This guide outlines the techniques and application considerations for determining the location of a fault on ac transmission and distribution lines. This document reviews traditional approaches and the primary measurement techniques used in modern devices: one-terminal and two-terminal impedance-based methods and traveling wave methods. Application considerations include: two- and three-terminal lines, series-compensated lines, parallel lines, untransposed lines, underground cables, fault resistance effects, and other power system conditions, including those unique to distribution systems. This guide provides assistance to power system engineers and operators in applying fault location techniques on their systems. They will learn the strengths and limitations of fault location data and when further analysis may be required. The user will also learn when more advanced methods are required or more data must be gathereed. New IEEE Standard - Superseded. Electrical faults on transmission and distribution lines are detected and isolated bysystem protective devices. Once the fault has been cleared, outage times can be reduced if thelocation of the fault can be determined more quickly. This guide outlines the techniques andapplication considerations for determining the location of a fault on ac transmission and distributionlines. The document reviews traditional approaches and the primary measurement techniques usedin modern devices: one-terminal and two-terminal impedance-based methods and traveling wavemethods. Application considerations include: two- and three-terminal lines, series-compensatedlines, parallel lines, untransposed lines, underground cables, fault resistance effects, and otherpower system conditions, including those unique to distribution systems.