What size fuse is used for a 25 KVA transformer on a 7200 volt wye primary system?

To determine the appropriate fuse size for a 25 KVA transformer on a 7200-volt wye primary system, it's important to follow the National Electrical Code guidelines for transformer protection. The general rule for fusing a transformer is to use a fuse rating based on the transformer's KVA rating while considering the primary voltage.

For a 25 KVA transformer operating on a 7200-volt wye system, the calculation for the fuse size involves both the conversion of KVA to Amperes and a safety margin. The formula to find the full-load current in Amperes is:

Full-Load Current (I) = (KVA × 1000) / (Voltage × √3)

Using this, for a 7200-volt system, the full-load current would be:

I = (25 × 1000) / (7200 × √3) ≈ 2.01 A

Next, according to code, fuses should be sized typically at a factor of 125% of the full-load current to allow for inrush and to avoid nuisance blowing while still providing adequate protection.

Calculating 125% of the full-load current:

I_fuse = 2.01 A ×