Fault in circuit - 3 bed house sockets are all on 1 ring main...?

[atkins_1]

I have a friend who had some problems with a tripping RCBO on their ring main, the whole house is only wired on 1 ring main which failed on an insulation resistance test. (0.001Mohm X ) An electrician took the circuit off the RCBO and left it on a MCB to stop the sockets disconnecting.
I changed their old board to a new CU and all the circuits are fine on the RCD's...? until 2 of the sockets are used, even by my socket tester (once it's switched on)
Why is the RCD tripping once the socket is in use as apposed to as soon as the circuit is switched on at the MCB...? I checked all of the sockets wiring in the whole house including switched spurs and the is no sign of shorts or any incorrect wiring/faults. The problem must be in the wiring but they don't want any work done on the house that will be messy.

I thought that the RCD would trip as soon as the circuit was switched on but it was fine, which confused me, but then it did trip when using 2 certain socket outlets..? So now ... what can be done, I would like to be able to put most of the sockets on an RCD but they don't want the hassle of having to make good any work that would involve making good after routing of new cables.

What do I do about these socket outlets that are causing the RCD to trip...? :mad2:

 

[bigbaddave]

Solving a IR fault of 0.001 by taking off the RCBO.. Really and that was the electrician??

Id be finding the fault, Was the IR done with everything disconnected or were you testing appliances (Load) as well?

 

[decolad69]

Tell them the fire will make a bigger mess of the decor!

 

[guest119]

Sounds like neutral and earth mixed up at those two sockets.
Plugging in draws a load and returns it to earth via the neutral connection. Nothing plugged in returns nothing to earth.
Was the ir test done live to earth or live to neutral or live plus neutral, to earth? Which produced the low reading? What ohms are you getting L-L, N-N, E-E at the db?

Boydy

 

[markc123]

0.001 lol Guessing literally every load was in circuit and he hadn't disconnected the RCBO's coiling lead's then.

Whoever's done it hasn't put a 6amp RCBO in by mistake have they? Loose-connections in the 2 sockets in question?

Fault find, possibiltys endless really.

 

[richy3333]

Err, why change a RCBO board for a CU with RCD(s)? It doesn't make sense? If the RCBO isn't faulty why aren't you fault finding on the circuit? Surely breaking the circuit down and IR testing will find the fault?

 

[atkins_1]

Solving a IR fault of 0.001 by taking off the RCBO.. Really and that was the electrician??

No reading was taken before they did that.
However the RCBO was faulty, no disconnection and test button was even missing...?!??

 

[Andrew Youll]

I would split the ring and treating it as two radials take your r1+r2 measurement on both radials as it would show if there had been a crossover of the neutral and earth as it should show as open.

Could it be a jb under the floor or hopefully not burried in a wall with a crossed connection. Also could fault face plate had a couple drop to pieces before.

 

[Guest111]

I would go for a crossed neutral/earth as someone else said,are the offending sockets part of the ring or spurs?

 

[SYKRAPS]

I would guess that it is a nailed cable at skirting level if you have inspected that all outlets are correct.

Why did you change the board before testing the circuits btw?

 

[pjcomp]

If I understand the OP correctly the problem is focussed on two particular sockets. If that's the case try changing the sockets - the internals of sockets can go rogue and cause RCD trips.

PJ

 

[Clive P]

Hi,

Try choc/blocs on the two offending sockets , then do your continuity and IR tests on the ring for starters. Everything for that ring disconnected at the board and test.

Regards.

 

[thekingiam]

i would guess ......... well actually i wouldn't, i would test everything.

 

[telectrix]

and while you're at it, test the gas joints with a match. well, BG "engineers" test the electrics with a voltstick, don't they?