What seems like a pretty straightforward solution turns out to be quite complicated. I have seen numerous instances where a 3 wire 600 volt primary feeds a 120/208 volt 4 wire system. Mikesh refers to 10-204, which specifies services, so would this apply here? Also, low impedence path for fault current from phase to ground on the primary feeder should be provided by the bonding, which is connected to the neutral on the 600 volt system. From what I understand, Mikesh is proposing using the neutral as a second bonding conductor but I could be misinterpreting here. If the minimum required bonding conductor is not adequate to interrupt fault current, maybe the rule needs to be reviewed.
