Does the edge box communication interface need separate EFT protection?

While edge-box communication interfaces such as RS485, CAN, and Ethernet operate at low internal circuit voltages, their external cables, often tens of meters long, can induce EFT interference in industrial environments, necessitating separate protection. Taking the RS485 interface as an example, we recommend the ESDSM712 from Yinte Electronics. Named SM712, it is specifically designed for RS485, featuring dual 7V and 12V shutdown voltages, an A/B line-to-ground junction capacitance of 5pF (does not occupy signal margin), and a common-mode choke CML3225A-510T. This device is a common-mode inductor from the CML series, 3225 size 3.2×2.5mm, 510T inductance 51μH, capable of filtering common-mode noise. Furthermore, a gas discharge tube 2R090L-5.5X6 is connected across the interface to ground. Named 2R with 090° terminals and an operating voltage of 90V, L-type pins 5.5×6 mm in size, serves as a primary discharge channel. The protection circuit is positioned adjacent to the connector, and the grounding pad is directly connected to the ground plane via an via, conforming to IEC61000-4-4. Experimental data from a 2kV test showed no packet loss during communication, indicating that the EFT threshold of the unprotected interface is only ±400V, while the fully protected interface can withstand over ±2kV. Therefore, independent EFT protection for the communication interface is an essential measure for ensuring the reliability of edge boxes.