deleon2kona
Member
one student argues:
A 10kVA 120/208 UPS has to be protected by a 60Amp disconnect. He also argues that he is bidding it correctly with a 20kVA UPS as it is capable of delivering 60A.
I argue back:
Not necessarily, becasue current draw is not based on the max of the device. That a load calc has to be performed, for example:
120V loads total 30Amps = 3600W
208V loads total 15Amps (* 1.73) = 5397W
3600+5397=9000W and a 10kVA is ample size
And regarding the disconnect selection, he has to determine the wire size/type before selecting the disconnect. That he selects wire size and type, then protect that with a disconnect with fuses properly selected.
Now, we both question:
What if the load is all 120V....10kVA divide by 120V = 83A...does that mean we have to use an 83A wire and the proper disconnect?
(thanks for helping out this pair of newbies)
A 10kVA 120/208 UPS has to be protected by a 60Amp disconnect. He also argues that he is bidding it correctly with a 20kVA UPS as it is capable of delivering 60A.
I argue back:
Not necessarily, becasue current draw is not based on the max of the device. That a load calc has to be performed, for example:
120V loads total 30Amps = 3600W
208V loads total 15Amps (* 1.73) = 5397W
3600+5397=9000W and a 10kVA is ample size
And regarding the disconnect selection, he has to determine the wire size/type before selecting the disconnect. That he selects wire size and type, then protect that with a disconnect with fuses properly selected.
Now, we both question:
What if the load is all 120V....10kVA divide by 120V = 83A...does that mean we have to use an 83A wire and the proper disconnect?
(thanks for helping out this pair of newbies)
