NM Derating

[iwire]

Re: NM Derating

Originally posted by gerns:
Not sure but since you are in resi wouldn't you use Annex B Table B.310.11 for your percent of derate, since you have divers loads.

Only if you are an engineer.

310.15 Ampacities for Conductors Rated 0?2000 Volts.

(A) General.

(1) Tables or Engineering Supervision. Ampacities for conductors shall be permitted to be determined by tables or under engineering supervision, as provided in 310.15(B) and (C).

(B) Tables. Ampacities for conductors rated 0 to 2000 volts shall be as specified in the Allowable Ampacity Table 310.16 through Table 310.19 and Ampacity Table 310.20 through 310.23 as modified by (1) through (6).


(C) Engineering Supervision. Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of the following general formula:.....

[ January 23, 2006, 04:21 PM: Message edited by: iwire ]

 

[George Stolz]

Re: NM Derating

Originally posted by gerns:
Just my assumption. That's why I'm asking you.

FWIW, I agree with your idea. We just lack the permission.

Wayne (Hurk27) has actually submitted a proposal to allow more flexibility to derating, based on the load diversity of residences. We're all interested to see how it goes.

 

[bjp_ne_elec]

Re: NM Derating

Pierre - what was your referecne to 240.4 (G) - I didn't quite follow how this was pertinent to this post?

Thanks

DBrett

 

[George Stolz]

Re: NM Derating

Brett, they were just clarifying that the small conductor rule of 240.4(D) does not apply to the applications listed in 240.4(G).

So, for those particular applications, according to 334.80 and Table 310.16,
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• <font size="2" face="Verdana, Helvetica, sans-serif">14 AWG NM cable is good for 20 amps</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">12 AWG NM cable is good for 25 amps</font>

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[eprice]

Re: NM Derating

Originally posted by bjp_ne_elec: ...Say I have eight (8) 12/2 NM cables run in a three foot (3') long nipple. Now I've gone over the 24", and I also have eight NM cables. Now, how does Table 315.10 (B)(2)(a) impact my derating....

Let me add one thing to the discussion. If the conductors are bundled for only 3' and the runs are at least 30' total length, then the exception to 310.15(A)(2) will, IMO, allow the derating of the bundled section to be ignored

 

[George Stolz]

Re: NM Derating

Originally posted by eprice:
If the conductors are bundled for only 3' and the runs are at least 30' total length, then the exception to 310.15(A)(2) will, IMO, allow the derating of the bundled section to be ignored

That looks like pure genius. Anybody disagree?

 

[pierre]

Re: NM Derating

That exception does not apply to NM cable, it is for AC and MC Type cables.

[ January 24, 2006, 09:46 PM: Message edited by: pierre ]

 

[ryan_618]

Re: NM Derating

Originally posted by pierre:
That exception does not apply to NM cable, it is for AC and MC Type cables.

Why would you say that?

 

[ryan_618]

Re: NM Derating

I have a proposal in to the 2008 for the deletion of the new part of 334.80, based on the exception to 310.15(A)(2). I am very interested to see how panel 7 acts on it.