800A in 2-3" RGS

[bob]

In your post you said

I have two existing 3" RGS buried in concrete.

.
Are the conductors in conduit or an enclosure?

[beanland]

The conduits are underground RGS from a main switchboard to a remote panel. They are buried (possibly in concrete), then rise through a concrete floor, and terminate above grade at the enclosure.

The conductors are in the conduit for part of the run and in enclosures on both ends of the run. Where the conductors exit the conduits they are in the enclosures, not in the conduits anymore.

[bob]

I think you will find that the conductor rating in the conduiit will be the max rating for the entire run.

[macmikeman]

Good point. THHN is 90C damp location. THWN-2 is 90C rated wet location. XHHW-2 is 90C rated wet location.

Yes, per NEC 100, all below grade locations are wet. Therefore THWN-2 or XHHW-2 are required to be able to use 90C rating.

Hey thats right, Bob Badger pointed that out to me about a month ago, but I guess it didn't sink in all the way yet....

[Strife]

It's not 8. It's 6 as the grounded conductor which only carries the unbalance current of the other phases doesn't count. And neither does the grounding conductor.

If there are 8 ccc in the conduit you must derate at 70%. The wire in free air can be smaller sized if you want.

[Robert Hutcherson]

Just curious,what is the calculated load of the remote panel?

[Smart $]

OK, good clarification. That makes sense.

However, are conductors located in an enclosure considered in a conduit/raceway (310.16) or in free air (310.17)? NEC 100 defines a raceway basically as a conduit. Enclosures are defined totally differently. Based on the definitions, I have assumed that if it is not in a conduit(aka raceway), it is in free air, we do not have a third choice.

Conductor ampacities under the NEC are, for the most part, determined by the wiring method used between enclosures and the like.

Free-air wiring is generally considered to be that which has substantial air-space around wires... but the amount of air-space is not specified by the NEC. Typically, this is for open conductors (i.e. not a jacketed multiconductor cable or wires in a raceway, for the majority of their length). The NEC does have some conductor-to-conductor spacing requirements, though.