I initially thought this would be an interesting article to support the discussion of electrical ground being a local phenomenon. Page 344 [id=330562697] mentions accommodating potential differences of 1,000 volts at opposite ends of the first trans-Atlantic cable, TAT-1.

But I'm going to post several pages in case it is of general interest to anybody besides a geek like myself. Use "view original" to read the text. These Bell Systems engineers did simply unimaginable things with analog technology before the digital age.

I can send a pdf of the entire chapter if anybody is interested.