In what version of the NEC was the requirement for isolated neutrals and grounds in sub panels first mentioned?
It was clarified in 2002 but it has always been required by UL 67.
Good question Bill…let me say this, I have a 1993 NEC and it has the requirement in it so it was atleast back before the 1993 NEC.
**[FONT=Swiss721BT-Bold][size=1]250.61(b) Load-Side Equipment. **[/size][/FONT][FONT=Dutch801BT-Roman][size=1]A grounded circuit conductor
shall not be used for grounding noncurrent-carrying metal
parts of equipment on the load side of the service disconnecting
means or on the load side of a separately derived system
disconnecting means or the overcurrent devices for a separately
derived system not having a main disconnecting means.
I read somewhere that it was covered way back to the 1940’s by the catch all code phrase “follow the manufactures instructions”.