page_title: Overhead line
section_title: Crossings
hierarchical_section_title: Overhead line / Crossings
context_page_description: An overhead line or overhead wire is used to transmit electrical energy to electric trains, trolleybuses or trams. It is known variously as:
  Overhead catenary
  Overhead contact system
  Overhead equipment
  Overhead line equipment
  Overhead lines
  Overhead wiring
  Traction wire
  Trolley wire
  In this article, the generic term overhead line is used, as used by the International Union of Railways.
  An overhead line consists of one or more wires situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid.
context_section_description: Trams draw their power from a single overhead wire at about 500 to 750 V. Trolleybuses draw from two overhead wires at a similar voltage, and at least one of the trolleybus wires must be insulated from tram wires. This is usually done by the trolleybus wires running continuously through the crossing, with the tram conductors a few centimetres lower. Close to the junction on each side, the tram wire turns into a solid bar running parallel to the trolleybus wires for about half a metre. Another bar similarly angled at its ends is hung between the trolleybus wires, electrically connected above to the tram wire. The tram's pantograph bridges the gap between the different conductors, providing it with a continuous pickup.
  Where the tram wire crosses, the trolleybus wires are protected by an inverted trough of insulating material extending 20 or 30 mm (0.79 or 1.18 in) below.
  Until 1946, a level crossing in Stockholm, Sweden connected the railway south of Stockholm Central Station and a tramway. The tramway operated on 600-700 V DC and the railway on 15 kV AC. In the Swiss village of Oberentfelden, the WSB tramway operating at 750 V DC crosses the SBB line at 15 kV AC; there used to be a similar crossing between the WSB and the SBB at Suhr, this has been replaced by an underpass in 2010. Some crossings between tramway/light rail and railways are extant in Germany. In Zürich, Switzerland, VBZ trolleybus line 32 has a level crossing with the 1,200 V DC Uetliberg railway line; at many places, trolleybus lines cross the tramway. In some cities, trolleybuses and trams shared a positive (feed) wire. In such cases, a normal trolleybus frog can be used.
  Alternatively, section breaks can be sited at the crossing point, so that the crossing is electrically dead.
caption: Annotated version of the at left photo, highlighting components   tram conductor   trolley bus wires   insulated trough
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