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.

 

[Charlie_]

You have also disconnected both legs back at the consumer unit?

 

[SparkyAndGeorge]

Anything outside any external sockets or flood lights?

 

[Mfctitch]

You have also disconnected both legs back at the consumer unit?

yes both legs are disconnected at the board

 

[ipf]

Tut, tut....kitchen faults. OP's head 'll be spinning. Start from scratch. Check at all sockets for direct spurs or even JB's behind units. Disconnect all sockets and FCU's...(neons). Test each leg after each disconnection. You don't mention any continuity testing.

 

[Mfctitch]

Anything outside any external sockets or flood lights?

Tut, tut....kitchen faults. OP's head 'll be spinning. Start from scratch. Check at all sockets for direct spurs or even JB's behind units. Disconnect all sockets and FCU's...(neons). Test each leg after each disconnection. You don't mention any continuity testing.

from short leg which we believe goes straight back to the board we are getting continuity on the L and E

 

[Octopus]

from short leg which we believe goes straight back to the board we are getting continuity on the L and E

When you say continuity, do you mean end to end on the cores or from one to another?

And what about the neutral?

I would do IR tests from both "ends" of the leg .............

what were the R2 readings for each of the L, N and CPC before you took the ring apart?

 

[ipf]

from short leg which we believe goes straight back to the board we are getting continuity on the L and E

What about neutral?........or do you mean between L and E, a short cct?

 

[hasel5]

Not being rude but do you actually know what you are doing?

 

[Mfctitch]

When you say continuity, do you mean end to end on the cores or from one to another?

from one another


And what about the neutral?
neutral to earth ok
neutral to live ok
only getting it on live to earth

I would do IR tests from both "ends" of the leg .............

what were the R2 readings for each of the L, N and CPC before you took the ring apart?

from one to another

 

[Mfctitch]

Not being rude but do you actually know what you are doing?

fair point
but at this time of night i'm not even sure what my own name is any more

but we are going through the slow process of taking sockets apart and testing

 

[ipf]

L-E fault on shortest leg wants sorting first, it seems.
What experience do you have?

 

[Octopus]

fair point
but at this time of night i'm not even sure what my own name is any more

but we are going through the slow process of taking sockets apart and testing

Who is “we”?

Basic rules of fault finding

Continuity of all cores
Ir of all cores
Split circuit

Repeat above

If you don’t confirm end to end continuity of the cores, you will go round in circles

 

[DPG]

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

 

[SparkyAndGeorge]

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.

 

[Wilko]

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