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Reply To: why -48v


-48V DC has been a traditional voltage for telephone applications. The reason for selecting that voltage has need that the voltage was enough to supply enough power to telephone equipments through several kilometres of telephone copper cable, low enough not to cause major electrical hazards and suitable for battery backup system.

why -48V DC instead of +48V DC. The reason for electing -48V in reference to ground are avoiding the nasty galvanic effects in telephone cabling