Calculating LB fill.........

[chevyx92]

Question #1 - I have a 3" pvc LB that say max fill is 178 cu in. (3) 350 MCM or smaller conductors . Is there a chart that shows LB fill anywhere? If not how do you calculate cubic in. fill on an individual wire? I see in the NEC they give in2 but no cubic inch, why not???

Question #2 - That same 3" pvc LB, on the cover says its a 3" (2 1/2) <-----------Exactly like that. Does that mean you can fill that LB based on 2 1/2" pipe??

 

[480sparky]

Start with 314.16.

 

[mweaver]

Skip ahead to Section 314.28...

Skip ahead to Section 314.28...

As I understand this...

You can just skip ahead to Section 314.28, which is titled : Pull and Junction Boxes and Conduit Bodies.

Note in the Section header: Conduit Bodies...

What you are looking for in particular is probably Section 314.28(A)(2) for angle pulls.


My understanding is...
What you will most likely encounter is that a typical (off the shelf) LB condulet may not provide the necessary diagonal dimension (six times the largest raceway) required for conductors of #4 and larger for the angle pull in the LB condulet. ...While the entry opposite a removable cover for your LB falls under the Exception to this Section, you are still subject to the requirements in the paragraph directly below the exception... Meaning your 3" LB will require a diagonal measurement, between conduit entries enclosing the same conductor, of 18" ...)

...my understanding is this is why "mogul type" condulets are manufactured. Some manufacturers call these "NEC Condulets" ...

I hope this is helpful...

mweaver

 

[chevyx92]

Start with 314.16.

Ok what am I missing. I see a chart that goes up to #6 with cubic in.? If I want to calculate how many 250 xhhw I can put in a 3" LB, how do you go about figuring the cubic in for them? Since the LB gives you a max cubic in. fill?

 

[chris kennedy]

I have a 3" pvc LB that say max fill is 178 cu in. (3) 350 MCM or smaller conductors .

Big problem when one is used to 4 wire systems. This is the Kennedy preferred install.

 

[CIECO]

The only to go.

 

[chevyx92]

Big problem when one is used to 4 wire systems. This is the Kennedy preferred install.

I hear you on that. But let's say you want to put (4) 250 mcm in there. I say its legal but how do you calculate the cubic in for 250 mcm so you know you're under the 178 cu in max fill of the LB? :Confused:

 

[infinity]

Ok what am I missing. I see a chart that goes up to #6 with cubic in.? If I want to calculate how many 250 xhhw I can put in a 3" LB, how do you go about figuring the cubic in for them? Since the LB gives you a max cubic in. fill?

For #4 and larger conductors forget the cu in dimensions calculation. You'll need to size the LB just as you would a pull box with the 6X dimension. The exception is if the conduit body is marked with a conductor size greater than the 6X calculation you are permitted to use that information. 314.28(A)(3).

 

[chevyx92]

For #4 and larger conductors forget the cu in dimensions calculation. You'll need to size the LB just as you would a pull box with the 6X dimension. The exception is if the conduit body is marked with a conductor size greater than the 6X calculation you are permitted to use that information. 314.28(A)(3).

So can you legally install (4) 250 xhhw in a 3" Pvc LB? I say yes because it's less than the (3) 350 mcm allowed on the LB?

 

[infinity]

So can you legally install (4) 250 xhhw in a 3" Pvc LB? I say yes because it's less than the (3) 350 mcm allowed on the LB?

That's a question I've asked too and I've never really found an answer. Logically you would think that 4-250's and 3-350's would require about the same amount of space within the condulet but I'm unsure if the NEC directly addresses that when the conduit body is marked "max. 3-350 kcmil conductors".

 

[augie47]

If you go to the mfg website you can normally find a conduit fill table (for Crouse Hinds it's document IF964) that gives the wire size and max number by condulet style.

 

[mweaver]

I completely misunderstood the OP?s original question regarding the conduit fill for larger than number 6 AWG when conductor sizing IS MARKED for the condulet, and how to transfer to other equivalent fills, which (as Infinity noted) is addressed under Section 314.28(A)(3).

As Augie47 noted, the manufacturer will most likely have this information.

