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… install an NTE5a BT / Virgin / OpenReach etc Master Socket

My guide to replacing a BT OpenReach Master Socket (NTE5a) … same for Virgin / Talk Talk etc.

Your master socket used to be something like this … and may still do.

PIC Front.

C1 = 1.8μF Capacitor
SP1 = Surge Protector
R1 = 470KΩ Out of service resistor

BT Master Socket Pre NTE5

Wiring diagram Master Socket.

BT Master Socket Pre NTE5 Wiring Diagram

There were 3 components, the Ring Capacitor, the Test Resistor and the Surge Protector. It you wanted to add extension sockets you wired them in the back of the socket on the same terminals as BT’s incoming cables.

The introduction of the NTE5 meant only BTs wires are fitted into the back of the socket with a test phone socket on the front – and any extensions are wired into a separate removable front plate/socket – this can be removed should there be an issue with the extension wiring, or to eliminate this from the investigation.

Wiring diagram NTE5A.

BT Master Socket NTE5a Wiring Diagram Latest Version>PIC Front

>PIC Back.

Early NTE5’s still had the Surge Protector, but in 2012 these were no longer put in as they can affect ADSL and VDSL speeds. If yours still has it, you can leave or replace the socket. Some people have cut the component out.

There are only 2 components in master sockets now – the Ring Capacitor and the Test Resistor.  New sockets (since around 2012) do NOT contain Voltage Surge Protector.

When fitting a new socket:-

  • Never strip any cables going into the IDC connectors.
  • Always connect to the next available bit of fresh, unused cable.

Standard incoming BT line (drop wire) BT_OpenReach_Virgin_incoming_line

Standard incoming BT line (drop wire) – Close up. The Steel Tension Cables can be other colours, but all 3 are always the same colour. BT_OpenReach_Virgin_incoming_line_zoomed

When placing the wire in the IDC, there is only one correct way.  The contact in the IDC connector is off centre, the side that the metal connector is closer to, is the side the wire is cut / ends.

IDC connector. NTE5A_Wiring_back_IDC

IDC insertion tool. NTE5A_fitting_IDC_insertion_tool

IDC tool lined up. NTE5A_Wiring_back_IDC_tool_1

IDC tool lined up, explanation. NTE5A_Wiring_back_IDC_tool_2

IDC tool placement. NTE5A_Wiring_back_IDC_tool_3

Incoming line placement in IDC. NTE5A_Wiring_back_IDC_1

Trimmed neatly – cut the wires individually, cutting them together will short them. NTE5A_Wiring_back_IDC_2

Tidied. Cable-tied (round outer sheath, not cables). Finished. NTE5A_Wiring_back_IDC_3

The NTE5’s come with 2 choices of mounting screw. If using a plastic backbox without any metal in the mounting holes, use the self taping screws, otherwise use the machine screw – the machine screws are also for use on the metal back box sunk into wall.  NTE5A_mounting_screws

Wiring extension sockets on the faceplate:-

2 = Blue with white rings
3 = Orange with white rings – Don’t connect for best internet speeds.
4 = Not on new sockets
5 = White with blue ring

Buy a full NTE5A kit with tool on Amazon – amzn.to/2yeSQSa

If your telephone does require a ring capacitor, use a decent microfilter that contains the ring capacitor.

Like these.


{ 24 comments… add one }
  • Gail August 1, 2016, 12:39

    Dave – I ordered NTE box from you and looked on your web page for wiring instructions as advised. My wires are black, green, white and orange – so am non the wiser for wiring after looking at your description……any ideas please.
    PS delivery was VERY swift thank you!!

    • Dave Fry August 12, 2016, 17:25

      Hi, sorry for the late reply! The phone line should be on either Orange and White or Green and Black. If you have a volt meter you can test for roughly -48 volts DC, accross either pair. Or you can go for trial and error – Try White and Orange to A and B first, if not Green and Black. Keep me posted. Cheers! Dave.

