Running 4-4inch IMC from a pad mount xformer up the side of a building to a 480 volt 1600 Amp main switch in a second floor electrical room. There will be 4-600 MCM THHN's in each.

The 4 inch LB's (not the extra length ones) say inside they are good for 3-4/0's. Is that all you can fit in 40% of this LB??? I was surprised by this, but had a bit of trouble finding the answer in the 05 NEC.

Probably will have to use a huge weatherproof box (CT Cabinet) to make the transition and run all 4 pipes thru it. Then nipple out the back to the Main Switch.

It is also surprising how hard it is to come in the side of this switch with 4-4 inch conduits...the frame bracing is in the middle of the side panel. 16-600's will be a formidible task.

The answer is in 314.28, which applies to not only boxes, but conduit bodies used as pull boxes.
6 times the size of the conduit for angle pulls.


The wording IMO is unclear, referring in A(1)and (2)only to "boxes" and then adding the conduit bodies in the "exception".

314.28(3) addresses the conditions under which a smaller conduit body can be used....it has to be marked with the maximum allowable number and size of conductors.(thus the 3-4/0 marking)

From expierience, skip the Lb's on any wiring above 350 mcm. It is worth the saved labor trying to wrestle 4 600's into.Especially 4 conduits worth. Get a Utility aproved cabinet.

I agree on skipping the LB's as a general rule. I have used appropriately sized wireways in indoor locations for years. They are much cheaper and in a 2 or 3 foot length so forgiving with large conductors.

The owner in this case was looking for the neatness of the final installation which would result from LB's but it I now see just can't happen---will have to be a CT cabinet or similar.