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Joined: Aug 2003
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It seems clear to me this language allows us to install NM cables in a sleeve of any length without derating. But, if we strip the covering off, now there are conductors in the raceway, and derating is required. No, IMO, whether the covering is stripped off or not, the conductors are still in the sleeve/conduit and the "where the number of current-carrying conductors in a raceway or cable exceeds three" part of the section would apply. The "or where single conductors or multiconductor cables are stacked or bundled" part is there for the cases where there is no raceway involved.
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Joined: Aug 2003
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24 1/4 " or MORE = pipe - better derate ...but if I have an inch and a half in insulation penetrating a top plate I need to derate. 334.80 IMO, the exception to 310.15(A)(2) will usually allow us to forget about derating in the above situations.
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Joined: Jul 2004
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Have you looked at 334.80 in the 2005 code? There seems to be no wiggle room on the "insulation" derating.
Greg Fretwell
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Joined: Dec 2003
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I do not see that 334.80 has a bearing on this discussion.
Common sense tells me I must derate, but the wording seems to contradict that.
If I install cables in a raceway I don't need to derate per 310.15(B)(2)(a). Doesn't make sense, but the wording is there.
Would you guys all agree with me that derating is a good idea? And, that the wording needs to be made clearer?
Earl
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Joined: Jul 2004
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"Where the number of current-carrying conductors in a raceway or cable exceeds three," does not say those CAN'T be cable conductors in a raceway, the following text you quote refers to cables not in raceways.
I agree it is poor wording but I believe they mean what you are saying is right.
Greg Fretwell
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Joined: Feb 2002
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SolarPowered ---
The NEC allows engineering. As do all national building codes.
The engineering to support my statement is very simple.
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Joined: Apr 2005
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quote:
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...or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways,...
Dean, I agree; better wording would be nice.
How about instead of "and not installed in raceways", "it just said even if not installed in raceways."
Not only that; but if they are bundled how do you maintain spacing. IMO if they're bundled you haven't maintained spacing.
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Joined: Dec 2003
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I did consult with Jeff Sargent of NFPA about this. Yes, we must derate (as common sense would tell us) for the number of conductors in the conduit, including the conductors in the cables.
The phrase: "and not installed in raceways" was intended to clarify the cables were stacked or bundled, not to confuse the requirement for derating of conductors in confined conditions. Who among us would like to submit clearer language for the next code? Ryan?
Earl
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Joined: Mar 2006
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312.5(C)ex applies to earlydeans' original post. You cannot put a 2ft piece of PVC in the top of a panel and route all the NM's through it.
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Joined: Dec 2003
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312.5(C) ex. does just the opposite. It gives explicit permission to run all your NMs in a single PVC conduit. The FPN also makes it clear derating is needed.
Earl
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