How to protect against electrical fast pulses (EFT) in PMS (Power Measurement Switch) devices?

The PMS needs to withstand EFT/Burst interference as specified in the IEC 61000-4-4 standard. EFT/Burst interference is characterized by high frequency (5kHz repetition rate), high voltage (4kV), low energy, but wide coverage. Protection requires a multi-stage approach: First, at the power input, use a common-mode inductor CMZ1211-501T combined with a Y capacitor (2.2nF/Y1) to provide a low-impedance return path for common-mode pulses. Second, add a π-type filter (PBZ1608E600Z0T ferrite bead + capacitor) before the board-level DC/DC input. For communication ports, use a common-mode inductor CML3225A-510T and a TVS diode (such as SMBJ6.5CA). PCB layout is crucial: all filtering and protection devices must be close to the interference entry point (connector), traces before and after the filter must be separated, and inputs and outputs must not be parallel. The grounding system must be low-impedance and complete to provide a discharge path for EFT current. On the software side, digital filtering is applied to potentially interfered input signals, and error checking and retransmission are enabled for communication. Through system design, the PMS can stably pass the EFT Level 4 test and will not malfunction or be damaged under pulse group interference.