Wiring Requirements for Communicating Thermostats
BACnet networks use a daisy chain configuration. A daisy chain means that there is only one main cable and every network device is connected directly along its path.
Figure 2 illustrates two improper network configurations and the proper daisy chain configuration.
Figure 2. Incorrect and correct network configurations
BACnet MS/TP Link Wiring
BACnet MS/TP link wiring must be
BACnet Configuration Requirements
•Follow these configuration requirements:
•BACnet wiring must use
•BACnet links are polarity sensitive; consistent wiring polarity must be maintained between devices.
•Limit each link to 30 controllers or 60 total controllers per Tracer SC.
BACnet Wiring Best Practices
The following wiring practices are recommended:
•Use 18 AWG, (24 pF/ft. max.), shielded, twisted pair communication wire (Trane purple wire).
•Strip no more than 2 in. (5 cm) of the outer conductor of shielded wire.
•Avoid sharing 24 Vac power between unit controllers.
•Ensure that 24 Vac power supplies are consistently grounded. If grounds are not maintained, intermittent or failed communication could result.
•Connect the shield portion of the communication wire at the first unit controller in the link.
•Use a Tracer BACnet terminator at each end of the link.
For additional best practices, see the Unit Controller Wiring Guide For the Tracer SC™ System Controller
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