a protective relay for detecting power arcing faults on a low - voltage spot network . the protective relay can monitor the voltage difference between each phase conductor , the voltage difference between each phase conductor and the neutral conductor , or the current on each phase conductor . using one of these three sets of values , the protective relay first filters the input signal so that only frequencies indicative of a power arcing fault on the low - voltage spot network are analyzed . the signals passed by the filter are amplified , rectified , and averaged and the peak of each signal detected . if the peak has a duration longer than a predetermined value , a fault indication is provided .