Sizing a wire trough

[dw7777]

I am trying to size a wire trough. I have 14 new panels, MLO, 240/120 v, 4 wire, Being feed with #8 wire on a 40 amp breaker. Each panel is going to be bx cable. They enter the trough on the top and they exit the trough through the bottom, in individual 3/4
conduits. The conduits then hit a 600 amp panel. There will be no juctions, only bonding bushings as the bx cable enters the gutter. Can anybody show me the correct way to calculate this? I'm thinking of using a 8"x8"x36".

 

[kwired]

Read 366.22 or 376.22 whichever applies - they both basically say about the same thing. 20% fill at any cross section and max 30 current carrying conductors. If more than 30 current carrying then derating factors of 310.15(B)(2) applies to the conductors.