First of all I want to thank everyone who took time to answer my question about sizing a box.
Probably I should have stated this question differently. We are trying to minimize the box since it is going to be installed in the bridge parapet wall and the bridge structural engineer needs to design his wall around the box. We found a box that is 12" horizontal X 10" vertical and 8" deep and the bridge structural engineer can live with that size so we are hoping that the 12" X 10" X8" box meet NEC.
Since I first posted this question I was able to talk to an Electrical Inspector. This is what he said. For the 3" conduits--3" X 8 = 24" For the 1.25" conduit--1.25" X 6 = 7.5" Minimum depth = size of largest conduit entering the box so depth = 3". Minimum size box = 24" X 7.5" X 3" = 540 cu. in. He said the bottom line is you need the cu. in. volume but you can change the size of length, width or depth as long as you maintain the minimum cu. in. volume of 540 cu. in. I told him we wanted to use the 12" X 10" X 8" box whcih equals 960 cxu.in. and he said the 12" X 10" X 8" box will meet NEC. I told him the wire sizes we are using and he said that we will not have problems with the 12" X 10" X 8" box.
Does anybody disagree ? Thanks
