Voltage monitor that protects 190-400VAC, 50/60Hz motors that provides a user selectable nominal voltage setpoint and the voltage monitor automatically selects between the 200V and 400V range. A unique microcontroller-based voltage and phase-sensing circuit constantly monitors the 3-phase voltages to detect harmful power line conditions. When a harmful condition is detected, the output relay is deactivated after a specified trip delay. The output relay reactivates after power line conditions return to acceptable levels. The Model 102 includes advanced single LED diagnostics. Five different light patterns distinguish between faults and normal conditions.