We recently moved into a house where there is cat5e wiring running from a telephone jack in each room, to the rear of the house near the phone junction box and electrical box. The wires are literally just hanging out of a sealed exit point in the siding of the house, not running into a box of any kind.

I wanted to set up a new wired network connection from an upstairs bedroom to the living room. New wiring installation is virtually out of the question, thanks to insulation, fire blocks all over the place, and the fact that the wife and I both don't want to mess up the drywall in our new home. So I have chosen to repurpose two of the cat5e wiring runs into one connection, by splicing the two appropriate wires together out back. I wired up a cat5e jack using punchdown connectors both in the living room and in the upstairs office, and just hand-spliced the wires together out back and tried to weatherproof them by passing the splice into a weatherproof cable box and securing them with strong electrical tape. They are untwisted for about 3-4 inches and are sharply angled at the splice point. I know it's not optimal but I wanted to at least see if what I was after was even possible given the unknowns of the wiring, etc.

Upon testing, I can get a solid connection over the line, so I know I've done the wiring correctly (used T568A due to the fact that these are originally phone lines and might be again one day). However, tests show that my download speed from my computer, connected to the router upstairs, to a laptop in the living room is only around 23 mbps, so I'm barely even getting fast ethernet speeds. I'm hardly expecting gigabit, with run lengths and connections like this, but what can I do at this point to increase throughput? There are factors I know I can control (how the splicing is done out back) but I don't know how much of a difference that will make. Then there are some variables like proximity to 110V lines in the walls, and quality of cable (it's all UTP) that are either unknowns or out of my control. I do know that the wires out back are fairly brittle, due to weathering, which is part of the reason I didn't want to poke around with those much. Does anything stand out as a glaring issue to anyone experienced with cat5/6 networking?

  • What download speed do you get with both computers directly connected to the same router or switch?
    – TomG
    Jan 1, 2013 at 20:54
  • That's how I've been doing it. Or do you mean in the same room? Its close to full speed -- the hard drive read speed becomes the bottleneck then, or so I'm assuming.
    – trpt4him
    Jan 1, 2013 at 21:20
  • What does the 23mbps through the new wiring compare to when you are not going through that wiring? i.e., you say "I'm not expecting gigiabit", what is your expectation?
    – TomG
    Jan 1, 2013 at 22:08
  • I think this is off topic for this site, maybe a better fit for serverfault or electrical engineering?
    – Steven
    Jan 2, 2013 at 1:37
  • 1
    FYI - T568A and T568B are identical in function, it's just the color scheme is different. In both cases, the blue (middle) pair is used for analog telephone, and orange+green is ethernet. However, gigabit ethernet uses all 4 pairs.
    – gregmac
    Jan 2, 2013 at 15:08

3 Answers 3


If you are running telephone and ethernet on the same cable then it is most likely interference from the telephone pair. POTS (Plain Old Telephone Sockets) have a constant voltage of 50V and ring at 75V with an engaged voltage of 35V.

It will not be the electrical 110V causing interference because your switch cancels the noise out because it if grounded(negative) to your home installation(on which your switch runs and knows about this frequency so it can eliminate is successfully).

Why will it pick up noise from the telephone voltage? Because the power is coming from outside your house on a separate ground loop that has a unique frequency resonance which is not the same as your houses' frequency(not talking about 50hz/60hz - But electromagnetic radiation). This will cause the switch to suffer packet loss because it cannot successfully XOR noise that is generated from the phone lines voltage frequency.

To solve this problem in order of cheapest to most expensive:

  1. Do not run the phone line on the same cable as Ethernet.
  2. Buy a VoiP router like Linksys SPA family and plug your phone line in there and route all traffic via ether to IP phones.(But also you can then run the phone out from the SPA because it is grounded at your home and you are within the loop)

Please Note:

Some distribution boxes have a lightning protector or surge protector installed that link in the actual earth(also called ground) but earth is used in UK, Some parts of EU and ZA(not sure about USA) to detect appliance fault and gives lightning a short path to the earth. Usually the earth bar is connected to a rod that goes into the ground outside the house or bound to the incoming phase shield which is earthed at the main power box. When I talk about ground I mean the actual negative(-) wire of an appliance or analog / digital circuit.


