Voltage drop per se is not an issue. The major factor is the that the total load on the regulator, both lamps and cable losses, not exceed the rating of the regulator. Basically what would be a voltage drop in a conventional parallel circuit turns into an increase in the voltage which the...
This transformation can be done with an open delta connection using two transformers, each rated 240x480 to 120/240, and connected as autotransformers.
For each transformer, connect the 240x480 winding for 480 volts, H2 to H3. Connect the 120/240 volt winding for 120 volts, X1 to X3 and X2 to...
