The 201A three phase voltage monitor is an autoranging plug-in voltage monitor designed to protect three phase motors regardless of size. It is used on a 190-480 volt AC 50/60 Hz three phase motor to prevent damage caused by single phasing, low voltage, phase reversal, or voltage unbalance. To detect harmful power line conditions in building automation systems, BAS, the unique microprocessor-based voltage and phase sensing circuit constantly monitors the three phase voltages. When a harmful condition is detected in a three phase motor, the output relay is deactivated after a fixed trip-delay time period. The output relay reactivates after three phase power conditions return to an acceptable level for a fixed restart delay time. The trip delay prevents nuisance tripping due to rapidly fluctuating power line conditions.

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