On Sat, 03 Nov 2007 11:42:45 +0000, Jim Alexander wrote:

"Bill" wrote in message
...

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?

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.

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.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html