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 Arc Fault — The Tap-Twice Reset Explained

When your SMA Sunny Boy detects an electric arc in the DC wiring, it stops feeding power and locks itself out — the red LED glows and Event 4301 appears. The lockout is deliberate: the system must not restart until the cause is found. SMA's official reset is a two-step affair: a qualified person inspects the array for damage first, then the operation inhibition is cleared either by tapping twice on the enclosure lid or via a parameter setting.

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

AFCI stands for Arc-Fault Circuit Interrupter. On AFCI-equipped SMA Sunny Boy inverters it's a listed safety function (certified to UL 1699B): it watches the DC current waveform for the crackling signature of a series arc — current jumping a gap in a damaged conductor. Normal solar current is smooth; arcing current isn't, and the detector knows the difference.

When it finds one, the inverter interrupts grid feed-in immediately and enters what SMA calls operation inhibition — a lockout that doesn't clear on its own. The red LED glows, and Event 4301 shows on the display and in the event list. This is the inverter refusing to re-energize a possibly smoldering circuit: an arc point runs hot enough to melt connectors and ignite roofing, so the system stays off until a human finds the fault.

SMA's manual section for this — "Resetting the Operation Inhibition after Detection of an Arc Fault" — is marked "Qualified person" and opens with disconnecting the inverter from voltage sources, then verifying that the PV modules, DC cables, and DC terminal block are not defective, and repairing or replacing anything that is. Only then comes the reset, and there are two official options.

Option one is the tap: with Event 4301 on the display, tap the enclosure lid of the Connection Unit twice in quick succession. It only works if the event is showing when you begin tapping — the inverter wants confirmation you're looking at the arc fault message right now. On success the inverter starts feeding again; a rapidly flashing blue LED just means WPS woke up – it deactivates on its own.

Option two is the parameter route: resetting the operation inhibition through the device parameters (Operation → Reset operating data → Reset operation inhibition).

One warning from SMA's own support article: do not command the reset repeatedly — it can damage the inverter. If 4301 comes back after a reset, the arc condition is still out there, and resetting again without finding it just re-energizes the fault.

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

Damaged, pinched, or abraded DC conductors — cables crushed under rails, chafed on sharp edges, or nicked at installation that finally broke down.
Loose or separated DC connections. Connectors that never fully seated or worked loose through years of thermal expansion and contraction are the classic arc source.
Cracked or corroded solder joints in modules, and deteriorating junction boxes.
Mismatched connector brands forced together, or aging MC4s with weakened contact springs.
Rodent damage, hail damage, UV-degraded cable jackets — anything that exposes or compromises the conductor.
Nuisance triggers are possible but uncommon: severe electrical noise can occasionally fool the detector, one reason the inspection matters — it distinguishes the real thing from the false alarm.

Safe steps to try

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

1. Read the scene: red LED plus Event 4301 (or an "Electric arc detected" message on older models) means the AFCI tripped. The inverter has already made itself safe by stopping feed-in — leave it that way.
2. Do not reset it yourself – by tapping or otherwise – until the array has been inspected. SMA's procedure requires the PV modules, DC cables, and connections to be verified damage-free first, and that verification means qualified-person work around live DC — qualified-person work.
3. Document everything for your installer: a photo of the display, the date and time, and anything unusual that preceded it (storms, roof work).
4. If you see or smell anything scorched — discolored connectors, melted plastic, a burning smell near the array or inverter — keep clear and treat it as a potential fire situation before calling anyone.
5. Understand the tap for what it is: the final confirmation step of a professional inspection, performed with the event on the display. that's the procedure working as designed.

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 before any reset attempt — every time, no exceptions. The inspection-before-reset sequence is SMA's documented procedure, and the manual section is marked for qualified persons because it starts with disconnecting the inverter from voltage sources. If Event 4301 returns after a reset, stop resetting and keep the system off: the fault is still present, repeated resets can damage the inverter, and continued troubleshooting of the PV wiring is required. If your installer can't identify the arc source, escalate to SMA Service. And if arcs keep recurring across the array's life, the system needs a thorough wiring-level remediation — this is not a code you learn to live with.

Frequently asked questions

What does "tap twice on the enclosure lid" actually do?

It's SMA's physical confirmation for clearing the arc-fault lockout. With Event 4301 on the display, two quick taps on the Connection Unit's lid tell the inverter to reset the operation inhibition — but only after the array has been inspected for damage.

Why won't the inverter just restart itself after an arc fault?

Because an arc means damaged high-voltage DC wiring; auto-restarting would re-energize the fault. The lockout forces a human to find the cause first.

The tap didn't work. Now what?

The reset only registers if Event 4301 is showing on the display when you begin tapping. If the timing was right and it still didn't clear, use the parameter route through the user interface — or rather, have your installer do it — and keep investigating the wiring.

Is it true you shouldn't reset repeatedly?

Yes — SMA's own support documentation warns against commanding the reset repeatedly – it can damage the inverter. A returning 4301 means the arc condition persists; more resets don't fix that.

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 Sunny Boy operating manual (manuals.sma.de) — 'Resetting the Operation Inhibition after Detection of an Arc Fault' (red LED + Event 4301; two reset options: tapping twice on the enclosure lid of the Connection Unit, or parameter setting; inspection of PV modules/DC cables/terminal block required first); SMA ArcFix AFCI technical documentation (manuals.sma.de); SMA Service support article 'SB-US-40/41 and STP-US-40/41: Reset Operation Inhibition via the Inverter User Interface'