🚀 go-pugleaf

In article <877274797snz@inf-eden.demon.co.uk>, Chris Kennington
<News@inf-eden.demon.co.uk> writes
>
>Mike:  Is there a technical reason why one should not use a cable
> with both inner and outer pins wired in parallel? 

Yes, because pin 3 is used in the UK as the ringer.  The line is
presented to the master socket as 2 wires (called the A wire and the B
wire.)  This line is presented to pins 2 and 5 of the socket, and these
pins are carried in parallel to all slave (extension) sockets.  The
ringing current is derived from the master socket using a capacitor and
presented to pin 3.  Thus, from the master socket onward, phone
connections in the UK use 3 wires.

Using an adapter cable where pins 2 and 5 (the outer pair, used for the
line in the UK) were wired in parallel with pins 3 and 4 (the inner
pair, used for the line in the US) in the UK would cause the bells in
any phones connected to ring nonstop.  A pretty good reason for not
doing so <grin>

Of course, why the UK has to differ in this respect, I don't know.  It's
my understanding that in pretty much the rest of the world the line is
presented as a pair to each socket and the phone derives its ringing
current via an internal capacitor, thus avoiding the complexities of
British wiring.  If you look at many phones nowadays, they usually only
use two wires anyway, in the manner I've just described.

ISTR from a discussion in uk.telecom that the British 3-wire method
arose because of the use of mechanical bells in older telephones, and
the 3 wire system prevented the bells in other phones from "tinkling" if
one instrument was dialled using pulse dialling (making and breaking the
line.)  More modern phones use tone dialling, hence the problem doesn't
arise.

-- 
Mike Tomlinson
Keep the internet tidy - kill a spammer today.