I have a 10/100Base-T ethernet cable with PoE IEEE802.3at/af installed in my concrete walls. Unfortunately only 7 out of 8 wires are alive. Wire #6 (green) was broken during construction works and there is no way to replace the cable.
Still, I would like to connect an IP camera to this cable if that's possible.
I crimped RJ-45 connectors on both ends so that dead wire became #8 (ground). I expected that 1 ground wire could be enough to make PoE work. My naive approach didn't work. PoE requires two pairs of wires for + and – (related question https://electronics.stackexchange.com/questions/386715/why-does-poe-use-duplicate-wires-for-power).
I wonder if I can solder another wire to white #7 (ground) and crimp the cable again so that it will look like:
1,2,3,6 - data
4,5 +
7,7 - (ground) // the second 7 will be soldered to original 7
// and inserted in slot #8 of an RJ-45 connector
I found several PoE cable DIY videos and they just solder + and – wires from a power adapter to white-blue/blue (+) and white-brown/brown (-) wires of an ethernet cable. To me, that looks similar to what I want to do.
Will such scheme damage my video recorder or camera? Will it work or it's a way to make a short circuit?
Video recorder. POE: 8 ports (IEEE802.3at/af). Power consumption: PoE: Max 25.5w for single port, 80w in total
IP camera. Ethernet RJ-45 (10/100Base-T)
Diagram of PoE injector device which does the same thing
Update
I connected the cable to my desktop PC and tested the network connection.
Looks like swapping 6 and 8 wires works fine and there is no need to swap pairs.
The only question left is + and – part of PoE
Best Answer
A fix can work, but not at full range. The reason is that at full range you will need all wires for power. On shorter range you can only use 2 and it is enough. You then have 2 to reallocate in case of other bad wires, like your 6th.
So what you can do is replace/swap the pair with 6th wire with let's say the pair with 7th and 8th (on both ends) and disable the pair with 5th to balance your PoE. So you will have 1-2-3-6 for data again, and keep 4-7 for PoE +/-.
To simplify things, if you use T568-A just replace the data orange pair with the brown one to use for data and if you use T568-B standard, just replace the green pair with the brown one. Then allocate the remaining wire for power instead of the ones from the brown pair.