this transformer can supply 250 amps of 120 volt single phase load - but it needs to be evenly divided in three and equally applied across all three phases - so still limits you to a single 120 volt load of 83.3 maximum.A 3-phase 30kva transformer will supply 83.3amps @ 208Vac, when determining the available amps at 120Vac (say from a 208/120 Loadcenter), the calculation or chart would be based on 1-phase. So the same 30kva transformer will supply 250amps @ 120Vac. Correct?
I typically see a 30KVA transformer used when going from 480V 3-phase to serve a 100A 208 3-phase panel. There is also debate on the primary breaker. When doing the math, the amps is 45.1A and per the NEC, you upsize to the next breaker which is 50A. Some people claim you drop the 0.1 but I cannot locate anything in the NEC saying to round down. As for the primary protection, provided the panel is close, you go from the transformer right to the 100A main breaker. Keep in mind that the main panel breaker does not count as transformer secondary protection so the primary can't exceed the 125% (or next size up breaker).
I typically see a 30KVA transformer used when going from 480V 3-phase to serve a 100A 208 3-phase panel. There is also debate on the primary breaker. When doing the math, the amps is 45.1A and per the NEC, you upsize to the next breaker which is 50A. Some people claim you drop the 0.1 but I cannot locate anything in the NEC saying to round down. As for the primary protection, provided the panel is close, you go from the transformer right to the 100A main breaker. Keep in mind that the main panel breaker does not count as transformer secondary protection so the primary can't exceed the 125% (or next size up breaker).
Rounding of calculation amperes [220.5(B)] is permitted, not required.I typically see a 30KVA transformer used when going from 480V 3-phase to serve a 100A 208 3-phase panel. There is also debate on the primary breaker. When doing the math, the amps is 45.1A and per the NEC, you upsize to the next breaker which is 50A. Some people claim you drop the 0.1 but I cannot locate anything in the NEC saying to round down. As for the primary protection, provided the panel is close, you go from the transformer right to the 100A main breaker. Keep in mind that the main panel breaker does not count as transformer secondary protection so the primary can't exceed the 125% (or next size up breaker).
Yes.A 3-phase 30kva transformer will supply 83.3amps @ 208Vac
No.when determining the available amps at 120Vac (say from a 208/120 Loadcenter), the calculation or chart would be based on 1-phase. So the same 30kva transformer will supply 250amps @ 120Vac. Correct?