Recommended Cable 

Choice of cable is a critical part of the installation process. Defective or unspecified cable can result in communication problems. This can result in hardware timeouts and an overall speed reduction of System procedures. Correct cable is particularly important for RS485 buses. 

Ensure the following when selecting cable: 

  • For the RS485 Comms Bus, use twisted-pair Mylar shielded cable only. 

  • For RS485 Ports, the individual cross-sectional area of the each conductor in the cable must not be less than 0.2 mm² (0.0003 in²). 

  • For RS485 Ports, the maximum permissible cable length is 1 000 m (3 281 ft). 

  • For RS232 Ports, the individual core cross-sectional area of the each conductor in the cable must not be less than 0.2 mm² (0.0003 in²). 

  • For RS232 Ports, the maximum permissible cable length is 25 m (82.02 ft). Cables must be: 

  • Neatly laid out 

  • Labelled correctly on both ends with cable markers 

  • Earthed correctly—connect the shield of the cable to the Earth terminal on the unit. In turn, connect the unit to a good Earth point. The earth must be a low resistance connection to Earth and not an arbitrary Earth connection. 

NOTE:  Connect the shield at one end of the cable only.

Keep cable joins to a minimum. However if necessary, connect cable joins using proper connecting strips. 

On shielded cables, connect the shield to ground (earth) as follows: 


  • Strip to the required length exposing the internal wires 

  • Untwist the excess length of metallic foil and plastic covering and remove the plastic 

  • Twist the metallic foil to form a wire tail 

  • Connect the shield lead to the Earth terminal. Earthing is at ONE end of the cable only.


Cable layout of an installation must be documented, and the documents placed under configuration control.

 

Daisy-chain formations are preferable to Star formations. 

Sites where transmission lines are long, or multiple star formations are used, may experience timeouts on certain ImproX Controllers or Terminals. These are caused by reflections on the RS485 lines. To solve the problem, it may be necessary to terminate the lines. Termination resistors are added at the end of a cable run only and not at every Terminal.