can I connect a 230 volt window a/c unit to a 208Y system?

Some equipment will run on either 208 or 230 V. The motors or heaters or whatever can tolerate that voltage variation. You should check the manual to be sure.

3-phase power comes into the building, and can be stepped down in voltage if necessary. That's common in commercial buildings, but not in homes.

You can use one phase of a 3-phase feed to create standard single phase power. It's common in an office building to split a 208 V 3-phase feed into 3 individual 120 V single phase branches, and run them into different areas.

You can visualize single-phase and 3-phase voltages with a vector diagram. If you draw 3 vectors of magnitude 120 V coming out of the origin, and spaced 120 degrees apart, the endpoints will form a triangle. The distance between any 2 of them is 208 V, which is what you would measure with a voltmeter. That's called the line-to-line voltage, which is how 3-phase power is usually measured. The origin is called the neutral, which is usually connected to Earth ground in the US, but not in some other countries.

http://www.oempanels.com/what-does-single-and-thre...

It's a bit borderline depending on quality of supply.

The geeky answer is that NEMA standards (which UL and other listing companies use to test by) intend safe operation +/-10%, which -10% of 230v is 207v, Which would seem safe, except the Utility Standard ANSI C84.1 allows +/-5%, which for 208v is 198v to 218v. So if your utility (or transformer) power is low, you could have trouble, if average or better you will be fine.

It will likely draw slightly higher amps, but I would guess if it's cord connected it wouldn't trip a breaker because cord connected appliances should by NEC be rated for maximum 80% of circuit capacity, so you should have head room. Shouldn't actually use more watts except for the one second the compressor starts, the rest of the time the amps are up, but the since volts are down, watts are the same.

208V is just two phases of a 3 phase circuit. There will be a label on the AC unit saying the required voltage. If 208 is in the range, all is good.

Hshshaixkkxakka

Yes you can, but it "may" not operate efficiently.

Read through this: http://ask.metafilter.com/49964/208y-power-does-it...