Derater, if it is already wired and you're just making sure it is safe there are a few things I would check. Are the neutrals and grounds bonded in the sub-panel? With a 3 wire feeder this sub should be treated as a service and the neutral and ground buses should be bonded together. If it is a 4 wire feeder, of course they should be separate. Is there a grounding electrode system, there should be. If you only have a 3 wire feeder and you isolate the grounds and neutrals you will have no ground fault protection. Any ground fault current will go straight to earth (if there's an electrode) and probably will not clear the fault, essentially leaving whatever device or load that caused the fault energized and posing an hazard. 2002 nec permits this installation, see 250.32 B2. Check it before you insist on a 4 wire feeder, this installation can be made safe. Make sure you bond the building steel.
[This message has been edited by BobH (edited 04-19-2005).]
