Box fill Counting ground conductors, NEC 2020 change

[brother]

I'm trying to get clarity on the change they made for counting the ground conductors in the NEC 2020 change for box fill. 314.16 (B) (5) says A 1/4 volume allowance applies for each additional equipment grounding conductor or equipment bonding jumper that enters the box, based on the largest equipment grounding or bonding jumper.

So my question would be, if you have a # 10 grounding conductor that has a volume of 2.5, do you take a 1/4 of the 2.5 , (2.5 X 0.25 = 0.625) and count
the additional grounding conductors? or is it done differently.

I think they made this change because too many issues come up where boxes had numerous grounds coming in (with huge wire nuts) and only counted as 1 conductor basically in reallity not leaving any space in the boxes. Got one job gong on and they have existing boxes and runs and got 4 pipes entering, and largest ground is #10 and rest are # 12's and they want to add a disconnect switch to the box. I dont really like adding/using extension rings too much because there times where I seen we had to remove them to get to some wiring and the had pipe coming out it! Only add them If i really have to and it more conducive to do so.

 

[LarryFine]

So my question would be, if you have a # 10 grounding conductor that has a volume of 2.5, do you take a 1/4 of the 2.5 , (2.5 X 0.25 = 0.625) and count the additional grounding conductors?

That's how I read it. If you have 12 EGCs, they are added as 3 #10s.

 

[don_resqcapt19]

If you have 4 or less EGCs you take the full volume of the largest EGC...the 1/4 volume only kicks in for the 5th and additional EGCs. For the ones over 4, you use 1/4 of the volume of each additional EGC, based on the actual volume of the conductor being used.

 

[wwhitney]

If you have 4 or less EGCs you take the full volume of the largest EGC...the 1/4 volume only kicks in for the 5th and additional EGCs. For the ones over 4, you use 1/4 of the volume of each additional EGC, based on the actual volume of the conductor being used.

That sounds like for, say, (4) #12s and (1) #14, you'd use an allowance of 1 #12 and 1/4 #14. But the language in 2020 314.16(B)(5) reads to me that it would be 1-1/4 #12 allowances--you always use the largest size present.

Cheers, Wayne

 

[don_resqcapt19]

That sounds like for, say, (4) #12s and (1) #14, you'd use an allowance of 1 #12 and 1/4 #14. But the language in 2020 314.16(B)(5) reads to me that it would be 1-1/4 #12 allowances--you always use the largest size present.

Cheers, Wayne

The second sentence that applies to more than 4 EGCs is not completely clear. I can see it being read either way, but my opinion is that it is based on the largest of the additional conductors.

 

[wwhitney]

The second sentence that applies to more than 4 EGCs is not completely clear. I can see it being read either way, but my opinion is that it is based on the largest of the additional conductors.

I agree it can be read either way. But the previous sentence uses the phrase "largest equipment grounding conductor . . . entering the box," so I think the more typical reading is that the second use of "largest equipment grounding conductor" means the same as in the previous sentence, rather than "largest equipment grounding conductor of the additional conductors."

Another issue with the ""largest equipment grounding conductor of the additional conductors" interpretation is that nothing says which of the 4 EGCs are the "first" 4 and which are the "additional." If you require that the "first" 4 be taken to be the 4 smallest, then the two interpretations will give you the same answer, as the largest "entering the box" will be one of the "additional" ones.

Cheers, Wayne

 

[LarryFine]

The second sentence that applies to more than 4 EGCs is not completely clear. I can see it being read either way, but my opinion is that it is based on the largest of the additional conductors.

Additional to what?

 

[Tulsa Electrician]

An example would be?
One #10 with five other #12
The fill for EGC would be @ 1-#10 and then #12 for the remainder or .5 of a #12

 

[wwhitney]

An example would be?
One #10 with five other #12
The fill for EGC would be @ 1-#10 and then #12 for the remainder or .5 of a #12

That was Don's interpretation.

But what if I say (4) of the #12s are the first four, so they get (1) #10 (largest size entering), and then the "additional" is (1) #10 and (1) #12, which gets 0.5 of a #10 (largest size in the additional)? Then you just get 1.5 of a #10.

The latter interpretation is more conservative and IMO is what is intended by the text. It's equivalent to treating the word "largest" in the second sentence to mean "largest entering," not "largest of the additional."

Cheers, Wayne

 

[Tulsa Electrician]

I see what your saying. Nothing in the verbage says use all of the largest first.
I do not have a 2020 to read. Can some one post up the section so I can read.
Thanks.

 

[don_resqcapt19]

That was Don's interpretation.

But what if I say (4) of the #12s are the first four, so they get (1) #10 (largest size entering), and then the "additional" is (1) #10 and (1) #12, which gets 0.5 of a #10 (largest size in the additional)? Then you just get 1.5 of a #10.

The latter interpretation is more conservative and IMO is what is intended by the text. It's equivalent to treating the word "largest" in the second sentence to mean "largest entering," not "largest of the additional."

Cheers, Wayne

I have never understood not counting the full volume of an EGC....volume is volume and it doesn't matter what color the insulation may be.

 

[wwhitney]

I have never understood not counting the full volume of an EGC....volume is volume and it doesn't matter what color the insulation may be.

Certainly agreed, the only justification I can think of is that the box fill computation is attempting to also impose a heat dissipation requirement, for which EGCs can be ignored as they don't dissipate heat during normal operations.

Cheers, Wayne

 

[CutToTheChase]

...for which EGCs can be ignored as they don't dissipate heat during normal operations.

or if they do, someone's got a problem

 

[LarryFine]

Certainly agreed, the only justification I can think of is that the box fill computation is attempting to also impose a heat dissipation requirement, for which EGCs can be ignored as they don't dissipate heat during normal operations.

Agreed; that and their being smaller without insulation.

 

[qcroanoke]

I have never understood not counting the full volume of an EGC....volume is volume and it doesn't matter what color the insulation may be.

Engineer I know says they defy the laws of physics......