Well you can do that, that is what PoE does, but normally you are limited to 48v maximum and need a power injector/divider.
And I would not risk more than that.
Thanks, I learned that it is called PoE, I just failed to mention that in my post. I really just asked the question because of the strong reaction to wanting to try Powerline Ethernet. I figured that there could still be a small amount of crosstalk due to the fact that there is ripple and minor surges when loads change in the house like the refrigerator kicking in. Plus on top of that the PoE wires are running parallel to the signal lines. Sorry, just being anal retentive.
Well the thing is, PoE and Powerline are not the same thing. With powerline you are using an already existing power electrical cable to transfer data
between systems. There's a lot that can interfere with this system. Noise, outlets, cable splits, etc.
With PoE you are using a special standard for ethernet cables that carries current that is needed for a network device to function using separate cables.
Also, by design, twisted pair cables are highly resistant to interference pickup, so they are better and you want to carry DC, so interference is minimum or none.
To use that technology you need an injector on the power side. Normally the devices must be PoE compatible, if not you need another equipment.
It seems you want to use it for other purpose, well I never tried that. Maybe it's possible too.
The following user(s) said Thank You: Brian Morgan
@supernov, at the time I read your post I was intrigued by the maximum "15 meter" length between your devices. After running the numbers, wishing to do PoE, I came up with a maximum acceptable distance to the switch of 45 feet given a 5V power supply and 21AWG effective wire gauge (twisted pair). Should I be surprised that the laws of nature are the same for you and me?
Maybe, but the 15 meters (or 49 feet) were chosen at random. It happened to be about the distance in between the devices. I know of someone running a 30 meter Lan cable just fine as well, I guess with an active switch or so. For power I think it's different as you really get voltage drops over larger distances.
Yes, it's the power drop of 10% that we need to be careful with. I am looking online for a 12V switch then I can sleep soundly but they all seem to be 5V.