Correct Understanding of Common Misconceptions in RS-485 Wiring

485 signal lines can be run together with strong power supply lines.

In actual construction, since wiring is done through conduits, sometimes the contractor binds the 485 signal line together with the power line for convenience. However, strong electrical signals can severely interfere with weak electrical signals, leading to instability in the 485 signal and communication.

485 signal lines can be wired using parallel lines or unshielded wires.

Since the 485 signal is transmitted using differential mode, which relies on the voltage difference between 485+ and 485-, if there is an external interference source, using twisted pair for 485 signal transmission minimizes the effect of interference on both 485+ and 485-. The voltage difference remains unchanged, thus minimizing the interference to the 485 signal. Similarly, if a shielded wire is used, external interference can also be minimized.

Using ordinary shielded twisted pair cables (network cables) is sufficient.

Due to rising raw material prices, the market is flooded with mixed quality cables, with some unscrupulous merchants using alloys to replace copper wires for network cables, coating them with copper to deceive customers. The distinguishing method: check the cross-section of the cable; if it is copper-colored, it is copper wire; if it is white, it is alloy posing as copper. Alloys are generally brittle, prone to breaking, and have much poorer conductivity than copper, which can easily cause problems during construction. It is recommended to choose standard 485 cables, which are shielded twisted pairs, where the transmission lines are made of multiple strands of copper wire twisted together. Thus, even if one small copper strand breaks, it won’t affect the overall functionality.

485 wiring can be arbitrarily configured in star or tree topologies.

The standard for 485 wiring requires a daisy-chain configuration. If star or tree connections are made without using 485 hubs or repeaters, it can easily cause signal reflections that lead to bus instability. Many contractors use star or tree connections during 485 wiring; sometimes the entire system is stable, but other times problems arise that are hard to diagnose, usually due to improper wiring. If site constraints require star or tree connections, using 485 hubs and repeaters from Shenzhen Fuyongtong Technology Co., Ltd. can help resolve these issues.

485 bus must be grounded.

Many technical documents state that the 485 bus must be grounded, but do not detail how to ground it. Strictly speaking, the 485 bus must have a reliable single-point ground. There should only be one grounding point along the entire 485 bus to prevent multiple grounding points, which could lead to common-mode interference. For reliable grounding, the ground connection (usually the shield wire) must have good contact to ensure consistent voltage. In actual construction, for convenience, wires are often cut into segments and reconnected, but if the shield wire is not properly connected, the grounding may become segmented, leading to inconsistent voltage and common-mode interference.