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 the 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
- Check addresses
- Check for duplicate addresses.
- Verify that the address range is sequential.
- Check for sources of interference
- Check bus voltages:
- (+) to COM must be within 2.0 to 3.0 VDC
- (-) to COM must be within 1.5 to 2.54 VDC
- (+) to (-) must be within 0.3 to 1.0 VDC
Note: Values may fluctuate due to ongoing communications; this operation is normal provided the voltage is within the defined range.