> Wouldn't it also need a continuous copper pipe until it meets the ground? A pipe being made of copper or iron doesn't mean it's not connected to a plastic pipe or adapter upstream

Right.

> I've seen plumbers using a rubbery-looking tape between the threads when screwing two metal pipes together, which might not be conductive

Probably PTFE (teflon) tape.

The thing to do with oldschool copper pipes though was to braze them together, which is conductive.