Abstract: A method and apparatus for detecting high impedance faults and other arcing phenomena in an electrical distribution system. Electrical signals on the distribution system are monitored and a number of frequency components isolated, such as zero-sequence current and voltage, second harmonic voltage, third harmonic current, eighth harmonic voltage and current, and a measure of magnitude of the components are taken over successive data acquisition periods. The measures of the component magnitudes are formed into a pattern for each data acquisition period, and the difference between patterns for successive periods are compared against a pattern threshold which is set to suit the characteristics of the distribution system. A pattern difference greater than the pattern threshold indicates the possibility of an arcing fault, which can then be confirmed by determining whether the frequency components are modulated at twice the fundamental frequency of the distribution system.