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Author: Michael Publish Time: 28-07-2025 Origin: Site
Often, when building a communication network in industrial automation, building systems, or even some devices driving data transfer, you will lay hands on RS232, RS485, or Ethernet (Cat5e, Cat6). Although they all transfer data, the standards vary in terms of protocol, cable structure, performance, and application. Being aware of the difference contributes to the aspect of cable choice.
Standard | Description |
A point-to-point serial communication protocol used for short-distance, low-speed data transfer. | |
A differential, multi-point serial communication standard ideal for long-distance and industrial environments. | |
Ethernet (e.g., Cat5e/Cat6) | A network communication protocol using twisted-pair cables for high-speed LAN and internet connectivity. |
Conductor: Single-ended, multiple wires (Tx, Rx, GND, etc.)
Shielding: Optional foil shield
Pairs: Pairs to be formed by the non-twisted
Use: Intermediate, outdated systems
Conductor: Tin or copper, twisted pair (1 or more legs), differential
Shielding: The appropriate foil and/or foil + braid is for EMI protection
Impedance: 120 Ω
Use: Automation, telecommunication plants, long cable runs, high untenable interference points
Conductor: 4 twisted pairs (UTP/STP)
Shielding: It’s optional; Cat6 might use individual shielding and also an overall braid.
Impedance: 100 Ω
Use: LAN, data cabling, internet
Feature | |||
Communication Mode | Point-to-point | Multi-point (bus topology) | Full-duplex or half-duplex |
Signal Type | Single-ended | Differential | Differential (balanced) |
Max Distance | ~15 meters | Up to 1200 meters | ~100 meters |
Max Speed | ~115.2 kbps | Up to 10 Mbps (over short distance) | 100 Mbps to 10 Gbps |
No. of Devices | 1 transmitter & 1 receiver | Up to 32 nodes (standard) | Hundreds of devices via switches |
Common Connectors | DB9, DB25 | Terminal block, RJ45, DB9 | RJ45 |
Impedance | ~100 Ω | 120 Ω | 100 Ω (Cat5e), 100 Ω (Cat6) |
Cable Type | Unshielded multi-core or twisted | Shielded twisted pair (STP/FTP) | Unshielded or shielded twisted pair |
Typical Use | Serial communication with PCs or PLCs | Industrial automation, Modbus RTU, HVAC | LAN, IP cameras, switches, computers |
Property | RS232 Cable | RS485 Cable | Cat6 Ethernet Cable |
Signal Type | Single-ended | Differential | Differential (balanced pair) |
Communication Protocol | RS-232 Standard | RS-485 Standard | Ethernet (IEEE 802.3) |
Typical Use Case | Direct PC/device link | Industrial automation, PLC, sensor network | Network infrastructure, internet, PoE |
Cable Structure | Multi-core, unshielded or basic shielding | Twisted pair, shielded (foil/braid) | 4 twisted pairs (shielded or unshielded) |
Shielding | Optional (rarely used) | Recommended (foil or foil + braid) | Optional (U/UTP, F/UTP, SF/UTP, etc.) |
Max Distance | ~15 meters | Up to 1200 meters | Up to 100 meters (for 1 Gbps) |
Max Speed | ≤115.2 kbps | Up to 10 Mbps (short runs) | Up to 10 Gbps (Cat6A) |
Connector Type | DB9/DB25 | Terminal block, RJ45 (for some converters) | RJ45 |
Impedance | Not standardized | Typically 120 Ohms | 100 ± 15 Ohms (balanced) |
Cost | Low | Moderate (due to shielding, industrial specs) | Moderate (mass produced, widely available) |
Noise Immunity | Poor | Excellent | Good (depends on shielding) |
Application | Recommended Cable |
Connecting a PC to a device over short distance | RS232 Cable |
Connecting multiple devices in an industrial network | RS485 Shielded Twisted Pair Cable |
High-speed data transfer in local networks | Cat6 Ethernet Cable |
Temporary or short-distance RS485 | Cat5e/Cat6 UTP/STP Cable (with caution) |
Sure, Ethernet cables (Cat5e/Cat6) are frequently used to build the RS485 bus connections because of the following reasons:
They are terminated with pairs (advantage for differential signaling)
This is because they have impedance that is structurally close (less than 20%) to RS485 spec, whose nominal value is 120 ohms, while RS232 gives a nominal impedance of 100 ohms.
They are easy to find and affordable.
⚠️ Important Note:
Impedance implication (Cat6: 100 Ω, RS485: 120 Ω) mismatch can cause ground wave effect that results in signal distortion at long distances or with high baud rates.
Use a shielded Cat6 (FTP or STP) when in an electrically noisy area.
✅ Best practice: Avoid using Ethernet cable for RS485 runs longer than two meters.
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michael@zion-communication.com
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