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Did they overfill my boxes?

742 Views 4 Replies 5 Participants Last post by  Jnaas2
Howdy all,

Back in the 1990's we had a new service put in and several circuits needed to be extended from where they ran into the old fuse box to the new breaker panel.

The junction boxes used are 4 inch x 1 1/2 inch steel boxes with solid flat covers.

There are 3 circuits in each box - 3 12/2 w/g cables going in and 3 coming out. That's rather significantly overfilled, isn't it?

If I understand the box-fill calculations, that amount of cable would require at least a 29.25 cubic inches wouldn't it? (And I'm not sure I understand the box-fill calculations.)

What are the maximum amounts of 12/2 w/g cables that can be spliced in a 4 x 1 1/2 inch box?

1 - 5 of 5 Posts
12 x 1.75 = 21cu for the conductors. I believe 6 caps will be another 6x1.75=10.5 , meaning you would need 31.5. That is based on my location, I suspect you may have to subject even more volume per wire? How did you come up with 29.25 ?
E60, wire nuts do not count as fill under the NEC.

A 4 sq x 1 1/2" box is good for 9 #12's and has a volume of 21 CI.
12 gauge wires are 2.25 each unless they are less then 12 inches and just pass thru the box, Internal clamps are 2.25 total, all grounds count as 1 conductor 2.25 = 14 x 2.25 =31.5, Add extensions
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