how to calculate fuse size for 3 phase transformer?

To calculate the fuse size for a three-phase transformer, first determine the transformer’s full-load current using the formula: ( I = frac{P}{sqrt{3} times V times text{PF}} ), where ( P ) is the power rating in watts, ( V ) is the line voltage, and PF is the power factor. Then, select a fuse rating that is typically 125% to 150% of the full-load current to account for inrush and overload conditions, ensuring proper protection without nuisance blowing.