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Why Telcom Equipments are fed with -48V

  1. Nov 17, 2008 #1
    Almost all Telecom Equipments are fed with -48V why not +48V?
     
  2. jcsd
  3. Nov 17, 2008 #2

    mgb_phys

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    Anti-corrosion. Originally the DC power was fed down the telephone wires to power remote equipement a +ve voltage on a metal wire encourages corrosion a negative voltage (relative to earth) reduces it.
    For equipment inside the electronics rack it doesn;t really matter.
     
  4. Nov 20, 2008 #3
    Hi
    But even Telecom equipments (Rack type) are working with -48V..
    Is it the same reason or any other specific reason for that??
     
  5. Nov 20, 2008 #4

    mgb_phys

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    Yes, you don't want to have to build a local and remote version of the same kit.
    And even kit in a rack might be put out in a street corner box and fed from a central exchange.
     
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