Have a major problem

[Octopus]

Ok. This is based on real fault finding.

Rcd tripping. Socket circuit was the cause. A nail had clipped the live core, the damp , very newly plastered wall was allowing a path to the metal back box which was connected to earth. Disconnect earth to back box and rcd would hold.

The nail was about 9 inches from the back box.

 

[westward10]

As I said a metal back box may provide a return for the wet plaster but we have no idea if metal back boxes in the OPs case are employed.

 

[Ian1981]

I’ve had a low insulation resistance reading between live and earth on a new build however it’s between the mains fed switch (permanent live in) and the metal back box buried in block work wall.
A reading of 1.75Mohms and that’s when all cpcs are removed from the back box and I’m just testing between live at the switch and an un earthed back box.
Oh and there’s no earthing conductor connected to the source as no meter fitted.

 

[james stas]

 

[james stas]

he says its going back to the substation and bypassing the rcd, he metered the wall to a nearby socket earth and got 177 volts. says all readings were above 299 megohms. he got really nasy when i asked for a report and said how insulting it was. im a terrible human for nearly killing people and now i question his honesty and integrity. i only asked for a report in a polite manner

 

[james stas]

this is all with a brand new board. so it is possible to fit a light, test, leave and the whole wall is live?

 

[westward10]

I think you have to accept some kind of joint responsibility. He didn't fit the capping correctly, you refitted it damaging the cable. Should his testing have picked up the fault well you will not know unless you recreate the circumstances at the time.

 

[james stas]

my nail was making the capping live i am told and there was no imbalance between neutral and live because it was going back to the substation.,,....

 

[Ian1981]

That is a strange cable brown, blue and black conductors.

It’s grey man not blue and your a spark

 

[westward10]

It’s grey man not blue and your a spark

I know I took a closer look and deleted it

 

[james stas]

westward,the sparks not been blamed for anything. pls re-read my first post. i'm here on a humble fact finding mission not to insult electricians. i have alrdy been told its my fault totally infrount of customers and collegues and i apologised and i was told repeatedly how bad i am.

 

[jackhammerJIM]

he says its going back to the substation and bypassing the rcd

So the rcd sees an imbalance and operates ...

 

[jackhammerJIM]

Unless it had an underlying N-E fault

 

[james stas]

apparantly not because it wasnt going to an earth it was going back to the substation iamtold and it would never trip?

 

[westward10]

westward,the sparks not been blamed for anything. pls re-read my first post. i'm here on a humble fact finding mission not to insult electricians. i have alrdy been told its my fault totally infrount of customers and collegues and i apologised and i was told repeatedly how bad i am.

The root cause of this was the capping not staying in place, had it been fixed correctly you would not be in this situation. Guarantee it you had contacted him to say it fell off he would have said just nail it back on.

 

[jackhammerJIM]

apparantly not because it wasnt going to an earth it was going back to the substation iamtold and it would never trip?

And how is it getting back to the substation

 

[Ian1981]

So does the nailed cable go into a metal back box on the wall to say an outlet/switch?

 

[Deleted member 9648]

I feel for you James. As the others have said there is a possibility that correct testing may not have highlighted an issue. But IMO a damp wall and damaged insulation on a buried cable would result in a poor IR reading which would flag up to an electrician not to energise.
I think it would be reasonable of you to put your hands up to an error in damaging the cable, but I also think it would be reasonable to argue that an IR test by the electrician should have flagged the problem before the cable was energised.

 

[KEV 1 N]

this is all with a brand new board. so it is possible to fit a light, test, leave and the whole wall is live?

I did the same thing when I fitted my kitchen last year fixing wall units, as soon as I'd drilled the hole I knew it was close to the cable for the under cupboard lights. So I tested the cable, no Insulation resistance faults and live, neutral and earth had continuity (unbroken), so I thought I must have missed it. When it came to grouting the tiles (at night with the counter lights on, I was getting a shock when applying grout and resting my other hand on electric cooker (earthed). Took the wall unit off, hacked the plaster away, there it was (as you had done) screw nicked live cable making capping live, only noticed when wall was damp! I too was getting around 100volts from wall to earth.

 

[The Ghost]

Why the hell didn't the plasterer get a shock then???