How can the protection circuit of the power FTU be kept away from interference sources?

Keeping the protection circuit away from interference sources prevents malfunctions. Spatially, spatial isolation and electrical shielding are employed. Spatially, the protection relay, trip coil, and other components are at least 200mm away from the switch operating mechanism and at least 150mm away from the motor drive circuit. Electrically, the protection circuit is powered by an independent power supply module WRB2405S-3W. Shielded twisted-pair cables are used for signal lines, with the shielding layer grounded at a single point. On the PCB, a 0.5mm thick shielding cover is installed in the protection circuit area. The protection input signal uses RC filtering (1kΩ + 100nF) and ESD5V0D8B protection. Through this design, the coupling of interference sources to the protection circuit is reduced by 40dB, and the malfunction rate is less than 0.001%, meeting the IEC 60255 protection relay immunity requirements.