RS-485 Voltage Drop Fix
Excessive voltage drop on RS-485 trunks causes marginal differential signal levels. Devices at the far end may see corrupted data or fail to communicate reliably.
Common Causes
- Trunk length exceeds spec (e.g., >4000 ft without repeaters)
- Undersized wire gauge (24 AWG or thinner on long runs)
- Multiple tap points or daisy chains adding resistance
- High node count drawing excessive bias/termination current
Fix Steps
- Measure differential voltage (A–B) at far end with multimeter; aim for >200 mV idle.
- Shorten trunk or add RS-485 repeaters to segment long runs.
- Use 22 AWG or 18 AWG cable for runs over 1000 ft.
- Reduce node count per segment; use repeaters for large networks.
- Confirm proper termination and bias resistors per spec.