NEC, Table 314.16(A) Metal Boxes

[friebel]

My question is as follows, when I use Table 314.16 (A)Metal Boxes, I calculated the Cubic inches to be more than the Table shows. Can you please explain the difference.
Example: A square box 4" x 4" x 1.5 = 24 cu.in.
Table 314.16 (A) for that square box = 21 cu. in.
I also notice that for all square box cu. in. calculations, that the Table is always 2 cu. in. less than my calculation. Please explain the difference. Thank-You in advance for your help.

 

[bphgravity]

Re: NEC, Table 314.16(A) Metal Boxes

I think it has something to do with the actual gross volume verses the minimum volume as specified in the Table. If a manufacturer makes a 4 x 4 x 1.5 box, it must have a minimum volume of 21 cu.in. however the manufacturer can label their box with the actual volume as permitted if it exceeds the Table's value.

[ November 05, 2004, 08:59 AM: Message edited by: bphgravity ]