The on-hook DC voltage should measure between 42 and 55 volts, depending on the CO type and the locality. This is the nominal -48 volt Central Office battery.
On-hook AC voltage will be present during ringing, and it will vary widely depending on the number of ringers on the line, the cable condition, and the type of central office. You can expect to see anywhere from 30 to 120 volts AC.
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