Keelan,

While it is true that tip and ring get their name from the construction of the p
lug, in reality the tip is ground and the ring is at around -48Vdc referenced to
 tip (while the set is on-hook).  Off hook the line voltage drops to
anywhere from 5v to 20v depending upon loop current, which in turn is dependent
upon the loop length, switch impedance and inherent current limiting, and the te
lephone set.  Also, the ac ringing signal is impressed upon the -48Vdc ring
voltage -- typically this is a cadenced 90Vac 20Hz sinewave designed to actuate
the mechanical ringers in old sets.  These days all of the ringers are electroni
c but the 90Vac ringing signal is still employed.  So the ring on the old
bantam plug was actually the hazardous part, but we haven't lost many operators
since the advent of crossbar and electronic switching systems.  :*)

Now, why is -48Vdc used in telecom systems? (note the minus sign).  Here's a clu
e -- think electrochemistry.

Jim


> Interesting note -- Tip and ring get their name from the construction of an
> operator's plug-board plug -- tip was the tip, and ring was the ring below
> the tip. The positive voltage was put on the tip line, because that was the
> part of the plug that the operator had the least chance of touching.
>
> Hope this helps.
>
> - Keelan Lightfoot
>