Telephone Wiring Colour Code

Telephone Wiring Colour Code NTE5

The following pictures show the BT Telephone Wiring Colour Code as found in various situations. Please note you must use the correct inserter tool to push the wires in to the phone socket IDC connectors. Failing to do so will open the blades up and the socket connector will no longer hold the wires, with no option but to throw the socket away. Don’t strip the wires when terminating the telephone cable, as the blades are designed to bite through the insulation and make a connection.

For new sockets, spare parts and the correct inserter tool click here Sockets and Parts

Telephone Line cable coming in to property from the pole

NTE5This picture shows the external Dropwire cable from the telegraph pole or lead in wired directly to the rear of the BT Master Socket NTE5. Terminals are marked ‘A’ and ‘B’ and can be screw type terminals, or IDC inserter type as shown in the photo.

Normally, the first pair used for your telephone line is solid Orange, solid White. This applies to Underground fed properties with older cable, and overhead ‘Dropwire’.

A second telephone line with a different phone number would terminate on solid Black, solid Green.

Other colours present might be 3 red, or 3 yellow wires. These are not used as conductors and are in fact steel support wires to prevent the phone cable from sagging or stretching when used overhead. BEWARE when cutting or stripping this cable, the wires are EXTREMELY sharp and will leave a nasty prick in your finger. Good wire cutters are essential when cutting BT Dropwire.This cable is heavy duty to cope with any kind of weather.

In the picture I have stripped back the cable, cut the steel support wires approx 1cm length, folded back and taped around. This protects your fingers from a painful spike when terminating. Do not underestimate the danger of the steel support wires. Follow my telephone wiring colour code and things should work first time for you.

Telephone Master Socket Wires

BT-Master-SocketThis is the Telephone Wiring Colour Code for the NTE5 BT Master Socket, with the cable feeding extension sockets attached to the customer removable front plate. You can see the Test Socket revealed to allow you to check the BT line before your own wiring.


This is how the Telephone Wiring Colour Code looks wired with the stripey telephone cable. Note that this is the latest type available with a Bell Circuit Filter (the cylindrical protrusion next to the terminals)

Telephone Wiring Colour Code – What do the wires do?

Telephone Extension Sockets have 6 connections labelled 1 to 6. Only 3 connections are used. These are labeled 2, 3 and 5.
2 and 5 give you dial tone and allow you to make and receive calls. 3 is used for the bell circuit to link other extensions in the house back to the master socket. Without it the other phones wouldn’t ring on an incoming call.

Increase Internet Speed

The change in this practise though came along with Broadband as the ADSL filter now has the component to enable each phone to ring. The Bell Circuit, pin 3, should therefore not be connected if you would like faster broadband. By removing this on all telephone extension sockets in your house you will almost certainly see increase internet speed instantly!
telephone-wiring-colour-codeThis picture shows a conventional telephone extension socket correctly wired with the stripey cable.




Extension-Socket-Colour-CodeHere is the same socket wired with the latest solid colour coded BT cable (which oddly is the same colour code as very early BT cable). No need to terminate the brown wire. Always leave slack so that if you make a mistake you simply pull out the wires and re terminate. Slack cable can be tucked inside the box before securing the front.

Click here for Telephone Connection colour codes and description of what the wires do.

All images used on this site about Telephone Wiring Colour Code, Telephone Extension Socket and Telephone Master Socket NTE5 are subject to copyright and are not permitted to be used without my written permission.