PHPaul
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A distribution transformer (the one on the pole that feeds your house) takes single phase high voltage (varies, 2,000vac is pretty much the minimum, can be as high as 35KV, according to Wiki) and performs two functions:
1. Steps it down to 220v
2. Provides two legs plus neutral
This example uses a 7.2KV primary, different distribution voltages are still stepped down to 220v by using more or less windings on the transformer as needed.
EDIT: A bit more research indicates that the two legs are indeed 180° out of phase as far as the AC waveform is concerned. As long as 220 is taken by tapping both legs, it's still considered single phase.
It's rare these days, but older machinery (say, 1940's) did use what is effectively "2 phase" power by using each leg to ground.
1. Steps it down to 220v
2. Provides two legs plus neutral

This example uses a 7.2KV primary, different distribution voltages are still stepped down to 220v by using more or less windings on the transformer as needed.
EDIT: A bit more research indicates that the two legs are indeed 180° out of phase as far as the AC waveform is concerned. As long as 220 is taken by tapping both legs, it's still considered single phase.
It's rare these days, but older machinery (say, 1940's) did use what is effectively "2 phase" power by using each leg to ground.
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