Are LB’s legal

[MrMeAuggie]

Hey guys, I ran into an issue with an inspector where I was replacing the meter and relocating the distribution circuits to a new panel board. He “let it slide”, but said that LBs are subject to needing the pulling radius based on the conduit size, same as a junction/pull box would be. How does an LB have an UL listing if this is true. He took me to article 415 for pull boxes and said that in there it specifies LBs, but I can’t find anything on it, and 6 times the radius of the conduit would mean the LB would have to be massive, so I believe he’s wrong, but I’d like a Mike holt interpretation on the matter if we can because I do a lot of work in that inspectors area and used 2in conduit to get new SER’s into the house often.

 

[infinity]

Yes the 6X (LB) or 8X (C) rules apply when the conductors are #4 or larger. You can use the info stamped into the conduit body and ignore the 6X and 8x rules.

 

[don_resqcapt19]

In general, standard LBs used with conductors 4 AWG and larger are not legal, assuming you are not using conduit that is oversized for the conductor fill.

It is not 6 times the radius of the conduit. The 6 time the trade size of the conduit is the minimum distance between the conduit entries within in the LB. If you are running 2" conduit, you need 12" between the conduit entries. There is some help in 314.28(A)(3) in the last paragraph. Note that the middle paragraph is for a special type of LB that is not commonly used. Most LBs are marked as required in the last paragraph setting the maximum size and number of conductors that the LB has been listed for. You calculations can be made based on the conductors you want to use and the total volume of the conductors that are listed.

There are also mogul LBs that do meet the 6x between conduit entries that is required for an angle pull.

 

[tortuga]

It is not 6 times the radius of the conduit. The 6 time the trade size of the conduit is the minimum distance between the conduit entries within in the LB. If you are running 2" conduit, you need 12" between the conduit entries.

Its interesting in the case of PVC I don't know of any conduit bodies like that the mogul kind or whatever you can get with rigid.

There is some help in 314.28(A)(3) in the last paragraph.

Yeah a common 2" example is a single phase feeder with 4/0, 4/0, 2/0, and a #4 aluminum XHHW-2 conductors pulled in, thats less than the max permitted XHHW-2 in CH9 C11, so the LB does not need to have 12" between entries.

But then 314.28(A)(3) goes on to say:

For other conductor sizes and combinations, the total permitted crosssectional area of the  fill shall not exceed the cross-sectional area of the conductors specified in the marking,
based on the type of conductor identified as part of the product listing.

 Informational Note: Unless otherwise specified, the applicable product standards evaluate the fill markings covered here based on conductors with Type XHHW insulation.

Here is a old table I have but I dont think its changed:

LB, LR, LL​	Source: 2012 UL 514B Table 40 P121​	​	​	​
XHHW Wire​	XHHW in2​	Max Fill in2​	LB Trade Size​	Max Qty​
4​	0.0814​	0.2442​	1”​	3​
2​	0.1146​	0.3438​	1-1/4”​	3​
1/0​	0.1825​	0.5475​	1-1/2”​	3​
3/0​	0.2642​	0.7926​	2”​	3​
300​	0.4536​	1.3608​	2-1/2”​	3​
400​	0.5782​	1.7346​	3”​	3​
500​	0.6984​	2.0952​	3-1/2”​	3​

 

[tortuga]

So looking at a 2" PVC lb to confirm one can see its marked for three 3/0 XHHW and the max conduit fill of the LB becomes 0.7926
However if I did the math right our 4/0 4/0 2/0 #4 adds up to a fill of 0.9398.

 

[tortuga]

Another common residential example would be a 4/0 SER cable that needs to travel in a short section of 2" conduit entering thru an LB, then its even more complicated, as chapter 9 table1 note 5 tells us to use the actual dimensions of the SER cable.
So we need to go the the product specs and look that up.
A 4/0/-4/0-4/0-2/0 SER cable specs say its 1.496 Square Inches then going back to the UL table I'd need a 3" LB.

