What does Growatt Error 302 'No AC Connection' mean?

Short answer

Error 302 means the Growatt inverter cannot see the grid. The usual causes are a power cut, a tripped or switched-off AC breaker or isolator, or an AC wiring fault. Check that the breakers are on. If they are on and the mains is working, the installer should check the AC cabling. It clears itself once the grid is detected.