Finding fault in damaged ethernet cable - Page 1
Forum section: electronics / repair

author: Woozellin
author_rank: Newbie
timestamp: June 13, 2023, 08:21:19 pm
content: Hey guys!I'm looking for some feedback on how to find a fault or test an ethernet cable over long distance. This is a ~250ft run from our house to our garage, outside, buried about 3-5inches, in pvc pipe. (Would have been deeper, but our yard is a rock minefield...Pretty much cant stick a shovel in the ground without hitting a rock.)This is a run for a wifi access point in the garage. It's been working fine for years, but a while back I noticed that it went from 1gbit to 100mbit connection (LED on that port changed color). And now it is getting no connection at all. (The port LED intermittently comes on and off.)This is regular cat5e bulk cable (yeah, wish I knew about the heavy duty shielded stuff years back when we ran this.) It's ran inside gray pvc pipe that slots together. It's mostly ran thru the yard, but does cross under the driveway also.What I think happened is, a while back, we had a concrete sidewalk poured, and, unfortunately the ground was soft, and I think the concrete truck stopped right over this pipe. I think it may have cracked the pipe or sheared a pvc connection point, which may have damaged the cable (or at least some of the wires) or opened the sheathing, and has allowed water ingress, which may be causing corrosion which would better explain the slow deterioration and intermittent nature. This is just a guess though.There are actually 3 runs of cat5e in the pvc, one for the AP, one for backup, and one being used for phone line. I have already switched to the backup cable, but it is now having the same issue..I have used an ethernet tester and it's showing that some wires are connected, some are broken (in both cables.) Though I'm not entirely sure how reliable this is as even though it's lighting a LED for each wire it tests, it still need to use a second one for ground return.. I have tried splicing the 'good' wires from both cables, into one rj45 but it's still not working.I do have one of those cheapy ethernet wire trackers, however, it's having a hard time going a couple inches thru ground, and pvc. Plus, since some of the wires are still 'good' - this can't really tell me where the fault is.Sorry for the novel! Before I tear into the 3rd 'phone' line, I figured I'd ask if anyone has any ideas or feedback on things I could try to either a) find the fault along the wire (I'm open to modifying things, or building something that could do this). Or b) test each wire of the 4 twisted pairs, and check for possibly a short (from corrosion) between wires or a voltage difference between wires to see if some are truly unaffected. I feel like this would be easier with a known good wire to use as ground..Thanks, I appreciate any ideas or feedback! I REALLY don't want to dig this up (it wouldn't be too bad, if not for the THOUSANDS of rocks) - although it's starting to look inevitable..

author: kripton2035
author_rank: Super Contributor
timestamp: June 13, 2023, 08:34:04 pm
content: you need something called a TDR meter, that will display where is the fault on a cable.some details here on the basic principlehere some "not low budget" ethernet tester that has an integrated TDR meter

author: Ranayna
author_rank: Super Contributor
timestamp: June 13, 2023, 08:40:31 pm
content: Honestly? If a cheap crappy tester already shows issues, and you can confirm that the tester works by testing a known working patch cable, that seems conclusive for me.I have often seen these tester show false good, but never false bad.You *might* be able to splice two cables together, if, and only if, you have four working pairs in total. Pins 1-2, 3-6, 4-5 and 7-8 of the Ethernet port are a pair. You cannot split these, especially at this length. Since you say that 100 mbit/s works (on both cables?), you can try to use the 1-2 and 3-6 pairs of both cables.But the twisted pairs in a cat cable have different turn rations. I have to admit that i do not know how much these really matter.But there very well can be damage on these pairs that the tester cannot see, but do not allow gigabit. The crap testers only do continuity checks at DC, while gigabit Ethernet is at 62.5 MHz.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: June 14, 2023, 12:16:56 am
content: These long, underground runs can be frustrating when they start throwing problems.Ensure that the terminations at each end are fine before deeming the underground cable as fail.The problem with cat-5 fed into conduit underground is how it is often not done with care in regards to kinking the cable and preventing randoms from walking on the cables before they are pulled through and terminated.Bane of my life at one point.I recommended this product if you are frustrated with cheapy testers and intend to try and fix it yourself.

