Check the ESD specification for your RS-485 transceiver: if it is only rated per HBM, then system-level ESD is needed (IEC61000-4-2). To protect RS485 transceiver, ESDA14V2BP6 is recommended.
Please check schematic in figure ESD14V2BP6 protection device schematic in AN5245.
ST485 transceiver can be split in 2 families:
with system ESD protection (ST485E series)
without system ESD protection (ST485 series)
When ST485E series cannot be placed close to the ESD source, it is required to use external ESD protections in order to avoid any EMI coupling with internal PCB tracks. EMI coupling induced by ESD can generate latch-up failures in your system.