Do I need ground for RS-485 if it is galvanically isolated?
Yes it will work. Perhaps 47k is little to high (it's a very big resistance). It depends on how many nodes you will connect. 47K is OK for each node, but then you can put additional lower resistance at the both ends.







simulate this circuit &ndash; Schematic created using CircuitLab

The Vcc and GND are floating power rails of each independent power source, the shield of the cable is connected to the earth. GNDs of nodes are not connected together as well the Vcc.