Why did this fail????????

Status
Not open for further replies.

iwire

Moderator
Staff member
Location
Massachusetts
And when the EC needs to use a pull ell instead what happens?

HUBKILE00023_F30_PE_001.jpg


There is no way to make the code bullet proof for every installation unless it requires the largest fitting or box for needed for the possible conductor cable combinations that can fit in the conduit connected to that fitting.

There is no substitute for using our heads.:smile:
 

mivey

Senior Member
I think that the % of available fill area should be consistent, not dependent on the # of conductors
But that neglects the...I can't think of the cable term so I'll call it packing factor. The # of conductors determines how good they will pack.

Remember the packing factor in materials science and the simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP)?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Don,

You asked me what fill rules was I talking about?! None. You are talking from the Code's viewpoint, I am reasoning why the Code is not logical or consistent, or why their rules defie common sense due to the historical development of the document. I am only trying to present a scenario how it could be reworked in a conscise fashion.


Simply,
  • Deal with fill first and anchor it to the conduit,(eg. fill is determined by the sum of crossectional area of the conductors, regardless of their insulation thickness. I think that the % of available fill area should be consistent, not dependent on the # of conductors)
  • deal with fittings second, minimum fill is equivalent to the connecting conduit,
  • Increase fitting size when:
    1. terminations or
    2. directional changes required.
Next step would be ampacity. based on the current desity and thermal dissipation ability of the raceway profile and ambient temperature. We have new energy efficiency rules, yet the motor table did not change. Size the cables and overloads to the nameplate!

All these can be built into a small handheld calculator along with other code related formulas and tables on a replaceable chip, so it can be replaced as the Code changes. It would allow the electricians to perform what is called today 'engineering calculations' to use the optimum size equipment ALL the times.

This can revolutionize the trade since with the reduction of material to the optimum needed will enble the industry to spend more money as they get more for the bang, ergo more $ is left for labor. Inspectors work would be simplified and the electricians would greatly improve their installations' accuracy.
Laszlo,
I don't see how we could require that all of the conduit bodies be sized per the rules in 314.28(A)(1) and (2). Maybe that is not what you are saying, but that is what read.
It is my opinion that the current rules work fine, and if anything the 8x and 6x factors in the two code sections should be increased. It is often difficult to install large conductors, without damage, in a pull or junction box that is sized to the code minimum. Especially if it is below 45? or so.k
 

neutral

Senior Member
Location
Missouri
And when the EC needs to use a pull ell instead what happens?

HUBKILE00023_F30_PE_001.jpg


There is no way to make the code bullet proof for every installation unless it requires the largest fitting or box for needed for the possible conductor cable combinations that can fit in the conduit connected to that fitting.

There is no substitute for using our heads.:smile:


two heads are always better than one:)
 

realolman

Senior Member
II installation 314.156(C)(1)
.....The maximum number of conductors permitted shall be the maximum number permitted by table 1 of Chapter 9 for the conduit or tubing to which it is attatched.

314.28 Pull and Junction Boxes and Conduit Bodies

The six and eight times rules appear in (A) which deals with raceways containing conductors of #4 AWG or larger

#14.28 (A)(3) allows conduit bodies of dimensions less than those required in 314.28(A)(1) and (A)(2) to be used for installations of combinations of conductors that are less than the maximum conduit or tubing fill permitted by table 1 of chapter 9 ... provided the conduit body is marked with the maximum number and maximum size of conductors permitted.

Table 1 is based on percentage of cross fill area.

... seems to me that allows the calculation of combinations of conductors of smaller size than the max fill stamped on the LB
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
II installation 314.156(C)(1)
.....The maximum number of conductors permitted shall be the maximum number permitted by table 1 of Chapter 9 for the conduit or tubing to which it is attatched.

314.28 Pull and Junction Boxes and Conduit Bodies

The six and eight times rules appear in (A) which deals with raceways containing conductors of #4 AWG or larger

#14.28 (A)(3) allows conduit bodies of dimensions less than those required in 314.28(A)(1) and (A)(2) to be used for installations of combinations of conductors that are less than the maximum conduit or tubing fill permitted by table 1 of chapter 9 ... provided the conduit body is marked with the maximum number and maximum size of conductors permitted.

Table 1 is based on percentage of cross fill area.

... seems to me that allows the calculation of combinations of conductors of smaller size than the max fill stamped on the LB
How does that permit the calculation for installing more conductors of a smaller size in the conduit body?
 

elohr46

Senior Member
Location
square one
good discussion guys, learning something new every day, life is good. question: If I ran a 4'' emt that had a 4" LB in the run with 3 500 kcmil thhn copper conductors to a 400a panel I would be ok as long as the LB was rated to accept the 3 500's. It would be a violation to substitute 6 4/0 thhn copper conductors for the 500's.
 
