Editing Overhead line (section)

==Overhead catenary==
[[File:Two images showing catenary and trolley wire systems.jpg|thumb|left|Catenary (upper photo) is suited to higher-speed rail vehicles. Trolley wire (lower photo) is suited to slower-speed trams (streetcars) and light rail vehicles.]]

[[File:Overhead rail P1220601.jpg|thumb|right|Overhead feeding rail on the [[Réseau Express Régional|RER]] [[RER C|Line C]] trenches and tunnels in central Paris]]

[[File:Overhead lines JR West 001.JPG|thumb|right|Compound catenary equipment of [[West Japan Railway Company|JR West]]]]

[[File:60163 Tornado 7 March 2009 Berwick.jpg|thumb|right|An older rail bridge in [[Berwick-upon-Tweed]], retrofitted to include overhead catenary lines]]

A catenary is a system of overhead [[wire]]s used to supply [[electricity]] to a [[locomotive]], [[tram]] ([[streetcar]]), or [[light rail]] vehicle that is equipped with a [[pantograph (rail)|pantograph]].

[[File:Overhead catenary bridge.jpg|thumb|Gantry with old and new suspended equipment at [[Grivita railway station]]<!-- Not to be confused with the [[Grivita metro station]] -->, [[Bucharest]]]]

Unlike simple overhead wires, in which the uninsulated wire is attached by clamps to closely spaced crosswires supported by poles, catenary systems use at least two wires. The catenary or messenger wire is hung at a specific tension between line structures, and a second wire is held in [[tension (mechanics)|tension]] by the messenger wire, attached to it at frequent intervals by [[Clamp (tool)|clamp]]s and connecting wires known as ''droppers''. The second wire is straight and level, parallel to the [[rail track]], suspended over it as the roadway of a [[suspension bridge]] is over water.

Catenary systems are suited to high-speed operations whereas simple wire systems, which are less expensive to build and maintain, are common on light rail or tram (streetcar) lines, especially on city streets. Such vehicles can be fitted with either a pantograph or [[trolley pole]].

=== Electrification support structures ===
Overhead line equipment may be supported above the running lines by a range of different methods. Support structures are often designed to allow mechanically independent registration (MIR) which refers to a setup where each contact and catenary wire for each track is mechanically independent from the adjacent wire runs. Support structures are required to provide ''support'' and ''registration'' to the OLE wires. In OLE terminology, ''support'' refers to vertical position of catenary wire (and of the contact wire via the catenary wire), while ''registration'' refers to the horizontal position of both catenary and contact wires. The metal parts the provide OLE registration are typically designed to adjust in the vertical plane as the pantograph moves under it. The generic types of support structures are summarised below.<ref>{{Cite book |last=Keenor |first=Garry |url=https://ocs4rail.com |title=Overhead Line Electrification for Railways |year=2021 |edition=6th |pages=136–147 |format=pdf e-book, occasionally updated}}</ref>

[[File:Nanded - Hyderabad Passenger Cavalry Barracks.jpg|thumb|145px|right|Gantry structures to support overhead lines in [[Hyderabad]], India]]
* Single Cantilever
** The most basic and common type of OLE structure that supports and registers one wire run above one track.
* Double Cantilever
** Similar to the previous but with two cantilever arms adjacent to each other on one mast. Often used where two wire runs converge.
* Back to Back Cantilever
** Two wire runs over two tracks supported and registered by one mast placed in the centre of the tracks with cantilever arms attached to opposite sides. Frequently used on tram and light rail systems but can appear on heavy rail lines.
* Two Track Cantilever (TTC)
** Two wire runs over two tracks supported by one mast with a boom structure extending over to the second track. TTCs typically provide mechanically independent registration, but subtypes exists called the "span-wire two track cantilever" which has both registration arms mechanically linked. TTCs are often used  where there are poor ground conditions or obstructions on one side of a two track railway. They are also sometimes used to minimised piling since only one track must be taken out of service for this phase of construction.
* Portals
** Also known generically as "gantries", portals are large structures with masts on either side and a fixed steel beam between them. They are frequently used on sections of railway line with more than two tracks. Portals typically provide mechanically independent registration, however variants exist with registration span-wires that mechanically link adjacent wire runs. Portals are sometimes used on two track railways over bridges and viaducts or where ground conditions are poor. This is because portals inflict fewer rotational forces on their foundations.
* Headspans
** An alternative method to supporting multi-track areas, headspans consist of a mast at either side of the railway and various cables running horizontally between the two masts (called span wires) to support and register all wire runs at tension. Because the tension of all wire runs and span wires are required simultaneously to hold up the OLE wires, headspans by definition do not provide mechanically independent registration and a failure of one OLE or span wire will bring all wire runs out of geometric limits. Headspans are cheaper and less obtrusive than portals and so are well suited to low speed complex multitrack areas like stations, station approaches, depots and sidings, and areas where visual intrusion is an important consideration. They are also capable of supporting tracks with speeds up to 200km/h (125mph) but provide significant reliability disadvantages over portals or TTCs for this application.
Tunnels, low overbridges and other location specific features (retaining walls, adjacent rockfaces etc) frequently require bespoke OLE structures that may incorporate some features of the generic types above.

