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Please note:

This is a site which looks purely at historical telephones & telecoms through the last 100 years plus.

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WIRING MODERN TELEPHONE SOCKETS (LJU's)

Fact-file: D.I.Y. extension wiring was introduced in 1986


Wiring Diagram for Master & Extension Telephone Sockets

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
 
Notes: A domestic single line telephone installation will have one master socket which is provided by the service provider (B.T., cable company etc.). A master socket contains a 1.8F 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 Linebox wiring instructions

In 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. Further NTE5 wiring instructions are contained in this leaflet. 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.
 

For further information on telephone sockets including NTE5 with ADSL faceplate visit the Line Jacks page.
BT NTE5 Linebox BT NTE5 Linebox
BT NTE5 Linebox BT/Openreach NTE5 Socket
LJU2/1A Master LJU LJU2/1A Master LJU LJU2 Secondary LJU LJU2 Secondary LJU
LJU2 Master Socket

LJU2 Secondary Socket

 

 


 

Instructions on how to convert old hard wired telephones to new-style wiring

 

 BT Line Cord fitted with plug 431A (4-way) or 631A (6-way)

BT Line Cord

Line Cord Type No: Length Number of Conductors
4/500 150/3000/5000 mm Four
4/501 420 mm Four
4/502 3000 mm Four
4/503 200 mm Four
4/504 3000 mm Four
4/505 150 mm Four
6/500 3000 mm Six
6/502 420/3000/5000 mm Six

6/505

570 mm Six

 BT Handset Cord fitted with plug 430A

BT Handset Cord

BT Type No. 4/503


Wiring Faults

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

Wiring Colours for CW1311 Internal 4/6 Way Telephone Cordage 

normally used to connect between telephones & line jacks 431A & 631A

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

ISDN Wiring for RJ-45 Sockets

Contact 1 White/Orange Contact 5 White/Blue
Contact 2  Orange/White Contact 6 Green/White
Contact 3 White/Green Contact 7 White/Brown
Contact 4 Blue/White Contact 8 Brown/White

Wiring Colours for 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

Note: The first colour is the base colour & the second colour is the trace colour


Wiring Colours for CW1293 Internal Telephone Cable

CW1308 is now more commonly used

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
31 Blue/Black Blue
32 Blue/Black Orange
33 Blue/Black Green
34 Blue/Black Brown
35 Blue/Black Grey
36 Yellow/Blue Blue
37 Yellow/Blue Orange
38 Yellow/Blue Green
39 Yellow/Blue Brown
40 Yellow/Blue Grey
41 White/Orange Blue
42 White/Orange Orange
43 White/Orange Green
44 White/Orange Brown
45 White/Orange Grey
46 Orange/Red Blue
47 Orange/Red Orange
48 Orange/Red Green
49 Orange/Red Brown
50 Orange/Red Grey
51 Orange/Black Blue
52 Orange/Black Orange
53 Orange/Black Green
54 Orange/Black Brown
55 Orange/Black Grey
56 Yellow/Orange Blue
57 Yellow/Orange Orange
58 Yellow/Orange Green
59 Yellow/Orange Brown
60 Yellow/Orange Grey

Wiring Colours for CW1128 & CW1326 External 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

Wiring Colours for CW1412 External Telephone Downlead Cable

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

Wiring Colours for  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 Orange White
n/u n/u 2nd pair Red Grey
n/u n/u 3rd pair Blue Brown
n/u 2nd pair 4th pair Green Black
Dropwire comes in 1-pair, 2-pairs or 4-pairs, the cable also has three steel tension wires to give support.

Early types 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 CW208 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 -

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.



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