Pantograph (rail)
A pantograph (or "pan") is an apparatus mounted on the roof of an electric train or tram to collect power through contact with an overhead catenary wire. Typically a single wire is used, with the return current running through the track. The term stems from the resemblance of some styles to the mechanical pantographs used for copying handwriting and drawings.
Read more about Pantograph (rail): Invention, Modern Use, Technical Details, Single- and Double-arm Pantographs, Metro Systems and Overhead Lines