220 wiring; why isn't a neutral necessary?

Hello ... probably the only thing I don't understand is how a neutral is NOT required on a 220V line to operate at 220.
A normal 110 circuit terminates at the panel with white to common and black (hot) to breaker. When a motor is turned on, I understand current *flows* from neutral to hot (even though it's AC, it flips 60 times a second; not dealing with AC?) I assume this is just boilerplate.
I have a 220V air compressor (2 hots, 1 ground) and it has no return, which is OK since there's no device requiring 110 (one leg). How can current flow with just 2 hot wires? I assume the 2 incoming "hot bars" (from outside) are in sync. Both bars are either positive or negative. So, when the "negative" phase occurs, where does the current drain? I can see how the ground will work... and maybe it *IS* used.
Can someone clarify?
Thanks a lot! I greatly appreciate it.
Mike
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Thanks Mark (or Sue?), by clarifying the hot bars are not ever the same polarity, current can flow between both breakers. So at any given time, either are + or -, correct?
Thanks again.
Mike
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quoting:

AC reverses polarity 120 times per second. So for 1/120th of a second, one wire is +, and the other is -. I like to think of it as the "push-pull" effect. At any givin half-cycle, one is pushing(+), and the other is pulling(-).
With one hot wire to ground, only that one wire pushing or pulling on it's own at any givin half-cycle. When the circuit is closed, the ground or neutral is sorta forced into push/pull action, except it isn't really pushing/pulling it's own electricity on it's own, so the voltage is half, or 120 volts.
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Generally you have 3 wires coming into your home, one of which is neutral. Across either of the other 2 wires to neutral is ~120 VAC. But between the 2 hots is ~240 VAC. So be careful about connecting one hot to another hot, because if they are different hots, it could be a 240 volt short.
So yes you do have 2 hots with 220/240 V and neither of them should be grounded. But at an given instant (except in middle of AC cycle) they are opposite polarities, so current will flow between them.
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