Correcting physical communication bus problems - Verasys - Field Device - ZEC510

Verasys ZEC510 VAV Controllers Installation Guide

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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.