Wireway conductor derating

[Muneepit]

376.22(B)

The adjustment factors 310.15(B)(3)(a) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under the provisions 310.15(B)(5), exceeds 30 at any cross-section of the wire way.

My question:
When you hit that magical number of 31 CCC's, do you just derate counting the number of CCC's over 30 or would you start derate all of the conductors?

So if you have 32 CCC's in the wireway, would the derating be based on 2 CCC's or 32 CCC's?

 

[infinity]

All 32. 30 or less you ignore any derating.

 

[Muneepit]

Wireway conductor derating

So I guess the "loophole" is the cross sectional area? Probably rarely would you have all 32 conductors crossing at one point unless everything come in one end? At that point, you would have more than 30.

I have seen many installations where there is a wire way over panels and wires are running every which way to their prospective panel.

Is there a reference in the code to derate all 32 in that situation?

Thank you for your time in answering.

 

[infinity]

You have already answered it 376.22(B). If the conductors in the wireway go straight through the wireway so that at no cross sectional point there are more than 30 CCC's then no derating applies. Wireways over a group of panels are notorious for violating this section. This is from the 2017 NEC where they added the any cross section wording.

376.22 Number of Conductors and Ampacity. The number of conductors and their ampacity shall comply with 376.22(A) and (B).
(B) Adjustment Factors. The adjustment factors in 310.15(B)(3)(a) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under the provisions of 310.15(B)(5), 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.