Have a major problem

[james stas]

Hi guys, i'm not an electrician ,I'm a builder.

a month ago we had an electrician in first fixing, after he left some capping fell off and i put it back on with a nail. turns out i nicked the cable but it wasnt live until yesterday when he second fixed the outside light and powered on and left. I wasnt on site but later the customers got a shock from the wall several feet from the cable, the whole wall was live , because it was damp from the plastering i had done (like 3 weeks ago) and i nicked the cable. so its all my fault i am told.

Should this not have been picked up on the insulation resistance test?
And why did the electrics not trip? i mean if i put the nail into the cable today would it trip or would the whole wall be live? i got a severe telling off for putting customers lives at risk but builders sometimes damage hidden cables and it always trips and never in my life have i heard of a whole wall being live like this was.

Please post honest opinions. i need to know if its my fault.

thanks
James

 

[Strima]

If the nail had just nicked the line conductor an IR test may not have shown a fault to earth as the wall may not have had a good path to earth, only when touched it would have completed the path to earth.

 

[Leesparkykent]

The RCD should of tripped though as there would be an imbalance between line an neutral...As westward10 says there is no guarantee an IR test would pick it up although you would of thought the metal back box that's earthed and in contact with the damp plaster would pretty much guarantee an unacceptable IR reading. Something isn't right IMO.

 

[westward10]

An IR test should have picked something up.

Why we can't see or know the full circumstances. The incident Des refers to is a classic example where the electricians were blamed for inadequate testing and whilst this may be correct the chances of correct testing identifying the fault is remote to say the least.

 

[Leesparkykent]

Why we can't see or know the full circumstances. The incident Des refers to is a classic example where the electricians were blamed for inadequate testing and whilst this may be correct the chances of correct testing identifying the fault is remote to say the least.

I believe with the Emma Shaw tragedy though it was concluded that the mcb had been reset several times blowing the CPC clear.

 

[westward10]

Never assume an rcd will prevent you getting an electric shock.

 

[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