Adaptive undervoltage protection for three-phase load using single current sensor

A contactor comprising:

• a processor;
• first, second, and third relays including respective first, second, and third relay contacts and configured to be operable by the processor to electrically connect or disconnect a load to or from a voltage input;
• and
• a current sensor electrically connected with a corresponding one of the first, second, and third relays, the current sensor is in communication with the processor for providing the processor with information about current from the corresponding one of the first, second, and third relays to the load;
• wherein the processor is configured to determine a failure condition when:
• after the first, second, and third relays are energized, the information from the current sensor indicates that there is no current across the corresponding one of the first, second, and third relays thereby indicating that the corresponding one of the first, second, and third relays is open and the load is running on two phases;
• or
• after the first, second, and third relays are energized, the information from the current sensor indicates that the current across the corresponding one of the first, second, and third relays is at lock rotor current for more than a determined amount of time indicating that the load is running on two phases.