George, I understand your perspective. Yet, the NEC is clear that the final authority is the AHJ. Don't misuncerstand, I am NOT advocating anyone taking a cavalier attitude toward listing marks!
Actually, there is only one difference in the ASTM specs between plumbing pipe and electrical conduit....conduit has a "smoothness" spec, while plumbing pipe is silent on the issue. (A good trivia q).
NEC requires that stuff be suitable for its' environment. That can be a problem when there is no manufacturer of a suitable product. I was once involved with sump pumps and such, that were to operate in highly corrosive places. Galvanised steel was out of the question....and there was no manufacturer of stainless steel conduit. Care to guess how the problem was solved? And, I hasten to add, by a manufacturer who had several products UL listed, and a listed panel shop.
