Trane BACnet MS/TP Installation, Operation And Maintenance Manual page 37

Trane SerialSpy Protocol Analyzer Software
Power Polarity Reversal
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Many jobs have a single transformer powering multiple Tracer UC400s. Strict polarity of the power wiring
from the transformer to the Tracer UC400s must be observed in these cases. It is very easy to inadvertently
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switch power polarity by simply offsetting the power plug on the Tracer UC400 by one position. This
condition might result in a very chaotic SerialSpy capture.
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Figure 26, p. 37 shows a very simple link with a Tracer SC+ at address 0 and Tracer UC400s at
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addresses 1, 2, and 3. The three Tracer UC400s share a transformer. When power polarity is reversed
on device 1, it begins polling and receives a reply from address 0 but continues polling as if unaware of
the reply. Often when this happens, an entire group of devices that share a transformer will not
communicate and the link appears clean.
Figure 26. Power polarity on device 1 reversed
BAS-SVX51L-EN 37