# Has anyone ever done a box fill calculation?



## manchestersparky (Mar 25, 2007)

Based on table 314.16(A) in the 2011 NEC
You do the math #12 = 2.25 cu in

4 x 4 x 1 1/4 = 18 cu. in = 8 # 12 awg

4 x 4 x 1 1/2 = 21 cu in = 9 # 12 awg

4 x 4 x 2 1/8 = 30.3 cu in = 13 # 12 awg


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## Dennis Alwon (May 9, 2009)

Assuming no device then 3 - 12/2 cables would be equal to 7 wires so a standard 1900 box should be fine. I am also assuming no clamps but standard NM cable connectors.


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## Hackster (Jun 15, 2013)

Dennis Alwon said:


> Assuming no device then 3 - 12/2 cables would be equal to 7 wires so a standard 1900 box should be fine. I am also assuming no clamps but standard NM cable connectors.


3 in and 3 out (splicing straight thru) would be 13, right? Still fits then.


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## Dennis Alwon (May 9, 2009)

Hackster said:


> 3 in and 3 out (splicing straight thru) would be 13, right? Still fits then.


#12--2.25*7 wires= 15.75


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## Dennis Alwon (May 9, 2009)

It works like this. If you know the cu. in-- often on the box then you can use it. For standard box sizes use T. 314.16(A) as already mentioned.

Now count the wires.

1 for each circuit conductor 
1 for *all* the grounds so if there are 3 cables you count 1 ground
1 for clamps
2- for each device

Then go to Table 314.6(B) and look up the Volume allowance for wire sizes
In your case #12 AWG is 2.25

So you have 6 circuit conductors, add 1 for the equipment grounding conductor's -- no device and no clamps-- Total 7

7 * 2.25 = 15.75 cu.in


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## Mulder (Sep 11, 2010)

Dennis Alwon said:


> #12--2.25*7 wires= 15.75


Six cables, times 2 conductors in each cable, plus one ground equals 13. 13x 2.25=29.25. Still ok.


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## Dennis Alwon (May 9, 2009)

Mulder said:


> Six cables, times 2 conductors in each cable, plus one ground equals 13. 13x 2.25=29.25. Still ok.


Oops my bad 3 cables in and out.. right 13 wires --

I need to read more carefully


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## Hackster (Jun 15, 2013)

Yeah, I'm just extending some circuits. I have about 13 different circuits and I'm figuring the best way to split them up into JB's. Thanks guys.


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