in one possible implementation , a method is provided for determining contactor health including measuring a differential voltage between a first utility line voltage and a second utility line voltage on a primary side of a contactor and on a secondary side of the contactor . the measuring is performed with both an unloaded current and with a load current . the unloaded and loaded measurements are performed at the primary side and the secondary side , and are made with the contactor closed . it includes determining a difference between a secondary unloaded voltage and a secondary loaded voltage and subtracting a difference between a primary unloaded voltage and a primary loaded voltage to provide a contactor voltage drop . the contactor resistance is determined by dividing the contactor voltage drop by the loaded current .