Electronics > Beginners
Ethernet cable questions
(1/4) > >>
sal_park:
Hi all,

Background:
I'm a software engineer but have some idea about EE stuff. I installed CAT6 cabling for my home network running 1G & 100M with PoE to various devices in my home. All cables run back to a patch panel and have work fine since I installed them 18 months ago. Last week I move the patch panel so had to pull all the cables out the back and the reattach them with the punch down tool in the new location. Long story short: none of the cables seem to work any more !

To try and understand what's going one I'm testing a minimal setup:

cat6socket -> cat6 cable (solid core) 10 meters long -> cat6 socket.

Nothing is plugged into either socket.

With this setup I'm seeing around 3 ohms between each twisted pair and around 150 ohms between different pairs. This was measured with my multimeter. Just a cheap VC99 which as far as I know is working.

Given I was suspicious of the above result as it makes no sense I decided to measure current down one of the pairs. Connecting a PP3 9V batter straight across the multimeter I get reading of 1.5A (only held it on for a second or so!). I then connected the multimeter (amp setting), CAT6 pair and battery in series and got a reading of 1.1A. To my mind this says that the 3 ohms measurement on that  pair is probably correct, although I'm not any the wiser in understand wtf is happening !

So, does this make sense ? Any idea what's going on ? Help !

TIA.

sal
Nerull:
It sounds like you've somehow shorted pairs together. A cat6 cable consists of 8 wires twisted into 4 pairs. There should be no connections between any of the wires if all you have is a socket-cable-socket. There are no, as far as I am aware, termination resistors in a punchdown jack, it's just a straight connection from the pins in the jack to the punchdown terminals.
wraper:

--- Quote from: sal_park on March 03, 2019, 05:55:26 pm ---cat6socket -> cat6 cable (solid core) 10 meters long -> cat6 socket.

--- End quote ---
What are those sockets? A lot of sockets have built in transformers and termination resistors.
wraper:
I would expect that you fucked up when reconnecting the cables. If you plug a cable with PoE into regular socket, usually it would damage the device.
sal_park:
"It sounds like you've somehow shorted pairs together."

I would agree with that, but am confused by the fact I'm getting 150ohms between different pairs. Can't make sense of that.

Here are the readings I took:

Green->Green/white: 3.2 ohms
Brown->Brown/white: 3.1 ohms
Blue->Blue/white: 3.2 ohms
Orange->Orange/white: 3.2 ohms

Green->any brown/blue/orange: 150 ohms
Blue->any green/brown/organge: 150 ohms
(didn't test any more after this).
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod