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I have a cat5e cable that has 1 pair (orange / stripped orange) damaged -- it's a 100 foot line and the damage is like 40 feet in behind a wall [repairing it is not an option].

I need to power a unifi AP over this line. I am OK with 100mbps speeds.

How should I wire this up cable up to the rj45 jack?

I have a netgear POE switch for the power.

Thanks!

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  • You might be able to get away with 2 pair. Certainly for the data, the question is really the POE. Model #s of the devices? – manassehkatz-Moving 2 Codidact Jan 21 at 6:17
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    unifi lite being powered by netgear GS308P -- I could also use a POE injector at the AP side if the switch doesn't work. Meaning NETGEAR -> 2 UTP CABLE -> POE INJECTOR -> REGUALR CAT 5e CABLE -> AP . Ideally I would want the netgear to handle the poe, but whatever works! – sci-guy Jan 21 at 6:44
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A starting note: If one pair of your cable is damaged, and this happened through some kind of physical abuse to the cable (or if you don't know how it happened), there is a very good chance that other pairs are also damaged, and you just don't have the equipment to detect it. If so, anything you try to with this cable is likely to work poorly, if at all.

Regarding data: in normal use, the orange pair would be carrying data, so you will need a nonstandard pinout if you want to use this cable at all. The standard pinouts are called T-568A and T-568B: ethernet pinouts

Note that the pins used for data are 1-2 and 3-6, and each of those pairs MUST be kept together (that is, 1-2 must be the same color pair, and 3-6 must be the same color pair.) For a normal "straight-through" cable, you would use either A or B (usually B, in my experience) on both ends.

One possible pinout that you could use with your cable: WGreen-Green-WBlue-Orange-WOrange-Blue-WBrown-Brown. From T-568A, this swaps orange with blue, keeps 1-2 and 3-6 paired as is required, and moves the orange pair into the unused center position (where it will remain harmlessly unused even if you wire both ends backwards, which is very easy to do by mistake.)

In order to use PoE with this setup, it appears that you will need what's called a "Mode A" PoE injector ("power sourcing equipment"). Quoting from https://en.wikipedia.org/wiki/Power_over_Ethernet -- "In mode A, pins 1 and 2 ... form one side of the 48 V DC, and pins 3 and 6 ... form the other side. These are the same two pairs used for data transmission in 10BASE-T and 100BASE-TX, allowing the provision of both power and data over only two pairs in such networks." This will be necessary in your situation, since all other PoE modes require all four pairs to be working.

Unfortunately, I can't find any documentation on whether your switch uses Mode A or Mode B for PoE. (Luckily, the PoE standard apparently requires the AP to accept either.) Wikipedia and some other sources suggest that Mode B is typical for injectors, and Mode A is typical for devices like switches, but this is far from guaranteed. If you already have the equipment, your best bet may be to try it and see; however it's not impossible that shorts in the cable could cause damage to your devices, so try at your own risk!

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    Perhaps a safer testing setup would be to make a short test cable with the center pair not connected and try that with the two devices involved. If that doesn't work, no point testing the real cable. (Well, at least assuming that the damaged pair is completely cut. If it's just untwisted so that it can't carry any data, it could still work for power.) – TooTea Jan 21 at 12:16
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    so pins 1-2 and 3-6 carry both data and poe? that would be great! I have a fluke network tester -- the other pairs are fine by the way – sci-guy Jan 21 at 16:26
  • For "Mode A" PoE (with 10/100, NOT gigabit), it looks to me like that's correct -- all data and power is carried on pins 1-2 and 3-6 only. If your Fluke tester says those pairs are okay, AND your power-sending device is Mode A (which seems sometimes hard to determine), I think you should be in the clear! – Glenn Willen Jan 21 at 18:12
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    It worked like a charm :) Maxed out at 100 mpbs on the AP but that's expected. Way better than digging up the whole yard to replace the cable. Also way better than the 1 mpbs I was getting in there beforehand. – sci-guy Jan 22 at 0:41

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