The communication bus is subject to a number of physical factors that can affect performance. Use the following list to check and correct common physical problems that affect the communications bus:
- Check the status LED to verify that the controller has power.
- Check the wires for the following:
- 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 the 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 configuration.
- Verify that the appropriate devices have two wires entering and exiting each terminal. Note: Devices at the ends of the trunk have one wire entering and exiting each terminal.
- 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 short circuits.
- Check terminations.
- Check for sources of interference.
- Check the following bus voltages:
- (+) to COM must be within 2.0 VDC to 3.0 VDC
- (-) to COM must be within 1.5 VDC to 2.54 VDC
- (+) to (-) must be within 0.3 VDC to 1.0 VDC
Note: Values can fluctuate due to ongoing communications; this operation is normal when the voltage is within the defined range.