  • Ted September 28, 2016, 12:18

    Hi Dave
    Very fast delivery, thank you.
    I have a wire from the eaves to a junction box the the master socket, old type. It has blue to 2, green to 3, brown to 4 and orange to 5. I want to replace the master by an NTE5a. How should I connect it?

    • Dave Fry November 3, 2016, 18:23

      Hi Ted,
      Did you sort this? As long as this is definitely the main line, Blue to B, Orange to A. Park the other 2 cables. Any wired extension sockets you have connect to the faceplate, not the A and B – these are for the incoming line only.
      Hope this helps. Cheers! Dave.

  • Hugh Levinson November 14, 2016, 12:19

    I have a master socket with bell filter in detachable front plate.

    Is the bell filter in series with the bell connection on the front plate socket?

    A plug in phone electronic phone ringer works when fitted to the front plate socket but not when plugged into an extension.

    • Dave Fry November 26, 2016, 15:12

      The bell filter only cleans the line, it doesn’t make the phone ring, the capacitor drives the bells / ringer. You phone isn’t ringing on the the extension, I’m guessing, due to the 3 wire not being connected, only the voice / data wires 2 and 5. This set-up is my preferred to keep BroadBand speeds at their best. On the extension socket introduce a good BroadBand filter that contains a ring capacitor. Or use a different faceplate with a ring capacitor.

      Hope this helps. Cheers! Dave.

  • Paul January 6, 2017, 17:27

    I have a black cylindrical tube that holds the main line coming into the house and then has another line coming out of it to go to the annex. Both these cables are black. I then have a white cable coming out which comes into the house to a standard socket. There is no evidence of a master socket. If you can email me I’ll send a pic of the box outside. I need to correct my lousy broadband connectivity but don’t know if I’m allowed to touch this connector.

    Many thanks

    • Dave Fry January 13, 2017, 14:47


      It’s likely this connector has jelly crimps in, and may be jelly filled itself – if it’s before the master socket – or unsure of master socket location, I’d avoid opening it.

      Normally the white cable – CW1308 or similar – is spec’d recommend for internal use only though…

  • Frankie February 1, 2017, 14:35

    Hi on opening my bt openreach master socket I seen the in coming lines orange and white jelly crimped….. orange to blue and white to blue / white is this correctly crimped,also ,do I put the orange to the A and white to B,if I chose to do so

  • Rob June 3, 2017, 06:18

    Hi Dave,

    The wires that go into the A and B slot are also white and blue. I’ve been told it doesn’t matter which way around they go. Is that true?
    It’s working anyway.

    • Dave Fry June 5, 2017, 21:15


      Now I’ve read the question properly Rob … I’d have wired the white/blue to “A” and blue/white to “B”. Some old faxes and modems needed correct polarity, but as you’ve said, it doesn’t matter – the polarity is never worried about any more.



  • Helen September 13, 2017, 16:07

    Hi Dave, I came across your page and I hope you can help. I have a Virgin installed socket that seems to be something like an NTE5 . I can’t find any pictures with the same wiring that I have. I just have one phone connected, no extensions. It used to work, then was a bit on and off and I thought I’d have a look – the removable section of the box just dropped off when I touched it (the screws weren’t fixed in at all) and I found 2 wires connected, 2 wires not connected at all – wondered if they had come out of somewhere? I have a blue wire connected to B and white connected to A. then I have a solid orange wire and an orange and white wire not connected to anything. can you help? Many thanks if you can!

    • Dave Fry September 15, 2017, 15:14

      Helen, if you have no extensions, you can use the socket without the front half faceplate, though it should have been left screwed on. Blue and Blue/White to A and B, with Orange and Orange/White as spare sounds fine. Have you tried leaving the lose plugging the phone diretly into the socket behind the front half faceplate (test socket)?

