What is RS485 Cable? How RS485 Communication Cable Works

■ RS485 Cable: What is it and How It's Done 

RS485 cable is a custom communication cable which is used to transport RS485 signals – a clever, attentive way of serial communication that could be used commonly in industrial automation, building management, and smart systems. By using a simple twisted pair of wires, RS485 allows for data transmission over a great distance and is both effective and cheap.

■ How Does RS485 Cable Work? 

RS-485 technology performs at the physical layer and employs differential signaling. The RS-485 cable is a principal device for achieving clean, reliable signal transmission in surroundings characterized by a lot of electrical noise and other factors that may interfere with communication over long distances. 

So, how do RS485 cables interlink these devices? 

Voltage Difference 

RS485 utilizes two lines which are called A and B. Data is transmitted through the A/B circuit by measuring the difference of voltage between the two wires. Intel (e.g. RS-232) uses ground-to-voltage mechanism. The differential system has some advantages: 

• Impressive immunity to electromagnetic interference 

• Consistent operational in rough climates 

• Extensive range (up to 1.2 km / 4000 ft) 

An RS485 telecommunication cable properly made consists of coupled pair wires to further cancel the noise as on long runs. 

Multi-Point Communication 

One of RS485's major strengths is its ability to work with multi-drop (multi-point) networks on a very large scale. This implies multiple devices (up to 32 or more) can be set up on a single cable bus. It's applicable in the scenarios like these: 

• Building management systems 

• SCADA Systems - Supervisory control and data acquisition 

• Automation of factories through PLCs 

It simplifies wiring tasks and reduces cost of systems. 

Data Rate and Distance Considerations 

RS485 has victory speed over distance depending on application needs: 

• Up to 10 Mbps for short cable runs (~12 meters) 

• Close to 100 kbps for distances as long as 1.2 km 

Your preference to RS485 cable type and shieldings extremely affects performance. This is especially so in environments with a high level of electromagnetic interference (EMI). 

Termination and Biasing 

By avoiding the signal problems like reflection, RS485 requires: 

• Termination resistors, usually 120 ohms, at both ends of the wire 

• Bias resistors that we use in order to keep the line also in a known situation when idle. 

To be considered for these cases while installing or choosing RS485 cable. 

Full-Duplex vs. Half-Duplex 

RS485 supports both transmission modes: 

• Half-duplex (2-wire): Here, one wire is used for sending information while the other is conducting the information from the other device which they took turns. Devices are alternating in communication. 

• Full-duplex (4-wire): Two pairs are used to carry out simultaneous sending and receiving of data. 

A side RS485 wire usually has one pair for a half-duplex situation or two pairs for a full-duplex situation.

■ RS485 Cable Construction 

A standard RS485 communication cable features: 

• Twisted pair(s): The number one way of minimizing crosstalk and EMI. 

• Shielding (Foil, Braid, or both): Protects against external noise. 

• Impedance-matched core (typically 120 ohms): It avoids reflections. 

• High-Strength Armor: The cable could be equipped with a strong armor that is meant for severe outdoor and underground installations. 

Some RS485 cable types also come with drain wires to ground the system correctly.

■ Recommended RS485 Cables from Zion Communication

Foil Shielded
SKU	PIC	Pairs	Conductor	Insulation	Shielding	Jacket Material	Environmental Suitability
73004		4	28 AWG Stranded TC	FPE (Foam Polyethylene)	Aluminum + Polyester Foil	PVC	Indoor Use
73005		5	28 AWG Stranded TC	FPE	Aluminum + Polyester Foil	PVC	Indoor Use
73006		8	28 AWG Stranded TC	FPE	Aluminum + Polyester Foil	PVC	Indoor Use
73012		12.5	28 AWG Stranded TC	FPE	Aluminum + Polyester Foil	PVC	Indoor Use
Foil + Braiding Shielded
SKU	PIC	Pairs	Conductor	Insulation	Shielding	Jacket Material	Environmental Suitability
73104		4	28 AWG Stranded TC	FPE	Aluminum + Polyester Foil + 65% TC Braid	PVC	Indoor (Not Riser or Plenum)
73204		4	24 AWG Stranded TC	PE (Polyethylene)	Aluminum + Polyester Foil + 90% TC Braid	PVC	Indoor Use
Armored Foil + Braiding + SWB
SKU	PIC	Pairs	Conductor	Insulation	Shielding	Jacket Material	Environmental Suitability
732046		4	24 AWG Stranded TC	FPE	Aluminum + Polyester Foil + 90% TC Braid + Steel Wire Braiding	LSZH/SWB/LSZH	Indoor, UV Resistant, Oil Resistant
732026		2	24 AWG Stranded TC	FPE	Aluminum + Polyester Foil + 90% TC Braid + Steel Wire Braiding	LSZH/SWB/LSZH	Indoor, UV Resistant, Oil Resistant

■ RS485 Application in Cable Systems 

RS485 cables are well-used in both commercial and industrial settings, for a large number of applications, such as: 

• Industrial automation – PLCs, motor controllers, sensors 

• Building management – HVAC control, lighting systems 

• Electricity measuring – Smart meters, solar inverters 

• Roads and traffic controls 

• Lab devices carrying out experiments and data loggers.

■ Protocol of Communication via RS485 

RS485 only addresses the physical level. The data structure or interpretation is not a concern; it's the manner in which this data is being sent. Those can be sorted into: 

• Modbus RTU 

• Profibus DP 

• BACnet MS/TP 

These protocols are designed over RS485 to allow interworking and standardization of different devices.

■ Conclusion

RS485 cable is a core component for the proper and accurate functioning of any system where data will be transmitted across long distances with devices connected. If you are finding the cables for factory floors or intelligent buildings management systems, then RS485 cable will help you in providing communication which is efficient, noise less and smooth. 

RS485 communication cable is not only user-friendly but it’s also an ultimate solution for engineers, system integrators, and industrial users who are into wiring their projects. Moreover, working with such a sophisticated device as RS485 communication cable is an excellent opportunity for an engineer to improve their skills.

Need OEM or custom RS485 cable solutions.? Email Zion Communication – a trustworthy manufacturer with ETL Certified RS485 interfaces and world-class delivery service.

Contact us for more information

michael@zion-communication.com

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