Good morning, Jim. The Code reference you cite is it, as far as interrupting capacity goes. The NFPA isn't going to stick it's neck out any further and the shouldn't. The rationale is that each application could be different, some having 10 kA, some having or 100 kA or greater fault current capacity. The engineering of any facility has to understand the utility's capacity at the service entrance and also be able to calculate fault capacities downstream.
I know you mentioned NFPA 70:2005, but the latest I have in 2002. I don't know that there's a significant difference between the two versions on the references I give below. I think what you're really looking for is a combination of both Article 100 (definitions of 'identified' and 'listed'), 110.3(b) and (especially) 240.10. (Other locations discuss special characteristics for feeders, service entrances, special uses, large electrical load equipment etc.) The test programs are vastly different, with testing of branch circuit protection breakers being significantly more rigorous than for supplementary protectors, in anticipation of a much more severe electrical environment. Also, look at 240.83(c). My recollection from working with circuit breakers is that 5 kA is a gimme, provided the basic construction requirements for branch circuit protection breakers are met. Anything higher requires testing. Regards, Peter L. Tarver, PE [email protected] > From: Jim Eichner > Sent: Monday, September 19, 2005 5:07 PM > > I'm sure it's in there...somewhere. > > I'm looking for where the NEC (2005 please) says > that the overcurrent > protection provided for branch circuits has to be > a circuit breaker with > an interrupt rating of at least X (I believe it's > 5000A), as opposed to > a supplemental protector. The closest thing I > can find is... > > 110.9 Interrupting Rating. > > Equipment intended to interrupt current at fault > levels shall have an > interrupting rating sufficient for the nominal > circuit voltage and the > current that is available at the line terminals > of the equipment. > > This doesn't really say it. It suggests that if > I could go buy a > supplemental protector rated for say 500A > interrupt and if I could > convince the electrical inspector that at the > location where it will be > installed (say in a sub-panel at the end of a > long run of No. 14AWG > wire) that's all the fault current available, > then that would be ok?! > > I thought they had to be "real" circuit breakers > AND they had to have > appropriate interrupt ratings. Yes? No? > > Thanks, > > Jim Eichner, P.Eng. > Compliance Engineering Manager > Xantrex Technology Inc. > e-mail: [email protected] > web: www.xantrex.com - 2005 IEEE Symposium on Product Safety Engineering 3-4 October Schaumburg, IL http://www.ieee-pses.org/symposium 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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
