# 310.15B2a Derating for multiple conductors.



## wildleg (Apr 12, 2009)

acro said:


> Say I have a wireway that is above and connects several enclosures, and houses an undetermined # of wires. Both power and control - some from enclosure to enclosure and some tie to conduits terminated at the wireway.
> 
> 
> Does that derating table apply directly? I have seen many instances where wireway was used to help simplify installations, but it just does not seem that the wires would have been derated 50% or more. As would be tha case if there where 10-20 conductors.
> ...


 .... .


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## acro (May 3, 2011)

OK


> Is there any consideration for the size of the wireway? Would the same derating apply to a 6x6 wireway as would apply to a 12x12 containing the same # of conductors? YES


Yes, the same derating applies, or yes there is consideration?


How does the size of the wireway play into the derating? Is there a particular code?

How do you determine if the wireway is overfilled? Other than not being able to get the cover back on.


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## Dennis Alwon (May 9, 2009)

Table 310.15 de rating is for raceways and cables not wireways. Look at 366.22(A)


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## Chris Kennedy (Nov 19, 2007)

If the inspector brings up 376.22(B) just say, "What wireway? Thats an enclosure."


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## McClary’s Electrical (Feb 21, 2009)

(4) 14's in a 1/2" pvc are subject to the same derating as (4) 14's in a 4" PVC


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## acro (May 3, 2011)

mcclary's electrical said:


> (4) 14's in a 1/2" pvc are subject to the same derating as (4) 14's in a 4" PVC



Yea, that's the thing that just sucks. Or at least does not really make any real sense.


I will look at 366.22(A). Raceway, wireway, I need to freshen up on the terms.


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## Dennis Alwon (May 9, 2009)

The reason why it doesn't matter what size pipe is being used is because in the end they will be bundled together. Now on vertical runs one would have a point but not horizontal runs.


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## 360max (Jun 10, 2011)

Dennis Alwon said:


> Table 310.15 de rating is for raceways and cables not* wireways*. Look at 366.22(A)


I know this thread is a year old, but a wireway is a raceway by NEC definition


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