Third rail

Third rail (top) at Bloor-Yonge station (Line 1) in Toronto, ON. for the Toronto Transit Commission. Energized at 600 volts DC, the third rail provides electrical power to the power-train, and ancillaries of the subway cars.
A British Class 442 third-rail electric multiple unit in Battersea. The maximum permitted speed of these units is 100 mph (160 km/h).
Paris Metro. The guiding rails of the rubber-tyred lines are also current conductors. The horizontal current collector is between the pair of rubber wheels.
London Stansted Airport people mover with central rail power feed
London Stansted Airport people mover, showing rail switch
A picture of an NYC Subway "e" train train making contact with the Third Rail. The rail in the foreground is the third rail for trains in the opposite direction.

A third rail is a method of providing electric power to a railway locomotive or train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit system, which has alignments in its own corridors, fully or almost fully segregated from the outside environment. Third rail systems are always supplied from direct current electricity.

The third-rail system of electrification is unrelated to the third rail used in dual gauge railways.

Description

Third-rail systems are a means of providing electric traction power to trains using an additional rail (called a "conductor rail") for the purpose. On most systems, the conductor rail is placed on the sleeper ends outside the running rails, but in some systems a central conductor rail is used. The conductor rail is supported on ceramic insulators (known as "pots") or insulated brackets, typically at intervals of around 10 feet (3.05 metres).

The trains have metal contact blocks called collector shoes (or contact shoes or pickup shoes) which make contact with the conductor rail. The traction current is returned to the generating station through the running rails. In the US, the conductor rail is usually made of high conductivity steel or steel bolted to aluminium to increase the conductivity. Elsewhere in the world, extruded aluminum conductors with stainless steel contact surface or cap, is the preferred technology due to its lower electrical resistance, longer life, and lighter weight. [1] The running rails are electrically connected using wire bonds or other devices, to minimise resistance in the electric circuit. Contact shoes can be positioned below, above, or beside the third rail, depending on the type of third rail used: these third rails are referred to as bottom-contact, top-contact, or side-contact, respectively.

The conductor rails have to be interrupted at level crossings, crossovers, and substation gaps. Tapered rails are provided at the ends of each section, to allow a smooth engagement of the train's contact shoes.

The position of contact between the train and the rail varies: some of the earliest systems used top contact, but later developments use side or bottom contact, which enabled the conductor rail to be covered, protecting track workers from accidental contact and protecting the conductor rail from frost, ice, snow and leaf-fall.[2]

Other Languages
Deutsch: Stromschiene
Esperanto: Kontaktrelo
فارسی: ریل سوم
français: Troisième rail
한국어: 제3궤조
Bahasa Indonesia: Rel ketiga
italiano: Terza rotaia
lumbaart: Terza rodaia
Bahasa Melayu: Rel ketiga
Nederlands: Derde rail
português: Terceiro carril
Simple English: Third rail
suomi: Virtakisko
svenska: Strömskena
Türkçe: Üçüncü ray
українська: Контактна рейка
ייִדיש: דריטע שינע
中文: 軌道供電