I think you're forgetting the wires? If you have one outlet with a 15-20A 120V circuit, then the wiring is almost certainly rated for 15-20A. If you just "combined" two 120V circuits into a 240V circuit, you still need an outlet that is rated for 30A, the wires leading to it also need to be rated for 30A, and it definitely needs a neutral. So you still need a new wire run if you don't have two 120V circuits right where you wanna plug in the box. To pass code you also may need to upsize conduit. If load is continuously near peak, it should be 50A instead of 30.

So basically you need a brand new circuit run if you don't have two 120V circuits next to each other. But if you're spending $65k on a single machine, an extra grand for an electrician to run conduit should be peanuts. While you're at it I would def add a whole-home GFCI, lightning/EMI arrestor, and a UPS at the outlet, so one big shock doesn't send $65k down the toilet.

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briandw 10 hours ago | parent | next [-]

Correct me if I’m wrong, but doubling the volts doesn't change the amps, it doubles the watts. Watts = V*A.

	▲	0xbadcafebee 4 hours ago \| parent \| next [-]
		Yes; I assumed 30A was minimum requirement for 240V service in US. Apparently I was wrong, 20A 240V is apparently normal. So in theory you could use a pre-existing 20A 120V circuit's wiring for a 240V (assuming it was 12/3 cable). And apparently 4-wire is now the standard for 240V service in US? Jesus we have a weird grid.
	▲	subscribed 10 hours ago \| parent \| prev [-]
		Doubling the volts halves the amps. P = I * V indeed.

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fc417fc802 11 hours ago | parent | prev [-]

I think you might've misread GP. (Or maybe I did?)

He's not saying you would use it as two separate 120v circuits sharing a ground but rather as a single 240v circuit. His point is that it's easy to rewire for 240v since it's the same as all the other wiring in your house just with both poles exposed.

Of course you do have to run a new wire rather than repurpose what's already in the wall since you need the entire circuit to yourself. So I think it's not as trivial as he's making out.

But then at that wattage you'll also want to punch an exhaust fan in for waste heat so it's not like you won't already be making some modifications.

	▲	projektfu 6 hours ago \| parent [-]
		The wiring (at least in the US) to the 120V outlets is just one half of the split-phase 240V. If you want to send 240V down a particular wire, you can do that, by changing the breaker, but then you lose the neutral. You also make the wires dangerous to people who don't realize that the white wire is now energized at 120V over ground. (Though it's best to test to be sure anyway, as polarity gets reversed by accident, etc.) Live wires should be black or red.