I have around 12 purely DC PCBs inside a metal case. Each has a MCU which connects to the main controller PCB with SPI or I2C. Each is powered by one shared ATX PSU which also sits inside of the case.
Obviously the case and any exposed metal needs to be connected to Earth. But every PCB is screwed directly to the case and around 4 PCBs have metal connectors or Pots that also touch or are screwed to the case.
I am struggling to get my head around what to do in regards to DC Ground and Earth, do I connect them if so how or do I isolate them?
I can't find any info on how this is done in a commercial application which would comply with the relevant EMC and safety standards.
What should I do with the shells of the Pots and Connectors on the PCBs? They are going to be connected to earth through the case, so should I isolate them from the DC ground on the pcb?
What should I do with the mounting holes? Should I have them plated and connect the DC ground to earth or should I not plate them and leave plenty of clearance around them for the screw heads?
It seems like I have the following options:
Connect DC Ground to Earth, it then wouldn't matter about the Pot and Connector shells.
Connect each shell to to DC Ground via an 1M/4.7Ω Parallel RC Tag. This would only be ok if each shell made a solid connection to earth.
Have a separate Earth plane on each PCB connecting the mounting holes to the shells.
Leave the shells and mounting holes completely isolated from the DC Ground on the PCBs