480, you need to think what is going on with the MAGNETIC part of the transformer action, and how the energy is pushed back and forth between Magnetic and Electrical energy, Simple Harmonic 'Motion'.
E max, M minimum....The ends of the winding are 180 degrees out of Phase ALWAYS on one phase transformer, thus the Voltage is maxxed out, the electrons travel twice as far(double Voltage as half leg voltage)
Finally, count the winding count across the 240 tap vs. each leg in ratio to the High Voltage side of the transformer
Say 7200Volt supply to 120, = 60/1 7200/240 = 30/1 or 60 windings highside vs 2 on low with 3 leads, one tap in center for neutral, the other two at each end.
The transformer is a electro-magnetic gearbox or coupling ....
Nicolai Tesla was one smart cookie.....