Cat 6 cable stopped working, sort of. - Page 1
Forum section: electronics / general

author: connectTek
author_rank: Regular Contributor
timestamp: February 16, 2023, 04:31:24 am
content: I had a customer call me that his internet had stopped working in his shed. I did not do original install. It was working previously as I had added an Acces point to it.The cable is a cat 6, underground about 60m( in conduit).I do a continuity test, no problem, I do a cable length test, 220m ,WTF!Now, I connected to my laptop, I it works fine, no problem, YET when I plug it back into the switch, ( on the shed side) no go.I changed switch in the shed and even the modem in the house.I'm stumped.Any help would be much appreciated.

author: james_s
author_rank: Super Contributor
timestamp: February 16, 2023, 04:44:35 am
content: Have you tested it for signal integrity with a cable tester? Is it rated for underground use? It's pretty likely that the conduit is filled with water submerging the cable. It's also possible the problem was with the termination on one of the ends.

author: Halcyon
author_rank: Unknown
timestamp: February 16, 2023, 05:03:44 am
content: Yeh sounds like possibly corrosion or something is impacting the cable integrity. Rather than trying to troubleshoot, it'll probably be easier to replace it with a new length cable (or fibre).

author: MrMobodies
author_rank: Super Contributor
timestamp: February 16, 2023, 05:35:25 am
content: Did you do a flame test on the conductors?

author: jonpaul
author_rank: Super Contributor
timestamp: February 16, 2023, 05:41:29 am
content: Of the 4 pairs, one is either poor connection, corroded eg at RJ-45 crimp connector, or dirt, corrosion creating a leakage paths to earth or another pair.Ger an Ethernet cable checker, orjust Short the four far end pairs togatherCheck resistance at the four near end pairs.Use wire table at correct L and AWG to find loop resistanceBon chanceJon

author: connectTek
author_rank: Regular Contributor
timestamp: February 16, 2023, 11:43:56 am
content: I have re terminated both ends.Yet when I directly connect my laptop it works fine, full speed ,no problems. It just doesn't work when connecting to a switch, of which I have replaced.

author: Psi
author_rank: Super Contributor
timestamp: February 16, 2023, 12:25:04 pm
content: Quote from: connectTek on February 16, 2023, 11:43:56 amWhen you exceed the length spec odd things like that can happen, sometimes it will work and sometimes it wont.Now I doubt it actually is 220m long, but that is a sign of something seriously wrong with the cable.One question though, are you sure your laptop is trying to use the cable at the same speed as the switch?1gig, 10gig 2.5gig etc.

author: JohanH
author_rank: Frequent Contributor
timestamp: February 16, 2023, 12:46:54 pm
content: It happened once that the local electronics shop had to send back their rolls of CAT6 cable to the importer when someone found out that the cable didn't actually work for longer lengths than 30 m or so. Continuity check was OK, but no devices wanted to negotiate after a certain length. So the cable was bad quality.But it's odd that it works with the laptop, but not the switch. Possible that the network card in the laptop is more forgiving?

author: connectTek
author_rank: Regular Contributor
timestamp: February 16, 2023, 05:40:21 pm
content: Thanks guys.Will pull new cable next week.Will update on what I find.Cheers

author: jonpaul
author_rank: Super Contributor
timestamp: February 17, 2023, 01:32:23 am
content: A lot of Ethernet cable made,in China is non-compliance to the IEEE and IEC,specs.Suggest you buy only Belden CAT 6, etc.See Belden site for attenuation, phase, abberation per m legnth and vs freq.Jon

author: py-bb
author_rank: Regular Contributor
timestamp: April 03, 2023, 09:46:01 am
content: Quote from: connectTek on February 16, 2023, 04:31:24 amI've got a damaged cable - one of the pairs got nicked (at least) in a single spot. Anyway it will ONLY work between NetGear switches, so you can have situations where devices connect but other devices wont.This is all I have to offer sorry.

