I'm looking for some help in identifying some specific requirements for the earthing of small generators (engine driven, say 5 - 10 kVA).
For reasons which I'm not entirely clear about, the client wishes to sell a 230V generator with the earth connection made to a mid point on the generator windings instead of one end, i.e. with respect to ground the output will be 115V - 0V - 115V instead of being 0V - 230 which would be normal. I'm trying to find good reasons to say why this is not permitted. Clearly the UK supply Regulations do not permit such an arrangement, but I don't think these would apply to a small generator. I have also identified that BS 7375 (Distribution of electricity on building and construction sites) says that a generated supply should be treated in the same way as a utility supply, and BS 7430 (Code of practice for earthing) recommends the use of an earthed neutral for 230V or three phase 400V generators. However, neither of these constitute what I would consider to be an unequivocal 'thou shalt not do it'. HSE publish a guide on electrical safety on construction sites but this essentially refers back to BS BS 7375 and BS 7430 for detailed guidance. From a safety point of view, the generator will be fitted with a residual current breaker and since in practice few small portable generators are ever actually properly grounded, it seems to me that the main safety concern is that it's not normal practice to do it this way and it only becomes dangerous when the generator is connected to a network designed with neutral point earthing. This may be sufficient reason to say it's not a sensible proposal, but if it is then I need to be clear on the point, not simply say it can't be done for un- specified 'safety' reasons. Can anyone else offer any insight into (a) any specific requirements which may govern this practice and (b) and reasons why it's actually unsafe? Thanks Nick. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
