The basic UK telephone wiring is what you will find on an ordinary
domestic phone line or "2 wire" extension from a PBX (Private
Branch Exchange). Unlike the American system where 2 wires are simply
daisy-chained from jack to jack, the UK system uses 2 wires for the
incoming line and 3 wires between jacks (4 in the case of a PBX). This
is because the components to ring the phones are located in the
"Master" jack where the line first enters the building.
Subsequent extensions are connected to "Secondary" jacks.
The Master contains 3 additional components:-
In newer installations the Master will be in the form of an "NTE5" which is a standard UK size plate (86x86mm) with 2 parts. The rear part of the socket is fitted to the box and has 3 connections A,B & Earth. The removeable front part has 6 connections for your extension wiring to connect to. Details of connections and designated wire colours are shown below.
Wire terminations will be either by screw terminals or "Punchdown" IDC connectors. With the punchdown connectors it is essential to use the proper tool to terminate the wire for a reliable connection. Disposable plastic tools are available very cheaply or even free when you buy your sockets. Long life professional tools are available for around £17. These are well worth the investment. The professional tool terminates and trims the wire in a single action.
Rules for Reliable IDC Connections
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