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By the shield I mean the metal rectangular tube covering the connector pins.

Is this shield designed to take ESD shocks, and does it protect the internal circuitry from static electricity? What would happen if there was a static discharge from your body to the metal shield?

utwentyseven
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There still needs to be a circuit to ground for the spark to happen, so a spark won't happen until the drive shield is plugged into something metal.

Once it is plugged in, it is as much part of the the metal that you could touch to discharge yourself as the system you plugged it into.

Dave X
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  • Thanks for your reply. Even without a spark, would there be possibility of damage to the thumb drive if you touch the shield without grounding yourself? – utwentyseven Feb 26 '18 at 13:13
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    If there is no path for electricity to travel, there would be no possibility of damage. – Dave X Feb 26 '18 at 14:13
  • I'd be grateful if you would clarify: Does this mean the shield is isolated from the internal circuitry of the thumb drive, and isn't used, for example, as a ground connection for the flash drive PCB? – utwentyseven Feb 27 '18 at 10:07
  • There's lots of USB devices, and how they connect the shield/cable ground to the system ground inside the devices depends on the manufacturer. If the device is plugged in, the cable/shield ground is connected to the chassis ground of your computer and is as grounded as it is. If the device isn't plugged into anything, you should be able to toss it to a person touching a VanDeGraff generator since there is no circuit to ground. – Dave X Feb 27 '18 at 22:08
  • As far as I understand, a potential difference is all that is needed for ESD to occur rather than a full circuit to ground. Otherwise disconnected peripherals will be immune to ESD. I suspect the shields are isolated in some way from the internal circuitry given that it would be poor design to connect them directly to electrosensitive parts of the device, but I'd be grateful if someone could verify this. – utwentyseven Mar 02 '18 at 13:27
  • If you don't connect the shields to ground somehow, then there is the possibility of a large potential difference. Try https://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf for some examples of ground connection design. – Dave X Mar 02 '18 at 14:47
  • Your link is helpful, but the circuit diagrams are specific to powered USB devices. The shields here have drain wires that connect to chassis/ground. I don't think it shows how the USB-A connector shields on thumb drives are configured. I'm inclined to think that they are just isolated in situ without drain wires or other connections. – utwentyseven Mar 02 '18 at 15:32