I have a plastic 38cu gang box. How many 12gauge wires can it hold? There will only the wires and wire nuts, no recepticles or switches. I have 3 cables coming (9 wires total) in and 3 going out and what to pig tail a fourth. It will simly be B to B, W to W and G to G. I know 12gauge is 2.25 cu but I’m not sure how to count the grounds, pigtail and wirenuts.
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A quick Google found this: http://code.necplus.org/sample/document.php?id=necss%3A70-2011%3Anecs70-314.16
See the examples at the bottom to make more sense of the lawyerese. In particular, all the grounds count as one wire, and wire nuts are covered by space allocated to the associated wires.
But note that there are good reasons for these rules -- you can't really cram much more into a box, at least not unless you're very careful about wire length and placement. Generally best to use a larger size box if it will fit. (And it's usually best to join the grounds first and push them to the very back of the box.)
All of the grounds count as one wire and the wirenuts are free.
if you have a total of four 12-2/wg I count 8 current carrying conductors and one for the grounds.
9 x 2.25 is 20.25 so you have plenty of room.