> CBFalconer yahoo.com> wrote:

>>In North America again (I don't know about elsewhere) the normal
>>phone uses 3 wires to connect to the two wires of the phone
>>circuit. The yellow wire carries the ring signal. Just disconnect
>>that and the phone won't ring, and the load is zero.

>
> I don't recall any system in North America that put ring
> voltage on a separate wire. The yellow wire is
> generally not connected unless one 4-wire cable is used
> for two separate telephone lines.
>
> In North America the "normal" line uses only 2 wires.
> The audio signal is applied between the "tip" and the
> "ring" of a single pair. "Ring Current" and "Loop
> Current" are also applied between the Tip and the Ring
> of the same pair.
>
> Commonly used drop cable has four wires: Green is the
> Tip and Red is the Ring (positive and negative,
> repectively for the DC loop current), while the Yellow
> and the Black wires are not used. (Note that the DC
> voltages used by telephone companies are negative with
> respect to ground, hence for DC the Tip wire is at
> ground potential, and the Ring wire has a negative
> potential. But the Tip is not at ground potential for
> Ring Current or for the audio signal.)
>
> One configuration often seen includes a second line on
> the same cable, using Yellow and Black as Tip and Ring.
>
> Historically the Yellow wire was, for a few years, used
> for a small AC voltage (nominally 6.8 volts) to power a
> lamp circuit on some telephone set models.
>