I happen to use 3-phase power, since my country is the country of ASEA and not the country hailing that con man Edison. His flawed DC mains system has one, and one good thing only: You can get 240V off of it. Sadly, it's not three-phase, but something forcing you poor people to add capacitors (see rule 9) to every motor. Our neighbours to the west, the Norwegians, are even purer. They have no neutral, but instead run their Schuko outlets off of two legs from a Delta-connected three-phase grid.
Thanks, that explains why I've seen all the dual pole breakers in Norwegian panels. Always wondered why one would break the neutral, but with this knowledge it makes perfect sense. One more reason for having polarity independent appliances and non-polarized plugs.
It's the same with mains on ships. I first came across it when working in the night club on M/F Nils Holgersson, on the Trelleborg-Travemünde route. We'd go aboard at about 5 in the afternoon, and work a few hours before the nightclub opened, then we'd have beers from the export-only stores (practically free Beck's), go to bed and wake up in Travemünde, and work all day during the return journey, getting off again in Trelleborg. Most times customs did not catch us trying to import export-only fags and beer.
Anyway, there were dual-pole circuit breakers. Another example, that perhaps illustrates the point better, is a fairly uncommon repair part sourcing we did about the same time. Friend of the boss worked at sea, assistant engineer on a freighter. They had an electrical winch on the forward superstructure, fed by a delta 3-phase cable, 380 Volts. The contactor had burned out, and they fitted another one, but were unable to source one with a 380V coil, and had to settle for 220V. The bodge was to use the ship's hull to get a neutral, and thus a 380V/sqrt(3) voltage. Problem was that they then caused very accelerated corrosion on the winch frame, because the very reason to do Delta mains on ships is to keep currents away from the hull. So we were asked to get a replacement coil for 380V, which was no big problem, and that solved the original issue.