Not a specific answer, but did you know....
In 1956, the definition of "grounding conductor" was: "Conductor used to connect an equipment, device or wiring system with a grounding electrode or electrodes."
In 1968, The term Grounding Conductor, Equipment, showed up in the NEC. It was defined as: "A conductor used to connect the equipment being grounded to the service equipment enclosure."
I'm coming at it a little differently trying to show how the definition has changed over the years and code cycles. I would venture a guess that when 'egc' started showing up in the code is about when one started seeing this wiring method become widespread. :smile:
i'm not sure exactly what code year it was required. just guessing from the houses that i have worked on i would say the early 60's. the first equipment ground wires that were used with 12/2 nm were a smaller size probably 16 ga.