When electrical power fails due to a substation tripping after detecting an anomalous load, linemen often had to follow overhead lines from pole to pole, sometimes on foot through difficult terrain, to find the downed line and/or tree that fell on the lines. To expedite the restoration of service, a fault indicator can be installed, either on overhead or underground lines, which provides a visual indication of where the fault occurred, allowing maintenance personnel to localise the fault and reduce the amount of visual inspection required. Often, once the fault is identified as being on a branch of the main line, that branch can be disconnected for repair while power is restored immediately to customers on other branches.
Some fault indicators communicate to the power company by cellular telephone signal or radio, while others simply blink a light indicating the fault is downstream of their location.