At 09:21 21/09/99 +1000, you wrote:
>Cser Laszlo wrote:
>
>>> Telephone used an earth ground for the return current.
>> How could this happen?  Was one of the wires accidentally tied to the
>> earth ground?
>

Paul B wrote:
>  This is a *very old* story.  You have to know that it was a rural
>situation where "party lines" were used.  A party line has two (or
>more!) subscribers on the one line!  One subscriber has bell connected
>between one wire and ground, the other between the other wire and
>ground, so there are in effect, two different bells.
>
>  Party lines for more subscribers used "selective ring" (now available
>for home businesses etc. - a resurgence!) where each was to respond to a
>different ring sequence.
>
>  "Duplex" circuits allowed a relay box at each of the 2 subscribers on
>a party line to have privacy.  Not only did the bell return to ground,
>but so did both line circuits in order to make the connection, after
>which they looped normally.
>
>  We had one of these when I was little, this was in Sydney, not rural.
>You pressed a button on top of the phone to seize the line.  Boy, I *am*
>old!
>

This is what is known as a ground start circuit, often used in simple PABX
systems. I can take this one step furhter back in time to the original
requirement of an earth return.

Back when the volcanos where erupting and Tomas had just invented the
telephoneectic device wire was not common. Telephone companies in order to
save costs (Expensive to put in poles) for a single country subscriber
often used the top strand of the fence to provide the telephone connection
(Phone conversations did get a bit nasty after some rain), and to save a
bit more money and time only a single line was used and an earth return was
employed.

The loop to ground indicates that Paul was connected to a manual exchage
where a wink would be recevied, so Duplexor and privacy? Not when Mavius
was on the switch. Also this box isloated only the subscribers on the party
line from each other, not from the remote connection, are,the first
subscriber from the exchange was always in control of the call. Didn't work
too well when relationships where streched! <G>


Dennis

P.S.
Party lines are still in use today, and can still be found (Although most
have been replaced because of winging neibours and flying bricks (That's
another story))



>> In the normal dry situation why did the circuit complete via the dog?
>> Why was the resistance between the dog's paw and the soil smaller than
>> between the stake and the soil?
>
>  Because the stake was next to the house, shaded from the rain!  (What
>rain?)
>
>> Please answer in a private mail.
>
>  You're kidding!
>
>  Sean has already been reminded to think in 3D resistance instead of
>1D, so that's well covered.
>--
>  Cheers,
>        Paul B.
>
>