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# Number of wires in a box

## Number of wires in a box

#1
03-26-02, 05:17 PM
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Number of wires in a box

I am using 12-2 and 12-3. What is the max number of wires I can run into a .18cu ft box in any combination. Thanks.

#2
03-26-02, 05:30 PM
Nazgulflyer
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2.25 cu in per conductor, grounds count as one, five conductors x 2.25 + one ground 13.5 cu in. yoke mounted device count as two wires so a recpt in the box would require a 16 cu in box or a single gang deep fiber box

#3
03-26-02, 10:07 PM
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Conductor....Explain

Don't mean to be dense about this but I am new to this. Can you explain what you mean by conductor?
Do you mean each black, white, ground, etc... is considered a conductor or do you mean each set of 12-2 or 12-3?
Where does the 2.25 cu in come from? Is that the length of each wire?

Sorry again for being dense. Thanks for the help.

#4
03-26-02, 10:28 PM
Nazgulflyer
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article 314-16

Box fill is based upon allowing a conductor to breathe, it allows a conductor of a certain size to dissapate heat while confined in an enclosure. Article 314-16 explains this but most think it is how many wires you can cram in a box. Not true an equip grounding conductor will never carry current (non iinductive) while under normal conditions. Therefore they are always counted as ONE. They will not dissapate heat. Any conductor carrying current will dissapate heat (IsqR) which will deteroiate the quality of the insulation. Adding devices in the box (yoke, hickeys or pendants) will also detract form the free air space to dissapate the heat generated from current (I). In simple terms, a crowed bus with no AC will get unconfortable.

#5
03-27-02, 12:43 AM
Debbie Ann
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Hello trytodoitright
You are not being dense at all, in fact you are being smart to ask questions when you don't understand something. I don't know the answers to your questions, but I'm certain that one of the regular members will help you out. I know you don't intend to cram as many wires as you can in a box because you asked what is the max number of wires allowed. My advice......always check
your math and wait for one of the regulars to answer you and explain what they mean in terms we all can understand. Be sure to ask anything and everything you need help with. I do believe that is why this forum and others like it exist....

#6
03-27-02, 05:07 AM
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Join Date: Dec 1999
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just get the deeper boxes

Just get the deeper boxes, unless you don't have the wall depth available. If you have a 2x4 wall, the deeper boxes will fit. If you are using 2x3 agains the foundation, then you may have to use the smaller boxes.

You quoted a .18 c.f box. I don't know where you got this number as boxes I've seen are in cubic inches. I'm a DIYer, not a pro, however. .18 c.f. is a huge box. A 16 ci box (regular outlet box) is only .009 c.f.

Nazgulflyer said that you can put both in and out 12-2 wires in the deep outlet box.

If you are talking about a box for a light, don't get the shallow boxes. A regular box has plenty of room for a 12-2 and a 12-3.

What are you trying to do?

#7
03-27-02, 08:46 AM
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cu ft??

BobF,

Thanks for the reply...I mistyped my post. The box is a regular switch\rect box. It was listed as a .18 cu in. I want to add a 3-way switch to an existing circuit. A 12-3 going out to my other switch and then split the current circuit to supply the power feed to my switch as well as the existing downstream rect. So I would also have 2 12-2 coming into the box.
Thanks.

#8
03-27-02, 12:21 PM
Wgoodrich
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What had to say is correct.

See below concerning the extra info you have now provided planned to be installed in that box.

1 - 12 / 3 equals 3 current carrying conductors.
2 - 12/ 2 equals 4 current carrying conductors total.
all the grounding conductors in the box is counted as one current carrying conductor.
1 switch device equals 2 current carrying conductors.

You would have a total of 10 current carrying conductors in a plastic box requiring that box to contain 22.5 cubic inch capacity in that box. You would need a minimum of a 3" deep single gang plastic box to install 2 - 12/2 and 1 - 12/3 in that plastic single gang device box.

If you are using a plastic box look inside the box. It should have the total cubic inch capacity of the inside of its box.

If you are using a steel box then you must add an extra current carrying conductor for the clamps that are required. This would call for a total number of current carrying conductors in a box of 11 requiring a minimum cubic inch of that steel box equalling 24.75 cubic inch. if this is a steel box. There is no steel device box that will allow those two 12/2 and a 12/3 in a single gang steel device box without some sort of extension box added.

http://homewiring.tripod.com/homewir...l/boxfill.html

Hope this helps

Wg

#9
03-27-02, 12:53 PM
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Mud Cleared

Wg,
Your response has cleared up any confusion I have. Thanks for putting it in "English".