What size disco would be required that is being fed from a step down 75kva transformer. The scenario is a 480a bus duct switch(size unknown) is feeding the 75kva transformer which feeds the disconnect switch which feeds a panel(size unknown).
Without secondary voltage known you can't figure what secondary current will be or actual load, you also don't state if this transformer is single or 3-phase? other things can be figured in but for the most part I just use KVA/volts/1.732 if 3-phase the 480 side will be 90.2 amps 3-phase, and 156.25 amps single phase, secondary will be 208.1 amps for a 208/120 volt secondary, and if a 240/120 single phase 312.5 amps.
These are max amperages without figuring in the 125% requirements but it should give you a start.
