> >
>

Calculating Box Fill

Calculating Box Fill

#1
01-09-18, 11:18 AM
Member
Join Date: Aug 2003
Location: Seattle
Posts: 179
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.

#2
01-09-18, 12:20 PM
Member
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,914
Sounds a little small. Maybe this will help...

https://www.ecmag.com/section/codes-...tions-part-vii

#3
01-09-18, 12:58 PM
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 13,980
Turn the old panel into the junction box.

#4
01-09-18, 01:25 PM
Member
Join Date: Aug 2003
Location: Seattle
Posts: 179
I have new plumbing coming through, which is why I am moving it.

#5
01-09-18, 01:57 PM
Member
Join Date: Jan 2007
Location: Des Moines, IA
Posts: 1,048
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.
#6
01-09-18, 02:22 PM
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 13,980
Run the plumbing behind the box or reroute the plumbing.

#7
01-09-18, 02:23 PM
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 13,980
A 6x6x6 would be very crowded and difficult to find a problem in later.

#8
01-09-18, 04:34 PM
Member
Join Date: Aug 2003
Location: Seattle
Posts: 179
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.

#9
01-09-18, 04:44 PM
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,145
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.

#10
01-09-18, 05:14 PM
Member
Join Date: Jan 2007
Location: Des Moines, IA
Posts: 1,048
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.

#11
01-09-18, 06:57 PM
Member
Join Date: Aug 2003
Location: Seattle
Posts: 179
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. .