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 4301 — When Your AFCI Detects an Electric Arc
Event 4301 means your SMA inverter's arc fault circuit interrupter (AFCI) detected an electric arc in one of your PV strings. An arc is electricity jumping across a gap in damaged wiring or a bad connection — it generates intense heat and is a genuine fire risk. The inverter has stopped feeding power into the grid. Do not restart it yourself; 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 Sunny Boy includes an arc fault circuit interrupter that constantly monitors your DC wiring for the electrical signature of an arc. A series arc happens when a connection in the DC circuit is loose, corroded, cracked, or damaged: the current keeps flowing by jumping the gap, superheating that spot. Event 4301 is the AFCI reporting exactly that — in SMA's wording, 'Serial el.arc in String X detected by AFCI mod.'
If the display shows 'String N/A' instead of a string identifier, the arc could not be pinned to one string — which simply means every string needs checking rather than just one.
The moment the arc is detected, the inverter stops feeding into the utility grid. That is the protective response doing its job: the priority is to de-energize the circuit before the arcing point gets hot enough to melt insulation or ignite nearby material. The inverter will not resume on its own — a manual restart is part of SMA's official procedure, but only after the fault has been found and repaired.
A little background on what the AFCI is actually doing helps explain why the inverter reacts so decisively. The arc fault circuit interrupter continuously analyzes the DC current waveform for the distinctive high-frequency 'noise' signature of an arc — normal solar current is smooth, while arcing current crackles. SMA's implementation targets series arcs: breaks or bad joints in the current path itself, which are the most common kind in rooftop wiring. When the signature matches, the inverter treats it as a fire in slow motion and stops feeding power immediately.
This protection exists because of how DC arcs behave. Unlike AC, which crosses zero a hundred times a second and can self-extinguish, direct current from solar panels sustains an arc stubbornly once it starts — there is no zero crossing to snuff it out. That is why a loose DC connector, which might merely run warm on an AC circuit, can become a genuine ignition source on a solar array, and why the electrical code requires arc-fault protection on these systems. The AFCI is not an optional extra; on the US models this technical document covers, it is a code-driven safety function.
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
- Loose, corroded, or aging DC connectors in a PV string
- Damaged or pinched DC cables from installation damage, UV degradation, or rodents
- Cracked or failing PV modules creating intermittent internal connections
- Incorrectly seated DC plugs at the inverter or combiner box
- Connections loosened over years of daily thermal expansion and contraction
- Poorly crimped or mismatched DC connectors making intermittent contact
- Connectors worked loose by years of thermal expansion and contraction
- UV-degraded connector housings letting moisture corrode the contacts
- Physical damage to modules from hail, foot traffic during installation, or falling branches
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 right away — an arc fault is one of the few inverter events that carries a real fire risk, and SMA's official corrective measures are all professional tasks: inspecting every module and cable in the affected string for damage, verifying the DC connections inside the inverter, repairing or replacing defective components, and only then performing the manual restart. If the AFCI self-test itself fails (events in the 8200 range), SMA directs you to contact SMA Service. Do not let anyone talk you into simply resetting the code and watching — the cause of the arc must be physically found and fixed.
Frequently asked questions
What exactly is an electric arc in my solar wiring?
It is current jumping across a small gap in a damaged or loose connection. The jump point gets extremely hot — hot enough to melt connectors and start fires — which is why inverters are required to detect it and shut down.
The display says 'String N/A.' What does that mean?
The AFCI detected an arc but could not identify which string it came from. Your installer will need to check all strings instead of just one.
Can I clear 4301 with a restart?
A restart is the last step of the official procedure, not the first — and only after the damaged component is found and repaired. Restarting first just re-energizes the arcing fault.
How urgent is an arc fault really?
Very. Unlike most inverter events, which are about grid compliance or lost production, an arc fault is about fire prevention. Treat it as a same-day call to your installer.
What does AFCI stand for, and what does it do?
Arc Fault Circuit Interrupter. It is a protection device that watches your DC wiring for the electrical signature of an arc and shuts the system down when it finds one — the solar equivalent of the arc-fault breakers now common in home electrical panels.
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 technical information 'SUNNY BOY-US — Enhanced AFCI Event Handling' (files.sma.de, SBx.x-1SP-US41-AFCI-Handling-TI-en-10), Event 4301 section.