And for a non galvanic isolation RS485 still all the
0v commons of the circuit should be tied together . And to the DIRT at one end only the MASTER END is it true for this aswell .
this???, what this

SHIELD where to tie it incase of non galvanic isolation situation .To the circuit common if PE isnt available , Then what is the need of third wire 0v .
1) ALWAYS tie shield to dirt on one end - no exceptions here.
2) NEVER use shield to carry anything (when tied in one end only you can't)
3) all signals must be referenced to something, thus the 3rd wire.

ALL the Noise will couple to the Circuit common if tied to shield .
tes, thus one end to dirt.

Any Leftover twisted pair in the cable what to do with em ,I hope they will resonate to some frequency ,and if grounded at one end would still resonate ,what to do .
resonate ???

Sorry I ask too much .
not too much, maybe to fuzzy questions (two ??? above)

Erik