From: Julian Macassey <firstname.lastname@example.org>
Subject: British Telecom Auxiliary Jack Wiring
Date: 10 Oct 90 14:59:26 GMT
Organization: The Hole in the Wall Hollywood California U.S.A.
In article <email@example.com>, TOBY@brownvm.brown.edu (Toby
> I have a friend who is going to the UK soon and has a modem which will
> support CCIT (?) protocols, which I understand are used in the UK.
> What I would like is any information on how to physically connect the
> modem to the UK outlets. I'm told that the UK has modular plugs, but
> ones quite different from US plugs. Any suggestions on how to attack
> this? Any company out there which supplies cords with a UK plug on
> one end and a US plug on the other?
I suppose this should become one of this groups "Frequently Asked
Below is a file I keep on this matter. I hope it helps. Yes, I
know various countries have silly protective regulations about what
you can do with the service you are paying too much for. But I am
interested in telecommunications not restrictive practices.
British Telecom Auxiliary Jack Wiring
British phones have 3 wires. There are two wires A & B (Tip &
Ring) coming into a house. There is no protector. In the primary jack
in the house is a 2 uF capacitor. On the end of this cap is the third
wire. The AC ringing signal is fed to the phone on this wire and its
DC counterpart. See diagram:
----| |------O (3)
(A) O----------------------O (2)
(B) O----------------------O (5)
Note: The Numbers in the diagram are the numbers engraved on
the jack terminals. If the phone rings continuously, reverse 2 and 5.
The ringer is fed by AC current on pins 3 and 5.
BT consider the A terminal to be ground. B is measured as 45
to 50 volts above ground.
Wiring Colour Codes:
The standard inside wire is classic "3 pair". A jack is wired
Pin # Wire colour
So if you have a US device that you need to wire into a UK jack this
is what you do. Get a US line cord and cut the jack off one end. Go to
your local UK electrical shop and have them terminate the end with a
UK jack. The center two wires in a US line cord are the phone line, so
they should terminate on UK jack pins 2 and 5. Then you plug the UK
end into the wall and the US end into your phone, modem, answering
You can also buy a line cord with a US plug on one end and
spade lugs on the other. Using a screwdriver you screw the line cord
onto the terminals in a jack or junction box. This works all over the
Julian Macassey, n6are firstname.lastname@example.org ucla-an!denwa!bongo!julian
N6ARE@K6IYK (Packet Radio) n6are.ampr.org [126.96.36.199] voice (213) 653-4495