Here are some FAQ's and what Carlon has to say about their nonmetallic zip boxes.
Carlon FAQ's It would be interesting to know how many guys actually apply the required volume reduction of one conductor based on the largest size present in the box, for the built in quick "N" clamps in round ceiling and multigang boxes, when used.
I think most EC's just assume that the manufacturer has already made the reduction in the volume, which they have not. In other than 1-gang boxes, having more than one NM cable per KO in boxes with the quick clamps seems to be a pretty common listing violation as well.
Pretty small stuff as far as things go I guess, but still listing violations nonetheless.
