What cables are required for RS485?

1, Basic types of RS485 cables
RS485 cables are mainly divided into two types: twisted pair cables and armored twisted pair shielded cables.
Twisted pair cable (STP-120 Ω)
Twisted pair cable is one of the most common cable types in RS485 communication, typically labeled as STP-120 Ω (for RS485&CAN), with a pair of 18AWG. This type of cable consists of two wires twisted together, which can effectively reduce electromagnetic interference and improve transmission quality. STP-120 Ω cable is suitable for indoor, pipeline, and general industrial environments. The outer diameter of the cable is about 8.2mm, with a gray sheath, and it has the characteristics of low cost, easy installation, and maintenance.
Armored twisted pair shielded cable (ASTP-120 Ω)
Armored twisted pair shielded cables add an armor layer on top of twisted pair cables, providing higher mechanical protection and anti-interference capabilities. This type of cable is also labeled ASTP-120 Ω (for RS485&CAN), with a pair of 18AWG cables, an outer diameter of approximately 12.3mm, and a black sheath. Armored twisted pair shielded cables are suitable for places with severe interference, frequent rodent damage, and lightning and explosion protection requirements, such as outdoor installation, factory automation environments, etc.
2, Model and characteristics of RS485 cable
In addition to the basic types, RS485 cables can also be derived into various models according to different application scenarios.
RS485-2 type
The RS485-2 cable consists of two wires (labeled A and B) and supports basic data transmission functions. This type of cable has a simple structure, low cost, and is suitable for data communication in two-point or master-slave network structures with low requirements and simple wiring environment.
RS485-3 type
The RS485-3 cable adds a ground wire (GND) on the basis of RS485-2, which improves the system's anti-interference ability and reduces problems caused by poor grounding. This type of cable is particularly suitable for use in environments with strong electromagnetic interference, such as factory automation.
RS485-4 type
The RS485-4 cable not only includes A/B differential signal lines, but also adds positive and negative power lines (V+and V -), allowing direct power supply to connected devices through the bus. This type of cable simplifies system design and reduces the need for additional cables, making it ideal for building remote terminal units (RTUs) in distributed control systems, especially when simplified wiring is required.
RS485-5 type
The RS485-5 cable integrates all of the above features - A/B differential signal lines, GND ground lines, and V+/V - power lines, and may include shielding layers. This cable has the highest level of anti-interference performance and is very suitable for working under extreme conditions. For applications that require extremely high reliability and are subject to strong electromagnetic field interference, RS485-5 is the best choice.
3, Guide to selecting RS485 cables
When choosing RS485 cables, the following factors need to be considered:
transmission distance
The larger the cable diameter, the farther the transmission distance. However, it is also important to pay attention to the shielding effect of the cable. A good shielding effect can effectively reduce external interference and thus improve transmission distance.
electromagnetic interference
In environments with strong electromagnetic interference, it is recommended to choose cables with better anti-interference capabilities, such as RS485-3 or RS485-5 cables, or to choose armored twisted pair shielded cables.
cost
If the budget is limited, you can choose the RS485-2 cable with lower cost. However, in situations where high reliability and long-distance transmission are required, priority should be given to cable types with better performance.
Application scenarios
Choose the appropriate cable type based on the different application scenarios. For example, in outdoor or harsh environments, armored twisted pair shielded cables should be selected; In situations where simplified wiring is required, RS485-4 cables can be chosen.
Equipment compatibility
When selecting cables, it is also necessary to consider the compatibility of the equipment. For example, if the device supports national standard wires, then RVVSP2 cable diameter should be selected; If the device supports US standard cables, then the STP-120 ohm cable should be selected.