Third rail

A third rail is a method of providing electric power to a railway 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, and they use 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 cases 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 metres).

The trains have metal contact blocks called 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. The conductor rail is usually made of high conductivity steel, and the running rails are electrically connected using wire bonds or other devices, to minimize 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.

Third rail (model railroading)

The use of a third rail in rail transport modelling is a technique that is sometimes applied in order to facilitate easier wiring.

Two-rail versus three-rail system

Early toy trains used two metal rail tracks like most real trains. However, manufacturers quickly found that using a center rail for electric power and the two outer rails for common or ground made electrical contact much more reliable and less prone to short circuits. Three rail contact also negates the need for insulated wheels, an important consideration before plastics became widely available. Most scales and gauges that predate HO scale used three rails for electric operation.

Three-rail system

A key advantage for three-rail track is reverse loops, where a train enters a loop through a turnout and then exits through the same turnout in order to change the train's direction. With two-rail track, when the track reverses on itself, this causes a short circuit. With three-rail track, because the center rail remains constant and the outer rails are electrically identical, this causes no problems.

Third rail of politics

The third rail of a nation's politics is a metaphor for any issue so controversial that it is "charged" and "untouchable" to the extent that any politician or public official who dares to broach the subject will invariably suffer politically.

It is most commonly used in North America. Though commonly attributed to Tip O'Neill,Speaker of the United States House of Representatives during the Reagan presidency, it seems to have been coined by O'Neill aide Kirk O'Donnell in 1982 in reference to Social Security.

The metaphor comes from the high-voltage third rail in some electric railway systems. Stepping on this usually results in electrocution, and the use of the term in politics relates to the risk of "political death" that a politician would face by tackling certain issues.

American examples of usage

A wide range of issues might be claimed detrimental to politicians tackling them, but those below have all been explicitly described using the "third rail" metaphor:

  • Withdrawal of Social Security benefits
  • Podcasts:

    Third Rail

    ALBUMS

    Third Rail

    ALBUMS

    Third Rail

    ALBUMS

    Third Rail

    ALBUMS

    PLAYLIST TIME:

    Run Run Run

    by: Third Rail

    (Ooooooooo)
    (Ooooooooo)
    Up in the morning at half past eight
    You can't have your breakfast 'cause you'll be late
    You tie your tie like a hangman's noose
    Ain't no time to drink your juice
    So you Run, Run, Run, Run
    Yeah you Run, Run, Run, Run
    Stand on the corner and wait for the bus
    It's late again, you start to cuss
    The paper's filled with all bad news
    Fat lady stands on your polished shoes
    So you Run, Run, Run, Run
    Yeah you Run, Run, Run, Run
    [Spoken]
    ... Of the latest quotations from the New York Stock Exchange:
    Heart Attacks up two & three quarters
    Mental Illness split three for one
    Ulcers up one
    General Chaos, that's General Chaos is up one quarter
    The Great Society unfortunately is down five points
    Down at the office all is still
    The boss is at a funeral
    A note on the door 'No Work Today'
    Our chief competitor passed away
    So you Run, Run, Run, Run
    Yeah you Run, Run, Run, Run
    Up in the morning at half past eight
    You can't have your breakfast 'cause you'll be late
    Tie your tie like a hangman's noose
    Ain't no time to drink your juice
    So you Run, Run, Run, Run
    Yeah you Run, Run, Run, Run
    Oh you Run, Run, Run, Run
    Oh you Run, Run, Run, Run




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