Is schedule 80 electrical conduit appropriate for 4/0 4/0 2/0 wire?
According to table C.9 referenced in this answer, 2-1/2&quot; Schedule 80 can handle up to 5 x 4/0 conductors, so you're fine even for a full hot/hot/neutral/ground (and ground definitely doesn't need to be as big).
Actually, it isn't exactly like that. 4/0-4/0-4/0-2/0 cable probably takes a bit more than the individual wires, but is relatively round (which helps) and I found plenty of references to running it through 2&quot; conduit, so 2-1/2&quot; gives you a little more room to work with.