My first brush with real weirdness was when my partner and I moved our integration business into a building in Seattle that had been built as a railroad service foundry in 1899 without electricity, then electricity was run to it sometime in the early 1910s. When we scoped out the building, there was a 480/277 panel, so we assumed that the other panels were subs from that. But we kept getting weird readings on the 480V lines and some of the subs, so I went up on the roof to get a good look at the pole pigs (the power pole was in the middle of the building, likely because they had added onto the original structure and wrapped around the pole). I saw only two transformers, one big and one small, with just two wires coming off the primary lines. I knew about open delta and I knew about 4 wire high leg delta, but only for 240V and we had 480/277. Turned out the original service was 240/120V 3ph 4 wire open delta, something I did not know existed. That then also meant that somewhere buried in the bowels of that building there must be a 480Y transformer. Took us a few hours to find it (wiring was nuts in there), a 75kVA in a dry sump covered with a diamond plate solid top, so the transformer was just cooking away in there. It had turn-to-turn shorts inside and the insulation was basically crumbling off of the line and load cables.
The Landlord refused to pay for anything regarding that, kept thinking it was a “utility problem”, which of course it wasn’t and even though my partner was a registered PE, he refused to accept that he had to pay to fix anything that had to do with electrical power, he said that was our problem. We ended up calling the Fire Marshall, who condemned the building until that was fixed. Because of the pole being in the middle of the building, Seattle City Light wouldn’t give it a new 480V service drop, or even ANYTHING new, so the landlord had to pay to have them put in a new pole on the corner of the street to drop a new service.
We didn’t change anything with the old service drop, we just tied the new 480 service into the existing 480 panel and disconnected the circuit to that burned out 240-480V step up transformer, assuming we would have to put in a little single phase tranny for the lights and plugs. Found out later though that City Light never disconnected the old service (probably because it was too old for their records), but since there was only the one new service drop assigned to our address, there was only the one meter being read and of course only one bill. So we ended up with free power for the 120/240V loads. I just took a look at a satellite map of that building, the pole in the middle is no longer there so someone eventually figured it out but we had that for over 3 years that way.
