Electric arc monitoring is effected by exploiting the discovery that electric arcs are fractal phenomena with all essential information that signifies "arc" contained in each fractal subset. These fractal subsets are logarithmically distributed over the arc spectrum. Monitoring of arcs is most advantageously effected on a fractal subset of low logarithmic order where the amplitude is higher pursuant to the 1/f characteristic of electric arcs (22), where cross-induction among neighboring circuits is lower, and where travel between the arc and the arc signature pickup (23) is longer than at the high frequencies customary for arc detection. Fractal subset transformation reduces the danger of false alarms. Arc signature portions may be processed in out of phase paths or treated as modulated carriers.