As it seems the OP grounded his telephone but it is most likely earthing the cable not actual negative.

Doing this can cause damage to the telephone network costing you thousands dollars and/or cause death or serious bodily injury from electrical shock. Remember that the ground of your home has a different impedance than ground from the telephone network and can result in 110V electrical shock! That is why it is illegal to rewire telephone sockets in many countries. For your own safety.

  • not sure if i am misunderstanding you but i grounded my home phone together with my cable and some gas flex pipe all to the ground bus in my main panel (using AWG 10 wire). are you saying that phone shouldn't be grounded together with the rest?
    – amphibient
    Jan 2, 2013 at 22:49
  • How? You mean the incoming telephone line? or what. Jeez.. does the telephone have a shield that you grounded it? Possibly it is just lighting surge not actual ground.. you must post a pic because that is weird?
    – Piotr Kula
    Jan 2, 2013 at 23:37
  • Telephone happens at a totally different frequency spectrum (namely a few Kilohertz at most) than fast Ethernet (around 100 MHz). These two don't interfere each other, even, if cables run along many meters. I can tell so, because in my former office, we ran everything over CAT5e: Gigabit Ethernet, POTS, ISDN and even USB (through some special converters / extenders).
    – Kai Petzke
    Sep 25, 2021 at 9:15
  • using extenders is fine as it mulitplexes the signal into an ethernet frequency. the problem here was two different kind of voltages really running on the same cable. This causes electromagnetic interference that cant be handled by the noise cancellation hardware on the switches.. since it has no reference of it.
    – Piotr Kula
    Oct 5, 2021 at 8:28

I think you may be suspecting that the existing telephone wiring is CAT5 cable when in fact it may not be CAT5 at all. Four pair telephone wire can look a lot like CAT5 cable when in fact it is constructed in a different manner. The wire gauge may be different and the characteristic impedance of the cable may be different. Also note that cable specified for data comm such as Ethernet have special twist specifications for each pair in the cable that are different from one another.

Very short run Ethernet over improper cable can be made to work but when you start talking about trying to send the signals over a respectable distance then factors such as wire gauge, characteristic impedance and elimination of impedance discontinuity on the wire run can play a huge role in the success of the connection. I can say with pretty good assurance that the use of the twisted splices that you described making are certain to represent a nasty impedance discontinuity in the cable run. These can cause signal reflections in the cable can result in significant loss of signal strength and quality at the receiving end of the cable. Remember that 100 MBit Ethernet is an RF signal and the attributes that I mention for the transmission line need to be good quality and to design specifications for it to work properly.

  • The cable is definitely CAT5e, it is labeled as such. Point taken on the splices introducing impedance issues. I wonder if crimping both ends and using a coupler would be better or worse?
    – trpt4him
    Jan 3, 2013 at 13:55

I guess, your best bet is to get a waterproof box and a low cost Gigabit switch. Then crimp plugs onto all those cables hanging outside and plug them into the switch. And then put everything into the waterproof box.

Alternatively, get an ethernet patch panel AND a switch AND the waterproof box AND enough short cables, then connect all the hanging cables to the patch panel, and use short ethernet cables to connect the patch panel to the switch. This variant might be easier, as connecting cables onto a patch panel is somewhat more straightforward than fiddling them into an RJ45 plug and crimping that one.

Your manual splicing of ethernet cables causes reflection of the signal, and that causes high noise level and many retransmissions. I have been in a similiar situation as you, and I have tried the splicing myself, and had lots of problem. Then I choose the solution with the switch and everything got well.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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