Fault finding - perplexed - help!!!

[Octopus]

Last night one of my neighbours asked me to look at a fault which had developed after new skirting boards were fitted!

Today I went round, isolated the circuit and the IR test from the board confimed a L-E very low IR, not too much of a surprise as the RCD wouldn't hold if anything was switched on on the ring.

So I split the ring in the "offending" room and confirmed IR >30 on the leg going back to the board, and IR of >30 on each "link" after that. Odd I thought.

So I refitted the first socket - IR down to about 0.80 Mohms - changed the socket for a new socket, IR value hardly budged - very odd.

Took the socket off the wall and re-tested each leg either side of the socket (and from both ends) , IR>30, scratched my head, put socket back on - IR back down to sub 1 Mohm!!, changed socket again, still below 1Mohm!!

Put if all back together, as I've got previous booked job this afternoon and obviously ring is out of action.

Going back for another look, Friday am probably

Thoughts/suggestions/ideas ???????????


Ta ta for now.

 

[Electro-tech]

Breeze blocks conduct if damp,do a continuity test around the wall. Test the wall for voltage.

 

[Daveyb100]

Thinking out of the box here...also try nulling the test leads and then try a few readings there..if youre doing lots of measurements on pendants the leads start coming apart and produce all sorts of funny readings as the dogleg between the lead and the plug starts to wear....you never know!

 

[Octopus]

The saga continues..... here are my findings from a brief visit today!

Here is a photo of a reading off my metrel immediately I've done an IR (at 1000v) which shows that there is a "retained" voltage on the cores of the offending "half" of the ring and the IR reading between L & E of 0.96.



It takes about 30 seconds for the voltage to drop back to almost zero - suggesting that something is acting as a "capacitor" on said circuit. The other "half" of the ring drops back to zero immediately after the test.

Both the MCB and RCD will hold!

I've tried to trace the circuit round the house and all I can say is that the ring has been extended in a rather unusual fashion!

Any comments, questions, or thoughts would be useful

 

[electromonkey]

I'm stumped. A re wire of the offending part of the circuit may be more cost effective for the customer?

 

[Octopus]

Anyone else got any bright ideas?

 

[andekoch]

Can you turn it into 2 radials by removing the offending socket? Or as suggested rewire either the cct or just the legs either side of the offending socket. Seems to be cable damage when skirtings replaced, either when old taken off (crushed cables) or when put on (nail or crushed). Crushing seems most likely since when the pressure comes off all will seem normal but squash the cables and you get the short again.

 

[Octopus]

Can you turn it into 2 radials by removing the offending socket? Or as suggested rewire either the cct or just the legs either side of the offending socket. Seems to be cable damage when skirtings replaced, either when old taken off (crushed cables) or when put on (nail or crushed). Crushing seems most likely since when the pressure comes off all will seem normal but squash the cables and you get the short again.

If I turn the ring into 2 radials the customer will still have 1 circuit with a fault!

Its the "capacitor" type action I'm puzzled by - if anyone can offer a suggestion or two it would help with fixing the fault!

 

[bozobro0]

If it was puzzling me that much,i would grab one of me sparky mates to come along and have a gander.What might not be obvious to me,might be obvious to him.May be worth considering.

 

[electromonkey]

Like Andykoch said Murdoch. Have your 2 radials. The one with the fault will have to lose 1 socket. Wants to keep that socket, could you disconnect it (removing the fault), then spur from another socket to re supply power to it?

 

[electromonkey]

Insert before "wants" *If your customer*

 

[Octopus]

As it stands he'll be losing a socket as the "feed" cable dissappears under the landing floor and to where?? A jb I suspect!

Any other ideas please?? Help??

 

[Octopus]

Re: Fault finding - perplexed - FIXED !!!!!!!!!!!!!!!!!

My neighbour hacked at his nice newly plastered wall and this is what we found:



The nail was touching the live and nothing else. I am of the opinion that the wall had been "wetter", conducted to the closest back box, and thus why at first the tripping had started but latterly hadn't.

Nice new bit of cable installed - tested OK

Got to deliver my bill next - not sure how that will go down!

 

[Capita]

Nice - sounds a nice head scratcher !! This is why i'm so glad I dont do any domestic work

I was going to suggest trying to locate the nail heads in the skirting if at all possible, clean a spot for test leads and test continuity between nail head(s) and conductors, that way after exhausting splitting rings etc you would have had proof a nail had nicked the wiring ?