author: Mr.B
author_rank: Unknown
timestamp: June 14, 2023, 12:32:39 am
content: A TDR tester, as suggested above, is the easiest way to locate the break or short.However, if you can use the duf cable(s) as a draw wire, it will be a lot cheaper to replace the cables than buy a TDR tester.This assumes the conduit runs the full distance and has not been too badly damaged...

author: Muttley Snickers
author_rank: Unknown
timestamp: June 14, 2023, 12:57:04 am
content: If any water or condensation has accumulated inside the conduit then the cables are likely to be saturated and prone to corrosion and inturn intermittent then permanent problems. Depending on the diameter of the conduit you may need to pull a new cable through using either the existing cables or a couple of joined cable snakes. Using 60 meter 3 then 4mm snakes we can generally push the rods up to 100 meters depending on the conduit diameter.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 14, 2023, 03:16:04 am
content: This reminds me of a job where the lights in an outdoor retaining wall started to trip their breakers after about 8 years of use.The homeowner had the underground electrical conduit installed and inspected coming from the crawlspace to the retaining wall.We were able to determine it was when the cement mason came to pour a short run of steps that he found the conduit to "high" so instead of calling the electrician to correct the problem he instead took it upon himself to take a sledgehammer and pound the conduit deeper into the Earth

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 14, 2023, 05:18:03 am
content: Speaking as an electrician who has done extensive data cabling.I'd just replace the cable straight up. You know it's bad, and finding where the fault is with a TDR isn't going to help change that.Pull the cable out (tie a pull string on first so you can pull a new cable through later), check along the length of the cable for damage, then follow that same distance down the conduit run and dig where X marks the spot to find yourburied treasurebroken conduit and repair as needed before pulling a new cable through.Using a string first allows you to cut and retie the string as needed to complete the repair of the conduit (i.e. if a section of the conduit needs to be replaced etc.)If the old cables won't come out due to a crushed conduit, I'd either just start digging at the most likely point of failure (driveway in this case) or stick a snake wire/fish tape/etc in one end of the conduit and feed it in until it stops, pull it out and then lay it along the cround to see how far it goes (repeat from the other end too if you like for a sanity check). The end of your snake wire/fish tape is the magic spot.I've repaired a bunch of underground cables, both power and data using these methods, only a very few we needed to use a TDR to find the location, usually on the really long runs.

author: drhex
author_rank: Regular Contributor
timestamp: June 14, 2023, 01:14:00 pm
content: I bought a Fluke CableIQ tester when moving into a new house with extensive network cabling done by an incompetent electrician. Absolute life saver for me and does all the things you want here.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 15, 2023, 02:09:27 pm
content: Simple mechanical inspection should be relatively quick and easy because the cables are in a PVC pipe. Just cut off the end connectors and pull the cables out of the pipe to inspect for damage.

author: openloop
author_rank: Regular Contributor
timestamp: June 15, 2023, 09:25:05 pm
content: Um...Why not simply use your nanoVNA?I assume that these days everybody and their grandma has one.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: June 15, 2023, 09:57:09 pm
content: I agree with the other posters; no messing around, scrap the cable and replace it. You can replace with similar or, why not use an optic fibre link with media converters at each end? Fibre is rust proof (I hope), is EMC insensitive and maintains electrical isolation between the house and garage. And it's 'tech'.

author: jchw4
author_rank: Regular Contributor
timestamp: June 16, 2023, 09:43:26 am
content: You can buy older Microtest (later Fluke) Microscanner Pro (there were several generations) for a few bucks on ebay.It will happily measure distance to the faultNote: Before becoming Microtest Microscanner it was Progressive Electronics PROSCANNER. I got mine for $10. Delivery was more expensive than the meter

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 17, 2023, 12:23:13 am
content: I can only agree with TERRA Operatives suggestions.If you feel you must try to hunt the problem electrically before digging and don't have a TDR (reflectometer / echometer) at hand, the poor man's method is measuring capacitance against a known length of identical cable. Capacitance is proportional to length.

author: DavidKo
author_rank: Frequent Contributor
timestamp: June 19, 2023, 07:22:35 am
content: If you are able to replace it than do it (cheapest way), you will need to do it anyway.It does not make sense to buy/rent any equipment for fault analysis. It is for one use case waste of money. Some NIC can do it for you (I had it available in BIOS) or some managed switches. At least my D-Link DGS-1210-xx can do cable diagnostic.