The standard cable for BACnet MS/TP is an AWG 18-22 shielded twisted-pair with a 120 ohm characteristic impedance and capacitance below 30 pF/ft (98 pF/m), covering distances up to 1200 m at 9600 baud.

Typical MS/TP cable specifications are: AWG 18-22 conductors (18 is more robust, 22 is more economical), 120 ohm characteristic impedance (matching standard RS-485), capacitance no greater than 30 pF/ft (a higher value shortens the maximum reach), and either foil or braided shielding (foil is sufficient indoors). Common reference products include Belden 8761 / 9841 / 9842 and Liberty Cable 18AWG/120 ohm, priced at roughly 1-3 euro per metre depending on the brand.

At 76800 baud the practical reach drops well below 1200 m; if you plan to run the segment fast, derate the maximum length and add repeaters or BACnet/IP backbones rather than fighting reflections later.