481200 meters is the figure commonly cited in technical literature. However, Park, Mackay, and Wright, in their book Practical Data Communications for Instrumentation and Control document EIA/TIA-422 and EIA/TIA-485 networks operating with cable lengths up to 5 km (over 16000 feet!) at data rates of 1200 bps. Undoubtedly, such systems were installed with care, using high-quality cable and good wiring practices to minimize cable capacitance and noise.