Having some issues with the CAT3 cable in my home. A few weeks ago, I added a 4 to 1 coax converter to the access panel in my office area as that is where the main coax cable entered my apartment.

I didn't want my internet modem there as I had more devices in my living room that I want wired. So I added the internet modem + 5 port switch to the living room. I wanted to use one of the ethernet ports on the modem to send ethernet back to my office area using the CAT3 in the wall. I converted the coax + RJ11 wall plates to coax + RJ45 and used the "B" wiring standard on both ends. Plugged the end of the CAT3 cable in the office area into another 5 port switch and this is where I ran into issues. That ethernet connection from living room to office area doesn't work. I tested the connection using a tone tracker and the alternating tone makes it back to the office area with no issues. The distance does not exceed the ~386ft of CAT3 limitations either.

The other weird thing is that the two bedroom connections to the switch in the office area works just fine (checked with tone AND data transmit). Office area wall plate to the switch works too. Not sure what is going on with the ONE connection I want working... grrrrrr.

I've added a wiring diagram to clarify what I am trying to achieve.

Anything I should check? I want to add the standalone wireless router back by my office because the wifi range isn't that great back there as well in the nearby bedrooms. No real central place to put the current modem. The apartment is long and narrow. I understand the limitations of CAT3 but it is all I have so I'm trying to work with it.

Wiring Diagram

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    Do you have a tester that checks all 8 pins for proper connections? A toner is useful but not really enough. Something like amzn.to/3H7ntIs or amzn.to/3efzX4q or one of the cheaper varieties. Dec 22, 2021 at 23:24
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    @manassehkatz-Moving2Codidact I just purchased one, it will be here in the morning. I did just double check both ends and they are wired correctly. I even cut the wire from the punch down wall plug in the living room and added a RJ45 connector to it and plugged the new end straight into my modem and nothing. Wondering if there is an issue with the cable behind the wall. I guess I will find out tomorrow when the tester comes.
    – Jeffery
    Dec 23, 2021 at 1:02
  • sometimes the wires break inside the insulation, or one of the RJ45 contacts gets kinked or hung up, the "blinkenlights" tester will let you know if that happened.
    – Jasen
    Dec 23, 2021 at 6:07
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    There's also the possibility that having been used for phone, some splice/tap you haven't identified is causing the problem. Phone wiring works fine with those - ethernet wiring does not.
    – Ecnerwal
    Dec 24, 2021 at 16:14

1 Answer 1


You can't really use CAT3 for useful Ethernet these days. 10BASE-T at most by specification. 10/100 if you're having a good day, but don't rely on it. Certainly not gigabit.

If you're not able to pull some new cable, and if wireless is insufficient, use MoCA Ethernet adapters, since you already have coax everywhere.

  • Yeah, the internet needs more cats these days, preferably 6 or more. (CAT 6)
    – Jasen
    Dec 23, 2021 at 6:09
  • I think I will go this route... it will make sense to have the maximum speed I can for my desktop and then I can take the ethernet connection from the the MoCA adapter and feed it into another switch in my office for those components and then send one of those outputs from the switch back to the switch I put in the wall to feed the two bedrooms.
    – Jeffery
    Dec 23, 2021 at 16:57
  • Ok, best of luck! If you've found this answer useful, you can accept it by clicking the checkmark to the left.
    – Brad
    Dec 23, 2021 at 19:37

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