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.

SMA Inverter Event 401 — Why the Inverter Left the Grid

Event 401 is SMA's 'Grid incident' message: your inverter disconnected from the utility grid because it detected a stand-alone (islanded) grid or a very large, sudden change in grid frequency. It's a protective disconnection, not an inverter failure. The inverter reconnects on its own once the grid is stable — if 401 keeps appearing, your installer and possibly your grid operator need to get involved.

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 SMA inverter is a grid-following device: it doesn't set the grid's frequency, it matches it, moment by moment. To do that safely it watches the grid continuously, and it has a non-negotiable rule — if the grid stops looking like a grid, get off it immediately.

Event 401 is that rule firing. SMA's official explanation: "The inverter has disconnected from the utility grid. A stand-alone grid or a very large change in the grid frequency was detected." Two scenarios hide in that sentence. The first is islanding: your section of the network became electrically separated from the main grid — a breaker opened upstream, a fault isolated your feeder — and the inverter found itself alone with your neighborhood's loads. Running on in that state would be dangerous for line workers and for your equipment, so anti-islanding protection cuts it loose. The second is a violent frequency excursion: the grid's 50 or 60 Hz wobbled so hard and so fast that the inverter couldn't responsibly stay synchronized.

Note the workbook phrase "off grid-parallel" — that's exactly what's being described. Grid-parallel operation is the normal state where your inverter feeds in alongside the utility supply; Event 401 is the inverter leaving that state, deliberately and protectively.

SMA marks this event page "Qualified person," which tells you something about how they see it: the corrective measures ("Make sure there is no power outage or work being done on the utility grid and contact a grid operator if necessary. Check the grid connection for significant short-term frequency fluctuations.") are investigation steps for someone who can assess the grid connection, not chores for the homeowner. Your part is simpler: notice it, log it, and let the inverter's automatic reconnection do its job.

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

Work on the utility network. Planned maintenance, switching operations, or fault repairs upstream can island your feeder briefly or swing the frequency hard enough to trip the protection.
Storms and grid faults. Lightning strikes, downed lines, and automatic recloser operations elsewhere on the network create exactly the kind of violent frequency transients 401 is built for.
A genuinely unstable local grid. Long rural feeders, areas with weak grid infrastructure, or networks with a high share of fluctuating generation see more frequent excursions — and more 401s.
A large local load or generator switching. Industrial equipment starting up, or a big standby generator transferring, can yank the local frequency enough to register.
In rare cases, a measurement issue in the inverter itself — but SMA's troubleshooting treats repeated 401s as a grid problem first, and the statistics back that up.

Safe steps to try

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

1. Check whether your area actually lost power or whether work is happening on the lines. If the neighborhood is dark, 401 is just your inverter reporting what everyone already knows — wait for the grid to return and the inverter will reconnect by itself after its monitoring period.
2. Don't touch the inverter's settings. In particular, do not change the country data set or any grid-monitoring parameters yourself — SMA requires the grid operator's agreement for changes to the monitored operating limits, and wrong settings can make things worse.
3. Log each occurrence with date and time. A 401 during a thunderstorm is the grid's problem resolving itself; 401s on clear, calm days are the pattern that matters.
4. If the event clears and production resumes normally within the hour, there's nothing to fix — the protection did its job and stood down.
5. Check SMA's monitoring (Sunny Portal or the inverter's event list) rather than staring at the display; the event history shows whether this is a one-off or a habit.

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 installer if Event 401 appears frequently — several times a week, or on days with no plausible grid disturbance. The installer will check the grid connection for the short-term frequency fluctuations SMA's corrective measures describe, and may need to involve the grid operator: persistent frequency excursions can indicate a network problem the utility has to fix, or in rare cases justify an approved adjustment of the inverter's operating parameters. If 401 is accompanied by a complete failure to reconnect over many hours while the grid is demonstrably fine, treat it as urgent — the inverter may not be seeing the grid correctly at all.

Frequently asked questions

Is Event 401 an inverter fault?

No. It's a protective response to grid conditions — the inverter deliberately disconnected because the grid frequency moved too violently or the grid appeared to be islanded. The inverter itself is behaving correctly.

How long before it reconnects?

Once the grid holds steady inside the permitted limits for the required monitoring period, the inverter reconnects automatically. You don't need to do anything.

What's the difference between Event 401 and 404?

In current SMA manuals they share the same message ("Grid incident") and explanation. Treat them identically.

My lights didn't even flicker, but I got a 401. How?

Frequency transients that trip an inverter's protection can be too brief or too subtle for you to notice — the inverter samples the grid far faster and more precisely than human senses.

Can I make the inverter less sensitive so this stops happening?

Only through proper channels. The frequency trip limits are grid-code parameters: changing them needs the grid operator's agreement and is done by qualified personnel. Desensitizing protection on your own would be unsafe and non-compliant.

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 — SMA Sunny Boy Smart Energy Operating Manual (manuals.sma.de) — Troubleshooting, Event messages: Event 401 (message: 'Grid incident'; explanation: inverter disconnected from utility grid, stand-alone grid or very large change in grid frequency detected; corrective measures: rule out outage/utility work, contact grid operator if necessary, check grid connection for significant short-term frequency fluctuations)