why -48 volt

Discussion in 'General Electronics Chat' started by shahnawaz, Jan 26, 2009.

  1. shahnawaz

    Thread Starter Active Member

    Dec 30, 2008
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    0
    hi dear all

    i really appreciate and thanks to ur support.
    well i have another question dearssss

    why we use DC -48 volt for telecom equipments instead of +48 volt DC.
    and what impact really does on the equipment when we use same ground points for rectifier and inverter. i mean can we use any earth point same for AC and DC circuits.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
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    I certainly thank you for that explanation.

    The link contains information I for one did not know.
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    There's yet another reason for the positive ground that most people don't know about.

    In the early days of telephones, the lead acid batteries were built with the lead forming the actual casing...this was grounded to the office floor. The negative terminal (lead sulphide) was suspended inside the casing and floating "below" ground potential.

    Of course, with modern battery construction, this original reason no longer applies...but with tens of millions of phones in operation by the first ten years of the past century...there was no point in changing!

    Now you know!

    :)

    eric
     
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