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Damaged cat5e cable and some strange behaviour

This is a discussion on Damaged cat5e cable and some strange behaviour within the Cabling and Network Cards forums, part of the Tech Support Forum category. Hi all, sorry for long post. we currently have an issue with a cable (about 75 metres). It connects one


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Old 08-12-2017, 06:18 AM   #1
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Hi all, sorry for long post. we currently have an issue with a cable (about 75 metres). It connects one netgear unmanaged switch to another one in a different building. At the remote location, there are 3 devices connected to switch. A couple of days ago it stopped responding (well almost - I'd get maybe 1 ping reply out of 30). I asked someone at the site (I dont work there) to take the long link cable out of the netgear and plug straight into one of the devices - I got 100% ping replies from this device!

So I thought the remote netgear is faulty. I went to that site the next day with a new netgear. New netgear didn't work either. I cut off the rj45 ends and did a continuity test on all 8 wires inside the long cable - all responded except the solid blue wire. I traced the cable and found that something had chewed the cable (rodent problem on site) and the blue wire was visibly cut. So I put a join in and now all 8 wires are passing the continuity test. I put new ends on and test with rj45 tester and it says all pairs are correct but the 'short' warning light is on.

We cannot run a new cable to this place so I'm going to put a wireless signal over there. However this is what is happening when each device is plugged directly plugged into the long cable and I'm desperate to know why..

Device 1 responds 100% pings (the device is this -
https://tibbo.com/store/soi/controllers/ds100.html)
Device 2 and 3 responds maybe 3% pings
(The devices are swann CCTV servers)

Hope someone can help! Thanks, John
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Old 08-12-2017, 06:48 AM   #2
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You'll have to examine the whole length of the cable.....with great scrutiny. Continuity does not indicate the absence of a short.....a short will provide continuity, especially if it crosses over to a viable conductor. Somewhere along the line you are missing the insulating jacket between two (or more) conductors.

*Rodents must chew even if they are not hungry.....their teeth constantly grow.
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Old 08-12-2017, 07:30 AM   #3
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Quote:
Originally Posted by johnc83 View Post
I cut off the rj45 ends and did a continuity test on all 8 wires inside the long cable - all responded except the solid blue wire. I traced the cable and found that something had chewed the cable (rodent problem on site) and the blue wire was visibly cut. So I put a join in and now all 8 wires are passing the continuity test. I put new ends on and test with rj45 tester and it says all pairs are correct but the 'short' warning light is on.


I'm desperate to know why..

Either there are multiple points of critter intrusion or your repair is faulty. It is VERY easy to mis-crimp an end. And the splice (repair 'join') will degrade the signal even if done properly. Each break in the line reduces the rated distance by something like 50' as I recall from my days of installations and repairs.
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Old 08-13-2017, 03:03 AM   #4
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Thank you for your replies. This cable goes into an underground pipe between the two locations and the fact that I've had to make joins can well make me believe the cable will never be back to its former glory. However I still don't understand why this 1 device is happy with it - if you look at the spec of it, it is a 10baseT device. Is this something that would be happy with a dodgy cable but the other devices (presumably 100MB devices) will not accept such a poor connection?
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Old 08-13-2017, 05:36 AM   #5
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First you got to love mice if you are a repair tech. Frustrating as it is it keeps us working.

Attenuation at 100 mbps is much higher than at 10 mbps due the frequency increase. Every time you added a connector the signal get attenuated even more.

This is much the same way with RF signal too. Here every time I add connected I got to deduct 1.5 dBd from my received or transmitted signal so just on one cable with two ends I lose 3dBd or half of my effective signal. And if I add patch cables then I loss even more of the available signal. Also on long runs my signal at 3.5 Mhz is way better than say at 28Mhz as cable attenuation increase as the frequency increases.

This we repair radio techs fight for every dBd we can improve a signal by.

So with in mind it would be best if you can simply replace the damaged cable save yourself some headaches later as the line deteriorates even further from the mice damage as the line oxidizes since at higher frequencies the signals hugs closer the wire surface area.
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Old 08-13-2017, 10:40 AM   #6
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Thanks for that. Very useful information. I was sure it would be quite technical but it makes sense. The switches at both ends are 100MB but I am thinking if these were both 10MB switches then everything would probably work ok. However this clearly would be a bandaid for a bullet hole as no doubt it would be a matter of time before it deteriorated to the point where even 10MB won't work. Thanks again for all the replies, much appreciated!
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Old 08-13-2017, 10:51 AM   #7
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If the cable has been placed in a conduit (pipe) provisions have already been made for the replacement of the cable (that's what the conduit is for). How many cables are running through the pipe?? Unless numerous cables have been bundled together you can use the old cable to pull a new one in place.....just make sure the new cable is tied firmly to the old.
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Old 08-13-2017, 12:09 PM   #8
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^^ In a perfect world, but I found that rarely worked as well as people might have hoped. Obstructions, dust accumulation, moisture, corrosion at fittings, for example can make that impossible. I have had it work, but I could never expect that it would. I've even seen cases where the conduit was crushed or deformed by vehicle traffic over a driveway or parking lot.
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Old 08-13-2017, 01:25 PM   #9
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Anything underground should be raintight.....should be. And....it'll be rigid conduit....no thinwall. But time does take a toll on anything exposed to the elements.....

Part of my electric service is in conduit.....where it goes under my deck. 4" PVC sch 40......200A service. Part of my house wiring is in conduit.....a friend of mine wired the house (commercial electrician).....
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Old 08-13-2017, 11:49 PM   #10
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That was my plan (I bought a 300m reel of cable to attach to the faulty cable and pull through) this worked perfectly at a previous site but in this one the old cable would not budge an inch and I didn't want to apply too much force because who knows what else I would damage.

I am going to install another ENS202 at the site. We've had great results with these at a couple of sites where there was no option to run a cable. I sound like an advert here but these really are very good. Thanks again for the replies

https://www.broadbandbuyer.co.uk/prod...MaAsc-EALw_wcB
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