A Pantograph is the name commonly given to the arms that collect current from overhead lines on electric trains or trams. The term originates in the similar appearance they share with the earlier devices for copying writing and drawings, both being constructed of hinged interlocking arms. They set up standing waves in the wires which can degrade current collection. This means that on some systems adjacent pantographs are not permitted. They are the successor technology to trolley poles, which were widely used on early streetcar systems and still are used by trolleybuses and some heritage streetcar systems.
List of metro systems using pantographs
Some metro systems uses pantographs instead of a third rail.