Ethernet Wiring Bleg

What’s the chance that I have a bad RJ-45 jack? What’s the QC like on them? The one I’m using is similar to the one described here. I just put in a CAT-5e run, and can’t get it to work (about sixty-five feet). All the wires have continuity, and there don’t appear to be any shorts, but there’s no signal through the cable. Any ideas what the problem might be or how to troubleshoot?

16 thoughts on “Ethernet Wiring Bleg

  1. Joe

    Any chance the line is running near an AC line? If they are in parallel for more than 6 inches, it can disrupt the signal.

    It is possible to have a bad jack or a bad connector. If this is DIY connectors and you have re-crimped the ends a couple times the jack is most likely bad. Maybe 1 in 200 are like that.

    In a former life, I installed a heck of a lot of network line….

    1. Rand Simberg Post author

      There is a line a few inches away, but I don’t think the wires are running parallel. I haven’t crimped it at all — that’s not how the connector works. It slices through the insulation and grabs the copper.

      1. Joe

        Ah, punch-down connectors. The only way to know for sure is to use a network cable tester (about $30 at Home Depot) – shows all the connections and which are giving fits, appear crossed, etc. Without one, it is a long hard trial and error sort of thing. But you already know that. Hopefully you have enough extra cable for doing this.

  2. Glenn

    Triple check the wiring diagram; individual continuity doesn’t help if the wires are incorrectly paired.

    Can you fit your meter probe inside the socket to check from there to the wire?

    I haven’t looked that closely inside the sockets to know if there’s any structure to the conductors. The plugs are trivial.

    1. Rand Simberg Post author

      I’ve done it twice now, and the wiring looked right both times. I might be able to probe the socket, though. But I wish I’d thought to check that before I trimmed the wire ends.

  3. Al

    Do you have the spare cable and tools to temporarily give up on the jack-to-jack connection and convert your run to a plug-to-plug cable instead? (Testing the cable separate from the jacks.)

    Second random thought: in some styles of socket the wires making contact on the plug-side of the socket aren’t particularly sturdy. That is: I’ve had a couple where I keep a dental pick nearby to attempt to make the ‘pins’ press more firmly. (Or “at all”). The problematic sockets tend to be much older though.

  4. Josh Reiter

    I’ve crimped a couple of dozen ethernet connectors to know that those twisted pairs can be tricky. You want to mess with the twists as little as possible. Its easy to unravel the twisted pairs when trying to wrangle the wires into the connector. It’s also easy to kink those little wires which will crack the insulation and that’s it, got to start over. And you can’t strip off too much of the outer insulation either. I like it butted up right up to that connector as snug as I can get it. And of course make sure it is the T-568B wiring standard.

    1. Eric Weder

      Good point about the “B” standard. I don’t know anywhere that uses “A”, it’s like it’s a trick to fool novices.

      Also, while it may be too late now, you should always leave a couple of feet of slack in the cable run – you never know when it might come in handy, and you can always hide it inside the wall.

  5. Brian Wohlgemuth

    My guess is bad cable. I’ve had a few go on me post install. Something just gets yanked and it’s all crap.

    Get a cheap tester to see that you have connectivity across all four pairs.

  6. Dale Amon

    It’s useful to have a loopback connector as well so you can plug the far end into it and let a tester inject signals and test two way connectivity. I’ve not done it in a decade though… if a cable doesn’t work, I tend to just toss it these days.

    1. Leland

      I have to agree with Dale. Most stores sell Cat5 cable at high margins. I found a supplier that’s not as expensive. I buy bulk from them about twice a year and then toss out anything that’s bad. As for QC, I don’t tend to throw out a lot from infant mortality. Rather, something will happen as Brian describes “gets yanked and it’s all crap”. The marginal cost isn’t worth my time to test.

  7. Josh Reiter

    I had one cable that I wasted 3 RJ45 connectors on and wouldn’t connect. I ended up cutting about 6-8″ off each end of the cable and then it worked. My guess is either I got back down into a part of the cable where the twists were nice and tight. Or, there was a broken wire(s) at either end of the cable. But if that last attempt hadn’t of worked I was just gonna chunk it and scrounge up another cable. I know of a pro installer that had to look at the same wall drop about 3 times before he found it was a broken wire in the cable. But I will say that most of the time when I crimp a connector and it doesn’t work it’s because I didn’t get the wiring pattern right. If you don’t have good light those green and blue wires can look a lot alike.

  8. Man Mountain Molehill

    RJ45s are crap, plugs and sockets. Replace everything. CAT5 cable is basically gussied-up telephone wire, and not very good for fast signals like 100baseT.
    65′ is a long distance. Can you try operating the same computer on a short cable to see if it works that way? Implicates the cable or plugs if it does.

    1. Josh Reiter

      I think 65′ is fine for Cat 5e. I think 5e has a bit additional shielding running though through it that helps clean up the signal. It’s what’s recommended if you want to go up to full giga speeds I’m just thinking off the top of my head from a convergent technologies class but I think it was 150 foot recommended runs for CAT5. I’d imagine you could probably double that before you start to see dropped packets when going out that far. But otherwise totally agree that otherwise you just have to swap out stuff till it works.

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