We are installing a large tower UPS into a computer room, and I want to make sure I specify the safety switch correctly.
Assumptions:
- The UPS is a 230V 50A UPS, single phase input
- Output is 208V single phase
- The main panel is a commercial panel fed by three phase to the building but all of the circuits coming from that panel are single phase circuits.
My questions are:
1) Should the main panel should be equipped with a 50A breaker or smaller (based on projected load)?2) Given the UPS is a single phase input, is it required by code that the breaker also be single phase? I have seen contractors use existing three phase breakers but wire them for a single phase application. Since the documentation for this is rarely done well, I'm skeptical about doing that.
3) In the UPS room, in front of the UPS itself, we would like to have a safety switch with a fuse. Again, by code and convention, are we required to get a single phase safety switch? Or can we wire into a three phase safety switch and just not use one of the three pins?4) I assume a safety switch rated for 100A fuses can be equipped with smaller fuses?
5) On the output from a UPS, is it generally recommended that you install another fused safety switch? I guess that gives you the ability to shut off the load in an emergency to the end equipment, but aside from that would run the risk that if you were at the border of the UPS capability you might accidentally turn off the entire machine room. Presumably any decent large UPS would start to warn you of an impending overload condition?