a central processing unit (CPU);

a sensor circuit connected to the CPU and configured to sense a current or a voltage waveform in the circuit interrupt protective device, the current or voltage waveform originating from an AC mains;

an analog-to-digital converter (ADC) coupled to the CPU and configured to acquire the current or voltage waveform sensed by the sensor circuit;

a fault detection module coupled to the ADC and configured to receive the current or voltage waveform acquired by the ADC, the fault detection module operable to detect a fault event based on the current or voltage waveform; and

a fault duration module coupled to the ADC and configured to receive the current or voltage waveform acquired by the ADC, the fault duration module operable to obtain a duration of the fault event based on the current or voltage waveform;

wherein the duration of the fault event is obtained by computing a second derivative for a portion of the current or voltage waveform, finding a local maximum or local minimum for the portion of the current or voltage waveform, and setting the local maximum or the local minimum as a starting time or an ending time for the duration of the fault event.