Conduit body sizing

[smallfish]

How is it determined what size conduit body (LR) is allowed for 4#500kcmil type THHN conductors? Thanks.

 

[bikeindy]

How is it determined what size conduit body (LR) is allowed for 4#500kcmil type THHN conductors? Thanks.

By the size of the conduit required for fill.

 

[nakulak]

1) start with the trade size using the percent fill required for your application
to determine the conduit size

2) using that trade size, see if the specific conduit body that you want to use is made for that percentage fill (might be less)

3) check to make sure that the specific conduit body that you want to use is listed for that size/number of conductors (might be less)

ie - for 2 & 3 you need to check the actual fitting from that manufacturer.

example: a lot of guys run around using 40% fill for conduit in class 1 div 1, then buy seal offs and fittings with out checking them, and are completely unaware that those fittings come in 25% fill and 40% fill variety.

 

[smallfish]

Conduit body sizing

The O-Z/Gedney Catalog lists a 4" Trade size, Malleable Iron Conduit Body LR capable of holding a maximum of 3 #350MCM. An EC tells me he's going to use a LR conduit body to fit 4#500MCM and elbow out of a CT cabinet into a 20" wide space and run up and over to a service disconnect. I don't see how. I'll ask him later, but for now I just wanted to know if it was possible.

 

[don_resqcapt19]

Conduit bodies have to meet the same dimensions as pull boxes unless they are marked on the conduit body for the maximum size and number of conductors. Standard size conduit bodies can never be used with the same fill as the raceway when using larger sized conductors. Note that the listing in the catalog does not meet the code rule. The conduit body itself must be permanently marked with, the maximum number and maximum size of conductors permitted.
314.28 and 314.28(A)(3)

 

[smallfish]

Conduit body sizing

Thanks!
Did the math,as best as I could understand, and according to 314.28(A)(3) found that the maximum conduit fill in square inches of 40% for the 4" conduit being used was more than the area of 4#500MCM in square inches. So all I need do is find a conduit body listed for and permanently marked with, the maximum number and maximum size of conductors permitted. I'll call the supply houses tomorrow.

 

[don_resqcapt19]

smallfish,
Its not the percent fill that is the problem. It is the the distance between the conduit entries.

(2) Angle or U Pulls Where splices or where angle or U pulls are made, the distance between each raceway entry inside the box and the opposite wall of the box shall not be less than six times the metric designator (trade size) of the largest raceway in a row. This distance shall be increased for additional entries by the amount of the sum of the diameters of all other raceway entries in the same row on the same wall of the box. Each row shall be calculated individually, and the single row that provides the maximum distance shall be used.
Exception: Where a raceway or cable entry is in the wall of a box or conduit body opposite a removable cover, the distance from that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in Table 312.6(A).
The distance between raceway entries enclosing the same conductor shall not be less than six times the metric designator (trade size) of the larger raceway.
(3) Smaller Dimensions Boxes or conduit bodies of dimensions less than those required in 314.28(A)(1) and (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.

 

[smallfish]

Conduit body sizing

Bear with me please.
If a larger conduit is chosen for the conductors so that its fill becomes less, then a smaller distance is necessary between raceways entering the conduit body. Because there is more free space within the larger conduit, it is easier to train the conductors through the smaller dimensioned conduit body and into the conduit. If the conduit body is listed and marked with the maximum number and size of conductors, then this conduit body of smaller dimensions can take the place of the larger boxes that require the greater distance between raceway entries for angle and U pulls. Correct?

 

[iwire]

By the size of the conduit required for fill.

No, that will get you into trouble with large conductors.

For instance 2" EMT can take 4 - 4/0s but a standard 2" LB can not.

 

[don_resqcapt19]

smallfish.

If a larger conduit is chosen for the conductors so that its fill becomes less, then a smaller distance is necessary between raceways entering the conduit body.

Please cite a code section to support that statement.

If the conduit body is listed and marked with the maximum number and size of conductors, then this conduit body of smaller dimensions can take the place of the larger boxes that require the greater distance between raceway entries for angle and U pulls. Correct?

That is correct, but you can't just oversize the raceway and conduit body and do your own calculations. You have to use a conduit body that meets the rule for the distance between raceways or you have to us one that is marked on it for the size and number of conductors that you are using.
Don

 

[smallfish]

Conduit body sizing

don
I wrote "If a larger conduit is chosen for the conductors so that it's fill becomes less, then a smaller distance is necessary between raceways entering the conduit body" because I misinterpreted NEC314.28(A)(3). I read "combinations of conductors" to mean "combining conductors" (in my instance 4#500MCM). I now believe the code reads "...installations of combinations (of different sizes) of conductors...".
So, if I were to be pulling different sizes of conductors in the same raceway through a conduit body, I would be permitted to use a conduit body of dimensions less (i.e. distances between raceway entries) than those required in 314.28(A)(1) and (A)(2) if this combination of conductors' area were less than the maximum conduit fill area of the conduit being used permitted by Table 1 of Chaper 9, provided the conduit body has been listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted. Clear as mud? Is this correct?
If I were to be pulling conductors of the same size through a conduit body, then the conduit body size would require distances between raceway entries to be 6 times the raceway size as that for a box. Is this correct?
Does the Exception of 314.28(A)(2), referring to Table 312.6(A), permit a conduit body of only 6 inches wide, the measurement being from the wall of entry to opposite removable cover, when 4#500MCM conductors are pulled through the conduit body? Thank you for your consideration.

 

[don_resqcapt19]

small,

So, if I were to be pulling different sizes of conductors in the same raceway through a conduit body, I would be permitted to use a conduit body of dimensions less (i.e. distances between raceway entries) than those required in 314.28(A)(1) and (A)(2) if this combination of conductors' area were less than the maximum conduit fill area of the conduit being used permitted by Table 1 of Chaper 9, provided the conduit body has been listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted. Clear as mud? Is this correct?

I don't see anything in the code that would permit you to do that. It seems like there should be a way to make a calculation for that type of application, but there isn't one.

If I were to be pulling conductors of the same size through a conduit body, then the conduit body size would require distances between raceway entries to be 6 times the raceway size as that for a box. Is this correct?

Yes. The conduit body has to follow the same rules as a pull box, unless you are using the exception and have a conduit body that is marked for the size and number of conductors.

Does the Exception of 314.28(A)(2), referring to Table 312.6(A), permit a conduit body of only 6 inches wide, the measurement being from the wall of entry to opposite removable cover, when 4#500MCM conductors are pulled through the conduit body? Thank you for your consideration.

If the distance from the inside hub of the conduit body to the removable cover directly opposite the hub is 6" or more then you have met that part of the rule. That does have any effect on the second part of that same rule that requires the conduit opening to be 6 times the trade size of the conduit apart. This second part of the rule is where 314.28(A)(3) comes into play.

If I were to be pulling conductors of the same size through a conduit body, then the conduit body size would require distances between raceway entries to be 6 times the raceway size as that for a box. Is this correct?

The size of the conductors has no effect on this rule. As long as any of the conductors are #4 or larger this rule must be complied with.
Don

 

[1793]

No, that will get you into trouble with large conductors.

For instance 2" EMT can take 4 - 4/0s but a standard 2" LB can not.

iwire: can you tell me where I can find the information needed to perform the calculations. What Table needed for conductor information.