(right click on the link and change link URL address)
Share this article:
SPD for RS485 bus
SDP RS485 is a Surge Protection Device (SPD) specifically designed for RS485 communication lines.
When it is recommended:
- Long lines (>30–50 m)
The longer the cable, the greater its “antenna effect” which can pick up electromagnetic interference or induced overvoltages.
- Lines running outdoors or between different buildings
Cables exposed to indirect lightning strikes or differences in ground potential between buildings.
Without SPDs in these cases, RS485 transceivers can be easily damaged.
- Environments with high electrical noise
Proximity to power panels, motors, inverters, welders, elevators, etc.
Switching disturbances can couple onto the communication line.
- Areas with high lightning density or low atmospheric protection
In regions prone to thunderstorms, SPDs significantly reduce failures caused by indirect lightning strikes.
Recommended Installation Guidelines:
- Install an SPD at the point where the line enters the AC box
If the cable comes from outside or from a field (e.g., photovoltaic array), protect it immediately at the entry point.
- Place SPDs near critical devices
Inverters
Dataloggers
Energy meters
This ensures that indirect surges are blocked before reaching sensitive electronics.
- Proper grounding is essential
SPDs have a dedicated ground (PE) terminal.
Without proper grounding, the SPD cannot discharge surges effectively.
- Choose the right SPD type
Type 2 (Class C) for standard electrical boards.
Devices designed specifically for communication buses, with low capacitance to avoid affecting RS485 signals.
Additional recommendations
Use twisted pair and shielded RS485 cables; SPDs complement but do not replace good cabling practices.
Maintain equipotential grounding between panels to reduce potential differences.
For long runs across multiple buildings, consider SPDs at both ends of the line.
Please note that the installation of SDPs is recommended, as indicated in the Eastron meter manual.
