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State 443

Fronius Solar Inverter

Severity:

Source: OnlyErrorCodes.com — Every error code. One place.

Fronius Inverter State 443 — Isolation Fault

What Does This Error Mean?

Fronius State 443 is a DC isolation fault — the inverter's internal measurement has detected that the DC array is not properly isolated from ground. This is a serious safety event that requires a qualified solar electrician to inspect the array wiring before the system is restarted.

Affected Models

  • Fronius Primo
  • Fronius Symo
  • Fronius Galvo
  • Fronius SnapINverter Series
  • Fronius GEN24 Plus
  • Fronius Eco (TL)

Common Causes

  • DC cable insulation damaged by UV exposure, animal chewing, or abrasion on sharp racking edges
  • Water ingress into MC4 connectors or junction boxes causing a partial ground path
  • Degraded panel insulation — particularly on older or low-quality panels
  • Very large array system where the cumulative leakage current exceeds the inverter's threshold
  • Incorrect inverter grounding configuration for transformerless inverters

How to Fix It

  1. Shut down the system correctly before inspection.

    Switch the solar AC isolator to OFF. Then switch the DC isolator(s) at the inverter to OFF. This makes the DC array as safe as possible — note that panels still generate voltage when illuminated by sunlight.

  2. Check Solar.web for the event and MPPT string affected.

    Log into Solar.web and review the Events log around the time of the fault. If the inverter reports which MPPT input triggered the fault, your electrician can test that specific string first.

  3. Arrange an insulation resistance test by a licensed solar electrician.

    An insulation resistance (IR) test measures the resistance between the DC conductors and earth. A value below 1 MΩ per kW of array size indicates a fault that must be repaired before restart. This test is the definitive step for State 443.

  4. Inspect all accessible MC4 connectors and junction boxes.

    Check for cracked, melted, or poorly mated connectors. Any sign of black marks (arcing) or discolouration is a red flag. Check junction box gaskets for gaps or damage that allow water in.

When to Call a Professional

State 443 is a safety trip that requires a licensed solar electrician to perform insulation resistance testing before the system is restarted. Do not attempt to reset and run the system without professional inspection.

Frequently Asked Questions

What is the difference between State 241 and State 443 on a Fronius inverter?

Both are isolation/earth fault events but triggered by different monitoring thresholds or measurement methods inside the inverter. The response is the same for both: professional inspection before restart. Check the Solar.web event description for detail.

How long does it take to fix a Fronius State 443 fault?

If a damaged cable or connector is found, repair or replacement typically takes 1–2 hours. If the fault is in a panel's internal laminate, the panel must be replaced — this takes longer. Finding the fault with IR testing first speeds up the repair.