64
UNT Controller—Unitary (UNT) Controller
grdloop
UNT
15 VDC
DVM < 5 VDC/VAC = OK (Isolat
DVM > 5 VDC/VAC = Earth Gro
100k ohm
1/4-watt
DVM
Field Wiring*
*AICOM, BICOM, ZBUS COM, AOCOM, BOCOM
24 VAC
24 VAC
24 VAC COM
Line
Voltage
Figure 34: Testing for Ground Loops
•
Connect the DVM across the 24 VAC and the 24 VAC common
terminal of the UNT. Read the voltage with all typical loads
energized.
A reading of 24 VAC is required when the line voltage is nominal.
If you read a value less than 20 VAC, make sure the primary voltage
matches the transformer’s voltage rating. For details, refer to the
Power Source and Loads section of this technical bulletin and
recalculate the VA requirements for the UNT.
You have completed the UNT isolation tests. If you plan to connect this
UNT to the N2 Bus for communication to other devices, refer to the
ASC and N2 Bus Troubleshooting Technical Bulletin in FAN 636.3 or
1628.2.
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