'Neutral Conductor' is defined in article 100 as being "intended to carry current under normal conditions" so that's basically NEC defined as current carrying. You are already allowed to undersize the neutral conductor in a 3 phase system, so I think that's all the allowance you're going to get. 3 phase is usually for commercial operations, with many more continuous heavy loads, than residential, or even single phase commercial service. It makes sense that we would have to oversize the conductors a bit more, although I never quite understood that "not more than 3 current carrying conductors in conduit" thing. Seems it should be based on conduit fill, and how much current is on the other conductors; but I guess that would be even harder to understand than table 310.16.
Aloha, R. Walters r...@solarray.com Solar Engineer On May 13, 2010, at 10:17 PM, Marco Mangelsdorf wrote: > Thanks for sending that link, William. > > OK…let’s try it from a different perspective. > > When you’re running, say, three three-phase hot conductors from point A to > point B with a neutral conductor, should that neutral be considered “current > carrying” from the perspective of more than three “current carrying” > conductors in a raceway? And thereby necessitating de-rating the current > carrying capacity of the hot conductors? > > marco > > Marco: > > You have opened a can of worms. I hope you are happy! > > Are you looking for the legal definition or to discover if the neutral > conductor actually carries current? The answer to the legal definition is in > 310.15(B)4 (2002), and the answer is: It depends (on the type of service). > This on-line article sums it up well: > http://ecmweb.com/nec/code-basics/electric_conductor_size_matters/ > > William Miller > > PS: In my opinion, the neutral is a current carrying conductor in any > system. Disconnect it at your peril. > > William > > > > At 02:41 PM 5/13/2010, you wrote: > > Content-Type: multipart/alternative; > boundary="----=_NextPart_000_0078_01CAF291.3BA43F40" > Content-Language: en-us > > I have a disbelieving business partner who believes that the neutral > conductor in a standard 120/240VAC service is a current carrying conductor. > > Could someone please disabuse him of that notion? > > Thanks, > marco > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.819 / Virus Database: 271.1.1/2870 - Release Date: 05/12/10 > 20:26:00 > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org >
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