Trough Conductor Fill

[TWGJ24]

I have a 12"x12"x10' Trough under 4 panels with (2) 2" EMT Conduits that are less than 24"s in length to each. I have 120 current carrying conductors in this trough splice free going to the designated panels non lighting circuits. All are number 12. Using article 300 and 310. I want to be sure I am correct in using these on a 20A Breaker since I have already derated the number 12 once from 30A to 24A at 80 percent. 310.15(b)(2)(a) i know is used as necessary for ambient temp. Please someone explain.

 

[tkb]

You need to look at 376.22 (A) and (B)

376.22 Number of Conductors and Ampacity
The number of conductors and their ampacity shall comply with 376.22(A) and (B).

(A) Cross-Sectional Areas of Wireway. The sum of the cross-sectional areas of all contained conductors at any cross-section of a wireway shall not exceed 20 percent of the interior cross-sectional area of the wireway.

(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. 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.