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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?

Thanks!
Jim
 

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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 ?
 

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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.
 

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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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