Mailing List Archive Mailing List Archive
>Posted on 15 Jan 1997 at 11:15:43 by Marc Dufour > >> Bill, using the housing of a light to conduct in water is out of >> the question > >It's a totally unrelated field, but it may give a good reason to do >so. Any given crossection of the light will carry two currents: equal in magnitude but of opposite signs in a concentric configuration (coaxial). There will be no external field created except at the two far ends. John >It used to be the tradition for subways to use the steel rails the >train is running on to carry the return (negative) power current >supplied by the notorious Wthird rail". This is analogous to using >the light case to carry current. > >However, it was found that this induced stray currents that corroded >metal installation near the subway lines, or worse, affected signal >circuits. > >Subways use "low" (600-800 volts) DC voltages, so this means high >currents. By contrast, high-speed mainline trains use high >(11,000-50,000) AC voltages, with much lower amps and less trouble in >that respect. > >So, nowadays, many modern subway systems have negative rails >insulated to avoid those destructive stray currents. > >--------------- Pour la Republique Francaise du Quebec ------------------- > In the French version of "2001: A Space Odyssey", > the last word uttered by HAL is "GOD"... > ~~~~~~ last dive: The almost fully frozen canal Soulanges, 5mfw ~~~~~~~~ > Marc Dufour - [\] ACUC6 31874 - TDI CD-0197 - http://www.accent.net/emdx-= >---------
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]