This paper presents a new numerical spectral domain algorithm devoted to blocking unsuccessful automatic reclosing onto permanent faults and fault distance calculation. Arc voltage amplitude and fault distance are calculated from the fundamental and third harmonics of the terminal voltages and currents phasors. The electric arc is modeled with its voltage waveshape defined numerically on the basis of a number of arc voltage records obtained in the high-voltage laboratory. From the calculated arc voltage amplitude, it can be concluded whether the fault is a transient arcing fault or a permanent arcless fault. If the fault is permanent, automatic reclosure should be blocked. The algorithm can be applied for adaptive autoreclosure, distance protection, and fault location. The results of algorithm testing through computer simulation and real field record are given.