be touching the probes when taking readings (this is especially a problem if it's an auto-ranging model) or are diagnosing 'short circuits' between cores by energising one then testing the other with a neon screwdriver or volt stick.

Any of the above is not only dangerous but a waste of time which will take you round in circles with false positives.

Apologies if I guessed wrongly ...

 

[Mark42]

Cheers for that
as we can not find out why we have 240v coming down the earth on both legs
we have run a temp 2.5mm T&E replaced 32 amp with 20 amp MCB so that the kitchen is working and safe.
tomorrow is another day

An interesting and novel use of the word 'safe'