Do the edge box protective ground and signal ground need to be isolated?

The protective earth (PE) of the edge computing box must be isolated from the signal ground to prevent power frequency ground loop current from burning out the interface. Isolation is achieved using a safety capacitor, specifically a Y capacitor (1000pF 2kV ceramic capacitor recommended), bridging PE and signal ground to provide a high-frequency discharge path, blocking DC and power frequency signals. The signal ground is designed to float. External interfaces such as RS485 and CAN use isolated transceivers, such as the ADI ADM2483 or TI ISO3080 with an isolation withstand voltage of 2500Vrms, and are paired with the Etymotic TVS ESDSM712 (SM712 has dual shutdown voltages of 7V and 12V, placed on the bus side after isolation for further protection). Furthermore, the switching power supply's primary and secondary sides are connected to a Y capacitor, which is grounded without isolation, thus enhancing EMC. Therefore, the isolation principle is that the primary side PE and secondary side signal ground are connected via a Y capacitor for high-frequency connection, preventing DC transmission. Complete isolation is only suitable for battery-powered scenarios. Industrial edge boxes must use capacitive coupling isolation to balance safety and EMC.