I don't know what you are driving at. There is no limit to single phase amperage.
True. In theory.
OTOH, AFAIK, mankind has not (yet) built any single-phase gear larger than that used at the now-mothballed Neckersheim, DE GKN 1, Block 1 reactor complex. Electric railway "traction" current side generated 174 MW as 14,500 Volts @ 27,000 Amps, was stepped-up to 110 kilovolts for delivery.
That was the largest. It did have not-so-small competition around the world, including Amtrak's NorthEast corridor electric rail service grid..
Hanermo?
Either "get out more" or Google more before ass u me'ing Single-Phase is some sort of obsolete cripple.
It saves the US grid a great deal of WIRE where spaces are vast.
Spacious, and less densely populated yet Australia, plus select parts of Andean South America, take that economy further yet with Earth-return grid service.
ONE wire + Mother Earth.
Not my cuppa, but WTH, beats packing-in Kerosene or Diesel fuel on burros or cooking over dried Llama-turd.
3-Phase needs three wires, minimum.
And that is actually a very-damned USEFUL "sweet spot", economically, and part of why it is so widely used. TWO phase needs
four wires, minimum, more than three phases are no bargain, either.
As to a Single-Phase VFD "upper bound"? Not hard to push that limit. Just more expensive than using 3-Phase. Pick yer method for providing a strong enough and clean enough capacitor bank or functional equivalent, and drive the VFD off its "DC Bus" input.. presuming it HAS such, of course.
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