I recently bought a place already wired with Cat 5E (8 ports, leading to a central closet). However attempting to get link, nothing works. On closer examination, it was obvious that the ends in the closet were wired backwards (brown on pin 1, etc). The jacks that I've pulled out of the wall do look to be correctly done. However, testing with a network cable tester shows zero link between any of the jacks and any of the ports in the closet - I had expected to just see a 1/8, 2/7, ... 8/1 mismatch, but instead get nothing at all.

The runs are accessible and look neat, though they take some bends that seem quite sharp and are in some cases much longer than they need to be (the person who put this in was a professional electrician but I suspect this was the first time he ran network cabling).

My best guess at this point is that he either bought bad cable, or put so much tension on it that he snapped wires. Though it seems surprising/unlikely that I wouldn't get at least one active wire on one of the 8 lines.

So, my question: is there anything else I should try or test before I go ripping out everything and running new cable?

Update: for the exciting conclusion, see my answer in this question below.

  • 2
    Have you visually confirmed that the one end of the wire actually goes to the other end of the wire, and not to some other patch panel or wiring closet, or are you trusting the labels on the jacks? It seems odd that nothing is contiguous.
    – smithian
    Oct 17, 2012 at 21:27
  • 1
    Maybe they are numbered wrong?
    – hookenz
    Oct 17, 2012 at 23:46
  • When you move into premises that are already cabled never assume anything and always test or get someone else to test, that all wiring is correct. Oct 18, 2012 at 2:40
  • @smithian +1 for a good question - I was definitely suspicious about that, especially as they also wired the phones with identical blue CAT5 (argh), and there are no labels on the jacks or the lines in the closet (ARGH). But because the runs are visible I was able to visually trace, and no, no other patch panel I can find.
    – Jack Lloyd
    Oct 18, 2012 at 14:30
  • 1
    Did you test your cable tester itself? Oct 19, 2012 at 7:26

3 Answers 3

  1. Don't run CAT6 cable

  2. If the bends in your cable don't exceed the minimum bend radius for the cable type then it's not an issue.

  3. If the cable lengths don't exceed the maximum cable length (in your case 100 meters/328 feet) then it's not an issue.

  4. Why run new wiring when you can simply test the existing cable (not the terminations but the cable itself) and then reterminate one or both ends.

  • 1
    Why not run CAT6?
    – HostBits
    Oct 17, 2012 at 20:44
  • 1
    Because it's unneccessary. CAT5 and CAT5e are both perfectly acceptable for speeds up to 1Gbps and CAT6a should be used for 10Gbps.
    – joeqwerty
    Oct 17, 2012 at 20:49
  • 5
    If you're running new lines, for the cost difference, you might as well run CAT6. Yes, CAT5e is perfectly fine for 1Gps, but a few years down the road you may need CAT6 to the workstation.
    – HostBits
    Oct 17, 2012 at 20:54
  • 1
    Yes, but then you'll most likely have to replace the CAT6 with CAT6a for 10Gbps. Why run CAT6 for 1Gbps when CAT5e will do and the jump to 10Gbps should be CAT6a. If you're running anything up to 1Gbps then go CAT5e, if you're running 10Gbps then go CAT6a. CAT6 is a non-starter.
    – joeqwerty
    Oct 17, 2012 at 20:56
  • 4
    How many places actually need anything faster than CAT5? Most places/users wouldn't even notice the difference between 100Mb and 1Gb. Reality: Extremely few users transfer the volumes of data that would make higher speeds noticeable. Oct 18, 2012 at 2:48


Considering there is so much contention on this, I've updated the answer:

There are two basic options here:

  1. Rewire. As mentioned above, if you can't be certain all the existing cabling is worth reusing, you may be better off starting from scratch. Hiring a contractor that will run everything, and certify the runs is certainly easier, but maybe not cheaper.
  2. Fix the problems with the existing cabling. Here you must check each cable run for shorts, and each end for proper termination, ensure the cables are run within specification, and within the specified bend radius. You should also determine if Plenium cabling has been run (if required). You should get a good cable tester/certifier, and check all the work after it has been corrected.

There is a cost/benefit tradeoff on either option. If you choose to go with the rewire, I personally see no reason to run older standards, unless the cost is truly too great to run CAT6a.

  • Terminating CAT6a is a tremendous pain in the ass if you don't need 10G. And let's be honest, who's running 10G through structured cabling anyway?
    – smithian
    Oct 17, 2012 at 21:25
  • 1
    Maybe for the one doing the cabling, I'd hire a contractor to do it and certify it.... oh and I think someone once said "Change is the law of life. And those who look only to the past or present are certain to miss the future."
    – HostBits
    Oct 17, 2012 at 21:30
  • Yes, and someone also once wired their facility for 100Mbps token-ring, and found out that the future is mutable and inconstant. Also, Jack doesn't sound like he's getting a contractor any time soon if he's hunting down his own wiring faults.
    – smithian
    Oct 17, 2012 at 21:40
  • Whoever downvoted, care to explain why?
    – HostBits
    Oct 18, 2012 at 0:09
  • 2
    I'm downvoting because this is very poor advice. Without first making a proper assessment of the situation and what will be involved in rectifying it, it's just insane to start running all new cables. I suspect you've never had to foot the bill for such work. It's an absolutely trivial job to re-terminate the ends of cables that need it, especially considering that it would have to be done on new cables anyway. Oct 18, 2012 at 2:44

Last night I decided to reterminate the obviously bad ends in the wiring closet just to see what would happen (and because I haven't done my own cables in a few years and figured even if it did nothing I could use the practice). After reterminating I can get link on all ports. So seemingly they somehow managed to do everything OK except royally screwing up the network closet. I don't understand why my cable tester showed zero signal before, perhaps they had not crimped them tightly enough to get a good contact, used bad RJ45 connectors, or maybe my $6 cable tester was priced at that for a reason.

I'm accepting joeqwerty's answer because his advice re reterminating and testing before rewiring was sound. I'm still pretty skeptical of the cabling work, given the total newb errors in the terminating, and if I have troubles in the future I will likely rewire with 6a for 10 gigE so definitely a +1 for Cheekaleaks's answer as well. I don't really need 10 gigE, but the extra cost of 6a vs 5e pales in comparison to my labor input in rewiring, so a new 5e install wouldn't make sense here.

Thank you both for your responses.

  • 1
    the cheap cable testers will completely fail when hooked up to specific types of miswires. designing a product that could handle all types of miswires would cost more. :) i bet if you looked in your documentation (if it's not too cheap to include any) it would tell you that no indicators means either no connection at all, or indicate a specific miswire.
    – longneck
    Oct 18, 2012 at 14:57

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