4301 on a SMA Solar Technology AG Sunny Boy: The inverter has detected an electric arc in the displayed string. If "String N/A" is displayed, the string could not be uniquely assigned
Short answer
On a SMA Solar Technology AG inverter, 4301 means: The inverter has detected an electric arc in the displayed string. If "String N/A" is displayed, the string could not be uniquely assigned. The inverter stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 24 September 2026 · 1 source
What it means
The manual says: The inverter has detected an electric arc in the displayed string. If "String N/A" is displayed, the string could not be uniquely assigned.
Part involved: AFCI - series arc detected in string.
When it shows: The inverter has detected an electric arc in the displayed string. If "String N/A" is displayed, the string could not be uniquely assigned.
Likely causes:
- SMA corrective measures: Disconnect the inverter from all voltage sources. Check the PV modules and the cabling in the affected string or, if the string was not displayed, in all strings for damage. Ensure that the DC connection in the inverter is correct. Repair or replace defective PV modules, DC cables or the DC connection in the inverter. Start manual restart (if necessary).
Is it safe?
Switch the inverter off at its isolator and call an engineer.
| Does the inverter stop? | Yes |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The inverter stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Manual restart by a qualified person after repair.
What you can check
- Read the event number and message in the SMA Energy app / Sunny Portal (ennexOS) or the inverter's web interface and note the date/time for your installer. A red LED on the inverter means an event has occurred.
- An electric arc was detected in the DC cabling - do not touch the panels, DC cables or inverter; contact your installer promptly. If you smell burning or see smoke, switch off the inverter's AC supply at the consumer unit if safe and call emergency services.
What the engineer will check
- Disconnect inverter from all voltage sources; inspect PV modules, DC cables and connectors in the affected string (or all strings if 'String N/A'); check DC connection in the inverter; repair/replace; then start manual restart.
Who to ask for: MCS PV installer.
Certification: Qualified electrician (BS 7671; MCS-certified PV installer for work on the PV array/DC side).
What you might notice
Sources
- Operating manual SUNNY BOY 3.0/3.6/4.0/5.0/6.0 ↗ · SBxx-1AV-41-BE-en-21 Version 2.1 · page 96 · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026