Wireway conductor ampacity

F

farmantenna

Senior Member
Location
mass
I have 28 apt feeders from 3ph 120/208 service that have to get to 7 4- stacked meter modules (everything is in basement) and no wall above them so will need a wireway. It's crazy to think an inspector or anybody would allow all those conductors (84) to go in one wireway without a crippling ampacity adjustment? Art 376 no adjustment up to 30 conductors.

My question is would you use just the # of conductors over 30 to determine which line in 310.15(c)(1) or once you're over 30 the ampacity reduction would start at 45%?
30 conductors no adjustment
34 conductors 40% or 80%?

Luckily Massachusetts amends 310 table if diversity is likely.

Opinions?
 
30 CCC's no derating. 31+ CCC's derate all of the conductors to the percentage in the table.
 
How long is the wireway as compared to the total length of feeders? 310.14(A)(2) exception many apply. In the 2017 and older codes it was 310.15(A)(2) exception.
 
don_resqcapt19 said:
How long is the wireway as compared to the total length of feeders? 310.14(A)(2) exception many apply. In the 2017 and older codes it was 310.15(A)(2) exception.
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Don, did the NEC ever clarify that the exception was applicable to wireways with more than 30 CCC's at any cross section? I've heard it debated both ways, some say that it's not applicable.
 
infinity said:
Don, did the NEC ever clarify that the exception was applicable to wireways with more than 30 CCC's at any cross section? I've heard it debated both ways, some say that it's not applicable.
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Yes, there were PIs for both wireways and gutters and the panel statements made it clear that the exception always applies.
Public Input No. 3279-NFPA 70-2020 [ Section No. 376.22(B)
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(B) Adjustment Factors.
The adjustment factors in 310.15(C)⁠(1) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under 310.15(E), exceeds 30 at any cross section of the wireway. Conductors for signaling circuits or controller conductors between a motor and its starter and used only for starting duty shall not be considered as current-carrying conductors. Where adjustment factors are required to be applied, it shall be permitted to apply the provisions of the Exception to 310.14(A)(2).
Statement of Problem and Substantiation for Public Input
There has been much debate on the internet code forums about the use of the Exception to 310.14(A)(2) for ampacity adjustment in wireways and gutters. Respected code authorities are not in agreement on the use of the exception. Where code experts are not in agreement on what the code requires, that is a strong indication that the code is not clear on the issue. This proposal is intended to add language to the code to make the issue clear.
Committee Statement
Resolution:The existing language is clear and the proposed text is not necessary. The requirements in 376.22(B) are based on the number of current carrying conductors in a wireway. These requirements modify the “adjustment factors for more than three current-carrying conductors” where there are 30 or less current carrying conductors in the wireway. The requirements in 376.22(B) do not modify the adjustment factors where there are more than 30 current carrying conductors. Further, 376.22(B) does not modify the ambient temperature correction factors. As there is no modification for ambient temperature correction, the ambient temperature correction factors in 310.15(B) and the requirements and exception in 310.14(A)(2) apply.
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Thanks all! The feeders will be 50'-125' and the wireway section will be 8' , maybe shorte. Things are fuzzy right now. I can split it into 12 shortest and 16. I forgot about that 310.14 exception. Never used it.

With this inspector I'll have to present the situation before we execute anything.
 
farmantenna said:
Thanks all! The feeders will be 50'-125' and the wireway section will be 8' , maybe shorte. Things are fuzzy right now. I can split it into 12 shortest and 16. I forgot about that 310.14 exception. Never used it.

With this inspector I'll have to present the situation before we execute anything.
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If you can limit the number of CCC's to 30 or less at any cross section then you can ignore any derating. If not then you'll need to calculate the 10'/10% exception.
 
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