EGC count in the Jbox

Ponchik

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
For box fill calculation, the first 4 counts as one based on the lasrgest size. After fourth one, each conductor counts as a quarter volume.

so if I have (4) 10-2 cable and (3) 12-2 cable in the box, my EGC count is 1 3/4 of #10?

TIA
 
wwhitney said:
Doesn't make much sense, seems like it should be 1 count of #10 and 3/4 count of #12.
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I agree. Why this was added to the NEC is beyond me. Was there ever a real world problem with the old method? I'm guessing that the substantiation for a code change for a section that had been around for 50 years was bogus.
 
wwhitney said:
That's what 2023 NEC 314.16(B) says.

Doesn't make much sense, seems like it should be 1 count of #10 and 3/4 count of #12.

Cheers, Wayne
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The whole thing has never made sense to me. The volume of the conductor does not change based on the function of the conductor. Why aren't all EGCs counted individually like grounded and ungrounded conductors?
 
infinity said:
I agree. Why this was added to the NEC is beyond me. Was there ever a real world problem with the old method? I'm guessing that the substantiation for a code change for a section that had been around for 50 years was bogus.
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It actually reduced the volume required when you have an isolated ground receptacle in the box. With the old rule, you had one volume for the normal EGC and a second volume for the isolated ground receptacle grounding conductor.
 
IMO the entire box fill thing should just be deleted. For one thing, in 25 years, I don't recall an inspector even once looking at and calculating my box full. Second it just seems like a design issue. Any reasonable electrician isn't going to want to fight with a overstuffed box where you have to fight to get the device in and/or take half an hour being as neat as possible to save space . The rule might have some value to a brother in law, but the NEC should be a how to book for DIY's.
 
electrofelon said:
IMO the entire box fill thing should just be deleted. For one thing, in 25 years, I don't recall an inspector even once looking at and calculating my box full. Second it just seems like a design issue. Any reasonable electrician isn't going to want to fight with a overstuffed box where you have to fight to get the device in and/or take half an hour being as neat as possible to save space . The rule might have some value to a brother in law, but the NEC should be a how to book for DIY's.
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I have only made a few inspections, as I only fill in when our inspector is not available, but cited that more than once. These were so full, I doubt you could have install a receptacle.
 
electrofelon said:
3rd, it's such an inexact rule anyway with no consideration for what type of size of device.
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I've been saying that forever. They added barriers to the fill calculation a few cycles ago. I mean really who dreams up this nonsense. A 1/32" sliver of metal and you have to count it but a USB receptacle is the same deduction as a single pole switch. Wouldn't it be better if the devices had their volume marked on them?
Deduction 002.jpgDeduction 001.jpg
 
electrofelon said:
Just imagine all the other things that are wrong or done horribly, it's a lost cause. it's an issue with training and competence. An inspector could always cite 110.2
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It is never a good practice to cite a general rule. Much better to cite a real rule.
The inspection authority has no control of over training and competence. They can only inspect what has been installed.
Yes I know that there are "qualified person" rules in the code, but in the real world those are not enforceable.
 
infinity said:
I've been saying that forever. They added barriers to the fill calculation a few cycles ago. I mean really who dreams up this nonsense. A 1/32" sliver of metal and you have to count it but a USB receptacle is the same deduction as a single pole switch. Wouldn't it be better if the devices had their volume marked on them?
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That is a great idea. There were proposals to require a double volume for the larger devices, but they did not pass.
 
If you do the math, the NEC has given a ton of clearance for conductors. For example, a #12 THHN is 0.12" in diameter. If you use the code minimum length of 6", a single conductor displaces a volume of 0.0216 in³. In the code required 2.25 in³ you could fit about 100 of them, not accounting for voids between them, etc.
 
I just think it is a pointless rule in practice. There are just too many variables: device size, neatness of makeup, length of conductors. I remember I installed one of those four gang size radio RA things a while back. Took me about an hour to to make up the box absolutely as neatly and as tight as possible to get that thing to fit in there.
 
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