Electrically isolated RS485 bus system
Overvoltage protection for RS485 ports:
The maximum permissible external differential voltage seen by the RS485 transceiver chips according to the data sheet of the semiconductor manufacturer is around +/- 12...14V. Voltages exceeding these values will inevitably result in destruction of the transceiver chips.
When using shielded cable, it is unlikely that such high differential voltages will occur, since extreme coupling onto the transmission line expresses itself as a rise in potential on all cable conductors.
When using the isolator on transmission lines outside of buildings or when the cabling conditions are unclear, use of the 66203 Isolator is recommended. This isolator model has built-in overvoltage protection, which limits the maximum occurring differential voltages to a harmless ±9V using fast protection diodes