RS485 Communication System Cable Selection
1. What Type of Cable Should Be Used for RS485 Bus?
It is recommended to use shielded twisted-pair cable, with specifications such as:
- 2x24AWG stranded conductor or 2×0.5mm single-core hard copper wire
- Characteristic impedance of 120 ohms
Shielded twisted-pair cables help reduce and eliminate bandwidth interference between the two RS485 wires, as well as common-mode interference from the surrounding environment.
Many engineers tend to use Category 5 or Super Category 5 cables for RS485 communication, which is debatable due to the following reasons:
- a. Ordinary network cables lack a shielding layer, making them ineffective in preventing common-mode interference.
- b. Network cables, typically 0.2mm², have a thin wire diameter, which reduces the transmission distance and limits the number of connected devices.
- c. Network cables are often single-strand copper wire, which is more prone to breakage compared to multi-core wire.
2. How to Route RS485 Communication Cables?
- a. Ensure that communication lines are kept away from high-voltage power lines, avoiding parallel arrangements with power lines or bundling them together.
- b. Opt for a ring structure instead of a star structure. Star structures can produce reflected signals, negatively impacting RS485 communication.
3. Use the Same Type of Cable Throughout the RS485 Network
For consistency and better performance, it is advisable to use the same type of cable and minimize connections along the line.
4. Common-Mode and Differential-Mode Interference
- Common-mode interference occurs between the signal line and ground and is asymmetrical. Methods to eliminate it include:
- a. Use shielded twisted-pair cables with effective grounding.
- b. Use a linear regulated power supply or a high-quality switching power supply.
- Differential-mode interference occurs between the two signal lines and is symmetrical. To eliminate it, add a bias resistor to the circuit.
RS485 communication cables are not expensive, and you can often find high-quality RS485 cables at affordable prices in China. KMCABLE, as a source supplier of RS485 cables, offers sufficient stock with excellent quality. Welcome major purchasers to inquire.
