0
\$\begingroup\$

I'm making a simple project regarding switching USB connection between two computers. I would like to know if it is safe to connect USB shielding for pc1, pc2 and peripheral together, while keeping the power and data wires separate? For example when pc1 is connected to peripheral and pc2 is not, keeping the shielding connected together is dangerous for these devices?


The setup consists of one desktop computer and one laptop which is connected through a powered dock (all powered from the same outlet). So if I understand correctly desktop PC will have solid ground and by connecting the shielding together the laptop will be grounded by the PC. So overall it is safe to do?

\$\endgroup\$
7
  • \$\begingroup\$ Marcin K - Welcome :-) One part of the Stack Exchange approach is that questions should be edited to improve them, not deleted and re-posted. For any future changes, please make sure to edit the question instead of deleting & re-posting it. I also recommend, since you're new here, to please read the tour and help center to see the site rules & guidelines. Thanks! \$\endgroup\$
    – SamGibson
    Mar 14, 2021 at 18:46
  • \$\begingroup\$ The answer depends, in part, on the relationship between the cable shielding and ground. If the computers are laptops, they have, with very high probability, floating power supplies. Connecting the cable shielding together should cause no problem. However, if the computers are towers or desktops, connecting the shielding may cause ground loops, which may adversely affect the signals. In worst case scenario, outlets could be wired incorrectly, and damage would occur, but such damage would probably occur merely by connecting the usb cables, even with no shielding connection. \$\endgroup\$ Mar 14, 2021 at 18:55
  • \$\begingroup\$ Sorry for reposting the question, I thought it died already and wouldn't be read again by anyone. \$\endgroup\$
    – VIAX
    Mar 14, 2021 at 19:33
  • \$\begingroup\$ The setup consists of one desktop computer and one laptop which is connected through a powered dock (all powered from the same outlet). So if I understand correctly desktop PC will have solid ground and by connectiong the shielding together the laptop will be grounded by the PC. So overall it is safe to do? \$\endgroup\$
    – VIAX
    Mar 14, 2021 at 19:35
  • 1
    \$\begingroup\$ Before I would worry about the shield connection, I would worry about the data and power connections. The USB connector mechanically makes sure that power is first to connect and then data. It also makes sure that the data is first to disconnect before power. So switching both power and data with the same switch does not guarantee this, and can damage something during the switch. \$\endgroup\$
    – Justme
    Mar 14, 2021 at 19:55

1 Answer 1

0
\$\begingroup\$

My personal experience is that bonding the shield at two sides causes the USB not to work. I was in a hurry of connecting Picoscope with no space inside a box and made a new cable with a 90 degree USB connector. My zeal of EMC addicted suggested me to bond the shield at both ends to the connectors shell (without a second thought...): damn to me, it did not work. Always in a hurry, I checked what is done in other cables that work and it was not connected: so quick and dirty, dismounted the newly made connector and removed the solder ball that I put there with a lot of effort. With many equipment, possibly supplied from different sources, you would create a wonderful ground loop, ad this would have stopped me: but the Picoscope is fed from the same computer, so I thought that was not an issue.

\$\endgroup\$
2
  • \$\begingroup\$ I am very interested in understanding what caused the failure. Did the USB work if the picoscope ground probe was unconnected, and only failed when the ground probe was connected? Or did it fail from the start? If the former, is my understanding correct that the circuit you connected the ground probe to was grounded through another USB port connected to the same computer? \$\endgroup\$ Mar 14, 2021 at 21:55
  • \$\begingroup\$ @MathKeepsMeBusy It failed from the start and the pico did not light up the red led, that means that the USB connection is not established. The pico was connected only to the "computer", that in reality is a Raspberry PI that controls this measuring box. Being in a hurry I did not investigate further; simply accepted that continuity through the shield must be interrupted and terminated it only Raspy side. \$\endgroup\$
    – andrea
    Mar 15, 2021 at 6:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.