How do I determine the correct overcurrent protection for a 600 Volt class transformer?
A. A transformer has all the same component parts as a motor, and like a motor, exhibits an inrush when energized. This inrush current is dependent upon where in the sine wave the transformer was last turned off in relation to the point of the sine wave you are when you energize the transformer. Although transformer inrush could run up to 35 times full load current under no load, it typically is the same as a motor…about 6 to 8 times normal running current. For this reason it is important to use a dual element slow blow type fuse – the same type of fuse you would use with a motor. If using a circuit breaker, select a breaker with a time delay – again the same type you would use with a motor. If the time delay is not sufficient, you may experience “nuisance tripping” – a condition where the breaker trips when energizing the transformer but when you try it again, it works fine. Secondary overcurrent protection Overcurrent devices are used between the output terminals of the transformer
