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Wiring Information

Wiring modern telephone sockets (Line Jacks)

Wiring Diagram for Master & Extension Telephone Sockets

Wiring diagram
Pin Use Master Socket   1st Secondary Socket 2nd Secondary Socket 3rd Secondary Socket etc. Pin
1 Not used § Green/White Green/White Green/White Green/White 1
2 ‘B’ wire (-50V to earth) Blue/White Blue/White Blue/White Blue/White 2
3 Bell wire Orange/White Orange/White Orange/White Orange/White 3
4 Earth (PABX use only) White/Orange White/Orange White/Orange White/Orange 4
5 ‘A’ wire (0V to earth) White/Blue White/Blue White/Blue White/Blue 5
6 Not used § White/Green White/Green White/Green White/Green 6

When ‘new-style’ wiring was introduced in the early eighties a domestic single line telephone installation would have a master socket which is provided by the service provider (B.T., cable company etc.). This was usually an LJU2/1A or a LJU3/1A type of socket. A master socket contains a 1.8µF capacitor to pass ringing current to the telephones, a surge arrestor 11A or 26A to suppress high voltage spikes etc. and a 470k ohm resistor for testing purposes. Additional secondary sockets are wired off the master as shown above, the colour codes shown are the standard, but may differ in some existing installations. The wiring diagram for a master LJU socket is shown here. Note that the pictorial view shown above only serves to indicate the two differing types of sockets and wiring connections. Contrary to how it might seem, C1 is connected to terminals 2 & 3, not 1 & 4

NTE5 Line-box wiring instructions

In more recent years NTE5 or CTE5 Lineboxes are fitted in place of master sockets, these have a removable (lower half) panel which house the terminals to connect wiring to the secondary sockets. § Terminal pins 1 and 6 may be absent on some versions of C/NTE5, but these connections are not normally used anyway. The NTE5 tends to have the same components inside as a master LJU, however later NTE5 sockets differ by not having a surge arrestor, have only pins 2, 3, 4 & 5 or 2, 3 & 5 connected, they also have a small coil in series with the ‘bell wire’ on pin 3 which acts as a filter.

On older installations (pre-1980) cream or grey cables were used. They contained conductors coloured blue to pin 2, orange to pin 5, brown to pin 3 and green to pin 4 (if used), on some conversions green was used for pin 3 and brown for pin 4. On some installations of internal extension wiring (post-2012) BT/Openreach have now come full circle and have reverted back to using white four core cable containing solid colours: blue to pin 2, orange to pin 5, brown to pin 3 and green to pin 4 (if used).

Additional Bells are wired between pin 3 (orange/white) and pin 5 (white/blue).

External overhead telephone line colour code: orange / white = line 1; green / black = line 2.

BT NTE5 Master Socket
BT NTE5 Master Socket

Wiring Faults

Telephone line dead or similar issues
NTE5 Test Socket

Most homes with a landline will have a master socket called an NTE5A, this socket has a concealed test socket in which you can plug in a phone to test the line.

To expose the test socket simply remove the two screws and gently pull off the front faceplate, be sure to do this gently as there may be wires connected to the back of it.

You will then see the test socket in which you can plug in a phone in order to test the line. If the line now works then it is very likely that you have a fault with your extension wiring or sockets. If the line is still dead then the likelihood is that the fault is outside your home, although it could still be a fault on your property.

The latest type of master phone socket is called an NTE5C, the same principal applies except that the front faceplate simply unclips from each side, rather than being screwed on.

Other telephone problems
Phone ringing continuously:
No ringing:
Ringing but no speech (or very poor speech) and can’t dial out:
Very poor speech quality, possibly poor bell:
Terminals 2 &5 swapped between sockets (2 at one socket connected to 5 on another & vice versa)
Terminal 3 disconnected
Wire broken between terminals 2 or 5
Terminal 3 and 2 or 3 and 5 transposed

