A conductor rail, also known as a third rail or power rail, is a system used to supply electrical power to trains, typically found in metro or rapid transit systems. Unlike an overhead line, which uses wires suspended above the track, a conductor rail is a rigid, semi-continuous conductor placed alongside or between the running rails. It is generally used for lower-voltage DC power transmission (up to 1500 V) and is a cost-effective solution for systems where clearances for overhead equipment are limited, such as in tunnels.