It's been pointed out many times that USB 2.0 can (more or less) safely be used with cat5/5e cables and connectors, at least as long as these requirements are met:
- Data pins are on its own twisted pair
- Power pins are on the separate twisted pair
- To keep it in safest way possible, the two pairs used are the "spare" pairs of 100M line, so on RJ45 pins 4, 5, 7 and 8
- You don't plan to mix any connection with POE ports/fed cables!!!!!
- You avoid plugging such cable from USB host to the network devices, since some (seen on 100M hubs) might have pair pins merged together, resulting in bridging your USB power lines.
- You really really have a good reason to use this in the first place
Now, with keeping all that in mind, I do have a good reason. However, I'm interested in knowing whether the same twisted pair topology is ok (mostly performance-wise) to be used with USB 3.0.
As USB 3.0 includes additional two natively twisted paired connections, I was thinking of using the first two pairs (normally used for ethernet) as new USB 3 StdA_SSRX−, StdA_SSRX+, StdA_SSTX− and StdA_SSTX+ pins, with old Data + and - pins used on third pair and power on fourth.
Could this decrease performance of the USB 3.0 (when used in non-excessive lengths)? What damage can be made in case of such use and plugging the host-side of the cable into Gigabit network port of the PC?
The reason I'm interested in this is, that I need to have USB 3.0 connection between two boxes, that can be disconnected and connected easily on-the-go, cable length would be between 10 to 15cm, the reason for this connector is that both boxes already have RJ45 on them and changing them for USB would mean a few troubles here and there. Please, don't start to "why not this why not that", I'm interested in an actual answer, for informative purposes rather than suggestions on how to handle my case specifically. :)