Hi This an updated version of a message that I accidently sent only to Robert
Just a few reminders: In both Class I & Class II equipment you need 1 fuse to provide basic overcurrent protection. 1 fuse in the Line conductor of a Class I equipment also provides protection against short-circuits to ground when the supply polarity is correct. A 2nd fuse in the Neutral provides the same protection when the mains polarity is reversed A Class II equipment is not deemed to have the possibility of short-circuits to ground, and so only needs 1 fuse for overcurrent protection. Most standards allow either single- or double-pole fusing (except for the specific double-pole fusing requirements in many IEC 60601 medical standards), but if you use double-pole fusing then both fuseholders must be "shock-proof" to prevent someone getting a belt from the mains when removing the unblown fuse. Almost all modern "international standards" compliant fuseholders provide that protection, but many of the older designs don't. (Many years ago, I vividly remember getting a belt which threw me across the room in front of 2 USA agency witness-testing engineers. OTOH, the equipment was for the US market, using a 120V-0V-120V supply but we were using a standard UK 0-240V supply - which raises the hazard levels in this configuration - and used US spec-compliant fuseholders Listed by that agency - so that was OK!!!!!!) It would be totally impractical to ensure that both Line and Neutral fuses blow at the same time without some sort of sophisticated crowbar circuit. The only way you can ensure that both mains supply poles are broken at the same time is to use a double-pole breaker, rather than fuses, and very few standards (if any?) require this approach. Rules for use of breakers do however require that they break both/all poles at the same time. Regards John Allen From: [email protected] [mailto:[email protected]] On Behalf Of Robert A. Macy Sent: 25 November 2005 03:52 To: James, Chris Cc: [email protected] Subject: Re: neutral fusing I recall somewhere that *if* you have a fuse in both lines, you MUST have them open at the same time. In other words, you cannot have two, independent fuses there. If that requirement is not there, it should be. IMHO - Robert - On Thu, 24 Nov 2005 09:12:27 -0000 "James, Chris" <[email protected]> wrote: > Does EN60065 permit fusing in both line and neutral? > > > > Regards, > > > > Chris > > - 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/listserv/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 -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.362 / Virus Database: 267.13.8/183 - Release Date: 25/11/05 -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.362 / Virus Database: 267.13.8/183 - Release Date: 25/11/05 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.362 / Virus Database: 267.13.8/183 - Release Date: 25/11/05 - 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/listserv/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
