SMAJ12CA can handle much more energy than the internal protection in SN65HVD1786D.
ESD/transients/glitches in the real world is not as predictable as "16 kV discharge from a human body model".
I would use the TVS diodes.
SN65HVD1786D is meant for protection of power supply short with the RS485 lines.
If i use SMAJ12CA at the lines like this ( RS485 A --> SMAJ12CA --> GND ) and Say if 24V is shorted with RS485 A line; will this permanent short destroy the SMAJ12CA?
SN65HVD1786D is meant for protection of power supply short with the RS485 lines.
If i use SMAJ12CA at the lines like this ( RS485 A --> SMAJ12CA --> GND ) and Say if 24V is shorted with RS485 A line; will this permanent short destroy the SMAJ12CA?
Yes, to handle shorts to the power supply without failure, the voltage of the TVS diodes must be selected so they don't conduct at the supply voltage.
Otherwise they will overheat and fail to a short unless the power supply is very weak (low current limit).
SMAJ12CA is not the right TVS diode to handle shorts to the 24V supply.