Box fill

E

Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
I have been retired for almost 7 years. I have this old house partial rewire I am doing for my nephew. Feels good to get out and work a little but at 72 I am a bit slow. I was refreshing my mind on box fill. It's not helping the bad disks I have in my neck though.

Dealing with splices from Romex to some of the old BX I realized that metal device boxes are fairly useless. In most cases shorter depth boxes can't be used at all.

1 deduction for clamps in the box
1 deduction for ground wires (up to 4)
2 deductions for a device

so 1 14/2 Romex, 1 14/2 BX, 1 devise, clamps in the box would need 16 cubic inches which would have to be a 3 x 2 x 3.5" box.

Am I doing this right?
 
Eddie702 said:
1 deduction for clamps in the box
1 deduction for ground wires (up to 4)
2 deductions for a device

so 1 14/2 Romex, 1 14/2 BX, 1 devise, clamps in the box would need 16 cubic inches which would have to be a 3 x 2 x 3.5" box.
Click to expand...
I removed my calculation because it contained an error. Note to self don't post after you drank a few Manhattans.
 
Last edited:
Eddie702 said:
Dealing with splices from Romex to some of the old BX I realized that metal device boxes are fairly useless.
Click to expand...
That's only because back then fill requirements were less. Clamps, grounds didn't count and a device only counted as 1. Tails were cut so short so that you could push the device into the box that you barely could wire it. So don't blame the box, blame the guy who used that size box. Larger size boxes were available just as they are today. Cut the box out and replace it with a deep (3x2x3-1/2") metal box.

With new wiring, I always go bigger. It's so nice to be able to easily push the tails into the box and not have to fight with the device. Oh, and I always use metal boxes, not that cheap plastic junk!

-Hal
 
Second try, coffee only:
NM-14/2=3 conductors
AC-14/2=2
1 Device=2
1 Clamp=1
Total =(8) #14 conductors or 16 cu in.
Minimum size metal boxes: 3 x 2 x 3.5 device box or 4 x 1.125 square box.
 
Eddie702 said:
I have been retired for almost 7 years. I have this old house partial rewire I am doing for my nephew. Feels good to get out and work a little but at 72 I am a bit slow. I was refreshing my mind on box fill. It's not helping the bad disks I have in my neck though.

Dealing with splices from Romex to some of the old BX I realized that metal device boxes are fairly useless. In most cases shorter depth boxes can't be used at all.

1 deduction for clamps in the box
1 deduction for ground wires (up to 4)
2 deductions for a device

so 1 14/2 Romex, 1 14/2 BX, 1 devise, clamps in the box would need 16 cubic inches which would have to be a 3 x 2 x 3.5" box.

Am I doing this right?
Click to expand...
Article 314.16 (B) states the steps in 1 through 5. The verbiage can get a little confusing. The 2023 NEC adds a 6th section to the calculation if you have terminal blocks installed in the box. For example, Alumiconns if you are putting copper pigtails from the aluminum wire.
 
hbiss said:
That's only because back then fill requirements were less. Clamps, grounds didn't count and a device only counted as 1. Tails were cut so short so that you could push the device into the box that you barely could wire it. So don't blame the box, blame the guy who used that size box. Larger size boxes were available just as they are today. Cut the box out and replace it with a deep (3x2x3-1/2") metal box.

With new wiring, I always go bigger. It's so nice to be able to easily push the tails into the box and not have to fight with the device. Oh, and I always use metal boxes, not that cheap plastic junk!

-Hal
Click to expand...
I agree that metal boxes are better IMHO but there's the cost for one thing. And the only advantage to plastic is they have more room. Also, some of these partitions are not deep enough for a 3 1/2" deep box. You can get a 2 3/4' in there but not a 3 1/2". The old boxes are 2 1/2" deep. A lot of the J boxes are small octagon 3 or 3 1/2" whatever they were.

There is one j box in the basement with a 3 1/2" octagon with 4 14/2 bx cables in it that is original. Someone put a 3 1/2" box extension on it and put 1 14/2 BX and 2 14/2 Romex in it. Every time I walk by it I want to puke. Obviously it wasn't great to begin with but some idiot made it worse. Being in an unfinished basement he could have easily got power somewhere else. 7 cables in it total.
 
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