# Box fill math help



## Smileyboy (Apr 24, 2007)

I have 3 4/0 wires being spliced outside and changed over to 4/0 ser for a service in a basement. 

I usually grab the biggest box... Which has worked well for me. However I should know the math in this. Can someone help me out? 


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## Smileyboy (Apr 24, 2007)

And a ground wire. 


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## Dennis Alwon (May 9, 2009)

Smileyboy said:


> I have 3 4/0 wires being spliced outside and changed over to 4/0 ser for a service in a basement.
> 
> I usually grab the biggest box... Which has worked well for me. However I should know the math in this. Can someone help me out?
> 
> ...


It depends on the direction that the wires enter the box. I will show a few examples


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## Smileyboy (Apr 24, 2007)

That's right! It's the bottom and back of the box. 


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## JoeAPinkley (Apr 3, 2016)

Really great information you have shared with us.


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## MechanicalDVR (Dec 29, 2007)

JoeAPinkley said:


> Really great information you have shared with us.


Agree, illustrations are so much better than just text. Visualization is easier to understand.


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## zac (May 11, 2009)

Dennis Alwon said:


> It depends on the direction that the wires enter the box. I will show a few examples


It's interesting that a straight pull vs a bending radius requires more space (8" instead of 6"). Would seam the other way around? 

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## 99cents (Aug 20, 2012)

zac said:


> It's interesting that a straight pull vs a bending radius requires more space (8" instead of 6"). Would seam the other way around?
> 
> Sent from my SM-G930T using Tapatalk


Maybe because it's a pull point and you want elbow room. I thought the same thing.

Would you allow extra in these diagrams for splices?


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## MechanicalDVR (Dec 29, 2007)

99cents said:


> Maybe because it's a pull point and you *want elbow room. * I thought the same thing.
> 
> Would you allow extra in these diagrams for splices?


You are on to something there. When I was first being taught the old dogs would keep an actual loop of wire outside the box while pulling slowly. I always thought this practice was more trouble than benefit. The loop would often get hung up and then you'd have to pull back and start over.


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## Dennis Alwon (May 9, 2009)

If you think about the pull with large wires I can see why it needs to be larger for straight pulls. A loop is not easy to do with large conductors


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## zac (May 11, 2009)

Dennis Alwon said:


> If you think about the pull with large wires I can see why it needs to be larger for straight pulls. A loop is not easy to do with large conductors


It would seam easier to pull straight then let's say an LB? Thanks anyways for the info. 

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## macmikeman (Jan 23, 2007)

Aren't you supposed to buy Mike Holts books and illustrations?


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