SMA Sunny Boy Event 3501 (Insulation Failure) & Event 1302 (Waiting for Grid): Diagnostic Guide
SMA Sunny Boy (SB 3.0–7.7 US) lights its red LED and displays Event 3501 ("Insulation failure — Check generator") or Event 1302 ("Waiting for grid voltage — Check AC breaker").
Safe Breaker & WebUI Check
🔬 Root Cause Electrical Physics
Event 1302 means the inverter is receiving DC solar power from the roof, but 240V AC utility power is missing at its AC terminals (tripped solar breaker in your main panel or blown AC fuse in the exterior knife-switch disconnect). Event 3501 is a DC ground fault on Input A, B, or C.
⚡ Step-by-Step Multimeter & Diagnostic Test Procedure
For Event 1302: Check the 2-pole solar backfeed breaker in your main electric panel and the exterior fused AC disconnect switch beside the utility meter. Measure 240V AC across L1-L2 on the load side of the fuses.
For Event 3501: Unplug String A, String B, and String C one at a time (with DC switch OFF) and restart the Sunny Boy to see which individual string triggers Event 3501.
🛠️ Safe DIY Reset & Remediation Steps
- 1.If Event 1302 appears, reset the 2-pole solar breaker in your main service panel (push firmly to OFF, then back to ON).
- 2.If you have a lever-style AC knife switch on the outside wall next to your electric meter, have an electrician check the two 30A/40A cartridge fuses inside—one blown leg causes Event 1302.
👷 When to Escalate to a Licensed Solar Electrician
Isolating Event 3501 to String A, B, or C allows a solar tech to go straight to the 8–10 panels on that specific MPPT channel instead of pulling up the entire roof array.
🔋 Direct Replacement & Upgrade Hardware
Add AC-coupled backup to any working SMA Sunny Boy using an EcoFlow Delta Pro Ultra (/go/ecoflow) or EG4 hybrid system.
Frequently Asked Questions: SMA Sunny Boy Event 3501 & 1302 Fix
Does SMA Sunny Boy Secure Power Supply (SPS) still work during Event 1302?
If Event 1302 is caused by a neighborhood utility power outage, flipping the dedicated SPS rocker switch turns on the 120V 2,000W daytime emergency outlet!