The EL9540-0010 system terminal contains an overvoltage filter for the 24 V DC field supply. The filter protects the EtherCAT Terminal from line-bound surge voltages that can occur due to high-energy, dynamic disturbances such as switching overvoltages at inductive consumers or indirect lightning strikes at the supply lines.

The EL9540-0010 can be used to protect the terminal station, especially analog terminals, against damage in particularly harsh environments such as onshore and offshore areas and in shipbuilding. The power supply for the field supply is 5 A.

https://www.beckhoff.com/vi-vn/products/i-o/ethercat-terminals/el9xxx-system/el9540-0010.html