How does 277 volt work?
The voltage of 277 volts is the wye of a three phase 480 volt system. Just as the voltage of 347 is the wye voltage of a three phase 600 volt system. To obtain these voltages for any three phase system, take the three phase voltage and divide it by 1.73. 480/1.73 = 277 volts, 600/1.73 = 347 volts.