I tested a fully earthed metal switch plate with a neon mains tester. The test on the plate and screws showed a faint glimmer suggesting that the face plate is conducting current. No trip on RCBO or RCD. Testing the 'live' - it glows brightly as opposed to the very faint glimmer on the pate and screws. The switch is screwed to a timber panel and is fully earthed. IF the face plate is removed from the timber - NO indication from the face plate on the tester. Screw the plate back on and the neon shows a faint indication!. The face plate screws ONLY screw in to timber and there is NO contact with the wiring. Is this some for of inductance and no cause for concern. Must have been like this for ages. Cheers
Hi Paul, don't know! It just disappeared! Took your advice and fitted a 6 amp RCOB for the time being and installed some earths where I could fish them. This one is DEF earthed - I don't understand. I know there is a great deal of 'discussion' regarding the reliability of 'off the shelf' mains testers. Incidentally got a 107 and checked ALL the sockets in 'the other place' (to quote Shakespeare) and they all showed green and tripped a 30mA RCD - not a definitive test I know - but reassuring at this point. Re the switch, any ideas? B
That's the most likely explanation John but I don't see why it only happens when the switch is screwed back onto the wood? Unless there's a damaged cable touching the wood somewhere and the wood is damp, that sounds a bit far-fetched though doesn't it!
Would it cover all eventualities if I simply replace the cable ? The wood is absolutely bone dry - no chance of any conductivity here I guess. The wood is very old - mid 1700s - nail buried in the timber but not visible? Paul B may come back with some inspired thought!
What happens if you just put the neon straight onto the wood, or perhaps put a small screw or a nail into the wood and then test. Can you do an earth loop test to ensure that the earthing is effectively connected along it's path? Is it a TT system by any chance, if so it would be fairly common for there to be a little bit of voltage (albeit at very low current and not harmful).
I am only DIY Brian and I got your last question wrong ! so why would I know? Have you not got a multimeter? I really don't know what you would connect it to if you had! Just a thought with it being an old building, what sort of earth do you have? As the switch plate is screwed into wood how is the switch earthed? Could the neon screwdriver be reading the neutral, if you have a neutral passing by the switch. In any case I personally would not worry about it as neon screwdrivers are a bit hit and miss IMHO. Static electricity from you?
Do all your earths go back to a common point? Can't quite explain the switch phenomenon apart from what has already been mentioned, but perhaps there is some potential difference between your earths somewhere? Is everything cross bonded?
Paul, please don't misunderstand me - everything you say is good sound advice and is always taken on board. This 'problem' is indeed very odd. I have a multimeter and will have a look. Its PME earth by the way!
how odd. do you have a photo of this assembly? Are you able to insulation test the switch and do a zs test from it once powered back up?
Probably just a combination of different earth potentials. After all, you have 3(at least) things touching Earth. The screw, the wood(to brick-to floor), yourself(to floor). I had a cheapo tester(still got it somewhere) found 12v in the floor of my shed. Wooden floor, no electrics in there, only picked up 12v on some parts of the floor!!! Mr. HandyAndy - Really
The mind boggles as to how and why you found that Mr Handy.....visions of some fool on his knees prongs in hand...lol.
Completely by accident. It was only a digital pencil type tester(would tell you if there was more than 12v or more than 230v) Just noticed it flash, checked, and it was consistent. Mr. HandyAndy - Really
Morning all, 1 Can I do an earth loop/z/insulation test with my multimeter? Getting in a bit deep here - how do I do this? MO welcomed here. 2 And a thought from me This is a two way switch operating a 12 volt transformer for 8 12 lamps (provided by our host). Could there be some form of inductance/interference from the 240/12v transformer? 3 As a temp workround, I replaced the fancy brass switch with a standard plastic one, no earth obviously on it so taped it back (didn't think to check the wood screws at the time with the neon here) and went home. My wife was very dismissive of the MK replacement - 'I looks really naff'. So I cant take a pic or respond till I go up north again. The bottom line is that it's been installed for a number of years and I have never experienced anything suspect (i.e. kicks etc) from the switch and discovered this issue by accident - bit like Mr H's shed! If you guys think it's curious but not a prob cos of the time scale - I will leave it for now. Any more thoughts? cheers
And a thought from me This is a two way switch operating a 12 volt transformer for 8 12 lamps (provided by our host). Could there be some form of inductance/interference from the 240/12v transformer? And now he tells us. LOL
Morning Paul, et al Doughhhhh! In you experience is this the likely cause and there is little that can be done (or needs to be done) to sort it out? Sorry cheers B
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