I read in !emc-pstc that Ted Rook <t...@crestaudio.com> wrote (in <sbe6c255....@peavey.com>) about 'CLASS 11(DOUBLE INSULATED) & 2/3-CORE CABLE', on Mon, 5 Nov 2001: >Could the grounding safety issues we are confronted by have been avoided if >the >incoming AC supply had remained 'balanced' that is, not referenced to local >ground anywhere?
No; France and Norway have 'IT' systems, in which grounding is only to prevent static charge build-up; the neutral is grounded through an impedance at the sub-station. AIUI, this is used in mountainous districts where ground paths are long and of low conductivity. There are significant differences between the French and Norwegian systems. > >Or to put it another way. > >Some where along the way it was decided to ground the neutral at the premises >entrance. Why? This applies in the US and many European countries, but not to UK or France. > >What is the advantage? and to whom? Several advantages, to the user and to the utility. > >I feel I should already know the answer, but I don't. > >Any offers? - Multiple grounding reduces 'ground lift' with high-current faults; - Reduced ground return impedance ensures that protective devices operate on live to ground faults; - Protection against open-neutral faults, capable of frying cables and installations. > >(which reminds me of the fact that it was the catalog of an American parts >supplier which taught me why we have fused domestic plugs in the UK and not >elsewhere; because the UK domestic wiring uses ring distribution through the >house. The ring has a single thirty amp rated fuse and so can supply over >twice >the current rating of an individual outlet. Primary protection takes place >inside the appliance outlet plug which has 13A fuse rating. The resettable >magnetic breakers that are so familiar to everyone in 120V territory are >unknown >in the UK.) Not so; the rings in my house have 32 A miniature breakers, not fuses. The lighting circuits have 6 A breakers. The water heater has a 16 A breaker. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
