BAS-SVX51L-EN 13
Best Practices
Maintain consistent wiring polarity between devices.
BACnet
®
links are polarity sensitive. Mixing plus and minus terminals between devices will cause network
communication failure. Designate one color as positive and consistently use this color for all positive link
terminals on the site.
Observe network cable and conductor termination best practices during installation.
The following wiring practices are recommended:
• Trane purple wire is acceptable 2-conductor cable and it is best practice to use this wire for
non-isolated device network communications. 3-conductor cable is required for isolated device
network communication. See Table 1, p. 8 for a list of non-isolated and isolated Trane devices.
• Connect the shield portion of the communication wire to the ground terminal of the link termination
block at the Tracer
®
SC+. The Tracer
®
SC+ provides the ground for the BACnet
®
MS/TP link.
• Splice and tape the shield between wire segments at each unit controller connection point in order to
maintain a continuous shield and avoid connection to ground.
• Consider labeling the communication links at each device to make servicing easier. For example,
when at device #10, the two comm wires could be labeled “From device 39”, and “To device #11”.
• Do not run BACnet
®
MS/TP cable:
– in the same conduit as 24 Vac power.
– alongside 24 VAC power, which is not contained in a conduit.
– alongside conductors being driven by binary outputs.
– in the same conduit as conductors be driven by binary outputs.
– near electrical motors or variable frequency drive modules.
• Strip no more than 2 in. (5 cm) of the outer conductor of shielded wire.
Avoid sharing 24 Vac power between unit controllers.
Important: If sharing a transformer with multiple controllers is necessary, verify that polarity
has not been mixed. 24 Vac hot/ground polarity must be maintained.
Ensure that 24 Vac power supplies are consistently grounded.
If grounds are not maintained, intermittent or failed communication could result.
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