Telephone Cable Wiring Colours

CW1311 Internal 4/6 Way Telephone Cordage 

Contact 1

Black

system phones

6-way only

Contact 2

White

‘A’ wire

4 & 6-way

Contact 3

Green

Earth wire

4 & 6-way

Contact 4

Blue

Bell wire

4 & 6-way

Contact 5

Red

‘B’ wire

4 & 6-way

Contact 6

Orange

system phones

6-way only

CW1308 Internal Telephone Cable

Pair No. ‘A’ wire ‘B’ wire
1 White/Blue Blue/White
2 White/Orange Orange/White
3 White/Green Green/White
4 White/Brown Brown/White
5 White/Grey Grey/White
6 Red/Blue Blue/Red
7 Red/Orange Orange/Red
8 Red/Green Green/Red
9 Red/Brown Brown/Red
10 Red/Grey Grey/Red
11 Black/Blue Blue/Black
12 Black/Orange Orange/Black
13 Black/Green Green/Black
14 Black/Brown Brown/Black
15 Black/Grey Grey/Black
16 Yellow/Blue Blue/Yellow
17 Yellow/Orange Orange/Yellow
18 Yellow/Green Green/Yellow
19 Yellow/Brown Brown/Yellow
20 Yellow/Grey Grey/Yellow
21 Violet/Blue Blue/Violet
22 Violet/Orange Orange/Violet
23 Violet/Green Green/Violet
24 Violet/Brown Brown/Violet
25 Violet/Grey Grey/Violet
26 Pink/Blue Blue/Pink
27 Pink/Orange Orange/Pink
28 Pink/Green Green/Pink
29 Pink/Brown Brown/Pink
30 Pink/Grey Grey/Pink

CW1293 Internal Telephone Cable

Pair No. ‘A’ wire ‘B’ wire
1 White Blue
2 White Orange
3 White Green
4 White Brown
5 White Grey
6 Red Blue
7 Red Orange
8 Red Green
9 Red Brown
10 Red Grey
11 Black Blue
12 Black Orange
13 Black Green
14 Black Brown
15 Black Grey
16 Yellow Blue
17 Yellow Orange
18 Yellow Green
19 Yellow Brown
20 Yellow Grey
21 White/Blue Blue
22 White/Blue Orange
23 White/Blue Green
24 White/Blue Brown
25 White/Blue Grey
26 Red/Blue Blue
27 Red/Blue Orange
28 Red/Blue Green
29 Red/Blue Brown
30 Red/Blue Grey

CW1128 & CW1326 External Cable

Pair No. ‘A’ wire ‘B’ wire
1 White Blue
2 White Orange
3 White Green
4 White Brown
5 White Grey
6 Red Blue
7 Red Orange
8 Red Green
9 Red Brown
10 Red Grey
11 Black Blue
12 Black Orange
13 Black Green
14 Black Brown
15 Black Grey
16 Yellow Blue
17 Yellow Orange
18 Yellow Green
19 Yellow Brown
20 Yellow Grey

CW1406, CW1411 & CW1417 External Dropwire Cable

CW1406 CW1378 & CW1411 CW1417 (CAD55M)
1-Pair No.12 2-Pair No.10/10B 4-Pair No.14 ‘A’ wire ‘B’ wire
1st pair 1st pair 1st pair White Orange
n/u n/u 2nd pair Grey (slate) Red
n/u n/u 3rd pair Brown Blue
n/u 2nd pair 4th pair Black Green
Dropwire comes in 1-pair, 2-pairs or 4-pairs, the cable also has three steel tension wires to give support.

CW1406, CW1411 & CW1417 External Dropwire Cable

Pair No. ‘A’ wire ‘B’ wire
1 White Orange
2 Black Green
Double sheathed external grade telephone cable
available in white & brick brown colours.
Item code: 055354

Early type of external dropwire cable were constructed of one parallel pair in a figure-8 configuration.

BT dropwire reference No. 1 No. 2 No. 6 No. 8
CW Reference CW1166 CW1208 CW1247 CW1320A
Conductor Type Solid cadmium copper Solid copper covered steel Solid copper covered steel Solid cadmium copper
Nominal Conductor Diameter (mm) 0.91 0.71 0.81 1.14
Conductor Size (mm2) 0.65 0.4 0.52 1.02
Minimum Insulation Resistance @500V DC (MΩ.km) 24 24 50 24
Minimum Insulation Thickness (mm) 0.75 1.02 0.8 1.52
Nominal Insulated Conductor Diameter (mm) 2.41 2.75 2.41 4.18

Colours for CW1109 Jumper Cable used on Main Distribution Frames (MDF) inside BT Telephone Exchanges

Application

‘A’ wire

‘B’ wire

TXE4 & misc. non PSTN BT circuits Blue Yellow
System X circuits Green Black/white
System Y (AXE10) Orange Turquoise
Private circuits Pink Grey
Featurenet & Redcare circuits Red Yellow
DACS & WB900 Circuits Green Yellow
P wire busying Green

Jumper wire colours

CW1109 Jumper wire is available in various colours, including, red/white, red/black, blue/yellow, blue/white, green/white, green/black and pink/grey. It is used for connecting MDF’s and for Krone disconnection strips.

Note regarding telephone cable colours

When describing telephone wiring the colour grey is often referred to as slate. This is to avoid any confusion between green and grey as the first three letters are both the same.