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Electrical help selecting box size?
You have installed a 4-inch square metal box that is 1-1/2 inches deep for use as a junction box. What is the maximum number of #10 THHN copper conductors that could be installed in the box? (Assume no grounds or fitting devices.)
3 Answers
- Jim WLv 79 years agoFavorite Answer
Compute the volume of the box. Inside dimensions should be used, divide by the required volume for each size of conductor. If I remember it's 2 for a 14, 2.25 for 12 and 2 for 10 that gives the number you can install in the box. Then subtract 1 count for each fitting or cable clamp. Best to check the code book for the numbers to be sure.
Source(s): 50+ years in the electrical industry - 9 years ago
Go to the library and look under box fill on the 2011 NEC. Wish I had my NEC with me, I would guess for 10AWG probably no more than 6 current carrying conductors. Neutral conductors in most jurisdiction do not count as current carrying conductors, same for grounds.
Don't forget to de-rate for temperature highs and quantity of wires.
- dtstellwagenLv 79 years ago
Apprentice homework question? You need to do your own homework, but if this helps in the US the answer can be found in 314.6
Uh, you didn't ask, but current carrying conductors and derating don't matter for box fill, all grounds only count as one.
Source(s): Local 46 Electrician