Laszlo,
I don't see how we could require that all of the conduit bodies be sized per the rules in 314.28(A)(1) and (2). Maybe that is not what you are saying, but that is what read.
It is my opinion that the current rules work fine, and if anything the 8x and 6x factors in the two code sections should be increased. It is often difficult to install large conductors, without damage, in a pull or junction box that is sized to the code minimum. Especially if it is below 45? or so.k

Don,

Thanks for the dialogue, I appreciate it.

The 314.28(A)(1) and (2) should be modified and tied to the largest conductor size in the conduit not the conduit OD. It could be applicable to all conductor sizes for custom JB sizes. Fittings can be made with allowance for various bending radiuses although I doubt that the manufacturers interested in making more than two - standard and large - sizes. Again a handheld database filled tool could spit the answer right back and let the electricians know that a standard JB will work or do they need to call for a custom. I agree that in some cases the distances are too short for trouble-free pull, but the above should take care of it since it anchored to the conductor OD and establishes the bending/pulling space based on it. The issue of MV cables perhaps should also be addressed.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Don,

Thanks for the dialogue, I appreciate it.

The 314.28(A)(1) and (2) should be modified and tied to the largest conductor size in the conduit not the conduit OD. It could be applicable to all conductor sizes for custom JB sizes. Fittings can be made with allowance for various bending radiuses although I doubt that the manufacturers interested in making more than two - standard and large - sizes. Again a handheld database filled tool could spit the answer right back and let the electricians know that a standard JB will work or do they need to call for a custom. I agree that in some cases the distances are too short for trouble-free pull, but the above should take care of it since it anchored to the conductor OD and establishes the bending/pulling space based on it. The issue of MV cables perhaps should also be addressed.
Laszlo,
That idea makes sense as it is tied to the real limiting factor...the conductor size. As far as the database, that would be nice too, but there would have to be a table or formula in the code so that there would be a real code rule. Lots of time to work on this...proposals for the 2014 code aren't due until the first Friday in November of 2011.
The rule in 314.71 could be written in the same manner for the MV conductors. That section doesn't even talk about conduit bodies...maybe because it is rare to find one that meets the minimum bending radius for the higher voltage conductors.
 

realolman

Senior Member
How does that permit the calculation for installing more conductors of a smaller size in the conduit body?


314.28(A)(3) seems to me to be a part of, and a specific modifier of 314.28(A) and (B) which contain the 6 and 8 times rules

314.28(A)(3):
Boxes or conduit bodies of dimensions less than those required in 314.28(A)(1) an (A) (2) shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used ) permitted by Table 1 of Chapter 9, provided the box or conduit body has been listed for and is permanently marked with, the maximum number and maximum size of conductors permitted.

I think that says if the LB is marked with 3-4/0 AWG maximum, that would allow you to install more than three conductors smaller than 4/0 and larger than #4 if their combined cross section area is less than specified in Chapter 9, Table 1... 40%

If the LB is not marked, it has to be 6 times the conduit size.

If the LB is suitable for bending and installing 4/0, why would it not be suitable for smaller conductors?

If the LB is marked for 3 - 4/0, we can't install any more than three conductors larger than #4 in it, but we can use conduit fill for conductors smaller than #4? :-?

IMHO 314.28(A)(3) says we can, if the cross section of the combination of conductors is less than the maximuim fill permitted by Chapter 9 Table 1

.
 
Last edited:

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I think that says if the LB is marked with 3-4/0 AWG maximum, that would allow you to install more than three conductors smaller than 4/0 and larger than #4 if their combined cross section area is less than specified in Chapter 9, Table 1... 40%
Just to throw a monkey in the wrench, one could also say that the code statement means that you cannot exceed either niumber, even individually.

You cannot exceed 3 conductors, and you cannot exceed 4/0 in size. After all, would you argue that you could install two conductors larger than 4/0?


(Just to clarify, I want the 'or equivalent area' side to win.)
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
314.28(A)(3) seems to me to be a part of, and a specific modifier of 314.28(A) and (B) which contain the 6 and 8 times rules

314.28(A)(3):
Boxes or conduit bodies of dimensions less than those required in 314.28(A)(1) an (A) (2) shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used ) permitted by Table 1 of Chapter 9, provided the box or conduit body has been listed for and is permanently marked with, the maximum number and maximum size of conductors permitted.

I think that says if the LB is marked with 3-4/0 AWG maximum, that would allow you to install more than three conductors smaller than 4/0 and larger than #4 if their combined cross section area is less than specified in Chapter 9, Table 1... 40%

If the LB is not marked, it has to be 6 times the conduit size.

If the LB is suitable for bending and installing 4/0, why would it not be suitable for smaller conductors?

