Volume Allowance for Conductors

[Little Bill]

How are the in.3 derived for the volume allowances in Table 314.16(B)?

The table only goes to #6 and I need to find out what the allowances would be for #2 & #4.

 

[Smart $]

Good question... :?

 

[Little Bill]

Good question... :?

I've been trying to look at Chpt. 9/Tbl 8 to see if I can figure out how they are derived, but I'm not having any luck.
I'm no math wiz, but thought I might see a pattern or formula there somewhere, but to no avail.

 

[iwire]

How are the in.3 derived for the volume allowances in Table 314.16(B)?

The table only goes to #6 and I need to find out what the allowances would be for #2 & #4.

Why would you need to know that?

At that point the conduit size is what determines box size.

 

[Smart $]

Why would you need to know that?

At that point the conduit size is what determines box size.

I mentally considered that as the reason larger conductor sizes aren't listed...

...but 314.16(B) doesn't provide an "out" clause or pertinent exception. 314.16(B)(1) starts with "Each conductor". 4 AWG and larger are still conductors and there's no allowance or exception provided. Note how 314.16(C) restricts its requirements to 6 AWG and smaller conductors.

Also note last sentence of 314.16's general statement: "Boxes and conduit bodies enclosing conductors 4 AWG or larger shall also comply with the provisions of 314.28."

 

[iwire]

Lucky for me most of the inspectors I deal with are not interested in trying to make an issue out of nothing.


When all else fails apply common sense liberally. :thumbsup:

 

[Smart $]

When all else fails apply common sense liberally. :thumbsup:

(Note I'm considering what others may deem as common sense)

 

[don_resqcapt19]

This is another flawed code section. 314.16 says it applies to conductors larger than #6, but does not give you the information required to do a box fill calculation.

314.16 ...Boxes and conduit bodies enclosing conductors 4 AWG or larger shall also comply with the provisions of 314.28.

The section should be changed so it only applies to conductors #6 and smaller. The size of the box for larger conductors should be based on 314.28.

 

[infinity]

I agree that this is poorly written but doesn't the fact that the table stops at #6 AWG automatically direct you further to 314.28?

 

[Hv&Lv]

I agree that this is poorly written but doesn't the fact that the table stops at #6 AWG automatically direct you further to 314.28?

I agree here. "straight is 8, angle is 6". (cleaned up)

Many are taught this crude reference, but it isn't easily forgotten...

 

[kwired]

I think if you were to give a volume to 4 AWG or larger and calculate the volume required in the box you would have a smaller box required in almost all cases than you end up using with a box sized to 314.28.

One example: say we have 1 inch EMT with max fill of 26- 12 AWG THWN conductors and we are splicing all 26 and leaving via another 1 inch EMT. We need 117 cubic inches for those conductors in the box. 6x6x4 is likely smallest enclosure most would use for this (144 cubic inches).

If we to run 4 AWG conductors in the 1 inch EMT instead of all the 12AWG's we have to size the box according to 314.28, and box will need to be no smaller than 6 by 6 inches. I suppose if there was such a thing it could be only 2 inches deep and be legal, but likely all you will find is 6x6x4 and it works out for either installation - as long as not a straight pull for the 4 AWG instance - then you must have 8 inch minimum dimension which likely increases volume - but you could go with narrower dimension the other way.

My point is once you have bending space for the larger conductors, you usually have a fair amount of volume in the enclosure.

 

[Smart $]

I think if you were to give a volume to 4 AWG or larger and calculate the volume required in the box you would have a smaller box required in almost all cases than you end up using with a box sized to 314.28.

One example: say we have 1 inch EMT with max fill of 26- 12 AWG THWN conductors and we are splicing all 26 and leaving via another 1 inch EMT. We need 117 cubic inches for those conductors in the box. 6x6x4 is likely smallest enclosure most would use for this (144 cubic inches).

If we to run 4 AWG conductors in the 1 inch EMT instead of all the 12AWG's we have to size the box according to 314.28, and box will need to be no smaller than 6 by 6 inches. I suppose if there was such a thing it could be only 2 inches deep and be legal, but likely all you will find is 6x6x4 and it works out for either installation - as long as not a straight pull for the 4 AWG instance - then you must have 8 inch minimum dimension which likely increases volume - but you could go with narrower dimension the other way.

My point is once you have bending space for the larger conductors, you usually have a fair amount of volume in the enclosure.

I believe everyone having posted here realizes what you are saying... but without an actual fill allowance value (or exception), this conclusion cannot be anything more than assumption and speculation.

 

[kwired]

I believe everyone having posted here realizes what you are saying... but without an actual fill allowance value (or exception), this conclusion cannot be anything more than assumption and speculation.

All I am saying is the larger the conductors the larger the raceway needed to contain them becomes. The larger the raceway the larger the box becomes, volume usually takes care of itself.

If you size an enclosure with larger than 1 inch raceways according to 314.28 but only install smaller than 4 AWG conductors in it, you will not have volume issues in most cases.

 

[iwire]

All I am saying is the larger the conductors the larger the raceway needed to contain them becomes. The larger the raceway the larger the box becomes, volume usually takes care of itself.

If you size an enclosure with larger than 1 inch raceways according to 314.28 but only install smaller than 4 AWG conductors in it, you will not have volume issues in most cases.

We understand that, we are also electricians.:thumbsup:

 

[kwired]

We understand that, we are also electricians.:thumbsup:

Then why did the question come up in the first place

 

[Smart $]

Then why did the question come up in the first place

The OP'er is wanting to do a box fill calculation for #4 & #2 wires. Without a Table volume allowance for larger than #6, how do you know the box volume takes care of itself???

 

[kwired]

The OP'er is wanting to do a box fill calculation for #4 & #2 wires. Without a Table volume allowance for larger than #6, how do you know the box volume takes care of itself???

There is no volume requirement for those conductors. But I'm willing to bet if you used same raceways as OP has and sized the box to 314.28 but used only 6AWG and smaller you would likely still comply with 314.16.

 

[Smart $]

There is no volume requirement for those conductors. ...

Where does it say that?

 

[don_resqcapt19]

I agree that this is poorly written but doesn't the fact that the table stops at #6 AWG automatically direct you further to 314.28?

The rule in 314.16 says the rules in 314.28 shall also apply. That says to me that the volume rules in 314.16 apply to conductors larger than #6 even though the code gives you no way to do those "required" volume calculations.

9-39 Log #3648 NEC-P09 Final Action: Reject
(314.16)
_______________________________________________________________
Submitter: Donald A. Ganiere, Ottawa, IL
Recommendation: Revise text to read as follows:
314.16 Number of Conductors in Outlet, Device, and Junction Boxes, and Conduit Bodies.
Boxes and conduit bodies enclosing conductors 4 AWG or larger shall also comply with the provisions of 314.28.
Substantiation: There are no volumes 314.16 that let you apply the in this section to conductors #4 and larger. The only rules that apply to these larger
conductors are the ones found in 314.28.
Panel Meeting Action: Reject
Panel Statement: Although there are no prescriptive requirements in this section that apply to large conductors, the parent language about sufficient size
does apply.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12

red = text to be deleted

 

[Dennis Alwon]

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