author: wraper
author_rank: Unknown
timestamp: April 03, 2023, 10:03:52 am
content: Some devices are more tolerant to bad or too long cables than others. Nothing that surprising here. Also did you check in what mode it works, I would expect 100Mbit which uses only half of twisted pairs.

author: sokoloff
author_rank: Super Contributor
timestamp: April 03, 2023, 11:11:37 am
content: An underground conduit is a wet location. I ran fiber through mine to the garage to avoid continually replacing a dry-rated cable or chasing down 30 meters of gel-filled Cat-6 (and dealing with the mess of that on both ends).

author: bitwelder
author_rank: Super Contributor
timestamp: April 03, 2023, 11:50:04 am
content: Depending on the switch where the cable is plugged, there might be an option to check 'cable-diagnostics' which can also tell you for each twisted pairwhether it's OK (from its point of view) and even the approximate length.

author: connectTek
author_rank: Regular Contributor
timestamp: May 14, 2023, 08:13:01 am
content: I have installed a wireless link, problem solved.Thanks guys.

author: BTO
author_rank: Frequent Contributor
timestamp: May 15, 2023, 02:41:47 pm
content: OK, I DO THIS FOR A LIVING AND I'M VERY GOOD AT IT1. This comes down to what testing equipment you have and where your knowledge is at on this subject2. Re this"I do a continuity test, no problem, I do a cable length test, 220m ,WTF!"WTF.. Easy !!Firstly what does "No Problem" Mean ?I know what the general consensus is , but many a time have i seen a tech that said "No problem" and there was a problem.More specifically, you mean "No problem" In your opinionOk. so When you say CONTINUITY TEST do you actually mean a continuity test or was it a resistance test or did you usea Basic $20 network tester ?In any case, Continuity testing only gives you part of the picture , and it's only a basic testHENCE WHY YOU GOT THE PROBLEMyou apparently know the cable is 60m (The Max Segment length, by the book is 100metres)so when you say Cable Length test, do you mean T.D.R. ? (Time Domain Reflectometry)if so... you are getting the result of a longer cable because ... the way TDR Works is, it sends a signal down a cable (you need to enterthe AWG setting for the cable diameter and type) THIS COULD BE ONE ISSUE, It sends a signal at a known VOP (Velocity of Propogation)and when it hits an open or other fault a reflection is created that travels back to the sourceThe meter measures the time taken, Divided by 2 (to give the one way cable length)The signal was attenuated as a result of RESISTANCE on the cable (likely you have a bad joint, Rusted or Corroded cableand one of the pairs is broken but just barely hanging onYou want to do a WIREMAP TEST (with a tester that gives cable length readings on all pairs)all pairs should be approx equal length (but not exact)Another thing you could do is this...since it's a 4 Pair UTP(this is the cheap way around the problem)Get a multimeter, Test it with a known resistor in resistance mode for accuracyGo to one end of the cable, Chop off the connector and short the pairsshort Blue to Blue/WhiteShort Orange to Orange/Whiteshort Green to Green/WhiteShort Brown to Brown/Whitebut not to each otherNow go to the other end, crack out your multimeter and check the loop resistanceson a 20 metre cable you should expect to have less than 5 Ohms resistancecheck each pair to see which pair has the high resistance, it's likely you'll find at least onelet me know how you goUPDATE :ahh i see you found the problemDamaged Cablelet's always remember out basics shall weOSI MODELLayer 1 Problem (Physical layer) - aka Nicked Cabletherefore causing a non optimal connectionTHUS LEADING US TO OHM'S LAWCausing INCREASED RESISTANCEWhich in turn explains your 220m TDR ReadingAlways remembershort all the pairs on the end to the corresponding white wirebut not to each othertest the resistance on the other endALWAYS REMEMBER THE BASICS, they really do save you time

author: David_AVD
author_rank: Super Contributor
timestamp: May 15, 2023, 10:21:08 pm
content: Split pairs can also be a problem. The cheap testers won't discover that as the pin 1..8 still go to 1..8 , just not in the correct pairing.