From the Carlon website I found this document which addresses this issue from both an NEC and UL compliance standpoint.

The document can be found here : http://www.carlonsales.com/techinfo/codesstandards/CS-LB_Conduit_Body_Wirefill.pdf

mweaver

 

[cowboyjwc]

The reason for the cubic inch info is so you can splice in the LB. 314.16(C)(2).

What ever size wire that is allowed in the pipe size you are running is allowed in that size LB.

 

[mweaver]

Help me out here cowboyjwc, … I may be misunderstanding something …

Are you saying that Section 314.28, which is titled : Pull and Junction Boxes and Conduit Bodies, has no bearing on condulet dimensions in relation to installed conductors larger than #6 ??

mweaver

 

[augie47]

The reason for the cubic inch info is so you can splice in the LB. 314.16(C)(2).

What ever size wire that is allowed in the pipe size you are running is allowed in that size LB.

I don't see it that way at all. Although I wish it were true, IMHO, 314.28 limits you to the 6X ruling or what the fitting is listed and marked to contain.

 

[mweaver]

I agree with you Gus.

That is clearly what it says (to me...) within Section 314.28 …

mweaver

 

[cowboyjwc]

Help me out here cowboyjwc, … I may be misunderstanding something …

Are you saying that Section 314.28, which is titled : Pull and Junction Boxes and Conduit Bodies, has no bearing on condulet dimensions in relation to installed conductors larger than #6 ??

mweaver

Sort of. Read the exception for 314.28(A)(2). When you go to the table it sends you to you only need 4 1/2 inches. The conduit body should already be designed for that.

So let's say you need a 3" conduit for 4 250MCM, if you install a 3" LB it should already be sized properly.

Note that the 8 times and 6 times is for pull boxes. Conduit bodies fall under the exception that I mentioned.

Am I being clear?

Sorry also look at 314.28(A)(3)

 

[mweaver]

Cowboyjwc,

You are correct in that conduit bodies such as LBs will fall under the exception (entry opposite a removable cover), but the paragraph directly below the exception is still applicable to the exception, as follows:

"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"

... ALL conduit bodies do not fall completely under the exception, A 'C' ftg, would not fall under the exception in my opinion (this is not entry opposite a removable cover...)...


Yes, Section 314.28(A)(3) notes that if the conduit body is listed and permanently marked... a smaller dimension would be permitted (They are not all marked and or listed for this. Some manufacturers provide "mogul or NEC type" LBs to cover this...) ... This is my understanding...



If this were not the case, the exception could have been at the complete bottom of this Section… (at least this is how I see it and have been instructed by others…)

mweaver

 

[augie47]

Sort of. Read the exception for 314.28(A)(2). When you go to the table it sends you to you only need 4 1/2 inches. The conduit body should already be designed for that.

So let's say you need a 3" conduit for 4 250MCM, if you install a 3" LB it should already be sized properly.

I believe it depends on the "form" or "sty;e LB.. every LB (conduit body) will not accept the same condcutors as the conduit hence the market for "nec condulets"

Note that the 8 times and 6 times is for pull boxes. Conduit bodies fall under the exception that I mentioned..

Pull boxes, Junction Boxes and Conduit Bodies is the heading. The
exception" applies to "opposite a removabel cover, which doesn't apply in one dimension of the LB or any domension of a LR or LL.

Am I being clear?)

Sorry also look at 314.28(A)(3)

To me, 314.28(A)(3) proves my point, so I guiess it depends on how one reads it.

 

[cowboyjwc]

OK, it says where "a" raceway....is in the wall of a.....conduit body opposite a removable cover. It doesn't say both. then the conduit body only has to be 4 1/2 inches deep.

I wasn't talking about an LR or LL or T or C I was talking about and LB which is what the question was.

What I really keep trying to get at, is if an LB is for 3" pipe then the LB should already be 18" long or it shall be marked as per 314.28(A)(3) and if it isn't, it isn't and you must comply with the other provisions.

I could bet that no one here has ever put in a 3" pipe with a 6" LB.

I have used a larger one for splicing purposes, but never for pulling purposes.

Am I getting clearer yet? If you look at the handbook it only talks about boxes.