Switch-gear Capabilities

[Justin P. Le Blanc]

Is 480V (3 wire, delta) switch-gear with a 225 Amp main breaker able to supply both a 75 KVA transformer feeding a 225 Amp 120/208V panel, AND a 150 KVA transformer feeding a 400 Amp 120/208V panel, or is this a Code Violation? :-?

 

[Pierre C Belarge]

Depending on the actual loads to the transformers, maybe...not a good design though.

 

[charlie b]

You would be supplying a total of 225 KVA (75 + 150) from a gear that is limited to 187 KVA. As Pierre said, it's not a code violation (depending on the connected load), but it's not a good design either.

 

[mull982]

Adding your two transformers gives you a load of 225kVA. Full load current at this kVA load is about 271A which is higher than your feeder breaker.

225kVA / .48kV / 1.73 = 270.95A

Depending on the load factor on your transformers you might be able to get away with the breaker however it is a poor design as others have mentioned.

 

[Justin P. Le Blanc]

Thank you for your help.

 

[Mike01]

Xfmr. Inrush

Xfmr. Inrush

Another factor to remember is the inrush of the transformers, typically the xfmr inrush is 6-8 times the FLA for the initial inrush when you go from a de-energized to an energized state to saturate the core of the xfmrs. This might pose a problem that when both xfmrs are energized at the same time it might cause the ocpd of 225A to trip and you would never be able to energize the xfmrs. I agree if the loads are correct than it will work, however does seem like a poor design decision. I am curious to hear others opinions. Unless you can find a way to stagger the energizing of the xrfmrs. (what is the distance from the breaker to each transformer?)