Connect the Modbus Cables

  1. Connect the Modbus cables to the UPS(s). Use either 2–wire or 4–wire connection. Shield the cables as shown.
    • Shielded twisted pair cables must be used for Modbus connections. The shield connection to the ground must be as short as possible (ideally below 1 cm). The shield must be connected to each device.

    • Wiring should be done in accordance with local wiring codes.

    • Route signal cables separately from power cables to ensure sufficient isolation.

    • The Modbus port is optically isolated. The ground of the Modbus port is not connected to any other ground.

    Example: 2–Wire Connection with Two UPSs

    Example: 4–Wire Connection with Two UPSs

  2. Install 150 Ohm termination resistors at each end of each bus if the buses are very long and operate at high data rates. Busses under 610 meters (2000 feet) at 9600 baud or under 305 meters (1000 feet) at 19.200 baud should not require termination resistors.
  3. Install 400–650 Ohm bias resistors at or inside the system controller; one from D0 to ground and one from D1 to +5 VDC.
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