- Faults on distribution circuits are normally detected by simple overcurrent relays. Faults through a high impedance such as dry earth or asphalt do not have sufficient current to operate overcurrent relays and must be cleared manually. Such high impedance faults may pose a hazard to the public. Equipment is now commercially available to detect a high percentage of high impedance faults, but use of this equipment introduces operational issues which affect applications. This paper discusses technical as well as non-technical issues associated with applying high impedance fault detectors. Recognizing all the issues is important to the effective implementation of these new fault detecting techniques. 1995 IEEE.