[Asterisk-Users] False RING (incoming call) on Digium X101P FXO

[Rich Adamson]

> > I was surprised to see that it's 240 volts (peak-to-peak)!  Egad.. no
> > wonder it shocks fingertips.
> >
> > 20Hz (50ms cycle), 2 second long clean sine waveform.  I was just
> > surprised to see twice as much voltage as expected.
> 
> 240 sounds like a lot.  Are you sure you were doing DC measurement?
> Normal is +/- 90 - 120, generally at least 48VRMS or about 70V.

The ring generators in the central office are typically set for something
between 90 - 120 volts AC (RMS, not peak-to-peak) and have been since 
the hand crank phones disappeared. DC voltage has never been used in the
US.

Those telco's with long rural subscriber loops are likely to be towards
the upper end of the ring voltage, while metro offices are more likely to
be towards the middle to lower end. Depending upon the age of the central
office, the actual ring voltage will vary depending upon exactly how many
phone lines are being rung at exact same time.