After some reading I was convinced that I have three options:
- The best: connect A and B lines to a twisted pair, signal ground (SG) line to therd wire in the cable (or to a second twisted pair) and connect cable shield to protection ground (PG) only at one side (important!!!) of the network.
- If there is no sheld: I should connect A and B to a twisted pair and SG to therd wire.
- If there is no third wire: I should connect A and B to a twisted pair and SG to shiled on either sides.
I'd avoid using earth as third wire (Signal Ground) or skipping SG connection.
Is there anything I left behind?