How to size a 480 to 240/120V Transformer | Mike Holt's Forum -120/240V Single phase 60 amp power panel. 4 wire. Transformer will be mounted 1000ft from MCC 480V power source and about 20ft from 240/120 panel. This is Nonhazardous area installation. Questions: 1. Can you please tell me where in the NEC I can read on how to size the transformer? Or steps please? 2. How to Wire a Multi-tap Transformer - Functional Devices, Inc. It doesn’t matter which phase goes to which wire. For the above wye configuration, you would connect your neutral (GRAY) and any phase to the black and brown wires on the transformer for a 277 Vac primary. Similarly, any two phases on the wye configuration should be connected to the gray and black wires on the transformer for a 480 Vac primary. Step Down Transformer 480v To 120v Wiring Diagram Phase Wiring Diagram In Addition v Step Down Transformer Wiring. v Transformer Wiring Diagram Coachedby Me and – Volovetsfo. Connect a jumper between the X2 and X3 terminals. Step Down Transformer 480v to 120v Wiring Diagram Sample. This will serve as the neutral, and can be bonded to ground, if permitted or required by local code. 480 To 120/240 Transformer Wiring - schematron 480 To 120/240 Transformer Wiring 06 06 2 Comments on 480 To 120/240 Transformer Wiring a volt primary transformer with a volt secondary is operated at volts, regardless of whether the source is three phase 3-wire or three phase 4-wire. .