I am working in a customers home and they have a home full of cat5 cabling. I have put a router in the main network hub where all the cables from the house come in. I have used a phone to identify a cable and I plugged one end into the router and at the wall plate I plugged in an access point.

My problem is, the line works perfectly fine, clear audio for a telephone. But with data there is no response, no blinking lights, its just like the device isn't connected (but it is).

I thought to myself maybe the person who installed the cabling only connected the required pairs for telecom but not for data. So I took the wall plate off the wall and sure enough only the blue pair was connected. I used a 110 punchdown tool to punchdown the cable to match the standard found at the main hub. T568-A. But the data still doesn't work on any of the ports apart from 1.

So far I have tried using every other wall plate in the home. The only one that worked was one in the study (after me having to punchdown the data pairs).

Interestingly enough, after talking to the home owner, he studied electrical engineering. He also has no idea why phone works and data doesn't.

We thought their could be such thing as a telephone only jack. So that even when you punched down data is still wasn't electrically connected.

Extra notes.

  • ALL the ports in the house on the walls and in the main hub are all RJ-45 Cat5 (we think). Their is no RJ12/RJ11 plugs in the home.
  • The study port only worked after I terminated the data pins.
  • We have tried almost every cable in the home.
  • PoE support is required on the line once up

Any help is greatly appreciated, thanks in advance.

  • Are you sure it really is Cat5? What speed Ethernet are you trying to run on it?
    – brhans
    Jan 6, 2016 at 22:16
  • There is no writing on the cabling. It is just blue insulation with the normal 8 pairs with the usual colours. All the wires in the house are the same type of wire and the one we got working got 10/100.
    – Zac
    Jan 6, 2016 at 22:18
  • We are aiming for gigabit, but I think we are setting our goals a bit high.
    – Zac
    Jan 6, 2016 at 22:18
  • 1
    I believe Cat5 is only supposed to be good for 10/100M - if that cable is even Cat5. I think GigE needs Cat5e at least. The Orange/Green/Blue/Brown pairs don't mean its Cat5 - could easily be Cat3, which would only be useful for 10M. Compare the 'twistyness' of a pair in a known Cat5e or Cat6 with what you have. If you find your installed cable is less 'tightly twisted' then its almost certainly a lower Cat number and probably not much use for Ethernet. You may have just been lucky with the 1 you got working - is it the shortest distance by any chance?
    – brhans
    Jan 6, 2016 at 22:32
  • Ok, I will try that today. But doesn't it not matter why standard it is? Even if it was Cat3 would I still see the blinking lights on the connected devices?
    – Zac
    Jan 6, 2016 at 22:34

4 Answers 4

  1. Make sure that it's punched down the same on both sides (choose A or B)
  2. Make sure the cable is actually rated at Cat.5

Why this will do voice lines: The two inner lines on 8P8C are arranged the same as on 4P4C connectors (You often call these RJ45 and RJ11 respectively). The outside pairs are then grouped. This meant that a business could upgrade the cable and still use analog phones up to two lines before converting over to digital.

My attempt at a view:

4P4C______________________________ 8P8C (see the little 4P4C inside the 8P8C)

2-1-1-2 (Data lines 1 and 2)______ 3-3-|2-1-1-2|-4-4 (Data lines 1-4)

  • Ok, I have made sure both sides use T568-A. The cable that comes into the main hub is acutally terminated using a mod plug not a patch panel.(Thats not the only dodgy thing the installer did). But there is no writing on the cables to say it is cat5 or cat3, etc.
    – Zac
    Jan 6, 2016 at 23:49
  • I have not yet ever come across blue cat3 cabling. Did they ever make cat3 cabling in blue?
    – Zac
    Jan 6, 2016 at 23:54
  • That's not normal. All Cat. cable I've ever seen (I've used 1000' bulk reels 1' segments and everything in between) have markings on them. It makes me doubt that it's Cat. cable at all.
    – Dave
    Jan 6, 2016 at 23:56
  • Jacket color didn't used to be standardized. So that might not be of help. especially if the installer was "dodgy"
    – Dave
    Jan 6, 2016 at 23:57
  • The interesting thing is that I'm getting a decent speed on one of the PC's connected to this old cabling. I haven't looked at what speed it come up as on the pc but it was most likely at least 10/100. This is what is confusing me so much.
    – Zac
    Jan 6, 2016 at 23:58

The pairs in use for phone are 4-5 for line 1 and 3-6 for line 2. Each line only requires 2 wires.

For Ethernet 10 and 100 base, 1-2 and 3-6 must be connected as a minimum. Ethernet requires one pair for transmit, other for receive. For Gig base, must also have 4-5 and 7-8. May require better cable. POE also requires those to be connected as power is sent over them.

So if only the 4-5 pair is connected that's why the phone works, not Ethernet. Test your wiring - get a checker and plug one end into the wall jack, other on the other side of the cabling and it will see if all the pairs are connected correctly.


I suspect its depressingly common for electricians to claim they can wire up a house for data, and then do it wrong (its happened to me once, nearly multiple times, and the data wholesalers I use say its a common problem).

It sounds to me like the house has been wired incorrectly - most likely they have simply daisy-chained pair one between points, rather then running seperate cables back to a central point. If they have done this, you are SoL, and may want to look at an alternative solution (WIFI, PoE) to get round the problem - or maybe you can pull cables and rewire the house.

You should get yourself a cable tester. These are inexpensive devices (about US$10 - for the one I found on Amazon), and plug in each end of the cable to test you have continuity on all the pins, and that there are no crossed wires.

  • This is the really interesting part and here is why an electrical engineer and me together cant figure this out. Each port with a phone connected has its own wire. We can isolate each individual port in the house. In the bedrooms they have linked the ports together and we can see that by pulling off the wall plate and tracing and tugging on wires. We have made sure that the cables we want to use aren't linked. This is why we are so confused. I am taking a cable tester today. (Forgot it yesterday). Thanks anyway.
    – Zac
    Jan 7, 2016 at 2:09

It is possible that pairs got miswired. As other answers have pointed out, ethernet uses the outside pairs for 10BaseT and 100BaseTX. The pairs will autonegotiate for TX/RX on most modern hardware, if an outer pair got swapped to an inner pair then the cabling is no good. The pairs use differential signalling so swapping - and + on a pair is no good as well. If you suspect only the inner pairs are connected and its Cat5 Cabling you could make try making a quick crossover cable to swap the inner and outer pairs and test if you can bring the data network up.

Otherwise no lights = no link, a link is a negotiated connection between PHY's on either side of the cable, meaning an sustained electrical connection is maintained between chips on either side. Keep in mind that if the link comes up in 10BaseT mode then the amber light will not light up on a typical network card.

It may still test good with a continuity meter, if the cabling is OK for continuity and the link isn't established this means that the cabling does not meet 802.3 Physical Layer spec. If it is Cat5 I would not expect any sustainable 1000TX link maybe 1000T for short runs but you should really use Cat5E. But I would expect reliable 10BasetT and 100BaseTX links.

If it is Cat3 cabling then 10BaseT will be the only possible link that could be brought up, and runs of 100M is the theoretical maximum but in reality likely much less. You can easily tell Cat3 from Cat5 because the shield is missing, if you don't see a little bit of foil in your junction box from the end of each cable or you can easily feel individual conductors through the cabling insulation then it is Cat3.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.