480V 3-Phase Line Voltage Monitor Schematic

The above schematic is the beginning of a 480V 3-phase line voltage interface design for a transmitter site remote control system. This interface will output a voltage proportional to the three phases of the commercial electrical power feeding the site. If a phase is missing the sample voltage will drop by 1/3. If two phases are missing the sample voltage will drop by 2/3 and if all phases are missing the output would be zero.