How to design the EMC of the current transformer interface in an intelligent low-voltage monitoring unit?

The current transformer interface is designed with EMC protection to prevent secondary-side interference. A 7D390K (390V) varistor and an SMBJ24CA TVS diode are connected in parallel on the secondary side of the current transformer (CT). A PBZ1608E600Z0T ferrite bead (600Ω@100MHz) is connected in series on the secondary side of the current transformer (PT). Shielded twisted-pair cable is used for the sampling lines, with the shield grounded at a single point on the monitoring unit. A CMZ3225A-501T common-mode inductor is used for filtering at the PCB interface. The current transformer casing is grounded. With this design, the current transformer interface can withstand IEC 61000-4-5 4kV surge and IEC 61000-4-4 4kV EFT tests.