Posted by Foneguy on August 30, 2007, 12:16 pm, in reply to "-48 volts" --Previous Message--
-48 was used because the positive ground produced less "arc" across relay contacts. 48v dc was used because it was the best trade off for max power transfer in the voice frec (300 to 3000 cyc) to the farm house. The 20 cycle ringing and voicr frec were sumper imposed on the -48.
-130 dc and +130 dc were used to collect and return coins. Ringing was 130 v ac for the old coin phones. 117 v ac was used for the new coib phones ringing. Most phones made after 1970 tripped ringing at about 85v ac.
: An instructor at a class posed the question,
: Why do phone companies use the term -48?
: Were did it originate? Were did it start? He
: says he is not actually referring to the -48
: power used in the central office but
: something else. I don't know? Can some one
: help?
:
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