The present invention provides a system and a method for detecting current overload and leakage in a transport refrigeration unit. The method comprises the steps of: measuring, by a microcontroller ofan active fault detection circuit, a line current for each of one or more phases supplying power to a load of a refrigerant vapor compression system of the transport refrigeration unit; measuring, bythe microcontroller, a voltage received by the active fault detection circuit from a battery of the transport refrigeration unit and transmitted via a conductor of the active fault detection circuitto a microprocessor of the refrigerant vapor compression system; controlling, by the microcontroller, a switch along the conductor of the active fault detection circuit to control transmission of thevoltage, via the conductor to the microprocessor, controlling the switch comprises (i) closing the switch upon a determination that the voltage level is greater than or equal to an operational threshold voltage level, (ii) closing the switch upon a determination that the voltage level is less than the operational threshold voltage level, and (iii) opening the switch upon a determination that any of the one or more line currents exceeds a threshold. Other embodiments are described herein.