Critical What does this mean?
A safety-rated fault — there may be a risk of electric shock, fire, or equipment damage. Do not try to fix this yourself. Call a qualified electrician.
SMA Inverter Event 3501/3503 — Ground Fault Found, What to Do Next
Events 3501 and 3503 mean your SMA inverter has detected a ground fault in your PV array, or that the insulation resistance of the DC wiring is too low. In plain terms, electricity is finding an unintended path to ground somewhere in your panels or DC cabling. Take this seriously: SMA warns of danger to life from electric shock. Do not touch the array — call your installer.
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?
Is your system producing power right now?
What this code means
Your solar panels and DC cables are supposed to be electrically insulated from ground. Your SMA inverter continuously monitors that insulation, and event 3501 or 3503 means the check failed: either a genuine ground fault — a live conductor touching something grounded — or insulation resistance that has dropped below the safe threshold.
When this is detected, the inverter disconnects from the grid for safety, or refuses to connect in the first place if it finds the problem during its self-check. This is the correct protective behavior, not a malfunction of the inverter.
The fault usually traces back to physical damage: a cracked panel, a chewed or chafed DC cable, or a faulty connector letting in moisture. SMA's technical documentation notes the message can also appear temporarily in wet conditions — rain or heavy dew can lower insulation resistance enough to trip the threshold, and strong wind can press damaged cables against grounded mounting parts. But a recurring 3501 or 3503 always deserves investigation, because transformerless inverters such as the Sunny Boy can be destroyed by a ground fault during operation.
Knowing what the technician will actually do can make the service visit less mysterious. SMA's official procedure for a ground fault starts with timing: the measurements should be taken under the same conditions as when the fault occurred — ideally while the event is active — because insulation problems come and go with moisture and temperature. The technician first checks each string's open-circuit voltage against the system design, then measures the voltage from DC positive to earth and DC negative to earth on every string. If those two readings are stable and add up to roughly the full string voltage, a ground fault is confirmed on that string; the ratio between the readings even indicates where along the string the fault sits. Only after the fault is located and repaired is the string reconnected.
One more detail from the inverter itself: SMA's service manual notes that a ground fault may announce itself with the inverter beeping, the red LED lit, and the event number shown in the results menu. If you observe that combination — beeping plus red LED plus 3501 or 3503 — you are looking at the inverter's dedicated ground-fault alarm behavior, and it reinforces the message: stay clear and call for service.
What is this downtime costing you?
Rough estimate while your system isn't producing. Adjust the numbers to match your setup.
≈ – 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
- Damaged PV modules with compromised insulation
- Damaged, chafed, or rodent-chewed DC cables
- Faulty or moisture-damaged DC connectors and plugs
- Rain, dew, or persistent damp lowering insulation resistance below the threshold
- Wind pressing damaged live DC cables against grounded racking or frames
- Aging insulation breakdown in older arrays
- Water ingress into DC connectors, combiner boxes, or module junction boxes
- Animal damage chewing through DC cable insulation
- Cracked junction boxes on the back of modules
- Installation damage — pinched cables under mounting rails or overtightened cable clips
Safe steps to try
Work top to bottom, ticking off each step as you complete it. 0 of 5 done.
Is your inverter still under warranty?
Before paying for a repair, check — your installer may fix this free.
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 immediately — this is not a homeowner-fixable fault. SMA's official corrective measures for 3501 and 3503 are entirely technician work: measuring string open-circuit voltages, measuring DC positive to earth and DC negative to earth for each string, and locating the fault from the voltage ratios before anything is reconnected. Only a qualified technician with proper high-voltage DC measurement equipment should touch the array. If you ever smell burning or see smoke or sparking near the array or inverter, switch the system off using the documented emergency procedure and call emergency services if needed, then your installer.
Frequently asked questions
Can I just reset the inverter to clear 3501?
No. Resetting does not fix a ground fault, and the inverter will simply detect it again at the next check. Worse, reconnecting a faulty array can damage the inverter. Leave the diagnosis to a technician.
The fault only appears when it rains. Is that OK?
It is a known pattern — moisture lowers insulation resistance — but it still means something in your array is letting water in where it should not. It needs professional inspection, not tolerance.
Will event 3501 damage my inverter?
It can. SMA explicitly warns that transformerless inverters can be destroyed by a ground fault during operation, which is exactly why the inverter disconnects itself. Get it checked promptly.
Is it safe to touch the panels?
No. During a ground fault, high voltages can be present on parts of the array you would not expect, including frames and mounting hardware. Do not touch PV cables except on their insulation — and ideally, do not touch them at all until a technician has cleared the fault.
What is insulation resistance, in plain terms?
It is a measure of how well your array's live parts are electrically separated from ground. Healthy, dry equipment measures very high — millions of ohms. When insulation is damaged or wet, the number drops, and current starts leaking to ground. Your inverter watches that number continuously.
Need a professional?
This fault is a safety risk — do not attempt to fix it yourself. Contact a qualified solar electrician in your area.
Sources: meaning and troubleshooting verified against the manufacturer's documentation — SMA Solar Technology official service article 'Event 35, 3501 or 3503' (my.sma-service.com); SMA technical information 'Isolationsfehler in PV-Anlagen' (files.sma.de, Isolationsfehler-TIde-10).