The two most common forms of BACnet communications channels that you are likely to encounter are BACnet MS/TP over RS-485 and BACnet/IP over Ethernet. Every device on a channel must use the same type of communications. To transmit data between channels of different types you must use a router.
1.) BACnet MS/TP - This channel is a 9.6 kbps - 76.8 Kps twisted pair channel. I/A Series BACnet controllers are delivered with MS/TP transceivers. I/A Series BACnet controllers (MNB-300, MNB-1000, MNB-V1, MNB-V2, etc.) must be on an MS/TP channel. MS/TP channels must be configured as a POLARITY sensitive RS-485 BUS topology.
The RS-485 BUS should use LOW IMPEDANCE 22 AWG or 24 AWG twisted shielded cable with a distributed capacitance between conductors of less than 15 pF/ft and a characteristic impedance between 100-130 Ohms. Belden 89841 is commonly recommended and can be used with confidence. I recommend that a maximum cable length of 2500' be observed.
2.) BACnet/IP - This is a TCP/IP channel. This channel is typically an Ethernet backbone from which other BACnet MS/TP channels are derived to create a network. Maximum cable lengths are subject to standard Ethernet wiring rules. 10/100 BaseT segments cannot exceed 328 feet.
Here is what I have been recommending:
Windy City Wire:
1-800-379-1191
BACnet MS/TP 24 AWG:
http://harrier.smartwire.com/ecom/invmainprof.php?item=042002-S
BACnet MS/TP 22 AWG (increased physical strength and works with ARCnet):
http://harrier.smartwire.com/ecom/invmainprof.php?item=043006AL-S
Belden 89841 is commonly recommended by manufacturers of BACnet equipment and can be used with confidence.
If you know of a better method, please let me know!
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