===Overhead catenary systems in the United States===
The [[Northeast Corridor]] in the [[United States]] has catenary over the {{convert|600|mi}} between [[Boston]], [[Massachusetts]] and [[Washington, D.C.]], for [[Amtrak]]'s [[inter-city rail|inter-city]] trains. [[Commuter rail]] agencies including [[MARC Train|MARC]], [[SEPTA]], [[NJ Transit Rail Operations|NJ Transit]], and [[Metro-North Railroad]] utilize the catenary to provide local service.

In [[Cleveland, Ohio]], the [[RTA Rapid Transit|interurban/light rail]] lines and the [[Red Line (Cleveland)|heavy rail]] line use the same overhead wires, due to a city ordinance intended to limit air pollution from the large number of steam trains that passed through Cleveland between the east coast and Chicago. Trains switched from steam to electric locomotives at the Collinwood railyards about {{Convert|10|mi|km}} east of Downtown and at [[Linndale]] on the west side. When Cleveland constructed its rapid transit (heavy rail) line between the airport, downtown, and beyond, it employed a similar catenary, using electrification equipment left over after railroads switched from steam to diesel. Light and heavy rail share trackage for about {{Convert|3|mi|km}} along the [[Cleveland Hopkins International Airport]] [[Red Line (Cleveland)|Red (heavy rail) line]], [[RTA Rapid Transit#Blue, Green, and Waterfront Lines|Blue and Green interurban/light rail lines]] between [[Cleveland Union Terminal]] and just past East 55th Street station, where the lines separate.

Part of [[Boston]]'s [[Blue Line (MBTA)|Blue Line]] through the northeast suburbs uses overhead lines, as does the Green Line.

The [[Yellow Line (CTA)|Yellow Line]] on the [[Chicago "L"]] used an overhead catenary system for the west half of the route, transitioning to third rail for the east half. This was discontinued in 2004 when the entire route was converted to third rail.

On the [[San Francisco peninsula]] in [[California]], the [[Caltrain]] [[commuter rail]] system completed the installation of an overhead contact system (OCS) in 2023, to prepare for the conversion of its 160-year old [[San Francisco]] to [[San Jose, California|San José]] Peninsula Corridor to fully-electrified revenue service in September 2024.

=== Height ===
The height of the overhead line can create hazards at [[level crossing]]s, where it may be struck by road vehicles. Warning signs are placed on the approaches, advising drivers of the maximum safe height.

The wiring in most countries is too low to allow [[Double-stack rail transport|double stack container]] trains. The [[Channel Tunnel]] has an extended height overhead line to accommodate double-height car and truck transporters. [[China]] and [[Rail transport in India|India]] operate lines electrified with extra height wiring and pantographs to allow for double stack container trains.<ref name="spotlight">{{cite web|last=Das|first=Mamuni|date=October 15, 2007|title=Spotlight on double-stack container movement|url=http://www.thehindubusinessline.com/2007/10/15/stories/2007101551550600.htm|access-date=February 25, 2009|publisher=The Hindu Business Line}}</ref><ref>{{Cite web|title=非人狂想屋 {{!}} 你的火车发源地 » HXD1B牵引双层集装箱列车|url=http://www.trainnets.com/archives/34518|access-date=2020-07-01|language=zh-CN}}</ref><ref>{{Cite web|title=Aerodynamic Effects Caused by Trains Entering Tunnels|url=https://www.researchgate.net/publication/245307012|access-date=2020-07-01|website=ResearchGate|language=en}}</ref>