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.

 

[snowhead]

Thought,
There's a fualt on the rnig.

Did the 2 halves test O.K, without the "faulty" bit of cable,

 

[Charlie_]

So what tests did you carry out?

 

[Mfctitch]

Thought,
There's a fualt on the rnig.

Did the 2 halves test O.K, without the "faulty" bit of cable,

Thought,
There's a fualt on the rnig.

Did the 2 halves test O.K, without the "faulty" bit of cable,

As I had to admit at the start I rushed stright in without testing as I thought I had asked the right questions and had got them to remove plugs and turn off FCU's

I know big mistake

 

[Mfctitch]

So what tests did you carry out?

Ashamed to admit only ir on one leg
right near the end of the evening
the old saying of more haste less speed is coming to mind

 

[Charlie_]

You going back tomorrow?
You should forget about what you have already done.
Just start off methodically, test out the complete circuit, L-N,L-E,N-E.
Don’t take any short cuts, you will find it in no time.

 

[Mfctitch]

You going back tomorrow?
You should forget about what you have already done.
Just start off methodically, test out the complete circuit, L-N,L-E,N-E.
Don’t take any short cuts, you will find it in no time.

If not tomorrow then at some point this week
Are you saying reconnect the two legs and test it as a ring?
This will sound lazy and that's what's got me in this position a few of the fcu's have neons fitted so would it be ok to test at 250v rather than 500v

 

[Charlie_]

Yes I would put everything back as it was and start again from sqaure1.
Just switch all the FCUs off or remove the fuses and unplug all appliances.

 

[Mfctitch]

Ok will do
Asking questions now because of distance to job
If they come back as ok
Or I get a fault what would you suggest my next course of action should be in either case
Bearing in mind I thought I'd solved the problem by turning the ring into a radial

 

[snowhead]

What he said ^^^^.

Because, you've got a fault you didn't appear to have at the start. (does friend's friend know the difference between RCD and MCB?

You may find it's something (silly, in a rush) you've done, go back to everywhere you've been.
Is the old bit of cable still there?

 

[j1mbodrea]

Harmonized colours happen to be out since 2004... So not that new, lol
Hopefully you rectify the problem asap

 

[Mfctitch]

Morning everyone
i did double check the MCB RCD question and he assures me that this time it was the MCB.

As for the colours at the board they are the same and on the few sockets that we investigated they were the same

 

[Wilko]

Hi - with an mcb now tripping I’m placing a bitcoin bet on a trapped L behind one of the faceplates .

 

[Mfctitch]

Thanks for that bit of info I'll check that out but not would that not have blown as soon as I energised the system?

 

[Welchyboy1]

Hi - with an mcb now tripping I’m placing a bitcoin bet on a trapped L behind one of the faceplates .

^Likely to be on one of fcus too

May be on the switched side of the fcu and only tripped when its been switched back on?