If you use an overvoltage protected transciever like LT1785 (up to +-60V), then you can use transzorbs with rather high turn-on voltage, let's say 36V. This will have the additional benefit, that the parasitic junction capacitance of transzorbs are becoming so small, that signal transmission isn't badly influenced.

Also, use a slew rate limited RS485 driver to furtherly limit the current flowing through the transzorbs when charging the junction capacitance. Remember I = C x dU/dt.



Of course! I do always route not only the signal ground, but also the 5V supply voltage (at least up to the plug), to provide both, minimal common mode noise and the ability to power some extra circuitry, like RS485 to RS232 converter or one side of an isolated RS485 transciever.

Please do always use twisted pairs for the symmetrical RS485 signal and the 5V supply. And do never use the shield to transmit signal ground!

Kai