208/240 power question...

Right. In residential neighborhoods, you end up with two legs in phase, but opposite voltages coming into your house, center tapped. So the difference between your two 120V legs is 240V.

Right Three phase vs. single phase. Just dealing with 120V off your 3-phase UPS you get 120V. But, when you take two legs of the three, you get things 120degrees out of phase between the two, so by the time one leg is leading, the other is falling. RMS difference between two legs ends up being 208V between the two legs because of the phase difference once you work out the math.

You have to be careful of what you define as a 240V appliance. A 240V dryer or heater might not operate quite right on 208V...

But, something like a 6500 is designed to operate just fine on 208V, because that is the expected environment it will be going into. Note: Most computer gear runs just fine off 120V or 208V power or 220/230/240V power, as the power supplies are all auto-sensing for the voltage level for all areas around the world, and adjusts appropriately. That way, manufacturers can just ship the correct power plug for the region and not have seperate power supplies trying to figure out what power is what in what area of the world it ships to.

You also have to be mindful of *what* power supplies you put into your

6500. Some are 120V/208V. Some higher-wattage ones are 208V only, to stay within your current ratings (ie. they'll be 208Vx16A feeds, which is going to be more current than most wire run for 120V will take, but works just fine for 208V).

You aren't quite right on the wiring though.

240V residential is normally run with 12-3 NM cable in the house. Two phases of power, neutral and ground. It doesn't run in EMT or BX conduit like some areas used to have many years ago.

BUT, 208V commercial is normally run with 3 THHN inside EMT conduit. You still have two phases, and one neutral, but the ground run is the EMT conduit itself. The ground will be tied to the neutral at one point, probably the main PDU for your UPS, which is then grounded to the building ground.

My house is old enough that all oldwork is run in EMT or BX, which was the designed in ground for the 2 THHN conductors they pulled in each, so my home wiring is more like commercial environments. But residential is all done with NM cable now which is cheaper and quicker to run.

So, ultimately, your 6500 power supplies are designed to work on the

208V feed your 3-phase UPS will generate for it, and you don't have to worry about it.