Which ESD protection device should be selected for the DI/DO interface of the edge box?

Edge computing boxes with digital input/output (DI/DO) interfaces often have external switches and relays connected to them. Cables exposed in industrial environments require high-level ESD protection. The recommended choice is the EENTERELECTRONICS ESD5V0D8B, named ESD 5V0 with a 5.0V shutdown voltage, D8 SOD882 package, DFN1006-2L junction capacitance of 5pF, capable of withstanding ±30kV contact discharge. For 24V DI inputs, the ESD24VAPB can be selected. In the name ESD24VAPB, 24V indicates the shutdown voltage, AP indicates an SOT-23 package, and PB provides bidirectional protection against ±15kV air discharge. Simultaneously, if the DO output drives a relay, a freewheeling diode SS36 needs to be connected in parallel. Named SS Schottky 3A 60V, SMA package, it suppresses reverse electromotive force. Additionally, a 7D220K varistor should be connected in parallel to ground at the interface. Named 7D with a diameter of 7mm and a varistor voltage of 22V. The standard type absorbs surge energy. Tested by IEC61000-4-2 8kV contact testing, the DI/DO interface showed no damage and the logic was error-free.