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Answers to a recent question about a homemade USB cable mention that USB and other data (Thunderbolt, VGA, and HDMI) cables should not be coiled. So what is the proper method to manage long cables without coiling them, in order to minimize interference?

A specific situation is that all the cables I have access to (work environment) are very long. I have about 20cm of air between a Thunderbolt laptop docking station and a monitor connected via HDMI->VGA cable. But the cable is 3m long. A similar situation for another monitor and USB devices also connected to the station. Geometric and cosmetic constraints mean that the cables should not stray too far from their current location behind the desk, nor should they have an unwieldy appearance.

To clarify, these cables are not longer than the max rated length for each protocol. They are however wrapped up in coils, which the answers in the linked question mention is a "bad thing".

In the general sense what would be the proper way to route such long but to-spec cables, instead of coiling them, and why?

dotancohen
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    If I remember correctly you wires in the previous question had no screen. Screened cables will protected from self-interference from adjacent coils so I wouldn't expect any problem in that regard. Look at your HDMI. Are you seeing glitches on screen? – Transistor Jul 27 '21 at 15:24
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    In the link, "drawing too much power" and "original cable extended does not work" is completely irrelevant to however the cable was coiled or thick. There is no magic to do that. As an EE/SWE, who designs USB devices, I have more than 10 USB cables connect around my computers and equipments that are neatly coiled and organized, routed together with power lines, a few of them goes over 12 feet to reach inside an environment chamber, with no problem. If someone come up with a theory that casually coiled USB cable cause problems, it will be sensational engineering data to supprise the industry. – jay Aug 31 '21 at 22:18

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Sorry, but the answer is "don't." When you use cables greater than (or even close to) the max rated length for a given comms protocol, you are asking for glitches and failures to occur. Get the right cable for the job.

Carl Witthoft
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  • These cables are not longer than the max rated length for each protocol. They are however wrapped up in coils, which the answers in the linked question mention is a "bad thing". I'll edit this question to clarify. Thank you. – dotancohen Jul 27 '21 at 14:36
  • @dotancohen be sure to test and verify that uncoiling solves the problem! – Carl Witthoft Jul 27 '21 at 18:41
  • if the cable is built to spec I wouldn't expect a coil to be an issue. If it is then stop coiling them and run them back and forth. – Tiger Guy Jul 28 '21 at 04:11
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As mentioned, there is no "proper" way (proper is to keep cables short - shorter cables are generally cheaper too!). You can however do a careful bundle that looks like the 8 or infinity symbol. However rather than a simple repeat of the 8 loop, you should make each loop in the stack run in the opposite direction of the previous. The 8 shape is so that you can flip the wire around for going in the opposite direction without kinking it smaller than the minimum bend radius. The idea is that interferance generated by one loop is approximately negated by another, reducing the overall effect.

Note that cables that have proper protections against emi tend to also have the same against self generated interferance so this is not usually needed. However someone's poorly-built custom cable with no twisted pairs might benefit from it.

Abel
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