Hello,
Today me and a friend took a look at an existing design and finally we got lost in a discussion about grounding issues and how to connect earth ground, signal ground, chassis ground and shields. We talked about the necessity of correct earthing, ESD issues with the different methods and the connection of cable shields for external I/Os. Maybe someone who is a bit more experienced than me can comment on this because I don't feel very safe with all my argumentations and thoughts.
First of all any equipment powered from AC mains will either be double insulated (showing two concentric squares) or will require an earth connector cause of safety reasons. I would like to start with double insulated equipment:
1) Double insulated (Class 2 equipment): No safety connection to electrical earth exists. Because the potential of my internal signal ground is not fixed it can take on an arbitrary value.Safety: There are no safety concerns because no current will/can flow to any user touching the equipment in case of an electrical fault.
ESD: This is where I am a bit unsure. What happens for example if I would touch a possibly sensitive pin with an external testing equipment charged up to