I've used a lot of different cables for Compobus/S and never had any problem. The longest distance is around 150 meters in high-speed mode with a 2x0,5 unshielded round PVC-cable. But I've also used 3x0,5 shielded cable on the same type of machine without any problems. Besides the too long distance (Omron states max. 100 meters in high-speed mode) the Compobus-cable is also tied to a 3x400Volts 50Hz-powercable over al least 100 meters.... Never had a single glitch in communications.....