LB sizing

[augie47]

The way I read 314.28(A)(3) is that you are permitted to have a conductor fill in the LB less than what Chapter 9 Table 1 allows provided that the conduit body is listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted.

This section does not allow the LB to just be sized per Chapter 9 Table 1 it allows the manufacturer to specify the largest size and number of wires permitted in the LB provided that the fill does not exceed Chapter 9 Table 1 fill limits.

Chris

I think we are in agreement. If the conduit body is marked with a maximum conduit fill and if you don't exceed the fill requirements of Table 1 Chapter 9 then it is compliant. Correct ?
I guess I am still a bit confused. If I have a 2" LB in a 2" conduit run and the LB is marked "Max 3-2/0 XHHW", but I am installing 5-1/0 THHN & a #4, since that fill is allowable in the 2" conduit, does this male them allowable in the LB ?

 

[Dennis Alwon]

I think we are in agreement. If the conduit body is marked with a maximum conduit fill and if you don't exceed the fill requirements of Table 1 Chapter 9 then it is compliant. Correct ?
I guess I am still a bit confused. If I have a 2" LB in a 2" conduit run and the LB is marked "Max 3-2/0 XHHW", but I am installing 5-1/0 THHN & a #4, since that fill is allowable in the 2" conduit, does this male them allowable in the LB ?

I am not sure I agree. If the LB states 25% fill then I can't see how you can use the 40% table fill. The LB's marking can be confusing making one think you cannot have more than 3 conductors. IMO you can-- its the box size rule that is exempt here. Seems like everything else should be the same per manufacturer instruction.

 

[don_resqcapt19]

I think we are in agreement. If the conduit body is marked with a maximum conduit fill and if you don't exceed the fill requirements of Table 1 Chapter 9 then it is compliant. Correct ?
I guess I am still a bit confused. If I have a 2" LB in a 2" conduit run and the LB is marked "Max 3-2/0 XHHW", but I am installing 5-1/0 THHN & a #4, since that fill is allowable in the 2" conduit, does this male them allowable in the LB ?

In my opinion the answer is no. When the space between the conduits does not meet the requirements of 314.28(A)(2), then your only relief is the marking on the fitting as permitted in (A)(3).

(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 ortubing 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 don't know of any provision in the code to use a fitting marked for three 2/0s for the installation of more than 3 conductors of any size larger than #6.

There was a long and somewhat heated thread on this issue sometime back and I don't think any conclusion was reached. The two points of view were that you could use some type of volume calculation to adjust for other sizes and number of conductors or that there is no code provision to make such an adjustment.​

 

[augie47]

Thats what I thought for years, but there seems to be an obvious flaw.
Conductors are seldom exactly the ones expressed in the LB listing.
If the 2" LB is marked "max 3 2/0" would (4) #4s be a violation ?, 2-2/0 and 12 #2s ?
There has to be some determining factor.

I see it as:
(a) provided the box or conduit body has been listed for, and is permanently marked with, the maximum number and maximum size of conductors permitted.

then:
(b)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,

Perhaps as noted in Table 9 Note 6, one can calculate the area of the 'maximum allowed" and then compare that to the area of actual fill.

I really don't know, but there has to be a method.
​

 

[Cow]

I ran 4 250XHHW conductors to the panel, along the way through 2 - 3" standard aluminum LB's.

The LB is marked for 3*250MCM conductors.

but the LB is not permanently marked with the 4 conductors being allowed (all conduit bodies are rated for 3 conductors) .

Didn't you answer your own question?

I've used a 3.5/ 4" LB in the past(can't remember the brand) but it listed something like 6-7 250's, 5-350's, etc. It had a whole list of different wire sizes and quantities. So I know they make LB's that list more than 3 wires.

Hopefully you don't have to go HUGE to get what you want.

 

[ATI]

Alright I have an answer from the manufacturer, that may help or start a new debate. Although I still think common sense in a case like this should take precedent before a text book on an install.

*Above data is based on XHHW type conductors; Figures in ()indicate percentage fill of conductors #4 and larger. If other than (3) type XHHW conductors are to be pulled , the numbers can be calculated using maximum allowable % fill from stuffer sheet and the information from Tables 4 & 5, Chapter 9 of NEC.
*When installing all #6 AWG conductors or smaller in a conduit body, the maximum number permitted can be
See NEC Chpter 9, tables 1,4,3A,3B&3C
*Maximum conductor size on these conduit bodies is based on NEC, exception 370.18(a)(2). Refer to NEC Chapter 9 for percent of Cross Section of Conduit & Tubing for conductors.

 

[don_resqcapt19]

With all due respect to the manufacturer, I don't see how fill volume has anything to do with the question. For conductors #6 and smaller, we use volume for box fill.
For conductors #4 and larger, we use conduit spacing. I don't see any provisions in the code that let us use a volume calculation to size boxes, or conduit bodies when the conductors are #4 and larger. We are stuck with having 6 times the trade size of the conduit between the conduit openings or the maximum number and size of conductors marked on the box or fitting that has less than the required 6 x spacing.

 

[K8MHZ]

Correct, I understand the 6 * diameter of the pipe in 314.28. My dilemma is if I qualify under the exemtions in 314.28(3) smaller dimensions. The conduit body is not marked for the 4 conductors but is rated per manufacturer specs they gave me. Problem is conduit, wire and bodies are already installed and disassembling and reassembling would be catastrophe ( maybe a little exageration ).

I would get with the inspector and try to talk him into letting you slide on this installation with the agreement that on the next ones you will use listed fittings.

Nicely, perhaps even sheepishly, point out that you did contact the manufacturer (means you did some homework) and that the installation as you did it has been status quo, but in the future you have no issue with using larger LBs.

If the conductors are already in and show no signs of damage, point that out to the inspector as well.

I have had very strict inspectors allow 'adjustments' to the code if there is no indication of damage, no safety issues on aesthetically acceptable installations that would be of considerable cost to remove and replace.