I used to terminate the USB-B connector housing to the system ground but now I am not sure... We have this:
6.8 USB Grounding
...The user selected grounding scheme for USB devices, and cables must be consistent with accepted industry practices and regulatory agency standards for safety and EMI/ESD/RFI.
Which suggests nothing useful really. I have also run across the impressive EMC study http://www.ce-mag.com/archive/1999/julyaug/usb.html
The USB specification permits the connection of the USB shield to chassis ground at the host end only. We made no attempt to use discrete capacitors for shield termination, a technique sometimes used to connect signal ground to chassis ground at high frequencies but maintain low-frequency isolation.
So who does what these days?
1) leave the shield open on the device
2) connect it to device system ground
3) terminate to system ground with a resistor in case host side shield connection is floating
4) terminate to system ground with a capacitor for RF grounding
post edited by lbodnar - 2007/07/09 05:33:29