Conductor Ampacity

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nmbme

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Conductor ampacity is calculated in accordance with 310.15 based on 90?C conductor insulation rating, provided the adjusted or corrected ampacity doesn?t exceed that for a 60?C rated conductor.

Where more than two NM cables containing two or more current-carrying conductors are bundled together and pass through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor must be adjusted in accordance with Table 310.15(B)(2)(a). Figure 334-3

Author?s Comment: This new requirement only applies to wood framing members, and has no effect unless you bundle more than nine current-carrying conductors together.

15A Circuit. If we bundle three 14/2 and one 14/3 cable (nine current-carrying 14 THHN conductors), the ampacity for each conductor (25A at 90?C, Table 310.16) is adjusted by a 70 percent adjustment factor [Table 310.15(B)(2)(a)].
Adjusted Conductor Ampacity = 25A x 0.70
Adjusted Conductor Ampacity = 17.5A

Question, how can you exceed the 60 degree C(from the adjusted ampacity)if your more than 9 current carrying conductors?
Example:11 current carrying conductors = 50%
25A x 0.50 =12.5<<<< how is that exceeding ??

[ August 30, 2005, 10:10 PM: Message edited by: nmbme ]
 
Re: Conductor Ampacity

You are not quoting from the NEC, and you did not include a bibliography. I can't address your question, unless I understand your question.

But it seems to me that the bit about "not exceeding the 60C rating" (or in some cases, the 75C rating) is merely a reminder of that requirement. It might not be possible to "exceed" in the circumstances you are describing. But the rule is still in place, and it still applies, and it might trap you under different circumstances, so it is worth an occasional reminder.
 
Re: Conductor Ampacity

Thats it ? nothing else ? I thought for sure that the wording itself is self explainatory...geezzz
 
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