Warning What does this mean?

Your system is down or running degraded, but this is not an immediate safety danger. Work through the safe steps below.

Fronius Inverter STATE 502 Error: Meaning, Causes & Safe Fix

STATE 502 means the inverter has detected an insulation fault on your solar panels — unwanted leakage current between the DC wiring or panels and earth. The inverter will not start while the fault persists.

What should I do first?

Two quick questions — we'll point you to the right starting point.

Is this code still showing on your inverter's display?

What this code means

Your Fronius inverter constantly measures the insulation resistance between the solar panel wiring (DC+ and DC-) and earth. STATE 502 appears when that measurement detects a fault — current is leaking to ground somewhere in the array. This often shows up in rain or high humidity, when moisture gets into damaged panels, connectors, or cabling. As long as the fault persists, the inverter will not start up, as a safety precaution.

What is this downtime costing you?

Rough estimate while your system isn't producing. Adjust the numbers to match your setup.

System size (kW) Peak sun hours / day Electricity rate ($/kWh)

–per day

–per week

–per 30 days

≈ – kWh of lost production per day.

Estimate only — assumes ~80% real-world output vs. nameplate. Actual losses depend on weather, shading, panel direction, and your tariff.

Common causes

Moisture getting into damaged panel connectors, junction boxes, or cabling — worse in rain or high humidity
A damaged or degraded solar panel (cracked glass or backsheet)
Worn, chewed, or degraded DC cabling with compromised insulation
A faulty DC isolator or combiner box letting moisture in

Safe steps to try

Work top to bottom, ticking off each step as you complete it. 0 of 5 done.

Note the exact code and the weather and time it appeared — this helps your installer
Check whether the code clears on a dry, sunny day — do not touch any wiring
Look (from the ground) for obviously damaged panels — never climb on the roof
Try one documented restart: turn the AC breaker off, then the DC disconnector to OFF, wait a few minutes, then DC back ON followed by the AC breaker
If the code returns, stop and call your installer — do not keep resetting

Is your inverter still under warranty?

Before paying for a repair, check — your installer may fix this free.

Brand Year installed

Based on typical standard warranty terms — always confirm with your warranty card or installer paperwork, as terms vary by model, region, and purchase date.

When to call an electrician

Call your solar installer or a Fronius Service Partner if STATE 502 keeps recurring, appears in dry weather, or never clears. Do not touch DC wiring, connectors, or the array yourself — insulation faults can be a shock hazard.

Frequently asked questions

Will STATE 502 clear on its own?

Sometimes — it often appears in wet weather and clears when things dry out. But it usually comes back and gets worse over time, so have it checked even if it clears.

Is it safe to keep using my solar panels with STATE 502?

The inverter protects itself by not starting while the fault is active, so there is no generation. Do not try to bypass it or touch the DC wiring — book your installer.

Can rain cause STATE 502?

Yes — moisture getting into damaged connectors, panels, or cabling is the most common trigger. That is actually a useful clue for your installer.

Need a professional?

This fault may need professional diagnosis. Contact a qualified solar electrician in your area.

Sources: meaning and troubleshooting verified against the manufacturer's documentation — Fronius Operating Instructions (Symo/Primo) — 'Status codes and remedy' / 'STATE CODES' tables (Fronius docs 42,0410,0192 & 42,0410,1909 series)