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This document describes how transformer inrush current can cause nuisance tripping of standard trip circuit breakers during start up or application of power. Recommendations for selecting a high inrush compensated circuit breaker are provided. Protective devices like circuit breakers and fuses are essential, especially for transformers operating over 1,000V, to ensure safe operation and compliance with code requirements. A transformer can generate an almost infinite current. Our telecom client has an inverter with an internal 40kVA, 480V delta to 120/208V wye transformer supplying a bypass circuit for the inverter. The only time the transformer has a load on it is when the inverter is in bypass. Normally DC power is converted to AC power to feed the critical loads. From transformer secondary currents with lower loads that survive without a breaker trip, I see an open time of about 30ms. Feeding a 45kVA dry, three-phase transformer 480V to 160V AC, 55FLA, for generator. When a transformer is energized, it draws a large current for a few cycles to establish the eletromagnetic field. Inrush can vary depending on where the sine wave is during initial energization and how. The 13 loads on the first circuit breaker panel would reach a total of 70kVA/102A, the 12 loads on the second circuit breaker panel bring it to 41kVA/96A. Yes, both of your options would be.
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