Why USB-C GND is being connected to the shield of the cable after connecting?

[Pinkus]

I need some help: I have designed a circuit board with a USB C connector. Shield and GND are separated and are not connected to each other on my PCB (there is a C and R planned for later).

However, as soon as I plug in an adapter cable (e.g. USB-C->USB-A or USB-C -> USB-C) (still without a device at the other end of the cable), the shield of the cable is connected to GND. I tried several cables. Is this normal? With my older designs using Micro USB this never happend. I am a little at a loss.
Thanks for your help!

[coromonadalix]

normally   the usb ground is connected to the shield ....  provide better protection against noises / interferences ...    all my circuits  usb -c  and micro-usb  have their ground  common with the shield

the shield  one side or the other "normally speaking" must be ended to the ground ..


usb-c   pin 6 vss is tied to the pin 11 shield / metal casing  of the connector

[wraper]

I need some help: I have designed a circuit board with a USB C connector. Shield and GND are separated and are not connected to each other on my PCB (there is a C and R planned for later).

And that's the most stupid thing that is commonly done with zero clue why in hell you put this nonsense in. https://www.unit3compliance.co.uk/hdmi-more-like-hdm-why-thoughts-on-cable-shield-grounding/
As of why they become connected, IIRC it's because USB type C standard requires connection between the shield and GND wire at the ends of the cable.

[wraper]

https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%20August%202019.pdf

11. The receptacle shell shall be connected to the PCB ground plane.

That you are violating by adding RC nonsense.

With my older designs using Micro USB this never happend. I am a little at a loss.

Most of micro USB cables I've seen have shield and GND pin connected together with rare exceptions when they are not connected.

[selcuk]

For such cables, it's better to connect circuit ground and cable shield together with minimal inductance. That high frequency shorting with capacitor method is for long transmission lines (ethernet from building to building) to prevent common mode currents from occurring due to ground voltage differences. So no worries for USB.

If your device has a metal chassis and usb connector is a panel type, preferably you may connect the shield first to chassis then chassis to ground.

You may refer to Figure 17 and Table 5 on the below document. It shows EMC measurements for direct ground connections vs. capacitor, resistor, varistor etc.
https://www.we-online.com/catalog/media/o721297v410%20ANP116_Gigabit-Ethernet__EN.pdf

[Miek]

The shield should be connected to GND in the connector, it's part of the Type-C specification: https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-release-23

6. Shield and GND grounds shall be connected within the USB Type-C plug on both ends of the cable assembly.