third rail

plural third rails

1. The electrified rail that runs beside or between train tracks to power electric trains.

   The system voltage is 630 volts d.c. and the supply to the trains is by top-contact third rail with running rail return.

   1956 October, “Recent Changes on the Tyneside Electrified Lines”, in Railway Magazine, page 659

   3 more examples

   The locomotive third-rail pick up shoes are of the new standard S.R. type. [...] Whenever the locomotive was working hard there was unmistakable evidence of its higher power than its predecessors in the brilliant and explosive arcing between conductor shoes and the third rail; this was particularly vivid in Quarry Tunnel in the down direction, where the display equalled anything we have seen on the frostiest of nights in an electrified third-rail area.

   1959 March, “The 2,500 h.p. electric locomotives for the Kent Coast electrification”, in Trains Illustrated, page 125

   Rumour is abroad that, foiled by the Central T.U.C.C. in its attempt to close the Westerham branch, the Southern Region is considering third-rail electrification of the line with second-hand material. [this never happened and the branch closed later in 1961]

   1961 March, “Talking of trains”, in Trains Illustrated, page 134

   Although third-rail operation in the region dates back more than a century, it was in the 1970s that tunnels under Liverpool's city centre opened to bring together previously disparate routes.

   2023 February 8, Tony Streeter, “Kirkdale: home to Merseyrail's new '777s'”, in RAIL, number 976, page 36

   Synonyms: conductor rail, live rail

2. broadlyAnything that is controversial or dangerous to come into contact with, or is best avoided.

   tax hikes as a third rail in U.S. politics

   3 more examples

   Today's rapidly developing third rail (at least in some states) is supporting driver's licenses for illegal immigrants, as favored by New York Gov. Eliot Spitzer.

   2007 November 12, Jonathan Alter, “Congenital Lawyer Redux”, in Newsweek, page 48

   Despite ethnic resentment and suspicion, they [Ukraine's leaders] never contemplated breaking up the country. This was the third rail of Ukrainian politics, and very few were willing to touch it. Secession was taboo.

   2014 March 29, Stephen Sestanovich, “Putin's reckless gamble”, in The New York Times, archived from the original on 30 Apr 2020

   “But I felt that it dodged the subject. I don’t know whether the studio or Chris felt that that was a third rail that they didn’t want to touch, but I want to go straight at the third rail. I’m just stupid that way.”

   2025 July 2, Catherine Shoard, quoting James Cameron, “James Cameron calls Christopher Nolan’s Oppenheimer a ‘moral cop-out’”, in The Guardian, →ISSN, archived from the original on 12 Aug 2025