Thanks for the extra details David, I've never lived in a house with PME, but maybe that's because I've never lived in a town!
73 Stephen G4SJP On 14/05/2008 23:02, "David Woolley (E.L)" <[EMAIL PROTECTED]> wrote: > Stephen Prior wrote: > >> In older houses in the UK the neutral is bonded to a real ground at the fuse >> box, where the ground is usually a long copper rod just a few feet away. > > This configuration (TT) is rather rare (mainly rural supplies by > overhead lines). > >> There is rarely in my experience more than a volt or two on the neutral. >> >> More modern houses use PME (protective multiple earthing) where the neutral >> is bonded not at the house but locally at the final step-down transformer- > > The key factors about PME is that there is no earth wire from the > sub-station, the premises earth being regenerated from the neutral at > each property (TN-C-S). It also has neutral grounded to real earth at > multiple points in the distribution network. > > Whilst PME is increasingly used, "The Electrician's Gude to the 16th > Edition of the IEEE Wiring Regulations BS 7671" (ISBN 0-9537885-0-4) > suggests that the most common system is TN-S, where the the ground wire > runs back to the substation and is physically grounded there. > >> the argument being that this forms a higher quality ground I believe. The >> real danger with PME is that the neutral may well then rise above 0 volts, > > The danger is that mains earth, which is tied to neutral, can rise above > true earth by a large amount (the example in the book is 96volts) if > there is a break in the neutral between properties, as the return > current then flows between ground rods. > >> but in normal circumstances, because plumbing inside the house is bonded to >> 'ground', no potential (!) exists for electrocution. Until, that is, a ham >> decides to ground his equipment 'properly' outside. Then large amounts of >> current can potentially flow! > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
