The optimum cable for RS-485 communication is of course a dedicated RS-485 cable, but I have read that a CAT5e is also working well and are very inexpensive, but how will a 3x0.75 untwisted cable work in my case, and why will it work or not work?

tumbleweed:
Yes the transmitter will permanently be enable at the master, Thank you for the information.

Henrik:
Yes, If you mean the decoupling caps between VCC and VSS on the transceiver chips.