How do you explain the difference in 440V 460V and 480V?

In the United States, 480 Volts (AC) is a nominal system voltage before it is distributed to the device being powered. Line losses (measured in volts) occur throughout the distribution system due to current passing through wires and devices which have a resistance. Manufacturers of end use devices, such as motors, take this into account and list their devices as 460 volt devices.

So, what this means is that you will see transformers and circuit breakers with nameplates at 480 Volts (AC), and motor nameplates at 460 Volts (AC).

Older 3-phase motors may actually have nameplates for 440 Volts, but all new motors in this voltage range would be listed as 460 Volt motors.