Ryan:
I imagine that CB's of various type have been marked that way for quite some time, but have no specific date.
If I can recall the "Backing Feeding" rule triple mentioned was put into the NEC after an accident where the CB popped out when an electrician removed a cabinet cover to expose a panelboard and the energized CB prongs or blades? electrocuted him!
If I could get to my archives down in my dungeon, I could search for that information in the TCR (Technical Committee Report) or TCD (Technical Committee Documentation) back in?? 1983 I think.
