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When a high-impedance fault (HIF) occurs in any zone of a distribution system, it is very difficult to detect the fault because the fault current is very small and the time of its occurrence cannot be ascertained. This paper proposes a self-isolation method for an HIF zone in which the feeder remote terminal unit (FRTU) experiencing nil-voltage can identify and isolate autonomously an HIF zone by exchanging voltage and current information with the neighbor FRTUs on the feeder when an HIF occurs under the network-based distribution system. Also, the method was devised to enhance the reliability of HIF identification from the voltage sensor error. Furthermore, new and simple heuristics are proposed, which are required to classify the nil-voltage due to an HIF with nil-voltage caused by general fault outage, scheduled outage, and outage due to the reclosing operation of a protective device (circuit breaker or recloser). Index Terms--Distribution automation system (DAS), distribution system, feeder remote terminal unit (FRTU), high impedance fault (HIF), network-based system, self-identification, self-isolation.