> OP is not qualified to be speaking about it

I know that was supposed to be an insult, but it's actually true. I don't mind at all.

Not my wheelhouse. I'm just repeating what the electrician told me, verbally, about twenty years ago. I wasn't actually that interested, at the time, so it's expected that my memory of it is terrible.

There's all sorts of stuff I ain't qualified to write about, and I'm not embarrassed in the least, to say so. That's one of the reasons I hang out here.

I suspect that it was 277 volts. I'm pretty sure that's a thing. I'm sorta sure that he said 300-something, but, as was noted above, he may have been just using the most impressive number he could find, or he was talking about the tolerances of the switches. I'll bet that it came up, because we were discussing the budget he was charging my department, and I probably had a question about the stuff he was ordering. Otherwise, I don't see why it would have interested me. I've learned to leave contractors alone, while they work. The reason that I knew they were working on live wires, was because the lights turned on, as I was walking past, and there was a slight spark in the box he was tweaking.