General Modbus information

Shielded twisted pair cable must be used. The shield must only be connected in one end of the bus to avoid unwanted ground current in shielding. However, the shield must be unbroken along the complete bus length, except across galvanic isolated repeater.

Most controllers, gateways, compressor modules, frequency inverters etc. have no galvanic isolation in the Modbus interface. Therefore:

• Only data+ and data- wires should be connected to the gateway.
• Modules connected directly by Modbus must have the same ground potential (common PE wire / ground rod).
• Modules that refer to different ground potential (different ground rod) must be connected to Modbus via a galvanic isolated repeater, because different ground rods can lead to different potentials and may cause faults in the electronics.

For more information on Modbus, see documentation in the BEST Software: Choose compressor or device > Documentation > Modbus.