Emergency generators are required to automatically start upon a loss of normal supply voltage, according to 46 CFR, Subchapter J (Electrical Engineering). In conducting a test of the emergency generator automatic transfer of load function, if the normal system supply voltage is 480 VAC, to what value would the normal source output voltage have to rise to trigger the automatic transfer of emergency loads back to the normal power source?

Question

Accepted Answer

Option B: It would have to rise to a value between from 408 VAC to 456 VAC.. 46 CFR 112.50-1 requires emergency generator automatic transfer switches to restore normal power only after voltage stabilizes. For a 480V system, the transfer back to normal occurs when voltage reaches 85% to 95% of nominal, specifically between 408 VAC and 456 VAC, preventing nuisance tripping during transient voltage fluctuations.