11-10-2012, 12:52 PM
(11-10-2012, 09:37 AM)Mark Hennessy Wrote: The risk from PME supplies concerns an open-circuit on the Neutral, ahead of the RCD on your incoming mains. What happens is that everything in your house, including earth, goes high. The RCD doesn't trip out because it's lost power. So, you have a house that seems dead, yet by simply touching the metal case of any electrical device, you could get a nasty shock.
This page explains this, with a diagram: http://www.tlc-direct.co.uk/Book/5.6.3.htm
Mark
Interesting what you say there: it may explain a scenario I witnessed many years ago on a new-ish build house - presumably, therefore, with PME.
The householder told me that when she touched the radiator in the hall, she received a shock. As her hall floor carpet fibre was a nylon mix, I suspected nothing more than static, but since I was consulted, I had a look at it anyway. I casually touched the radiator at a place where there was no paint on it and - OUCH! That is 'hot'! Clearly not static!
The electricity authority were informed and duly attended: fault was confirmed by them. The upshot was that they had to dig a large trench in the road - about 20 metres long, back to a 'T' junction in the road - before they found the fault; it went on for about 3 days and nights. Being curious, one evening I spoke to the person supervising the work: "Real headache, this one. We've just got to keep digging back from the house until we find the trouble." Which they eventually did: an O/C neutral in a bitumen-filled junction box, so I was told. Peculiar thing was that several adjacent houses should have been also affected, but only this one house appeared to experience the fault. Perhaps the occupants of the other houses hadn't noticed, but I find that difficult to believe.Al.
