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Cabling Black Hole

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by clarkbr

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I'm stumped.
I have a 193foot run of Cat5 cabling from the switch to the user desktop.
The cabling has been tested and has passed all the connectivity tests.
Yes, you guessed it, nothing will connect on this cabling run. I have double checked allthe patch cables by connecting a laptop directly to the switch using them and they work fine. The same laptop connects perfectly on a 'identical' run of cabling located right next to the bad one.
I have an 'identical' run of cabling that I have plugged into the switch in the same ports thet the bad run was connected to and that run works just fine.
I think I have found a cabling black hole.
Any suggestions from the experts out in the field?

6 replies

by tomsal

..that is if you do a large quantity of cable drops/runs.

From your post I am guessing your switch is fine, all the switch ports are fine AND the NIC to the client machine you are trying to connect too is 1) Perfectly fine and 2) Installed correctly, configured appropriately for your network (domain, IP address, DHCP, DNS, etc. etc.).

If same computer you are trying to connect to with this 193 ft. cable run does connect to the SAME port on the SAME switch with ANOTHER (different) cable run then you have two ways of looking at this: the simple way and the complex way.

The simple way is by deductive reasoning which leads me to the point that, despite the fact your 193 ft cable run tests ok on connectivity it is in fact -- flawed. The complex way is just sticking to the sacre OSI model -- you rule out higher layers because the switch, NIC and client machine work fine with another cable attached. This brings us to the physical layer -- that's our problem. Solution: totally forgetabout your 193 foot cable run that is giving you problems, that cable is no good.

I've learned through the years that unless you are using very high end/sophisticated testing equipment -- the cheaper doodats that supposed test connectivity reallymean nothing. All they do is tell you "yeah the pulse of electricity reaches the other end". So because you get a "green light" on connectivity, it doesn't always mean its a quality connection.

by clarkbr

Thanks to TomSal for your analysis.
I have done a bit more 'digging' into the cabling in the floor. I have a total of five runs that have the same problem all running to the same point. I am guessing that there is some RF interference in the cabling run. The cable checked out fine before it was pulled into the chase. The strange part is there is one run in the same chase, to the same location that works just fine.
I guess the stars and planets must have been aligned when it was installed.

Thanks again to all.

by admin

"The cable checked out fine before it was pulled into the chase" as Tom pointed out, about all the hand held lower end tester check for is continuity.... but you still have to check installed.

:)

by oz_media

I'm under contract at North American Tel, I am in their office until tomorrow so I asked their head cabling tech. He has dropped thousands of runs over the past 23 years, long before CAT5. The toner you are probably using just shows signal not connectivity. His ISDN tester is worth about $12,000.00 and it still shows SOME connectivity on a dead line.

He aslo said in 23 years, he has NEVER seen a cable not work unless it is either too long (in the case of CAT5) or simply broken. When told about your issue, he laughed and said "tell him to install a new run, the cable's dead".

Don't know if that's what you wanted to hear but that's what I got.

by road-dog

to test? If it is a wiremapper, it only tells part of the story. A CAT-5 cable tester looks for arcane things such as near end cross talk and far end cross talk, things that will kill a connection, even if your 568 a/b pinout is fine.

As is, I suspect that your wire run might be hosed. If there is a 480 volt power conduit in the area, it could be a problem. A more likely scenario is that a few wires got friction burned while pulling.

Professional cable pullers do a cat-5 validation teston all runs prior to turn over. If they provided documentation, look for anomalies. If you find burned cables in the bundle, tell them you want a re-pull.

Good Luck!

by csrite77

Check any Hubs and Switches connected to this run. Especially Hubs check the Uplink port to see if the button is correctly Pushed in or out for uplink.

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