collector

Electric current collectors are used by trolleybuses, trams, electric locomotives or EMUs to carry electrical power from overhead lines or electrical third rails to the electrical equipment of the vehicles. Those for overhead wires are roof-mounted devices, those for third rails are mounted on the bogies.
Typically, they have one or more spring-loaded arms that permit the working engagement with the rail or overhead wire and a collector or contact shoe in running engagement with the wire or rail. The collector arm pushes the contact shoe against the contact wire or rail. As the vehicle moves, the contact shoe slides along the wire or rail to draw the electricity needed to run the vehicle's motor.
The current collector arms are electrically conductive but mounted insulated on the vehicle's roof, side or base. An insulated cable connects the collector with the switch, transformer or motor. The steel rails of the tracks act as the electrical return.
Electric vehicles that collect their current from an overhead line system use different forms of one- or two-arm pantograph collectors, bow collectors or trolley poles. The current collection device presses against the underside of the lowest wire of an overhead line system, which is called a contact wire.
Most overhead supply systems are either DC or single phase AC, using a single wire with return through the grounded running rails. Three phase AC systems use a pair of overhead wires, and paired trolley poles.

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