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Thread: Telephone and power supply

  1. #1 Telephone and power supply 
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    hi...

    Can someone tell me..

    The operation of a telephone does not depend upon the power supply.Even if the power is out, the telephone still works.How?


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  3. #2 Re: Telephone and power supply 
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    Quote Originally Posted by mohana
    hi...

    Can someone tell me..

    The operation of a telephone does not depend upon the power supply.Even if the power is out, the telephone still works.How?
    The telephone line has -48V when idle and +90V when ringing. In other words, the power is being supplied at the Central Office switching. If the power is out, the CO has back up batteries and gas-powered generators to keep the power on the line.


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