I’ve taken some more internal pictures of the V5 brain and the RS-485 drivers are SN65HVD1782. SN65HVD178x datasheet says that it is rated up to 70v for transient voltage pulse and up to 16kV for ESD, but it says nothing about maximum current or power dissipation in the event of ESD.
SM712 chip, that you have recommended, is rated at 19A current pulse and 600W power dissipation for ESD of up to 30kV. SM712 datasheet says that it has bi-directional asymmetric TVS diodes (+12/-7v) specifically designed for RS-485. However, it is a bit pricey at $0.87 per port for 2 channel device.
https://www.digikey.com/product-detail/en/littelfuse-inc/SM712-02HTG/F6450CT-ND/5019610
The cheapest TVS alternative for non-volume buying seem to be 4-channel TVS array NUP4102XV6T1G for about $0.24 per port. But it is rated only at 3A, 75W, and 16kV.
Another alternative is SMDA15LCC 4-channel TVS array which offers 300W of power dissipation for an ESD event at a cost of $0.30 per port. SMAxxLCC datasheet says it was designed for RS-422 which is electrically similar to RS-485, but it says nothing about peak current and voltage rating for ESD protection.
https://www.digikey.com/product-detail/en/smc-diode-solutions/SMDA15LCCTR/1655-2010-1-ND/9562577
SMDA15LCC seems like the best balanced solution in terms of cost per protection, but lack of max voltage rating for ESD protection bothers me.
Does anyone know if SMDA15LCC would be an acceptable option or SM712 is the only good choice?