Calculating Box Fill


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Old 01-09-18, 11:18 AM
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Calculating Box Fill

I am relocating a sub-panel and need to provide a junction box at the old location.

Entering the junction box I will have:
24 - #12 cables = 72 wires X 2.25 c. in. = 162 cubic inches
2 - #14 cables = 6 wires X 2 cu. in. = 12 cubic inches
6 - #4 wires
2 - #6 wires X 5 cu. in. = 10 cubic inches

TOTAL = 184 cubic inches plus what is needed for the 6 - #4 wires.

NEC Table 314.16B does not include the space required for #4 wire.
The box will only contain splices.

Are my calculations correct and does someone have the volume required for # 4 wire?
I would like to use a plastic 6"x6"x6" square box but it looks like it might be a bit small.
 
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Old 01-09-18, 12:20 PM
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Sounds a little small. Maybe this will help...

https://www.ecmag.com/section/codes-...tions-part-vii
 
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Old 01-09-18, 12:58 PM
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Turn the old panel into the junction box.
 
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Old 01-09-18, 01:25 PM
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I have new plumbing coming through, which is why I am moving it.
 
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Old 01-09-18, 01:57 PM
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24 - #12 cables = 72 wires
Exactly 3 conductors per cable? That is suspicious. Remember that the equipment grounding conductors are only counted as 1 conductor for the whole box based on the largest EGC present. So if your largest EGC is #6 you'd just add 1 volume allowance for the #6 EGC and use 48 rather than 72 for your #12 cables, for example.

I agree with pcboss to use the old panel as a junction box. I understand why you "can't" in this case. I certainly would not want to have to run all those cables into anything resembling the plastic box you mentioned!
 

Last edited by core; 01-09-18 at 02:35 PM.
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Old 01-09-18, 02:22 PM
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Run the plumbing behind the box or reroute the plumbing.
 
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Old 01-09-18, 02:23 PM
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A 6x6x6 would be very crowded and difficult to find a problem in later.
 
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Old 01-09-18, 04:34 PM
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What I am really looking for is the volume requirement for #4 wire. The table just goes to #6. Trust me, the sub-panel has to be moved. All other options have been evaluated and eliminated. Thanks to the person who stated that only the largest ground wire has to be added in and that those associated with the #12 and #14 cables are not counted.
 
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Old 01-09-18, 04:44 PM
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What about using a trough ? How much room do you have for a splice box ?
The 6x6x6 is not going to cut it.

This is a 6"x6"x24" trough. They come in 4x4, 6x6, 8x8.

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Old 01-09-18, 05:14 PM
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What I am really looking for is the volume requirement for #4 wire.
There isn't one. Because once you have even a single #4 conductor in there, you've opened Pandora's box and are now required to have minimum physical dimensions which depend on the conduit size and which direction the pull is going. Without knowing your raceway size it's impossible to say. But you are probably looking at something much larger than what you had in mind. You're going to have a big honkin' thing there no matter what.

Take a look at NEC 314.28 for your requirements. Or if you'd rather watch a video, there's this one from Mike Holt.
 
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Old 01-09-18, 06:57 PM
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Thanks Core, that is the answer I was looking for. I have 1" conduit so the entry points in the box need to be separated by 6". So the box size is a minimum of 8" square to accommodate the wire pull. The remaining splices of #12 and #14 wire need around 130 cu in. I am not sure how you combine pull and volume requirements but there should be plenty of room in an 8" box.
Thanks for the responses. .
 
 

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