  • Edward September 24, 2017, 16:02

    Hi i don’t have a master socket just a bakealite connector box with the incoming wire & 3 wires for the phone extensions which work fine , broadband rubbish ! how do I install a new master socket & keep the extensions ?
    Regards Edward

    • Dave Fry September 25, 2017, 14:09

      No master socket, though you have extensions? Is one of extensions a master socket, but just the old style? Is the BB router plugged into an extension?

  • Lee October 2, 2017, 20:22

    Hi, I’ve moved into a new build and there’s an OpenReach 5C Master socket installed. Randomly all the even numbers on the speed checker show fibre capability but the odd numbers on the other side of the road don’t (I’m an odd number!).
    I’ve unscrewed the master socket as it wasn’t installed correctly, and the main cable coming into the property has an orange, blue, and 2 white wires that appear identical. Our line isn’t working and just wanted to check what wires from the mains cable should be pressed into A and B if you could help please? Any help would be appreciated! I’m hoping the odd numbers on my road will be able to get fibre at some point too, strange when the contractors said they are all wired the same

    • Dave Fry October 3, 2017, 13:05

      Are the 2 white wires actually : a White wire with a Blue stripe and a White with an Orange stripe?
      Can you strip a centimetre or 2 of the sleeve. The wires should be 2 twisted pairs.
      Which 2 were in A and B. Do you have a volt / test meter of any kind?

  • Dean October 23, 2017, 15:55

    Hi can you help,put in new nte5 master socket as needed to move as the old one stuck under loft conversion floor,main wires in which go to A and B are in a black sheve and there are no colours,ie green or orange etc any ideas thanks.

  • dave November 27, 2017, 14:36

    Hi, we have a detached office to our property can i take an extension for my broadband by double wiring from the bt openreach MK3 to the office overhead and connecting to a new MK3 box.

  • Mac November 29, 2017, 15:34

    Excellent! Exactly what I needed to know to rewire my mother’s home phone system as broadband is mega-slow (am network professional and all the rest tests OK) so this is the next thing I’ll do.
    Thank you

  • Jeffrey Nicholas February 18, 2018, 19:56

    Hi Dave,
    We’re about to move into a property this week and the Openreach master socket is in bits on the window sill and there are four wires coming from the hole in wall where I assume the socket used to be.
    I have been informed by someone online that the white wire goes to A and the orange wire goes to B. There are also a green wire and a black one too.
    Will I have to call Openreach out or is it straight forward and what happens if i connect it wrong and short it out if that’s possible?
    I found your site on a google search and thought I would ask for your advice as you seem to be a wealth of knowledge on the subject.
    Kind regards

    • Dave Fry February 24, 2018, 13:00

      Hi Jeff,
      I have emailled you this … Please see attached pic. You can test which pair are live like this… It’s a 3 handed job! The phone may not ring on incoming calls like this, some phones need the master socket to ring, some don’t. But this will prove which pair are carrying the live line. White/Orange or green/black. White/Orange were normally primary. You can call 17070 and you should get a voice telling you your phone number.
      Avoid touching the wires together as you’ve stripped a bit off copper of each. When you strip them, do each one separately, and again, when you cut off the sripped bit of wire, cut one at a time.
      The voltage on the line is 50 Volts DC, low amps. If someone is ringing the voltage is 100 ish V AC, but again low amps.
      Polarity isn’t an issue, except for some old old fax machines and alarm systems.
      Let me know if this helps!

  • Richie C April 1, 2018, 10:40

    Hi Dave, I really hope that you can help me. I have a BT Openreach master socket (which works fine) but in a separate room I have an nTL socket which doesn’t seem to work – as in, I can’t get internet from it when wired up to my laptop. I spoke to BT customer help who say that replacing the nTL faceplate would solve the issue but she also told me to replace it with a £75(!!!) faceplate and to get an engineer to fit it for me at the expense of a further £129.99. I was wondering if there was anything that I could do/check which wouldn’t require an engineer to assist me. Thanks in advance. Rich

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