Insulation resistance between PV strings and earth is below minimum threshold. This is the most common Growatt fault on UK sites.
Common causes
Moisture in MC4 connectors (especially after rain)Damaged cable insulation from mechanical pinchingPanel junction box seal failurePanel frame not earthed
What to check
STEP 1
Disconnect all strings. IR test each string at 500 V DC — any reading below 1 MΩ is suspect. Start testing from the roof junction boxes downward
STEP 2
Inspect all MC4 connectors for moisture — the most common cause on UK sites after wet weather. Dry connectors with compressed air. Re-seat and retest
Escalate if
Fault persists after drying connectors and IR test finds no specific fault — check panel junction boxes for seal failure
Need full interactive diagnosis?
Faultpath walks you through decision trees, fault codes, and commissioning — built for solar & battery engineers.