Why telephone lines use -48V not +48V? What’s the difference practically in -ve and +ve voltages? Detailed answer would be appreciated.
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4\$\begingroup\$ mathscinotes.com/wp-content/uploads/2016/04/positiveground.pdf \$\endgroup\$– G36Aug 7, 2018 at 14:30
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3\$\begingroup\$ en.wikipedia.org/wiki/… 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. \$\endgroup\$– Tony Stewart EE75Aug 7, 2018 at 15:02
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5\$\begingroup\$ @Rumi. Why did you post this on Aviation.SE? Aircraft never used landline telephones! \$\endgroup\$– TransistorAug 7, 2018 at 16:15
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