Thanks for all your responses.
Raider: thanks, but I already checked 338 before posting my questions. I didn't find my answers there, as Markp suggested I might not.
Markp: why a burial depth of 24"? I guess I should have specified that this is a single-family dwelling. Table 300.5 says 18", yes?
PCBelarge: thanks for the UL reference. In this case, the USE would be entering the building solely for the purpose of termination in a subpanel - probably less than 3' from where it enters the buiding. So it sounds like that might make it okay by UL. I just need to find out if it needs to be in conduit for those 2-3 feet.
