ECN Forum Forums Code Related Discussion NEC & other Code issues Fill in blue boxes

Could anyone help me determine the fill on the blue plastic nail on box(4"x2"). Sometimes I have been in the situation where I needed to pull 4 12/2 w/G's in the blue box to connect to other circuits. I only count all the grounds 1 time, each individual conductor 1 time, the yoke (switch or receptacle) 2 times and each wire nut (clamp) 1 time. When I total this up it's 8 wires, 1 ground, 3 wire nuts, and 2 for the yoke. Total 14. I have seen this done many times in other jobs but it seems to be ok with most inspectors. Does anyone have some good input on this?

IMHO the wire nuts aren't clamps so you don't count them. If you don't put in a device (just a blank cover) you get 2 more back. It should end up being 8 wires plus 1 ground for a total of 9 (or 11 with a device).

The biggest single gang carlon nailup I have seen is the 3¼ deep and that is 22 cu/in, That is still too small for 11 #12s. (9 wires and the device)

2¼ x 11 = 24.75

As mentioned above, wire nuts are not clamps. See 314.16.

Clamps attach the cable to the box, not conductors together.

The easiest way to keep these things straight when first getting them straight, IMO, is to go down the list one by one:

So 4 12-2's with 1 device are
8 insulated conductors (314.16(B)(1))
0 Clamps (314.16(B)(2))
0 Support Fittings (314.16(B)(3))
2 counts for 1 device (314.16(B)(4))
1 count for all EGC's (314.16(B)(5))


Is 11 conductors x 2.25 = 24.75 cu.in.

That's way over for a single gang, even Carlon. (gfret, box fill is something best understood when the same math is done four different ways. )

And for those of us whose arithmeticer's don't work so good, Carlon boxes have the maximum number of each size conductor marked in the back of the box. Takes the guesswork out of it if you're not handy with the math.

Nice job Just George


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