What is the maximum cable length when using the RS-485 protocol between Control panels?

The maximum cable length while using RS-458 communication is 1200 meters from the first panel till the last one. 

Please note that a 120 Ohms resistor need to be installed on the first and  control panel on the RS-485 line in parallel to the RS-485 A/B

Please note that the cable must be 2 pairs – twisted and shielded 18-AWG

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