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Originally posted by Skins2881:

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Originally posted by sigcrazy7:
Why would it be acceptable to direct bury underground feeder, but be prohibited to put it in conduit?

I don't think it's prohibited in any way, there's just no table or charts to size the wire/conduit. I can't think of a reason to do it though. Direct burial cable is made to be buried without a conduit. If I'm spending the effort to do conduit run, then I'm going to use individual conductors.

It’s a little unusual. The contractor who built the garage installed a 2.5” underground conduit, so conduit is already there. Using it makes sense, however it meets the house on the opposite side of the electric service. We can either install a junction where it entered the house to transition from cable, run conduit all the way through the house back to the panel, or run UF uninterrupted from the panel and through the underground conduit. The latter seems the cleanest and least expensive, especially if he ever wants to finish the basement.

You reply lacks enough details to allow me to make a suggestion. But if I understand correctly you have conduit run from point to point, but on house side it would then need to be fished to the panel? The sticking point is a J-box? The costs associated with doing it all in UF and the effort required would rule that out as an option for me. I rather set junction box then run SER from there to panel. Way easier to fish that large sized UF

The plan is to run XHHW 2/0 SER from the main panel, through the floor joists in semi-finished basement, and then into the existing, contractor installed, conduit from the house to the outbuilding, terminating in a 24 space, 100a sub-panel. Alongside this, we want a separate service from the critical load panel (near the main house panel) to the outbuilding, using 10/3 UF through the floor joists, into same existing 2.5” conduit as the other 2/0 SER, and to a small six-space panel. This is for critical loads in that building, namely a chest freezer and perhaps a 240v-20a plug.

It makes no sense to dig a separate trench for the UF when there’s already a 2.5” conduit there. We also don’t want to have to run conduit from where the 2.5” conduit enters the house back to the main panel. Therefore, the use of cable for the whole run instead of individual THWN conductors for the underground conduit portion. If he decides to finish that room completely, using a junction box to transition to cable will require the box to remain exposed instead of cable behind finished walls.

Hopefully this better explains the scope of the project.