Fronius string inverters – the Primo, Symo, and older Galvo series – display faults as numbered state codes on the built-in screen or through the Fronius Solar.web monitoring portal. Exact codes can vary by model and firmware, so always note the exact state code shown before calling for service.
Common Fronius Error Codes
| Display Message / Code | What It Means | Severity |
|---|---|---|
| State 516 (Grid Voltage Fault) | Inverter detected grid voltage outside its acceptable operating window. Occasional occurrences are often utility-side. | Low – usually self-clears |
| State 305 / 306 (Insulation Fault) | Reduced insulation resistance in the DC circuit – commonly from moisture, damaged conduit, or degraded connectors at the panel level. This is Fronius’s ground-fault equivalent. | Safety hazard |
| State 509 (Arc Fault Detected) | Inverter’s AFCI circuitry detected a potential DC arc condition. | Safety hazard |
| State 480s (Internal Hardware Fault) | Broad category covering internal component issues – often the fan, internal sensors, or power stage. Frequently seen on Galvo and early Primo units approaching 10+ years of service. | Moderate-High |
| Display Blank, No Codes | Complete loss of power to the display or control board – a hard failure requiring on-site diagnosis. | Moderate-High |
This covers the fault categories homeowners encounter most often. Fronius’s full documentation lists additional state codes specific to certain models and firmware versions – if your display shows a code not listed here, note it exactly and a technician can look it up for your specific unit.
Ground Fault and Arc Fault: Why These Codes Are Different
Most inverter fault codes affect performance – annoying, but not dangerous. Insulation (ground) fault and arc fault codes are different. Both are safety detections built into the inverter specifically to catch conditions that can cause electric shock or start a fire, and both deserve a faster response than a typical production drop.
An insulation fault (State 305/306) means current is leaking outside its intended path, most often through damaged wire insulation, water intrusion, or a compromised connector. An arc fault (State 509) means the inverter’s AFCI circuitry detected current jumping across a gap instead of flowing through an intact conductor – arc-fault protection has been required on residential PV systems since 2011 under NFPA 70, Article 690.11.
Resetting the inverter will often clear either code and let the system restart production. That reset does not fix anything – it only clears the fault flag. If the underlying wiring damage, moisture intrusion, or failed connector is still there, the condition can recur, sometimes without being safely detected and interrupted the next time. Repeatedly resetting a system that keeps throwing an insulation fault or arc fault, instead of having it inspected, is how a manageable wiring issue turns into a safety event. If your system displays either of these codes, treat it as a signal to schedule a diagnostic inspection – not a nuisance to click through.
Repair or Replace?
Fronius inverters carry a standard warranty of 5-10 years depending on series and purchase date, extendable on some models. Fronius units are generally well-supported for parts availability, making targeted repair (fan, power board) a viable option even outside warranty – but full replacement becomes more cost-effective once a unit is approaching or past 12-15 years old.
Important Safety and Liability Notice
This article is provided for general informational purposes only and does not replace a professional, on-site diagnosis. Solar inverters operate at high DC and AC voltages and involve real fire and shock hazards; do not open, probe, or attempt to repair internal inverter components yourself. ElectriCare, Inc. makes no warranty as to the completeness or current accuracy of manufacturer error codes referenced here, which vary by model, firmware version, and installation, and assumes no liability for property damage, injury, or system damage resulting from actions taken based on this content. If your system displays a ground fault, arc fault, or any code you’re unsure about, do not repeatedly reset the inverter to clear it – contact a licensed technician for evaluation.
Related Reading
- Inverter Errors and Failures: Complete Troubleshooting Guide
- Solar Arc Fault Errors: Causes, Risks and What to Do
- Your String Inverter Is Failing: Repair, Replace, or Upgrade?
Get Your Fronius System Diagnosed
ElectriCare services Fronius Primo, Symo, and Galvo inverters, including warranty documentation support and full replacement when repair isn’t cost-effective. Insulation fault and arc fault calls are treated as priority service.
Schedule Fronius Inverter Service →
Sources and Further Reading
- Fronius Help Center – Official Support
- NFPA 70, Article 690 – Solar Photovoltaic Systems
- CALSSA – California Solar and Storage Association