Adventures in Administration: USB Extension Cables over Cat5e Ethernet

While working as an admin you come across some unusual requests. We have a conference room at work where we’ve been requested to have a fixed-position USB webcam, but they want to locate the usb cable approx 25+ feet away. They’ve also requested not to have a lot of running cables in the room, so this means also hiding the cables away in the wall. This would also mean some kind of adapter/extension cable. Looking around online, you can buy USB extension cables (some powered), that run 50-ish feet, but they’re usually in the $40+ range. I’m cheap, so I wanted a viable alternative.

Cat5e cabling is pretty plentiful and cheap, and, as you may know, has 4 twisted pairs inside. Originally we had the thought that we’d be able to use 4 of the strands (2 pair) for the USB wires and the other pairs for some audio jacks or whatever. Trying this, we were able to go over 30 feet to a USB card reader and it seemed to work OK, but upon trying it with a webcam, despite maintaining voltage, it wouldn’t be recognized. This was true, in the case of the webcam, for anything over roughly 7-8 feet.

Next we tried some shielded 22-gauge 4-wire security cable. Same results.

As a last-ditch effort I tried stripping the ends off of each of the strands in each pair and twisting them together and then attaching each pair to the stripped wires of a short USB extension cable, utilizing the twisted nature of the cables to reduce cross-talk and interference. To my surprise (mainly because I honestly didn’t think it would work, we were able to get a webcam talking with no issues with a 50+ foot section of Cat5e.

I cabled it thusly:

Orange-White \
              ---- USB Red (+5v)
Orange       /

Green-White  \
              ---- USB Data-
Green        /

Blue-White   \
              ---- USB Data+
Blue         /

Brown-White  \
              ---- USB Ground
Brown        /

Cabled on both sides, this apparently reduces enough noise and crosstalk to allow the signal to pass that length. 50-55ft. was all we tried, so it may go further than that.

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