Box Fill Calculation

[wwhitney]

Info on #4 conductor from a past thread.

So with 314.28 applying in lieu of 314.16, then we have, for a box with just one cable entry:

- A Hubbell HBL9450A 14-50 receptacle is 2.44" deep. So 314.24(B)(1) applies, and the box must be at least 2.69" deep internally. That means 314.24(B)(3) is also satisfied.

- If the cable entry to the box is via the back, 314.28(A)(2) Exception applies, and the box only needs to be 1-1/2" deep for compact stranded aluminum #4, or 2" deep for other #4 conductors, to satisfy that. Either way 314.24(B)(1) controls. But the upshot is you could install the receptacle in any 2.75" or deeper double gang (as the Hubbell brand requires a double gang, IIRC), no box volume computation required. If you got a different 14-50 receptacle that is listed for a single gang and 2.5" or less deep, you could put it in a 2.75" deep single gang, assuming you could get it to fit and still comply with the 6" conductor length rule (presumably not going to fit).

- If the cable entry is to the side of the box, then the width is now controlled by 314.28(A)(2), and we need to find the equivalent conduit size for the #4 cable. If we can use any conduit type and conductor insulation we like, you can fit (3) #4s and (1) #8 EGC in a 3/4" conduit, and the required width is 4-1/2". If we stick with reasonable choices like IMC and XHHW-2 insulation, the equivalent conduit size is 1", and the required width is 6". The height is not limited (other than mounting the device).

- If the cable entry is to the top or bottom, then it's same as the side entry case, except now the height has a minimum, and the width is not limited.

How does all that sound?

Cheers, Wayne

 

[Rick 0920]

The only document I could find on Carlon's website is an FAQ from 20 years ago. Do you have a more recent reference?

I'm a bit doubtful of this interpretation. I means yes, when you use the cable clamp on a multi-gang Carlon box, the bendable tab does bend into the former volume of the box slightly. But the volume taken up is no more than the interior portion of a button connector or the locknut of a metal cable connector.

And the clamping action is between two parts of the plastic box, there no clamp protruding into the box. So I'd happily argue that the clamp is not internal to the box (unlike the metal NM clamps you can get in 4 square boxes, for example).

Cheers, Wayne

I do not see any updated info on their website either Wayne. There are Articles and sections of the NEC that haven't changed in over 20 years either. That doesn't mean that the information in them is outdated and no longer to be complied with. Maybe Carlon hasn't felt the need to change this information. I have no idea. I just treat the manufacturers website info like the NEC. It says what it says, not what I think it should say or what I want it to say.

 

[wwhitney]

I just treat the manufacturers website info like the NEC. It says what it says, not what I think it should say or what I want it to say.

OK, sure, it says what it says. But the manufacturer's FAQ doesn't have the force of law or of the NEC. In this case they are just wrong. : - ) The clamping action is not occurring inside the box for the standard Carlon clamps, so no deduction is required.

Cheers, Wayne

 

[gjhayes66]

Hello All, I found this thread this morning researching if Nonmetallic Box Integral Clamps must be considered when calculating box volume. I found the attached on Carlon's Website this morning. It seem to say the Integral Clumps must be included in the calculations. Am I reading that correctly? The code quotes are old, but I don't think anything has changed. Thank You.

 

[Rick 0920]

Hello All, I found this thread this morning researching if Nonmetallic Box Integral Clamps must be considered when calculating box volume. I found the attached on Carlon's Website this morning. It seem to say the Integral Clumps must be included in the calculations. Am I reading that correctly? The code quotes are old, but I don't think anything has changed. Thank You.

According to Carlon, The reduction for the internal cable clamps inside their boxes is not calculated. There are some in here that disagree with this and you will probably never be failed on an inspection as most inspectors would not count them. The information is old and has not been updated, and you are correct that the NEC requirements have not changed on this matter. I passed this information along awhile back because I thought it was interesting. Most people, myself included, do not see these as factory installed internal cable clamps. But it is in black and white right where you read it.

 

[infinity]

According to Carlon, The reduction for the internal cable clamps inside their boxes is not calculated. There are some in here that disagree with this and you will probably never be failed on an inspection as most inspectors would not count them. The information is old and has not been updated, and you are correct that the NEC requirements have not changed on this matter. I passed this information along awhile back because I thought it was interesting. Most people, myself included, do not see these as factory installed internal cable clamps. But it is in black and white right where you read it.

This is another example of a code application that is ridiculously stupid. They put the conductor limit in the box but then you have to deduct from that number for the clamps? Why can't someone just require that the number stamped in the box actually reflects the clamps? And do these clamps actually take up any room?

 

[Dennis Alwon]

According to Carlon, The reduction for the internal cable clamps inside their boxes is not calculated. There are some in here that disagree with this and you will probably never be failed on an inspection as most inspectors would not count them. The information is old and has not been updated, and you are correct that the NEC requirements have not changed on this matter. I passed this information along awhile back because I thought it was interesting. Most people, myself included, do not see these as factory installed internal cable clamps. But it is in black and white right where you read it.

If carlon is giving a true account of the cu. in of the box then, IMO they have taken into account the clamp since it takes up space inside the box. If they didn't then they are giving inaccurate cu.in numbers.

We have argued this many time and IMO, you don't need to deduct for the clamp.

 

[Rick 0920]

I agree Dennis, but they stated in their literature that they did not take the clamp into account and it states that a 20 cu. in. box would have to reduced to 18 cu. in. if #14 was used. This may be because some of their boxes have a twist-out opening while others use the clamping function. Take single gangs for example, if you use the twist out opening box, per the NEC you would be required to staple within 8" of the box and not require a reduction because there is no clamp. If you used the clamp-type single gang, then that dimension could be increased to 12" because there IS a clamp. I'm not saying that I agree with Carlon. But per the NEC we are "supposed" to install and use materials appropriate to their listing.

 

[Rick 0920]

This is another example of a code application that is ridiculously stupid. They put the conductor limit in the box but then you have to deduct from that number for the clamps? Why can't someone just require that the number stamped in the box actually reflects the clamps? And do these clamps actually take up any room?

They do reduce the volume compared to those that have the twist-out openings. I agree that they should figure the clamps into their cu. in. calculation and put an accurate number inside the box.