Strange occurrance

[newguy88]

Hello!

First time poster, I am not an electrician I am a homeowner.

Before I start I should point out that I am trying to contact an electrician to come and assess this situation and will not be attempting any repair work myself - the circuit is switched off and I will not be turning it back on again until it has been assessed by an electrician. This question is to aid my own understanding as I dont understand whats happened!

We were fixing a board to the wall using nickel plated screws on the same wall as a lightswitch. We of course used a detector and mapped out where the electrical cables were in the wall and stayed WELL clear. Once the board was attached for good measure we used a no contact detector to make sure that we had not touched any of the electrical wirings when drilling and screwing.

When the detector is held extrememly close (in fact touching) the detector goes off at ALL the screws in ALL the walls in the house. The radiators (which are earthed and I have checked the earh cables myself) also trigger the detector.

The screws thwemselves are in plastic rawl plugs and only screws in proper "brick" (as opposed to plasterboard) walls are triggering the detector.

We have a modern consumer unit and nothing tripped during the drilling or screwing. Obviously we have turned off the lighting circuit and the screws then do not trigger the detector.

Would anyonje be able to explain whats happening? We are confident we did not drill into a cable, no circuit breakers tripped, and surely the whole wall cannot be live? Any advice?

 

[Bobster]

Those non contact detectors can not be trusted. They quite often give false readings.

They should never be used to prove if something is live or dead. To be used more as a rough guide.

 

[Darkwood]

Welcome to the forum

As a trade we do not use these kind of detectors for any kind of reliable testing as they often give false positives and if the battery goes or the item fails it could create a dangerous situation where by someone might believe something is dead when it isn't.
They also pick up what is known as induction which can occur on say a dead cable that runs in parallel to a live cable, an induced voltage can rise in the cable or other metalwork but at domestic level is no real harm to anyone.

I cannot say confidently that you are just picking up a false reading as only the correct test equipment can verify this but if you are getting said readings on any metal work (even the bonded pipes) then I would just get things checked out to be sure.

 

[ruston]

I agree with the two post above.
I would add that the stud and metal detectors are not accurate either, there has been numerous debates about their reliability.
IE, foil back plasterboard can fool them completely.

 

[tomspark93]

You will also find they will light up when your rub it up and down your arm. They can be good coffee stirrers though.

 

[Marvo]

As above, I wouldn't trust any non-contact tester. It's probably worth just getting a sparky in for an hour to test the circuits at the CU for peace of mind, he can also test the screws with a trailing lead.

 

[davesparks]

Non contact voltage detectors will light up from static, being waved around, being knocked, being close to a mobile phone or portable radio which is transmitting, being near fluorescent lamps. And they usually light up near live cables, but will also,often light up near dead cables or any other metal object which is in close proximity to a live cable.


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[Midwest]

Hello!

First time poster, I am not an electrician I am a homeowner.


Would anyonje be able to explain whats happening? We are confident we did not drill into a cable, no circuit breakers tripped, and surely the whole wall cannot be live? Any advice?

Unfortunately, in certain circumstances the whole wall can be live, as I found out a while back. The fault was an old one, when a previous resident had installed some dado rail, using harden nails. One nail had pierced the live only of a cable. The fault only came to notice when the plumber was installing & touching copper pipes in the adjacent bathroom.

I've a metal & cable detector, which others have said, make all sorts of spurious noises, with no sense of rational. The advice to have it checked out by an electrician is sensible. If there is a fault though, be prepared that it make take some time to locate.