Ethernet cable not working

[Scott_A_R]

I needed to have a wired network connection in a particular room in my home for a few days.
I'd already wired a nearby room, running a cable up inside walls, through an attic crawlspace, and down, and since the hardest part of the work had already been done, it would be easy to just temporarily move it from this room to the other one.

I did so, and the connection didn't work. This drove me crazy, and I tested every possible thing before concluding that there was a break--not unlikely, as I'd done some renovation in the room I'd taken it from in preceding weeks.

So I ordered an admittedly cheap 100 ft Ethernet cable from Amazon (plugs already attached). It came two days later, I ran the wiring (a real PITA job) and... it didn't work.

Now I was going a bit nuts, trying to figure out why both cables failed to work. So I went out locally and bought a LAN tester--a basic one, which basically lights up LEDs to test each wire pair.

First I tested the original cable, which I'd pulled. Sure enough, the 7 and 8 wire pair was dead. Possibly broken while doing... whatever. Fortified by the confirmation that I hadn't simply missed something, I tested the new wire I'd installed and... no problems found.

Argh! So, basically, the tester found no breaks or reversals, but I couldn’t get a connection through the wire. The problem wasn't the laptop I was using to test it: it connected just fine through other Ethernet cables.

So, my question is this: could the problem be simply that this was a cheap cable, and couldn't carry a reliable signal over 100 feet? That even though there was an unbroken connection that could complete a circuit for a battery powered signal, that the signal was crappy enough in some way to not enable a network connection?

Or what else could I be missing?

 

[bill001g]

If your cable is cat5e or better ...be sure it has tia/eia markings on the side ... then you should be able to run it at 1g at 100 meters. When you have never used a cable vendor before I tend to always test with the cables laying on the floor before I run it in hard places to remove.

Even if you have some of the junk CCA cables that are on the market that are not tia/eia certified they should still work at 100 feet.

Those cheap lan tester only test basic connectivity they do not test the ability to pass data. You could wire a RJ45 plug to cheap speaker wire and it the lan tester would say it is fine but not pass data......you can actually make speaker wire work at short distance a 10m I have done it when I was desperate at a convention.

Even if you had a fancy TDR all it would tell you is your cable does not pass data correctly which you already know. It could help you find where your other cable has a break or short but generally you end up running a new cable anyway.

What may work if you get really stuck is to cut the pair on pins 4/5 on your cable that has 7/8 broken. The devices should then negotiate 100m. What seems to mess up auto negotiation more than anything is when 3 of the 4 pairs work. It thinks it can run gig and never bother to drop down and try 100m.