I have a client that wants to install a 3 phase 75 KVA transformer back fed for a few receptacles. They currently have a 208 service but need a 50 amp 3pole, 4 wire 480 volt receptacle and a 30 amp 3 pole, 4 wire 480 volt receptacle. They may want future receptacles but that remains to be seen. My questions is how do I size the breaker and wire on the primary and secondary side if it's a step up transformer? I heard there are problems with tripping. Do i need an adjustable trip breaker? Can someone show me the calculation for both?