Author Topic: PoE Question  (Read 329 times)

magillver

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PoE Question
« on: February 19, 2018, 06:17:45 PM »
Hi All,

   I'm not normally an IT guy, I do commercial AV installations, so the bulk of my Pockethernet use is confirming/troubleshooting cabling issues, and checking for PoE. I've run into a couple of situations where I'm seeing a reading of -50V on the PoE. Can anyone tell me what that might signify? Thanks!

zeb

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Re: PoE Question
« Reply #1 on: February 24, 2018, 02:20:24 PM »
I've run into a couple of situations where I'm seeing a reading of -50V on the PoE. Can anyone tell me what that might signify? Thanks!
More than likely a phone line (analogue or possibly digital if they have their own PBX)!  Not tried it myself, though.  Phone services tend to run on pins 4 & 5 and are generally around -50V.

HTH.

snowmanjax

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Re: PoE Question
« Reply #2 on: February 26, 2018, 12:23:42 AM »
Most POE equipment uses the same wiring scheme (with respect to which wire is ground) as old school telecom, where the positive wire is the ground. It confused me for a little bit as well, until I delved into it. If you would like to know why the telecom industry uses positive as the ground, visit the following link:

https://www.poweringthenetwork.com/uncategorized/negative-48-volt-power-what-why-and-how/


Hope this clears things up for everyone. :)


Snowman