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Monday, September 5, 2016
Question:
If I use a gutter under a panel to bring PVC pipes into I need to derate after 30 conductors? Can I make a J box the same size as the gutter and just worry about the eight times dimension and not worry about derating on the wires?
Mike Thill
A
Answer:
Hey Mike thanks for your question. Yes, you need to apply an adjustment factor from 310.15(B) if the number of current carrying conductors at any cross section of a metal wireway or metal auxilary gutter exceeds 30 as stated in 376.22(B). If it is not made of metal the adjustment factor applies if there are more than 3 current carrying conductors. You have a good point; the wording in 310.15(B)(3)(a) is "in a raceway or cable" so if you used a box the adjustment factor does not apply. Maybe your AHJ will agree that you are using the wireway as a junction box and not require the adjustment factor to be applied. Submitting a public input for the 2020 NEC might be a good idea to improve the rules.