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Intermittent Errors from Electromagnetic Interference (EMI) on Communication Wiring

Likely causes

Communication wire routed too close to power cables — less than 300mm separation

Check: Measure separation distance along parallel sections of communication and power cables → locate sections with less than 300mm separation → compare intermittent error timestamps with large load startup times

What to do: Route communication wire in separate metal conduit → maintain 300mm or more separation from power cables → reroute communication wire

Communication wire shield grounding failure — single-point grounding not followed

Check: Check shield cable grounding connection point → verify if both ends are grounded (grounding both ends creates current loop) → measure grounding resistance (normal 10Ω or below)

What to do: Ground shield cable at one end only (single-point ground) → insulate the other end → add ferrite core EMI filter installation (one at each communication wire input/output end)

Inverter compressor electrical noise — high-frequency interference

Check: Check communication error frequency while inverter operates → verify if errors disappear when inverter stops → check communication wire noise waveform with oscilloscope

What to do: Route communication cable away from inverter as far as possible → install metal conduit → add ferrite core filter at communication board input

Field tip

When suspecting EMI, record error occurrence pattern: if errors only occur right after specific load startup or during inverter operation, EMI is the cause.

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