Electric shock, faulty earth terminal.

[Bill]

This is partly being written as a warning and also to ask if anyone else has experienced it and should it be expected to be found by any normal inspection.

We have just, last few days had a kitchen area replastered, therefore there was a lot of condensation in the room forming on various surfaces. One of these surfaces was the light switch, plastic front not metal. When I went to operate the switch it was very stiff as the plasterer had managed, as they do, to get plaster all over it and some was jamming it. So as I applied more than normal force to it my finger slipped off and caught onto one of the fixing screws, ouch, I got a reasonable belt off it, enough that my arm was numb and tingled for a while afterwards. On investigating it the problem was that although the earth wire in the cable was connected to the brass screw terminal in the back box the terminal was fractionally loose where it was crimped onto the box. Over a period of time this crimp appears to have corroded, possibly due to moisture in the kitchen over the last 25 years? Anyway using a DVM, the Meggar having vanished for the day, I measured a 100K, or there abouts, resistance between the screw terminal and the back box, therefore the box was not earthed and that's why it hurt! Moisture having provided a path from the live on the back of the switch to the metal of the box and hence the screws.

I'm not looking to apportion blame any where, apart from maybe at myself for having touched a damp switch, more just interested in if it would be reasonable to expect the fault to have been picked up on a routine electrical inspection or is this taking it too far?

[Stephen Dawson]

Have you found the fault that is causing the earth to become live??

[Lobster]

AIUI from others posts here, the earth strap to the back box is more of a nice-to-have rather than a must under the regs; which if so would indicate 'no', it's just you shouldn't touch a wet switch.

David

[Owain]

It would depend on the exact nature of the 'routine electrical inspection'. I've seen inspectors in commercial premises with a long wander lead probing every accessory as a check that there's an earth present, but that might only be done every five or ten years.

A domestic inspection might be more likely to take a representative sample rather than check them all.

Owain

[Jim Alexander]

Its debatable whether the hi-res to at that particular back-box whould be picked up, however the low-IR condition on the lighting circuit phase would be identified by the most basic of tests and it's the low-IR which is the main fault here.

One thing to note in passing is that you need to add the word "Report" to "routine electrical inspection". How effective a PIR is depends more on the Report bit than the Inspection bit. Shocked, well not lierally, when this was explained at a recent trade-show NICEIC free talk about PIRs

Jim A

[Andrew Gabriel]

I've seen inspectors in commercial premises who managed to inspect and sign off a large open plan office, just by checking that a kettle they found on someone's desk was capable of boiling up a couple of pints of water.

On another occasion, they managed to PAT test all the computers in the office over night. I guess they weren't used to doing unix desktop systems, and overlooked that 'uptime' the following morning revealed the computers hadn't been rebooted for months, even though they each gained a new PAT test pass sticker.

[Frank Erskine]

All nicely flash-tested, I hope :-))

[Ed Sirett]

Which only occured when the plasterer got going. IME plastering with the power on is a sure way to find all the underlying faults the exciting way.

[John Rumm]

I would be surprised is a routine inspection would find this. It does however highlight the significant difference between a light switch on a metal back box and a power socket - i.e. no direct earth connection to the fitting itself.

Last time I encountered something like this was after I rewired a friends house. I got a call to say "help" all the power had just gone out! Turns out he was plastering in wall chases and got a bit over enthusiastic with one of the larger ones (containing 6 cables) just above a light switch. Being a TT install, he had injected enough wet plaster into the switch to create 100mA (or more) of earth leakage and took out the master RCD.

[meow2222]

... sounds like a volty earth terminal

NT

[Andy Champ]

Windoze also logs this. ( I'm not sure 9x did, but all the NT variants do)

But anyone who came into my office and shut systems down without prior warning would be likely to have something painful applied to him.

Andy

[Andrew Gabriel]

We had prior warning, but as they were all Solaris systems, we just left them running until the electricians pulled the plug, and they're all set to reboot on power restoration.