Filter
Top Products
BAS-SVP10A-EN 25
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 theproper daisy chain configuration.
Figure 2. Incorrect and correct network configurations
BACnet MS/TP Link Wiring
BACnet MS/TP link wiring must be field-supplied and installed in compliance with the National
Electric Code (NEC) and local codes.
BACnet Configuration Requirements
• Follow these configuration requirements:
• BACnet wiring must use daisy-chain configuration. Maximum length is 4,000 ft (1219 m).
• 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 (BAS-SVN03x-EN).