Phone line

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This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Dutch POTS

Voltage and protocol:

  • a line that is not ringing has about 48V DC on it
    • Apparently standardized to be between 44 and 56
    • Apparently 32V in an internal home phone system
  • ringing is an alternation netween that voltage and 0V, at 10HZ (or 20Hz? or 25Hz?).
    • (Slow digital multimeters may pick this up better on the AC setting)
  • A line in use has ~5V or/to ~10V DC with tones/voice on top of it


  • There is the concept of Ringer Equivalence Number, which is an indication of load in somewhat arbitrary units, though may be locally standardized. Phones usually take 1, sometimes more.

(verify) all of this.