Patent ID: 7253996

Claim:
An arc fault circuit interrupter comprising: a line terminal; a load terminal; separable contacts electrically connected between said line terminal and said load terminal; a current sensor adapted to sense current flowing between said line terminal and said load terminal and through said separable contacts, said sensed current including a plurality of line cycles; an arc fault detection circuit adapted to collect a plurality of samples of said sensed current for each of said line cycles, determine a peak current value from said samples of said sensed current for each of said line cycles, determine a difference value for each of said line cycles from the peak current value of a corresponding one of said line cycles less the peak current value of the previous one of said line cycles, change the sign of said difference value on alternate ones of said line cycles, low pass filter the changed sign difference value for each of said line cycles to provide a low pass filtered value for each of said line cycles, determine a peak value from the absolute value of the low pass filtered value for each of said line cycles over a predetermined count of said line cycles, save the peak value as a saved peak value after the predetermined count of said line cycles, determine a hysteresis value as a function of the saved peak value, and generate a trip signal responsive to the sensed current and the hysteresis value; and an operating mechanism adapted to open said separable contacts responsive to said trip signal.