Conduit Bodies vs. Pullboxes

[aramg83]

Why are L-B Conduit bodies sized smaller than pullboxes where conduits of the same size terminate. Let me give an example:

If I were entering a pullbox from its bottom with a 4" conduit and exiting from one of the sides of the pullbox (in order to make an angle pull), the box would have to be sized 4"x6=24"D x 4"x6=24H with an arbitrary width.

A 4" conduit body is commonly sized at about 16" H x about 6" D.

Why are they different?

I guess I could see how 300.34 would allow the depth to be sized for typical conductor bending radius opposite a removable cover, but I don't see any such alleviations for the 24" height.

Is it simply because conduit bodies get a UL listing?

 

[iwire]

Keep in mind that you cannot fill a typical conduit body to the limits of the raceway it is connected to.

For instance it is typical for us to run four 4/0s and an EGC in a 2" EMT but a typical 2" LB is limited to just three 4/0s.

 

[hardworkingstiff]

Conduit bodies are often not rated for the size and number of conductors you can get into the conduit. Sizing a pull box the way you did gives full use of the conduit.

 

[aramg83]

10-27-2009, 04:07 PM

infinity
Moderator

Join Date: Jul 2003
Location: New Jersey
Posts: 11,608

Improperly sized conduit bodies are one of the most violated things I see every day. The conduit body is required to be sized according to the 6X and 8X rules used for pull boxes. The manufacturer can give some added leeway by printing within the conduit body the maximum condcutor size and number. Your scenario would be a violation.
__________________
Rob

Moderator

I found this. Why manufacture an LB condulet that doesn't adhere to the 6x rule?

 

[qcroanoke]

Why are L-B Conduit bodies sized smaller than pullboxes where conduits of the same size terminate. Let me give an example:

If I were entering a pullbox from its bottom with a 4" conduit and exiting from one of the sides of the pullbox (in order to make an angle pull), the box would have to be sized 4"x6=24"D x 4"x6=24H with an arbitrary width.

24" deep X 24" high X whatever width?
Correct me if I'm wrong, (I know someone will. lol) but shouldn't it be 24" wide X 24" high X whatever depth?

 

[aramg83]

I'm sorry, I'm using depth and width interchangeably. I meant the dimensions opposite the sides the conduits enter.

 

[augie47]

Many people, including inspectors, fail to note the provisions of 314.28 in regard to conduit bodies.

 

[steve66]

Keep in mind that you cannot fill a typical conduit body to the limits of the raceway it is connected to.

For instance it is typical for us to run four 4/0s and an EGC in a 2" EMT but a typical 2" LB is limited to just three 4/0s.

I wonder if any engineers ever take this into account. I frequently size conduits, but never consider that the run will almost always have fittings in it.

Is there a table somewhere that lists the wire size limits for typical fittings?

Steve

 

[iwire]

I found this. Why manufacture an LB condulet that doesn't adhere to the 6x rule?

Because we can use them per the listing and most of us desire inexpensive LBs.

We can purchase larger LBs if we ask but few of us do.

 

[iwire]

I wonder if any engineers ever take this into account. I frequently size conduits, but never consider that the run will almost always have fittings in it.

I know I went many years without taking it into account.

Is there a table somewhere that lists the wire size limits for typical fittings?

I have not seen one but sure could use one.

 

[augie47]

It takes a lot of searching but you will find this on Crouse-Hinds website and I found it to be a great help. I have not crosschecked it for other manufacturers.

http://www.crouse-hinds.com/crousehinds/InstallationDocs/IF964.pdf

 

[steve66]

Thanks. I'll put that in my notes.

Wow - you can fit (10) 750's in a 6 inch conduit! Not that I would ever spec. that.

Steve

 

[augie47]

Thanks. I'll put that in my notes.

Wow - you can fit (10) 750's in a 6 inch conduit! Not that I would ever spec. that.

Steve

Still one less than you can get in a 6" GRS Conduit.
Never ran 6", don't recall I ever saw 6", never met a man who ran 6".
Have you ever spec'd 6" ?

 

[sameguy]

power plants use alot of 6"

 

[iwire]

Still one less than you can get in a 6" GRS Conduit.
Never ran 6", don't recall I ever saw 6", never met a man who ran 6".
Have you ever spec'd 6" ?

I have not run 6" RMC but I have worked with it. We used it per specs to sleeve 4" EMT through floors.

Not fun to handle.

 

[infinity]

infinity
Moderator

Join Date: Jul 2003
Location: New Jersey
Posts: 11,608

Improperly sized conduit bodies are one of the most violated things I see every day. The conduit body is required to be sized according to the 6X and 8X rules used for pull boxes. The manufacturer can give some added leeway by printing within the conduit body the maximum condcutor size and number. Your scenario would be a violation.
__________________
Rob

Moderator

I found this. Why manufacture an LB condulet that doesn't adhere to the 6x rule?

Don't forget that the 6X and 8X rules only apply to conductors #4 and larger. So you could certainly use a conduit body with smaller conductors and the 6X and 8X rules would not apply. Pull 4-#1's in a standard 1.25" LB and you'll have a violation, use the same conduit and LB for 28-#10's and you're OK.

 

[steve66]

Still one less than you can get in a 6" GRS Conduit.
Never ran 6", don't recall I ever saw 6", never met a man who ran 6".
Have you ever spec'd 6" ?

No, but when the electricians once gave me a hard time about having to run 4", I suggested we might need 6" on the next project.

I wonder if the fitting issue is why 3" is almost never specified for 500's even though 5 THHN's will fit in 3" EMT.

Steve

 

[cadpoint]

Many people, including inspectors, fail to note the provisions of 314.28 in regard to conduit bodies.

Thanks for the refreshing thought, I've seen it said here to upsize this conduit body, I find it easy to meet this requirement.

I wonder if any engineers ever take this into account. I frequently size conduits, but never consider that the run will almost always have fittings in it.

Unless someone is paid to do a design/ layout, generally, no they don't care, how you get the job done! Don't we run it to our Code inside the premise of the building codes, and specifications?

Yes, sometimes this is exactly where someone might forget an accounting of, or the expense of a conduit fitting size and the reducing bushings, or for that matter a pull box, hopefully someone got to walk the job, for an eyeful.

314.28(C) is the real out. While the circuit designation is presented the square inches is also, it's a just matter of figuring the math against Table 9.

They like to ask around here...

 

[LarryFine]

Never ran 6", don't recall I ever saw 6", never met a man who ran 6".

. . . Wouldn't want to tick him off, either.

 

[sameguy]

Look up form 8LBs almost mogul size.