 

[wwhitney]

Yeah a common 2" example is a single phase feeder with 4/0, 4/0, 2/0, and a #4 aluminum XHHW-2 conductors pulled in, thats less than the max permitted XHHW-2 in CH9 C11, so the LB does not need to have 12" between entries.

Not following you--your next post says a 2" PVC LB is marked 3 x 3/0, in which case 2 x 4/0 + 2/0 + #4 would be a violation, as that combined area exceeds the area of 3 x 3/0.

Cheers, Wayne

 

[jaggedben]

In general, standard LBs used with conductors 4 AWG and larger are not legal, assuming you are not using conduit that is oversized for the conductor fill.
...

I see no reason that one couldn't use the same size conduit and larger LBs with reducers, in cases where other details work out.

 

[LarryFine]

I see no reason that one couldn't use the same size conduit and larger LBs with reducers, in cases where other details work out.

That's done regularly.

 

[augie47]

Another common residential example would be a 4/0 SER cable that needs to travel in a short section of 2" conduit entering thru an LB, then its even more complicated, as chapter 9 table1 note 5 tells us to use the actual dimensions of the SER cable.
So we need to go the the product specs and look that up.
A 4/0/-4/0-4/0-2/0 SER cable specs say its 1.496 Square Inches then going back to the UL table I'd need a 3" LB.

which makes more sense if you have installed 4/0 SER in a 2" standard LB

 

[infinity]

Not following you--your next post says a 2" PVC LB is marked 3 x 3/0, in which case 2 x 4/0 + 2/0 + #4 would be a violation, as that combined area exceeds the area of 3 x 3/0.

Cheers, Wayne

He never said that it was code compliant. I'm guessing that it being a violation was his point.

 

[wwhitney]

I see no reason that one couldn't use the same size conduit and larger LBs with reducers, in cases where other details work out.

One of those details is that if the conduit body has a volume of over 100 in^3, then it will not qualify to be supported by the conduit itself under 314.23(E), so independent support will be required. Looks like a 2-1/2" LB exceeds 100 in^3?

Cheers, Wayne

 

[infinity]

SER cable in a LB requires a bend radius of 5X the diameter of the cable. It would need to be greatly oversized to keep the bend at or above 5X.

 

[wwhitney]

He never said that it was code compliant. I'm guessing that it being a violation was his point.

Part of the quote was " the LB does not need to have 12" between entries" which I believe is not a correct conclusion.

Cheers, Wayne

 

[LarryFine]

Would stripping the sheath make a difference here?

 

[jaggedben]

One of those details is that if the conduit body has a volume of over 100 in^3, then it will not qualify to be supported by the conduit itself under 314.23(E), so independent support will be required. Looks like a 2-1/2" LB exceeds 100 in^3?

Cheers, Wayne

Yes. But there are many such details and I don't know why that one is particularly worthy of bringing up.

 

[jaggedben]

Part of the quote was " the LB does not need to have 12" between entries" which I believe is not a correct conclusion.

Cheers, Wayne

Actually the requirement in 314.28(A)(2) is not between entries. It is between each entry and the opposite wall of the conduit body, which is an important difference.

 

[wwhitney]

Yes. But there are many such details and I don't know why that one is particularly worthy of bringing up.

Many such details? What other repercussions are there attributable solely to having upsized the LB to larger than the conduit? I mean, you'll need reducers, but that's obvious. The support requirement is not obvious.

Cheers, Wayne

 

[letgomywago]

Another common residential example would be a 4/0 SER cable that needs to travel in a short section of 2" conduit entering thru an LB, then its even more complicated, as chapter 9 table1 note 5 tells us to use the actual dimensions of the SER cable.
So we need to go the the product specs and look that up.
A 4/0/-4/0-4/0-2/0 SER cable specs say its 1.496 Square Inches then going back to the UL table I'd need a 3" LB.

So I wish it was more common on this side of the country but on the east side they have these plastic sill plates for SE cable and you could but up to a conduit and sleave without the bend issue.

 

[infinity]

I'm not sure why you would want to fight a #4/0 SE cable into any conduit body. In many cases you can just use an elbow. I redid my 200 amp service where I ripped out the 2" LB and used 2" PVC with an elbow instead.