Screw through wire, how to locate?

[JamesH123]

Hi unfortunately I had a 'non professional' board and skim my ceiling and now can't contact them. Since it was done the lighting circuit keeps tripping and I suspect a drywall screw has gone through a wire. Is there a way of detecting where a short is?

As the ceiling is skimmed I can't see the screw locations, and due to nature of it I can't access from above.

There is a 'ring' of 5 spotlights and a dimmer switch.

Any help would be appreciated, as I don't want the ceiling to come down.

Thanks

 

[Nozzle]

You can use a rare-earth magnet to locate the screws - won't be any help deciding which one has gone through the wire though... but then the screw which is live is a good indicator

Nozzle

 

[phatboy]

Does the circuit still blow with the lights in this room switched off?

If not, disconnect the lights one at a time to identify which section of cable is damaged.

 

[JamesH123]

Yes it does still go with the lights off which I suppose means it is before the switch? Is there some kind of detector I could run along that section which would detect the damaged area/live screw? Thanks

 

[JohnW2]

Yes it does still go with the lights off which I suppose means it is before the switch?

What is it that is tripping - an MCB or an RCD (the latter with a test button).

If the latter (an RCD), then what you suggest above would not necessarily be true - the screw (if that's what it is) could be resulting in an intermittent neutral-earth fault (which would trip an RCD, but not an MCB) which would still be present with the switch off, regardless of where the fault was in the circuit.

Kind Regards, John

 

[sparkwright]

Is it a screw through a cable?

Could some wiring at the light fitting or somewhere else near where they have been working got disturbed?

 

[JohnW2]

Is it a screw through a cable? ... Could some wiring at the light fitting or somewhere else near where they have been working got disturbed?

Indeed it could be. My understanding is that the 'screw through cable theory' is pure speculation.

Kind Regards, John

 

[JamesH123]

Hi thanks for the reply , it is definitely not the fittings, I am 99% sure it wire damage.

It trips the RCD would there be anyway of detecting the neutral-earth fault you describe if that was the case?

Sometimes it does not trip for 20mins and other times instantly.

 

[sparkwright]

As the plaster dries out you may be able to see the screw locations.

What's above the ceiling? A nice easily accessible loft space by any chance?

It would be hard to screw through a cable unless a cable was lying on the old ceiling, or the wiring was 'notched' into the old ceiling where the joists are (a method of running cables through a ceiling without lifting floorboards which is not recommended).

 

[JamesH123]

Hi, above the ceiling is flat roof with no access and the plaster has dried now and can't see the screws!

 

[Nozzle]

You can use a rare-earth magnet to locate the screws.......

 

[sparkwright]

Then you need an electrician to pinpoint which cable is damaged by testing. Then work out how to repair or replace with minimal damage.

Were some cables added by cutting them into the old ceiling once upon a time?