Patent ID: 7164273

Claim:
A method to monitor various operating line conditions of a three phase electrical power source comprising measuring and displaying line conditions and generating an indicator to indicate a fault condition when any of the line conditions are not within a corresponding predetermined range, said fault conditions include a voltage fault comprising of a low voltage fault when the line voltage is less than a first predetermined low voltage and a high voltage fault when the line voltage is greater than a first high predetermined voltage defining a first voltage fault range and a frequency fault comprising a low frequency fault when the line frequency is less than a predetermined low frequency and a high frequency fault when the line frequency is greater than a predetermined frequency defining a first frequency fault range, said voltage fault further comprises a second predetermined low voltage greater than said first predetermined low voltage and a second predetermined high voltage less than said first predetermined high voltage defining a second voltage fault range such that said indicator is re-enabled when the measured line voltage is within said second voltage fault range, said fault conditions further include a ground fault comprising an open ground fault, and a polarity fault comprising a reverse polarity fault, said fault condition indicates an open ground fault when the measured ground signal is within a first predetermined range relative to the line voltage and a reverse polarity fault when the measured ground signal is greater than a second predetermined range relative to the line voltage wherein the power line and neutral line are electrically coupled by a first pair of power level shifting resistors, and the neutral line and ground line are electrically coupled by a second pair of power level shifting resistors, and the power line and ground line are electrically coupled by a resistor providing a pull up function where an open ground condition exists.