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Ethernet cable questions

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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).

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