A microcontroller-based system for detecting ground-fault and grounded-neutral conditions in an electrical power distribution system having line and neutral conductors comprising: a sensor circuit containing a single current transformer producing an output signal responsive to current flow in both the line and neutral conductors of the electrical power distribution system, said current transformer having an inductance that varies with temperature, characterised in that the system further comprises: an ambient temperature sensing circuit placed proximate to said current transformer, able to produce a voltage which varies linearly with ambient temperature conditions, a programmable microcontroller having a pre-determined ground-fault threshold value and a pre-determined grounded-neutral threshold value stored in a non-volatile memory, said microcontroller being programmed to calculate a modified ground-fault threshold value based on said predetermined ground-fault threshold value and the output of said ambient temperature sensing circuit, calculate a modified grounded-neutral threshold value based on said predetermined grounded-neutral threshold value and the output of said ambient temperature sensing circuit, use said modified ground-fault threshold value to detect a ground-fault condition, use said modified grounded-neutral threshold value to detect a grounded-neutral condition, and initiate the generation of a trip signal (Trip) upon detection of said ground-fault or said grounded-neutral condition in said power distribution system, and a circuit interrupter for interrupting current flow in said power distribution system in response to said trip signal. a sensor circuit containing a single current transformer producing an output signal responsive to current flow in both the line and neutral conductors of the electrical power distribution system, said current transformer having an inductance that varies with temperature, characterised in that the system further comprises: an ambient temperature sensing circuit placed proximate to said current transformer, able to produce a voltage which varies linearly with ambient temperature conditions, a programmable microcontroller having a pre-determined ground-fault threshold value and a pre-determined grounded-neutral threshold value stored in a non-volatile memory, said microcontroller being programmed to calculate a modified ground-fault threshold value based on said predetermined ground-fault threshold value and the output of said ambient temperature sensing circuit, calculate a modified grounded-neutral threshold value based on said predetermined grounded-neutral threshold value and the output of said ambient temperature sensing circuit, use said modified ground-fault threshold value to detect a ground-fault condition, use said modified grounded-neutral threshold value to detect a grounded-neutral condition, and initiate the generation of a trip signal (Trip) upon detection of said ground-fault or said grounded-neutral condition in said power distribution system, and a circuit interrupter for interrupting current flow in said power distribution system in response to said trip signal. an ambient temperature sensing circuit placed proximate to said current transformer, able to produce a voltage which varies linearly with ambient temperature conditions, a programmable microcontroller having a pre-determined ground-fault threshold value and a pre-determined grounded-neutral threshold value stored in a non-volatile memory, said microcontroller being programmed to calculate a modified ground-fault threshold value based on said predetermined ground-fault threshold value and the output of said ambient temperature sensing circuit, calculate a modified grounded-neutral threshold value based on said predetermined grounded-neutral threshold value and the output of said ambient temperature sensing circuit, use said modified ground-fault threshold value to detect a ground-fault condition, use said modified grounded-neutral threshold value to detect a grounded-neutral condition, and initiate the generation of a trip signal (Trip) upon detection of said ground-fault or said grounded-neutral condition in said power distribution system, and a circuit interrupter for interrupting current flow in said power distribution system in response to said trip signal.