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I hope this is an appropriate topic for this stack exchange. I have a cable run just shy of 15 feet that connects a few monitors (3) and usb 3.0 devices (a USB 3.0 hub) to one of the servers on the other end of the run, in the next room. There are a total of 5 cables ran together: 3 DVI/monitor, 1 standard AC power (to power the monitors and USB hub off the same battery system of the servers, it is only in the last 4 feet of run), and 1 USB 3.0.

When I first setup the run, I tested both a powered 15ish foot active extension cable and a non-powered 15 foot cable and determined that the active cable had considerably better transfer speed (actually hitting USB 3.0 spec) so I left it with that. Weeks later I started getting complaints of all of the USB devices connected through the HUB periodically disconnecting and reconnecting. I first thought the HUB was acting up, but I ended up disconnecting the active USB cable and trying the passive cable (running it through the doorway instead of with the others) and the connection issues went away entirely. I left it like that for a few days, and with no connection dropouts, I installed a new active USB 3.0 cable in the existing cable run, and tested again for speed/dropouts. Transfer speeds went back up to USB 3.0 spec and no dropouts.

Fast-forward another few months, and same issues as before have started to appear. I know setting this up originally I could have EMI issues with the AC power cord in the same run, there's just not another good way to run that AC line separately, and it's a fairly short section that the cables are actually ran together (I wanted to try it like this first and see if we had issues). I did get a pretty heavily shielded AC cable, FWIW. The only thing that has stopped me from yanking the power cable out from this line is that this seems to only happen after a period of time from starting with a brand new USB cable. What do you all think? Is it probably EMI or do you and other ideas that I could try as well?

Edit: In addition to the USB devices dropping out and reconnecting, there are reports that while typing, a key will suddenly "stick" and you'll end up typing something like thisssssssssssssssss.

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