Volume Allowance for Conductors

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Little Bill

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Location
Tennessee NEC:2017
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I don't get the ordeal. You do not need to do a volume calc if the conductors are #4 or larger. The volume is based on 314.28 using conduit size. We all know this and we all assume that the math was done based on conduit size that the art. address. You know a 1" conduit cannot have 3/0 copper conductors so the dimensions are probably based on the largest size possible for a given size conductor. Overkill in most cases for sure. Tell me where this is an issue for someone to know volume of the wires 4 or larger.

The op's question is simply answered by saying he must use 314.28

Ok, here is what I have. I have a 2" raceway containing six #2 conductors and one # 4 conductor entering a box from the top. Then two 1" raceways containing three #4 and one #6 in each raceway entering the bottom of the box. The box is/will be mounted on the wall. The box is for splicing the #2 conductors to the #4, and for splicing the #4 EGC to the #6 EGC.
I just need to know the box size needed. I'm not used to splicing large conductors and didn't think of 314.28.:happyno:
I'm used to 314.16 and the table (B) so I automatically went there.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I don't get the ordeal. You do not need to do a volume calc if the conductors are #4 or larger. The volume is based on 314.28 using conduit size. We all know this and we all assume that the math was done based on conduit size that the art. address. You know a 1" conduit cannot have 3/0 copper conductors so the dimensions are probably based on the largest size possible for a given size conductor. Overkill in most cases for sure. Tell me where this is an issue for someone to know volume of the wires 4 or larger.

The op's question is simply answered by saying he must use 314.28
If that was the intent of CMP 9, then why did they reject my proposal?
 

Dennis Alwon

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I think they were just saying that conductor fill does apply and didn't quite get the picture. It is not the first time they dropped the ball.
 
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don_resqcapt19

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Illinois
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retired electrician
I think they were just saying that conductor fill does apply and didn't quite get the picture. It is not the first time they dropped the ball.
I think that they clearly said that the rules in 314.16 apply to conductors larger than #6, even though there is no method that would let you apply those rules to the #4 and larger conductors. :?
 

Little Bill

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Location
Tennessee NEC:2017
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Semi-Retired Electrician
Ok, here is what I have. I have a 2" raceway containing six #2 conductors and one # 4 conductor entering a box from the top. Then two 1" raceways containing three #4 and one #6 in each raceway entering the bottom of the box. The box is/will be mounted on the wall. The box is for splicing the #2 conductors to the #4, and for splicing the #4 EGC to the #6 EGC.
I just need to know the box size needed. I'm not used to splicing large conductors and didn't think of 314.28.:happyno:
I'm used to 314.16 and the table (B) so I automatically went there.

The way I understand/calculate this, I would need a box at least 12" in height. Probably a 12x12, although I don't need that much width, it would look better than a tall skinny one.
Have I got that right? Or do any of you see a better option?
 

Dennis Alwon

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Chapel Hill, NC
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Retired Electrical Contractor
Sounds like you have a straight pull

ry%3D480
 

kwired

Electron manager
Location
NE Nebraska
Where does it say that?
Well now you just sent us back to the OP. He wanted to know why table 314.16(B) doesn't list any conductors larger than 6 AWG.

Care to tell us why it only goes to 6 AWG, as well as where do we find the volume required by a conductor larger than 6AWG if we are supposed to calculate box fill for these larger conductors? It is still my opinion that if you size the box according to 314.28 you will have enough space in the box. It is not like you are going to pull 500KCMIL into a box sized according to 1 inch raceways entering it. 3 inch raceway means you will have a minimum dimension of 18 inches at least one direction of this box and if a straight pull it will be at least 24 inches. Boxes with those dimensions have a lot of volume as compared to switch and outlet boxes or 4x4 or 4-11/16 boxes, none of which are large enough to comply with any situation where you have conductors larger than 6 AWG. Smallest raceway you will use 4 AWG with is 1 inch (unless you only pull one conductor in the raceway) so you will not have a box with a dimension less than 6 inches with 1 inch raceway. Start adding multiple raceways and your box will get larger to comply with 314.28.
 

