I believe this is because of the PCB design. When I add a wire link direct from the USB shield to the chassis (which is connected to PCB GND) then the issue is resolved.

I have tried a 0R link to GND instead of the resistor/capacitor solution, but this still fails.

It is not connected to any device via USB.

The test occurs while the unit is logging.

The failure occurs when doing a contact discharge ESD test on the USB shield (all other areas it is fine, just the USB shield it fails).

In response to the questions in the comments: As far as I can see, these were the only things added in addition to that example circuit to protect from ESD. According to the old ESD report, this was needed or the device failed. There is a metal tab fitted to the PCB which rests on the metal chassis. The shield is connected to ground via the 100k res/100nF cap. R1 is then connecting the shield to GND, and capacitor C3 is doing the same on the other connection. The large hole is where the tabs for the USB shield to have a mechanical connection to the PCB. You can see that the ground plance stops short of the USB socket.

The unit passes the test at -4kV, it is just the +4kV where it failsДЄnd more info required in comments will be added here.ДЄll I can show of the actual PCB is this:.

They do not work for the company any more so I am unable to find their reasoning for the design choices they made

I am not the original design engineer.

The common-mode choke, ferrite and TVS diode protection are all in.

This is a a work device and as such, I am not allowed to show the.

Require a redesign of the PCB or product so those suggestions are To find a solution which can be easily implemented and does not

I am not allowed to change any mechanical design on this.

The PCB is very irregular, and tight on space, making the ground.

Grounding the shield allows it to pass ESD, but is this something that should be done? Or should I continue to look for a better solution? If so, what is a good solution? There just seems to be a lot of different views on this so I am a bit unsure what to do next. Yet, in fig 12 it seems to show the USB shield should be tied to GND plane. THIS document says the shield should be connected to the chassis.

THIS link mentions the shield should only be connected to ground at the host, but no device should connect the shield to ground. This discussion HERE has different views, this HERE also has a discussion on it.

Looking online I can't seem to find anywhere that says explicitly whether you should or shouldn't ground the USB shield.

The only way I got it to pass was by grounding the USB shield directly. I tried a number of things, I put extra capacitors in parallel with the current one connecting the USB shield to ground (different values, high/low), I changed the resistor to different values (higher/lower resistance) and tried ferrite beads in parallel, and ferrite beads instead of the Resistor/capacitor as I had seen some places recommend, but still it failed. It seemed that it was an intermittent problem (some devices passed 3 in 10 tests, others failed all 10 etc) so it seems to me like the pass on the ESD test previously was likely a fluke. I rechecked some old ones using the previous IC and found that this also fails. Each time I perform the contact discharge test at +4kV, the device loses its memory (this is a datalogging device) and it needs a factory reset and restart logging to work again. Move on 5 years and I am redoing the tests. Apparently it failed a few times untill a capacitor/resistor was added between the USB shield and ground, and a small metal tab was introduced to add better contact between PCB ground and the metal case. There was a note from the testing facility that as the device was entirely metal (Stainless steel housing) only contact discharge up to 4kV was needed to pass (I am in UK). I checked the history of the device, and there were problems passing ESD before. Upon redoing the ESD checks, the device failed. Basically an IC is becoming obsolete so I need to test a replacement part. I have been given a device at work to do some testing on.

Esd usb to normal