Box fill

[Ron Buck]

I have a 12"x12"x4" junction box with 12-3/0 THHN and 3-#4 THHN conductors spliced inside. Looking at this box it seems to be over full how do i calculate this? Thanks for all your help.

 

[charlie b]

The process is described in NEC Article 314.16.

 

[ryan_618]

The process is described in NEC Article 314.16.

It is actually in 314.28, considering the size of the condcutors.

 

[LarryFine]

Looking at this box it seems to be over full.

I agree. Without looking it up, it sounds like it should be twice as large in every direction.

 

[finhead]

Except for conductors entering a box opposite a removable cover, pull box sizes are a function of the raceway size and the manner in which they enter the box.

If this box had a 1-1/2 inch conduit entering each wall, each containing three 3/0 AWG conductors, the minimun required box size would be 9 inches. Now if you add the 4 AWG conductors entering and leaving the box in a 1-inch conduit, the required size would not be increased by more than one inch.

This box is oversized