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Main question
Can I use a Cat 6a cable for USB communication? On the cable it says 650 MHz, is this sufficient for USB 2.0? The length of the cable would be about 6 meters (about 19 ft).
If so, would the following be the correct way to wire this?
Cat6a_Pairs
Cat6a_USBwiring
Follow-up question
If the answer to the first question is yes, would it then also be possible to combine it with I2C like below? Is my assumption correct that the pair-shielding will prevent either protocol from interfering with the other? (this way of wiring I2C with twisted pairs I got from NXP's AN255, see figure 30)
Cat6a_USBandI2Cwiring
I also assume the capacitance from the shielding is not too much for 6 meters of cable for I2C's standard 100 KHz clock? (I don't know how to calculate/measure this)

Background / Extra info
The reason I'm asking this is because I need to pass I2C and USB through a tube of small diameter (inner 16mm), which has several inconvenient bends in it (and it's inside a plaster/concrete wall). This limits the amount (and diameter) of cables I can get through without damaging them.

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1 Answer 1

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In theory, this should work. Cat6 cable is generally fairly high quality, low capacitance, low resistance, and high bandwidth. The twisted pair and individual shielding also helps. Host powered USB Extenders can use cat5 for up to 100m.

As for the capacitance for the i2c bus, you can get that information from the datasheet for the cable. Typical Cat6A capacitance is 330 pF per 100m. Look at this datasheet for an example.

To be honest, 6 meters is short. You shouldnt have any issue.

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    \$\begingroup\$ Although cable is probably not an issue, length is. USB has a max length of about 10 feet (timing issues). \$\endgroup\$
    – WhatRoughBeast
    Commented May 29, 2014 at 1:31
  • \$\begingroup\$ @WhatRoughBeast like most of usb, the specs are rarely followed to the t. I doubt most computers stick to the max spec timeout period, waiting a little bit longer, to minimize customer annoyance. But point taken. \$\endgroup\$
    – Passerby
    Commented May 29, 2014 at 2:14
  • \$\begingroup\$ Actually, the specified limit for a single USB physical connection is 5 meters. 6 meters will probably work. \$\endgroup\$
    – Dave Tweed
    Commented May 29, 2014 at 3:53
  • \$\begingroup\$ Is there a way to make sure it will work, in case it's more than 6 meters? (I don't know for sure yet) I've never heard of a Host powered USB Extender, is this something like a repeater? If so, are these things cheap? \$\endgroup\$
    – KJdev
    Commented May 29, 2014 at 11:14
  • \$\begingroup\$ It might be an issue that USB cable impedance is supposed to be 90Ω, while Ethernet cable has 100Ω. \$\endgroup\$
    – starblue
    Commented May 29, 2014 at 14:09

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