# Dual electrification

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This photo shows an overhead catenary power line above the foreground train, and a third rail on the ground beside it.

**Dual electrification** is a system whereby a [railway](/source/Railway) line is supplied power both via [overhead catenary](/source/Overhead_catenary) and a [third rail](/source/Third_rail). This is done to enable trains that use either system of power to share the same railway line, for example in the case of mainline and suburban trains (as used at [Hamburg](/source/Hamburg) [S-Bahn](/source/S-Bahn) between 1940 and 1955).[1]

## Examples

### Germany

- Line S3 of the [Hamburg S-Bahn](/source/Hamburg_S-Bahn) changeover at [Neugraben](/source/Neugraben_railway_station).

- [Birkenwerder station](/source/Birkenwerder_station) to be used by [Berlin S-Bahn](/source/Berlin_S-Bahn) lines S1 and S8 (third rail) and regional train RB20 (overhead lines)

### Greece

- [Line 3](/source/Line_3_(Athens_Metro)) of [Athens Metro](/source/Athens_Metro) uses third rail for the underground sections and an overhead power supply on the surface for access to and from the [Airport](/source/Athens_International_Airport).

### Norway

- between [Jar station](/source/Jar_station) and [Bekkestua station](/source/Bekkestua_station), where [metro line 3](/source/Kols%C3%A5s_Line) and [tram line 13](/source/Lilleaker_Line) share tracks

### United Kingdom

- [North London Line](/source/North_London_Line) changeover at [Acton Central](/source/Acton_Central_railway_station), London.

- [Northern City Line](/source/Northern_City_Line) changeover at [Drayton Park](/source/Drayton_Park_railway_station), London.

- [Thameslink route](/source/Thameslink_(route)) changeover at [City Thameslink](/source/City_Thameslink_station) (northbound) and [Farringdon](/source/Farringdon_station) (southbound), London.

- [West London line](/source/West_London_line) changeover between [Willesden Junction](/source/Willesden_Junction_station) and [Shepherd's Bush](/source/Shepherd's_Bush_railway_station), London.

- [High Speed 1](/source/High_Speed_1) changeover at platforms 5 and 6 of [Ebbsfleet International](/source/Ebbsfleet_International), Kent.

### United States

- South of [Pelham station](/source/Pelham_station) (New York), where [New Haven Line's](/source/New_Haven_Line) [M8's](/source/M8_(railcar)) change from 3rd rail to catenary (northbound) and vice versa (southbound).

- [Pennsylvania Station (New York City)](/source/Pennsylvania_Station_(New_York_City))

- [East River Tunnels](/source/East_River_Tunnels) between [Queens](/source/Queens) and [Manhattan](/source/Manhattan) in [New York City](/source/New_York_City), NY

- [North River Tunnels](/source/North_River_Tunnels) between [Weehawken](/source/Weehawken), NJ and New York City, NY

- Like Athens, the MBTA [Blue Line](/source/Blue_Line_(MBTA)) (Boston) uses third rail for the underground part, and switches to overhead catenary power at [Airport station](/source/Airport_station_(MBTA)).

### Mainland China

- [Line 4](/source/Line_4_(Guangzhou_Metro)), [5](/source/Line_5_(Guangzhou_Metro)), [6](/source/Line_6_(Guangzhou_Metro)), [14](/source/Line_14_(Guangzhou_Metro)), and [21](/source/Line_21_(Guangzhou_Metro)) of [Guangzhou Metro](/source/Guangzhou_Metro) use third rails in operation but catenaries in depots.

## Variations

### Both systems live

The system is usually used only in exceptional cases as it can lead to problems caused by the interaction of the electric circuits; for example, where one system is powered with [direct current](/source/Direct_current) and another by [alternating current](/source/Alternating_current) (AC), premagnetisation of the substation transformers of the AC system can occur.

### One system live

A similar arrangement to dual electrification is one in which both means of powering a [train](/source/Train) are present, but not live simultaneously. Such arrangements can be found in frontier stations and in sections of railway used for running tests.

## See also

- [Multi-system (rail)](/source/Multi-system_(rail))

## References

1. **[^](#cite_ref-1)** ["Archived copy"](https://web.archive.org/web/20170808035931/http://www.irse.org/knowledge/publicdocuments/8_TLP%20Signalling%20Interfaces%20to%20Electrification%20Issues%20v1%20%5BCompatibility%20Mode%5D.pdf) (PDF). Archived from [the original](https://www.irse.org/knowledge/publicdocuments/8_TLP%20Signalling%20Interfaces%20to%20Electrification%20Issues%20v1%20%5BCompatibility%20Mode%5D.pdf) (PDF) on 2017-08-08. Retrieved 2017-08-08.{{[cite web](https://en.wikipedia.org/wiki/Template:Cite_web)}}: CS1 maint: archived copy as title ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_archived_copy_as_title))

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Adapted from the Wikipedia article [Dual electrification](https://en.wikipedia.org/wiki/Dual_electrification) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Dual_electrification?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.