Why telephone lines use -48V not +48V? What’s the difference practically in -ve and +ve voltages?

Asked Aug 07 '18 at 14:24

Active Aug 07 '18 at 14:34

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Why telephone lines use -48V not +48V? What’s the difference practically in -ve and +ve voltages? Detailed answer would be appreciated.

edited Aug 07 '18 at 14:34

Eugene Sh.

asked Aug 07 '18 at 14:24

Rumi

4

http://mathscinotes.com/wp-content/uploads/2016/04/positiveground.pdf – G36 Aug 07 '18 at 14:30
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https://en.wikipedia.org/wiki/Cathodic_protection#Impressed_current_systems It is an example of cathodic protection of the wires to make the most positive voltage inside the building to earth ground where the corrosion can be easily managed and the extensive -48V wire network protected. – Tony Stewart EE75 Aug 07 '18 at 15:02
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@Rumi. Why did you post this on Aviation.SE? Aircraft never used landline telephones! – Transistor Aug 07 '18 at 16:15

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