RS-485 Ground Loop
Ground loops occur when multiple ground paths exist between nodes, creating circulating currents. This induces noise on the RS-485 bus and causes CRC errors, timeouts, and intermittent failures.
Common Causes
- Shield or ground wire connected at multiple points along the trunk
- Different building ground potentials at remote equipment
- Devices powered from different electrical panels with ground offset
- Using shield as signal return instead of isolated GND reference
Fix Steps
- Use single-point shield grounding; ground shield at one end only (typically controller).
- Ensure all devices share a common reference; avoid mixing grounds from different panels.
- Consider galvanic isolation (isolated RS-485 transceivers) for nodes with ground offset.
- Remove redundant ground connections; keep only A, B, and optional shield.
- Measure ground potential between nodes with multimeter; >1 V indicates problem.