I’ve found one utility where it seems to have been installed for new service about 40 years ago—Los Angeles Department of Water and Power. {The neighborhood also had the lovely ungrounded-delta 4800V primary distribution.} A pretzel plant was originally built with a 240V 800-amp 3ø 3-wire corner-grounded switchboard, with a hodgepodge of wiring over decades of existence. The plant-maintenance guys were puzzled by it, for some circuits had 2-pole 250V fused switches, served with two black conductors and a white conductor, but with ~240V (!) between all three conductors. In some areas, even though it was a grounded circuit conductor that should have been white, the installer put in non-white cable, apparently because it was three phase, a he’d be dammed if a motor would have a white wire to a three phase motor! To make matters worse, they had assorted 2-pole and 3-pole fusible switches, and some circuit-breaker panelboards that had 2-pole and 3-pole breakers, evidently depending on the free will of the installing contractor/electrician. For further confusion, even for corner-grounded service, motor-overload relays have to be installed in each phase, and connecting white wires to overload relays had the whole maintenance crew {about 8 guys; none over age 30} perplexed. It was hard getting them to understand that even “the white wire” to a motor needed to correctly read close to the same current as the “hot” leads.
Then to make it even more worse, because of load growth, a contactor installed a new 120/240V 1ø 3-wire 400-amp switchboard, but used no unique color code to differentiate between the single-phase system and the three-phase system, apparently because it was all “240 volts.” None of the maintenance crew had any significant electrical experience, so until we sat down with a big easel pad and markers and voltmeters testing energized equipment on the plant, it was a complete mystery. When I left, I think two guys had it figured out, and they promised to get it into others’ heads what readings to expect in troubleshooting.
