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In short, I have two questions:

  1. Does shielding matter for a USB2.0 cable inside a computer? The length is about 50 cm.
  2. Is the requirement that data wires should be thicker than data ones still valid if a USB device has a separate power source?

I have two devices (a water pump and an argb controller) supplied with USB 2.0 cables for connecting directly to a MB. Both devices are powered through sata. My MB has a single USB header, which is just enough to connect 2 devices. The simplest way would be just to plug the devices to the MB directly, but in the name of handiness and aesthetic I'd like to make an intermediate cable. Firstly, I made a cable putting 4 x 26 AWG wires (for power) and 4x 28 AWG (for data) into a paracord sleeve and it looked good until I realized that it missed shielding. Given the length of the cable about 50 cm, I am not sure that shielding might be neglected. Am I right? As a second option I found a shielded cable with 8 x 28 AWG wires inside on the local market. With that I could make a shielded USB cable for my needs, but then the power wires would be as thin as data ones. My guess is that with a separate power source it is not an issue, but I'd like to be sure. I would appreciate any thoughts.

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    \$\begingroup\$ Not only are you missing shielding - you're missing the correct & consistent characteristic impedance. At USB speeds, everything is a transmission line. Simply Hooking D+ to D+ and D- to D- is not enough. \$\endgroup\$
    – brhans
    Jul 25, 2021 at 1:34
  • \$\begingroup\$ Use the USB cable types designed for internal use. MOBO to front panel, \$\endgroup\$
    – Tony Stewart EE75
    Jul 25, 2021 at 2:38
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    \$\begingroup\$ @brhans Small nitpick: hooking D+ to D+ and D- to D- without shielding or proper impedance for such a short run is probably okay for USB 1.1 low speed, but 1.1 full speed, 2.0 high speed, and absolutely 3.x superspeed will definitely not work. So you might be able to use a keyboard over that link, but you can forget about hooking up a printer or a flash drive. \$\endgroup\$
    – Hearth
    Jul 25, 2021 at 17:20
  • \$\begingroup\$ Thank you, guys. I suppose that at least the water pump would send a more or less significant amount of data to the PC and so having a good cable is a must. I looked deeper into how a USB cable works and with that knowledge I decided that making a DIY cable is not a thing that I could handle at home :) Will look for a ready solution. \$\endgroup\$
    – tokitux
    Jul 25, 2021 at 20:23

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Assuming you are making a custom MB to 2 X USB cable. There is a pinout diagram for a usb 2 mb header here. https://www.dell.com/community/Optiplex-Desktops/745-MT-HR330-motherboard-USB-2-0-header/td-p/7302534

I would use shielded cable and 6 X cable.

Shield can connect to ground for both. Important if the devices have power supply separate.

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  • \$\begingroup\$ Thanks. I suspected that the shield and the ground wires might be connected to each other, now I know for sure :) \$\endgroup\$
    – tokitux
    Jul 25, 2021 at 20:11

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