> by code, plumbing repairs couldn't leave behind unbonded sections of conductive plumbing
I assume that's correct, but I think shady / lazy / amateur contractors can assume the inspector won't check work in the crawl space.
You could look it up yourself. It's not hard.
Here's a guide to the 1981 National Electrical Code. See page 297. section 250-23, grounding for alternating current systems:
"grounding electrode conductor ... which runs to building steel and/or water pipe or driven ground rod".
Page 299, "water pipe and/or other suitable electrode" as grounding point for neutral.
Page 365, section 250-81 goes into water pipes as ground in more detail. It usually can't be the only ground. That's in 250-81(a). But back then, there was an assumption that water pipes were a path to ground.
By 2011, use of a water pipe as ground was more restricted. It's still allowed, but you have to attach directly to the metal pipe where it comes out of the ground. See[2], page 238, section 250-51, "Grounding electrodes". (You're allowed 5 feet of pipe from building entrance). Also see 250-53(D)(2), where the risk of future replacement of a metal water pipe with plastic is discussed. Water pipes are now valid grounds only if they meet the general ground rod criterion - six feet of conductor buried in earth. (3m for pipes.) You can see the general progression from "pipes are grounds" to "only grounding rods driven in the ground can be trusted." Which is reasonable enough, given that most new pipe is plastic. At this point, grounding pipes is more about preventing them from becoming energized if something shorts to a pipe. Just as all electrical boxes must be grounded.
[1] https://archive.org/details/mcgrawhillsnatio00mcpa/page/296/...
[2] https://archive.org/details/nationalelectric0000unse_d8w8/pa...
Do you have a citation for this?
I was under the impression that using plumbing as equipment ground was never allowed, but that conductive plumbing has required to be bonded to ground for some time. I was further under the impression that by code, plumbing repairs couldn't leave behind unbonded sections of conductive plumbing.