LB Fill & Bending Radius

[jsch]

Thoughts requested regarding the use of a standard length 4" LB ( Not mogul) with four 750 kcmil alum xhhw-2 insulated conductors (compact).
It would appear to me the bending radius at 8 times the o.d. would be compromised on at least two of the four conductors making this a non compliant installation per NEC. The concern being insullation damage during initial install resulting in potential fault condition.

 

[infinity]

A conduit body can be used if it doesn't comply with the 6X rule only when the permitted condcutor information is listed on the conduit body. Where are you finding a bend radius for an LB?

314.28(A)(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.

 

[don_resqcapt19]

In general when using 2" and larger raceways with large conductors, the use of standard LBs is a code violation per the section that Rob cited.

 

[jmellc]

I've only seen a few of them, but a UB might be what you need. Sort of an LB made into a 45 degree angle. Opens wide, the shell is the cover. Co. I worked for had used 1 just before I came to that job. They all said it was easy to pull through. I think it had 350 MCM in it. I think some even have rollers at each entry, to make pulling easier. I'm sure they are special order at most places.

 

[steve66]

You can also use a larger size LB with reducing fittings, as long as the LB is rated for the wire used.

Example: 2" conduit run with a 2.5" LB.

Of course, that might be a little difficult since you are using a 4" run to start with.

Steve

 

[don_resqcapt19]

You can also use a larger size LB with reducing fittings, as long as the LB is rated for the wire used.

Example: 2" conduit run with a 2.5" LB.

Of course, that might be a little difficult since you are using a 4" run to start with.

Steve

However, if the volume of the oversized conduit body is 100 cubic inches or more, the conduit is not permitted to be used as the support for a conduit body that is of a larger trade size than that of the conduit. Independent support of the conduit body is required. 314.23(E) and the exception

 

[steve66]

That's a new one on me.

At about what trade size does a conduit fitting get close to 100 square inches?

 

[don_resqcapt19]

That's a new one on me.

At about what trade size does a conduit fitting get close to 100 square inches?

A 2.5" Form 7 LB, one of the smaller types of LBs, has a volume of about 106 cubic inches.

 

[shepelec]

When you factor in the aggravation of folding the cables into a standard LB, you'll find a mogul LB is well worth the money.

I'll never use a standard LB again with large conductors.

 

[xformer]

pardon my ignorance, but whats a mogul LB?

 

[steve66]

pardon my ignorance, but whats a mogul LB?

http://www.garvinindustries.com/Electrical-Fittings/Conduit-Bodies/LB-Style--Mogul

So a 3" LB on a 2.5" conduit run would probably need extra support. That's interesting.

I wonder how you could support an LB anyway??

 

[izak]

with a really expensive caddy clip that hasnt been invented yet

or... drill a hole in the back of it and bolt/screw/glue it to something

use a HUGE Mineralac hanger wrapped around it.

weld a bracket to the back of it and make it look REALLY stupid

does anyone besides me ever drill holes in the back of PVC Conduit Bodies to attach them to building structure?

really, I am concerned that I might be doing something wrong that also wont hurt anything

 

[jmellc]

I have drilled LB's & screwed to masonry wall with plastic anchors. I've used a standoff strap (minerallac) on the throat, have used a 2 hole strap on the throat, whatever was most practical at the time, or what I had available.

Do check out a UB & see if you could use it. If space allows, it would be 100 times easier to pull through. Big wire in any LB is still a pain. See lesco-inc.com & tulsa-ads.com, among others on Google. They show UB's, standard, but I have seen a UB with open sides, the cover is the shell. These sites also show an open sided LB, not a bad thing either.