ZEC410 VAV Controllers Installation Instructions
18
Communication Bus Problems
Several factors may influence the behavior of the Zone Communication bus.
I/O Wiring
The ZEC controller must be wired properly. If the ZEC controller is wired incorrectly, communication problems may
occur. These problems include devices going online and offline, to devices not coming online at all.
Incomplete Address
The VAV controller must have the address switch set to a range between 6–37.
Duplicate Addresses
Two or more devices on a communication bus cannot have the same address. Two controllers on the Zone
Communication bus cannot both have an address of 18, for example. If two devices on the same bus have the
same address, performance can degrade or serious communication problems may occur. These problems include
the devices not coming online and all communication stopping completely.
Check for duplicate addresses in the following ways:
•
If a specific device is not communicating, remove the device with communication problems and check if device
address remains online at the Smart Building Hub to determine if the device address remains online.
•
If the bus communication problems are severe and no communication is present, or you cannot determine
where communication is unreliable, partition (disconnect and isolate a portion of the bus for testing purposes)
and test the bus portion connected to the Zone Coordinator.
Correcting Physical Communication Bus Problems
The communication bus is subject to a number of physical factors that can affect performance. Consider the
following list of common physical problems that affect the communications bus:
•
Check status LED to verify power at the controller
•
Check wires
-
Verify that the wire is a 22 AWG (0.6 mm) three-conductor, twisted, shielded cable.
-
Verify that the shield is continuous and hard-grounded at one end.
•
Check wiring
-
Check for and eliminate T-Taps (wire configurations that create a T shape) and star configurations.
-
Ensure that the bus is wired in a daisy-chain fashion.
-
Verify that appropriate devices have three wires entering and exiting each terminal (devices at the ends of
the trunk do not have this wiring).
•
Check EOL switch settings
-
Verify that the zone bus EOL switch on the Zone Coordinator is set to ON and the Zone Coordinator is
located at the end of the zone bus trunk.
-
Verify that only the EOL switch at the end of the Zone bus is set to ON and all other Zone bus EOL
switches are set to OFF.
•
Check connections, polarity, and lengths
-
Verify that communications loops are less than 1,000 ft (304 m) total in length.
-
If you are using one transformer to power multiple devices, verify that the device 24 VAC power connection
follows the polarity of the common and 24 V terminations (see
System and Zone Bus Supply Power Wiring
Guidelines
).
•
Check for opens and shorts
•
Check terminations
