3908 on a SMA Solar Technology AG Sunny Boy: The permissible residual current reaches or exceeds the threshold
Short answer
On a SMA Solar Technology AG inverter, 3908 means: The permissible residual current reaches or exceeds the threshold. 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 permissible residual current reaches or exceeds the threshold.
Part involved: insulation / residual current (earth fault).
When it shows: The permissible residual current reaches or exceeds the threshold.
Likely causes:
- SMA corrective measures: If a residual-current device is installed, ensure that it is set correctly. Observe the behavior of the inverter and wait to see whether the inverter resumes operation on its own. Ensure that no insulation error is present and that the residual-current device is functional.
Is it safe?
| Does the inverter stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The inverter stops until the fault clears or is reset.
Resetting itself: yes.
Manual reset: Automatic when condition clears.
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.
- Do not touch the panels, cables or inverter enclosure - an earth (ground) fault may make exposed parts live. Contact your installer.
- Note whether it happens mainly after rain or in the morning dew - this helps the installer.
What the engineer will check
- Check the PV system for ground faults per SMA section 'Checking the PV System for Ground Faults' (insulation resistance measurement per string, damaged cables/connectors, water ingress, module defects); check any RCD type/setting.
Who to ask for: MCS PV installer with insulation-resistance test equipment.
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 95 · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026