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Also another note, I see people in telegram talk about having 277v, not sure if that's just in the U.S or elsewhere, but that 277v range isn't mining-friendly either, many folks are stuck with 1-2 MicroBT models that can take 277v.
The 277v is what you get from 480V 3-phase wye connection. Running from the center neutral point to any 1 of the phases gives 277V. In the past that connection was mainly used for lighting in factories that use 480V 3-phase to power their equipment - the balasts used for large flouresent or HPS lights has taps covering a very wide rage of voltages with 277v being one of them. Yes that is a problem for miners because as you said, most top out at 250v rating and running anything higher is a very bad idea...