Single phase UPS fed from 3 ph panel - what is load on panel?

[wdthrush]

I have a customer that has a single phase, 10 kVA online UPS that is fed by a 60A 2P breaker in a 100A 3 phase 120/208 panel. The UPS feeds a single phase panel with 120 and 240 loads.

I want to calculate the actual load on the 3ph panel. Would my calculation be 1) 10kVA/(208*1.73) or 2) 10kVA/208?

Using method one I get 27.7A and method two 48A. Which is correct?

Thank you.

AF

 

[GoldDigger]

You would use 10kVA divided by 208, (your second option) since you have a simple single phase load supplied by 208 volts.
If you properly calculate the phase angles of the currents in the two phase lines you are using, you will find that the sum of the phase currents times 120 times the phase angle will give you exactly the same results.
If, on the other hand, you need to know the kVA for loading on the supply transformer, it is potentially going to be greater than 10kVA.
this results from the inefficiency of using only two phases of a three phase circuit.
If you had three 10kVA UPs, one per phase, the transformer loading will be 30kVA.

Tapatalk!

 

[broadgage]

A "10KVA" UPS usually means that the equipment is able to supply a load of 10KVA. The input requirement will be greater than this due to internal losses, and also for charging the battery after an outage.

In the absence of more detailed information, it is usual practice to assume an input requirement of 150% of the stated output.

In this case I would inclined to size the breaker as directed by the supplier, but to assume 15KVA load when assessing the load on upstream feeders, transformers and the like.