# Box Fill Exercise (sharpen your skills)



## jar546 (Sep 21, 2018)

Alright, here we go!

You have a 4" square metal junction box 2-1/8" deep with NO integral clamps.  An 1-1/2" extension ring is added to the box.

The box has 6 cable assemblies that terminate inside the box with the following wires:

2- 12/2 with ground MC cables
3- 12/2 with ground, 16/2 MC-LED cables
1- cable assembly from Emergency Light mini-inverter

The above is broken down as follows:

5- 12 awg equipment grounds
1- 18 awg equipment ground (from EL mini inverter)

5- 12 awg neutrals

5- 12 awg hots

6- 16 awg LED dimmer control wires

11- 18 awg emergency light inverter wires (12-1=11 equip gnd grouped above)

FYI, the extension ring is not marked with cubic inch capacity.


There are no devices in the box, just the wires, ground screw, extension ring and cover plate.

Is there adequate space in the setup as described for box fill?


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## RJJ (Sep 24, 2018)

Yes


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## jar546 (Sep 24, 2018)

Wow, just one taker on this one?

No one does electrical inspections?  The could easily happen in a residence too.


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## ICE (Sep 24, 2018)

jar546 said:


> Alright, here we go!
> 
> You have a 4" square metal junction box 2-1/8" deep with NO integral clamps.  An 1-1/2" extension ring is added to the box.
> 
> ...



Can I get a picture?


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## jar546 (Sep 24, 2018)

ICE said:


> Can I get a picture?



No Sir.  You have all the information that you need.


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## Pcinspector1 (Sep 25, 2018)

If I understand the Q. 

*NO*, not enough room even when I buy the extension ring for your project. Need approx. *53.25 volume*

30.3 (4x2-1/8") + (22.5 RACO 1-1/2"extension ring) = 52.8 *No devises.

Did you measure the box, if it's a 4-11/16" x 2-1/8" = (42.0) volume + ext ring 22.5 = 64.5 you'd be good


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## jar546 (Sep 25, 2018)

Pcinspector1 said:


> If I understand the Q.
> 
> *NO*, not enough room even when I buy the extension ring for your project. Need approx. *53.25 volume*
> 
> ...



No sir, it is a 4" square box, not a 4-11/16" but if that were the case we would be good.

So here is the question,  RACO does list that extension ring as 22.5 BUT it is not embossed on the ring itself, therefore you have to take the same cubic inches as listed for a box that size which is 21.  I think you are off a little on you calculation for what you do need.  Actually, you are off a little on that........


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## Pcinspector1 (Sep 26, 2018)

Jar, from the response, the inspection of boxes must not be a high priority or its not an issue until the inspector see's some abnormal amount of wiring in a box. Calculating the components is far more complicated than I thought and appreciate the exercise you posted. I diffidently wouldn't go to court with my calcs!

According to EC&M, there is 1) Conductor volume, 2) Cable clamp Volume, 3)Support fitting volume, 4) Device yoke volume and 5) Equipment-grounding conductor volume that has to be calculated.

And then the box and ring allowable volume.

I'd be curious how other inspectors are alerted to box overfill, like when you see several conduits entering a box, like 4,5 or 6 conduits, do you start to have convolutions and drop your coffee cup?


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