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what is the recommended specifications for the cable used in BacNet MS/TP communication ?


MS/TP is a token-passing local area network (LAN) field bus that is built into all TAC BACnet
controllers. The protocol supports a combination of shared resource and peer-to-peer
communications, where more than one controller can be the network master at any given time.
Electrically, MS/TP adheres to standard RS-485, physically wired using two-conductor shielded
twisted pair cable.
RS-485 Cable Specifications
Cables used to form the RS-485 network should conform to the following specifications:
Wire Size: 22-24 AWG
Cable Type: Twisted-pair, copper wire, tinned
Shield: Braid
Nominal Impedance: 100-120 (
Velocity of propagation: 78%
Capacitance: <12.5 pF/ft between conductors and < 22 pF/ft between the conductor
connected to ground and the next conductor.
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