The short answer
Check breaker, AC cable, country data set and grid voltage.
Plain explanation
From the SMA manual for the Sunny Boy: Breaker on. AC cable undamaged. The rest of the checklist is below; work through it in order. Installer only: DC and AC work on a live PV system is dangerous, so owners should note the code and call their installer. Grid limits depend on your country, so check your national code and grid operator rules.
Steps from the source
- Breaker on
- AC cable undamaged
- Country data set correct
- Grid V in range
Source
SMA Sunny Boy 3.0-5.0 Operating Manual (SB30-50-1AV-40-BE-en-10), §12.2 p66files.sma.de ↗
Where installers ask this
- Grid Failure - Solar company has gone dark (r/solar)
- reddit.com/r/electricians/comments/8lm9ou/
- reddit.com/r/solar/comments/1ejmsau/
- reddit.com/r/solar/comments/18zrbij/
General guidance based on the manufacturer's manual or the named source. Always follow the current manual for your exact model and your national code. DC and AC electrical work is for qualified installers only. Not affiliated with or endorsed by any brand named; trademarks belong to their owners.