If the LB is marked for 3 - 4/0, we can't install any more than three conductors larger than #4 in it, but we can use conduit fill for conductors smaller than #4? :-?

IMHO 314.28(A)(3) says we can, if the cross section of the combination of conductors is less than the maximuim fill permitted by Chapter 9 Table 1

.
I just don't agree. I understand the logic of what you are saying, but I just don't see anything to support a field calculation.
 

realolman

Senior Member
Just to throw a monkey in the wrench, one could also say that the code statement means that you cannot exceed either niumber, even individually.

You cannot exceed 3 conductors, and you cannot exceed 4/0 in size. After all, would you argue that you could install two conductors larger than 4/0?


(Just to clarify, I want the 'or equivalent area' side to win.)

Ahh , you're a tricky one , Mr. Fine:smile:

Offhand, I would not make that argument, but I'd have to do the math, and Table 1 would then only allow 31%...I imagine diameters would get you somewhere.

But, if that's the case, you couldn't ever put more than three in a conduit fitting.

314.28(A)(3) seems to me to specifically modify 314.8 (A) (1) and (2) to allow you to put more than three conductors of smaller than maximum in a conduit fitting that is less than 6 times the conduit size...

If it doesn't do that, what is it there for?
 

RUWired

Senior Member
Location
Pa.
Just to throw a monkey in the wrench, one could also say that the code statement means that you cannot exceed either niumber, even individually.

You cannot exceed 3 conductors, and you cannot exceed 4/0 in size. After all, would you argue that you could install two conductors larger than 4/0?


(Just to clarify, I want the 'or equivalent area' side to win.)

And this rule screws everything up when your wanting to pull an equipment ground with the feeder.
 

realolman

Senior Member
I just don't agree. I understand the logic of what you are saying, but I just don't see anything to support a field calculation.


Well, 314.28(A)(3), says combinations of conductors that are less than the maximum conduit or tubing fill are permitted ... it seems to me you'd have to figure out if your desired combination fit.

To require the use of boxes for every three phase circuit over # 6 AWG with a ground and / or neutral and not allow the use of an entire set of fittings made expressly for the purpose, doesn't make sense to me.

You couldn't even oversize the conduit... you'd still be stuck by the three conductor thing. It's hard fo me to imagine any manufacturer stamping their product with every possible conductor combination.

I think the inspector in the OP was wrong.
 
Last edited:

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
The entire question can be avoided by using the "mogul" LB's such as mentioned in earlier posts. They provide the 6X measurement. Use of a box or wireay is just another option.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Well, 314.28(A)(3), says combinations of conductors that are less than the maximum conduit or tubing fill are permitted ... it seems to me you'd have to figure out if your desired combination fit.

To require the use of boxes for every three phase circuit over # 6 AWG with a ground and / or neutral and not allow the use of an entire set of fittings made expressly for the purpose, doesn't make sense to me.

You couldn't even oversize the conduit... you'd still be stuck by the three conductor thing. It's hard fo me to imagine any manufacturer stamping their product with every possible conductor combination.

I think the inspector in the OP was wrong.
There is nothing in the code that even eludes to a permission to calculate the conduit body fill. The code clearly requires that the conduit body be "listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted." How do you get around the requirement that the product be listed for the combination of conductors? There is nothing that tells us the process that is used to determine the maximum size and number of conductors. Without such information there is no way to make any type of calculation.
You don't have to use a box, there are conduit bodies that meet the 6x rule that can be used.
It looks like the CMP really needs to address this issue but that won't happen until the 2014 code cycle as there were no proposals for this section for the 2011 code.

I think we will have to agree to disagree on this issue...I don't think I will change your mind, and I know you won't change mine.
 

realolman

Senior Member
I'll tell you this... I'll never look at an LB the same way again.:smile:


There is nothing in the code that even eludes to a permission to calculate the conduit body fill.

What is it that 314.28(A)(3) is saying?
 
Just to throw a monkey in the wrench, one could also say that the code statement means that you cannot exceed either niumber, even individually.

You cannot exceed 3 conductors, and you cannot exceed 4/0 in size. After all, would you argue that you could install two conductors larger than 4/0?


(Just to clarify, I want the 'or equivalent area' side to win.)

Demonstrating on fundamental shortcoming of the Code. Rules are given but no reasoning or logical explanation is provided within that would allow the user to apply the Code logically. Hence the Handbook was born, but it has no interpretive authority.
 

SEO

Senior Member
Location
Michigan
Demonstrating on fundamental shortcoming of the Code. Rules are given but no reasoning or logical explanation is provided within that would allow the user to apply the Code logically. Hence the Handbook was born, but it has no interpretive authority.
Has anybody looked at the ROP's for the intent of the section?(Would have to go back a long time). Still don't know if the reasoning would make any sense.
 
Status
Not open for further replies.
Top