Smart $

Esteemed Member
Location
Ohio
Well now you just sent us back to the OP. He wanted to know why table 314.16(B) doesn't list any conductors larger than 6 AWG.

Care to tell us why it only goes to 6 AWG, as well as where do we find the volume required by a conductor larger than 6AWG if we are supposed to calculate box fill for these larger conductors? It is still my opinion that if you size the box according to 314.28 you will have enough space in the box. It is not like you are going to pull 500KCMIL into a box sized according to 1 inch raceways entering it. 3 inch raceway means you will have a minimum dimension of 18 inches at least one direction of this box and if a straight pull it will be at least 24 inches. Boxes with those dimensions have a lot of volume as compared to switch and outlet boxes or 4x4 or 4-11/16 boxes, none of which are large enough to comply with any situation where you have conductors larger than 6 AWG. Smallest raceway you will use 4 AWG with is 1 inch (unless you only pull one conductor in the raceway) so you will not have a box with a dimension less than 6 inches with 1 inch raceway. Start adding multiple raceways and your box will get larger to comply with 314.28.
I understand the practicability of the requirements. The [minor to the OP] issue is 314.16, (B) and respective Table thereof, has an unresolved grammar-logic dead end.
 

kwired

Electron manager
Location
NE Nebraska
I understand the practicability of the requirements. The [minor to the OP] issue is 314.16, (B) and respective Table thereof, has an unresolved grammar-logic dead end.

I guess you can say that. The requirements for this have had little or no change for as long as I have been in the trade and doesn't seem to be much of a problem though. Most changes have been editorial or relocation and not actual changes to any requirements.
 

Smart $

Esteemed Member
Location
Ohio
I guess you can say that. The requirements for this have had little or no change for as long as I have been in the trade and doesn't seem to be much of a problem though. Most changes have been editorial or relocation and not actual changes to any requirements.
That is correct. I don't recall ever noticing the issue until Little Bill started this thread yesterday.

I'm curious in light of this, and since you seem to be adamant on it being okay as is... say you have the scenario Little Bill posted recently... except you also have four (4) #12's entering, spliced, then exiting the same box in 3/4" conduit top and bottom. How do you apply the box fill requirement of 314.16(B)? Do you simply ignore the #2's and #4's? ...ignore the #12's? Please tell me...
 

kwired

Electron manager
Location
NE Nebraska
That is correct. I don't recall ever noticing the issue until Little Bill started this thread yesterday.

I'm curious in light of this, and since you seem to be adamant on it being okay as is... say you have the scenario Little Bill posted recently... except you also have four (4) #12's entering, spliced, then exiting the same box in 3/4" conduit top and bottom. How do you apply the box fill requirement of 314.16(B)? Do you simply ignore the #2's and #4's? ...ignore the #12's? Please tell me...

I have many times had both large and small conductors in same box. Because the box is relatively large because of the existance of the large conductors I never have had trouble wondering just how I am going to make the small ones fit, I guess I don't understand why you are so concerned about the volume when there is plenty of volume. If I have 4AWG conductors I will have at very least 6x6x4 box. Disregarding the #4 and larger for the moment that box can have 64 #12's in it. Although NEC says they will fit that is a rats nest in that small of a box, I am pretty sure 4 - #12's will not be too much problem.
 

Smart $

Esteemed Member
Location
Ohio
... I guess I don't understand why you are so concerned about the volume when there is plenty of volume. ...
I'm not concerned about the volume. You don't have to beat me over the head for me to grasp the practicality of it. I stated that umpteen posts ago.

It is simply an issue with the letter of the Code leaving one short of compliance certainty.
 

iwire

Moderator
Staff member
Location
Massachusetts
I'm not concerned about the volume. You don't have to beat me over the head for me to grasp the practicality of it. I stated that umpteen posts ago.


And not one person has said they are 'concerned with the volume' all we have been talking about it what the code rules actually say. :)
 
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