It looks like it was sometime between 1947 and 1953. 1953 NEC has the requirement located in Section 2581. I don't have a NEC prior to that, but I do have a 1947 NEC handbook, which does not show that there is such a requirement, but that could just be the author's fault.
Anyone with a NEC before 1953 can send them to me, I will take good care of it (them)!!!!
Ghoti, what are you asking? When it was recognized as a viable grounding means or when it was required to supplement the water pipe ground? I am guessing it was required to supplement the water pipe ground in the early 70's.
Thanks for history Bennie. We sometimes loose our perspective.
I also feel the requirement to supplement a metal UG water pipe was added in 1970's, as thats about the time plastic pipe became very common
You are close Tom, I don't know the exact time.
The first time I used PVC was in 1963. The job was in the Marshall Islands.
The wild pigs liked the glue, and became glue sniffers. They rooted up our 4160 volt lines and bit into them, once.
I965 NEC, Section 250-81, stipulates the supplementary electrode is required. The reason is when the length buried is not confirmed and the chance of plastic being used.