I am working with some project. For example,
1) 600V / 3PH panel. Feeding 150 KVA Xformr. 600V - 120/208. Primary current = 144.3 amps.....x 1.25 = 180 amps. Basing it on 75 degree column, so use 3/0 copper.
Secondary current 416.4 x 1.25 = 520 amps...so ( 2 ) parallel runs of 300 MCM copper.
2) 600V/ 3PH panel, Feeding 15 KVA Xformr. 600V - 120/208. Primary current = 14.3 amps.....x 1.25 = 18 amps. Basing it on 75 degree column, so use 12 copper.
Secondary current 41.5 x 1.25 = 52 amps...so #6 copper.
We have potential problem. For number 1) It was decided to use 250 amp breaker to feed Xfrmr, as inrush current might trip breaker. Would it be acceptable to use 250A breaker. If so, how can make out the sizing of secondary cable again? Would you explain the steps how to calculate this case?
1) 600V / 3PH panel. Feeding 150 KVA Xformr. 600V - 120/208. Primary current = 144.3 amps.....x 1.25 = 180 amps. Basing it on 75 degree column, so use 3/0 copper.
Secondary current 416.4 x 1.25 = 520 amps...so ( 2 ) parallel runs of 300 MCM copper.
2) 600V/ 3PH panel, Feeding 15 KVA Xformr. 600V - 120/208. Primary current = 14.3 amps.....x 1.25 = 18 amps. Basing it on 75 degree column, so use 12 copper.
Secondary current 41.5 x 1.25 = 52 amps...so #6 copper.
We have potential problem. For number 1) It was decided to use 250 amp breaker to feed Xfrmr, as inrush current might trip breaker. Would it be acceptable to use 250A breaker. If so, how can make out the sizing of secondary cable again? Would you explain the steps how to calculate this case?
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