a method for detecting high impedance faults , including : receiving an input waveform from a circuit ; computing a root mean square of the input waveform ; fitting a regression line to the root mean squares ; computing a deviation between the regression line and the root mean squares ; determining whether the deviations are above a threshold ; and outputting a value indicating that a fault has occurred in the circuit when the deviation is above the threshold and outputting a value indicating that a fault did not occur in the circuit when the deviation is below the threshold .