Junction box size

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Old 10-23-10, 10:32 AM
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Junction box size

Hi, I need to extend the run of quantity 9, 12/2 wires. Wonder what size junction box is needed to accommodate the connection of 9 wires. Junction box is to be flush mounted in between wall studs

Thanks,

Richard
 
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Old 10-23-10, 10:44 AM
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12/2 refers to Cables. How many cables are we talking about? Does each individual cable contain a ground wire? Do any of the wires "pass through" the junction box?
 
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Old 10-23-10, 01:30 PM
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I have 9 12/2 romex cables that will go into a new junction box to connect to 9 cables that will exit. I need to know what size box is needed to hold the connections. Each 12/2 cable has 3 wires, black, white and a ground copper wire
 
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Old 10-23-10, 02:18 PM
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I'm counting 42.75 cu in required for the box. 18 conductors, plus one for grounding conductors, times 2.25. Add 2.25 for clamps as well. Although dated, you may want to refer to Box Fill Calculations (NEC 2002) - Self Help and More
for a more definitive excerpt.
The junction box must remain accessible no matter where you mount it. It can't be hidden behind drywall or other permanent covering.
 

Last edited by pcboss; 10-25-10 at 10:35 AM. Reason: clarification on conductor count
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Old 10-23-10, 02:24 PM
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While you might be able to use a 4X4X4 deep box I would suggest a 6X6.
 

Last edited by ray2047; 10-23-10 at 02:47 PM. Reason: Wrong factor for conductors
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Old 10-23-10, 02:52 PM
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juncrion box size

Thanks, the box I purchased is 8x8 and 4 inches deep. Sounds like that is big enough?
 
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Old 10-23-10, 03:14 PM
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Originally Posted by richardb123 View Post
Thanks, the box I purchased is 8x8 and 4 inches deep. Sounds like that is big enough?
Yes.

.......................
 
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Old 10-23-10, 03:19 PM
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If you want something that you can put a pretty cover on, I can't remember the size of this 6-gang, but it's well over 42 inches:


8x8 = 64
64x4 = 256 cu in
So that's fine.
The bigger the better.
DO NOT SKIMP on the excess you leave for splicing, especially with solid conductors. It will be a lot easier if you leave it much longer than the required 6" or so. When I did the pictured box, I bundled the wires to be nutted and cut them about a foot above the cover plate. It's easy to fold the excess in, especially with 256 inches.
 
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Old 10-23-10, 09:48 PM
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Originally Posted by richardb123 View Post
Thanks, the box I purchased is 8x8 and 4 inches deep. Sounds like that is big enough?
Plenty big for this one but just make sure you strip the sheathing off longer than you normally do with standard junction box.

Just one warning do not intermix the neturals at all so becarefull with this one this is important part here. { I have to fix this kind of mess before }

The bare or green conductor that is not a issue at all.

Merci.
Marc
 
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Old 10-24-10, 09:53 AM
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Junction box size

Thanks all for the info. Very helpful.

French, I am planning for each incoming wire of each cable to directly Connect to every outgoing, no intermixing of the neutrals. I will pigtail one coped ground to the box.
 
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Old 10-25-10, 10:22 AM
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Originally Posted by richardb123 View Post
I will pigtail one coped ground to the box.
I would buy a ground bar to do the bares. They all must connect to each other and to the box, and a bar with screw terminals is by far the best way to do that. You could make them all up into a couple big crimps, but that's a real PITA if you ever need to modify anything.
 
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Old 10-25-10, 10:30 AM
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Junction Box Size

Ben, Thanks.

Not sure my 8x8x4 deep box has a slot or holes to mount a grounding bar. Any special way to mount a ground bar to such a box?

But it sounds like you are saying, all the ground wires need to be bundled/connected together. If I do not use a ground bar, how do I secure 9 ground wires together? Just twist/crimp them all together with no twist cap and pigtail a ground lead to the box?
 
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Old 10-25-10, 10:33 AM
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With that many ground wires you would need to use multiple wire nuts or crimps. I like the idea of the ground buss. You could drill the box and use nuts and bolts to connect to the box.
 
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Old 10-25-10, 10:36 AM
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PCboss,

Thanks but if I use multipel wire nuts or crimps, to me that implies all the grounds would not be bundled/connected together?
 
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Old 10-25-10, 10:41 AM
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Originally Posted by richardb123 View Post
I have 9 12/2 romex cables that will go into a new junction box to connect to 9 cables that will exit. I need to know what size box is needed to hold the connections. Each 12/2 cable has 3 wires, black, white and a ground copper wire
This is 18 two conductor cables for a conductor count of 36 + the grounding conductor for a total of 37. 37*2.25= 83.25 cubic inches. The earlier box sizing was based on only 9 cables, not 18 cables.

Your 8x8x4 box is fine.
 
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