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Author: Michael Publish Time: 28-07-2025 Origin: Site
■ RS485 Cable Length vs Baud Rate: The Limit on the Way.
RS485, however, is the most reliable industrial communication standard for the long-distance device connection. However, similar to other serial protocols, there is a compromise between the speed of communication (baud rate, signal repetition rate) and the length of the bonding cable. This article focuses on how far RS485 Cable can go and the factors that affect performance over distances.
■ Why RS485 Cable Length Matters
RS-485 is a differential line which reduces noise to a great extent and makes RS485 more reliable over long distances - that's the substantial reason why it is always better than single-ended RS232. Why do we see the RS485 shape most often:
Factory automation
Building control systems
PLC and sensor networks
Industrial fieldbus communications
On the other hand, if you keep pushing RS485 over certain boundaries, refuse to follow cable length and baud rates, then you might suffer data loss, corruption, or signal reflections.
■ Why RS485 Cable Length Matters
Here’s a general guideline:
Baud Rate (bps) | Maximum Recommended Cable Length |
9600 | Up to 1200 meters |
19200 | Up to 600 meters |
38400 | Up to 300 meters |
57600 | Up to 200 meters |
115200 | Up to 100–120 meters |
1 Mbps | Up to 15–40 meters |
Note: Actual performance depends on cable quality, shielding, environment, and impedance matching.
■ Factors that determine the cable RS485 length
There are a number of technical and environmental issues that can considerably affect the RS485 transmission:
1) The characteristic impedance of the transmission line should be at least 120Ω in conjunction with the line impedance to reduce the reflection of waves.
2) Low capacitance in a cable gives a power signal as compared to high capacitance in a meter. It is advisable to rack low-capacitance cables for long distances.
3) Shielded twisted pair wires offer shielding from EMI/RFI to a effectively protect your electrical devices in industrial areas or outside premises.
4) Employ 120Ω resistors at both ends of the balanced line to eliminate traces of signal reliability.
5) The RS485 cables to be installed in an outdoor zone/ high interference demand strong shielded structured cables and possibly armored cables.
■ RS485 Long-Distance Cable: Practical Design Tips
For optimum performance at over long distances, the following standards should be maintained:
✅ Use twisted pairs with a matching impedance of 120Ω
✅ Ensure termination resistors are fitted to both ends of the wire
✅ Keep the lengths of the stub connections as small as possible to prevent signal reflections
✅ Use a repeater or an RS485 hub for distances above 1200 meters
■ Conclusion
The required RS-485 cable distance depends on three main factors: baud rate, cable quality, and installation practices. RS485, provided that the correct cable type has been selected and the system appropriately configured, can be an efficient and cost-effective medium to long-distance serial communication method. For industrial-grade RS485 cables with our certified quality, Zion Communication offers you full cabling solutions through OEM/ODM support.
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