I am purchasing a Liebert Series 300 UPS. Input 480V, Output 208V. And I believe the output is 208Y, so three hot 120V legs, 208 phase-phase.
Two questions.
First, from a sizing standpoint, my data is all 120V single phase. I dont really know how that correlates to the input rating of the unit which is done, 30KVA, 65KVA, etc.,.
What throughs me off is if that is per phase, or across all three phase of the 480 input, etc.,.
To put things in perspective with a practical example...
I have a total of 500 amps of 120V equipment. So with phase balancing, figure 165 amps on phase A, 165 amps on phase B, and 165 amps on phase C of my UPS's 208Y output.
To support that, what size KVA UPS do I need? Using my ubdoubtly incorrect knowlegde, I was figuring something around 60KVA (500amps x
120V / 1000).The second question, when buying a UPS, everyone says I should get one where my real usage is close to the full capacity of the UPS. If I were to get a 60KVA UPS and only have 10KVA of load, I've been told it will waste alot of power. I sthat true? If so, how do you get around the inevitable situation where you will grow into the unit, and have to start small? Or do you simply have to deal with inefficiencies at low usage?
Thanks, John