A friend of mine has a 10kW SMA inverter. It trips on a 'DI Converter Fault' almost everyday at ~9:30am. Sometimes it's an hour or so earlier... sometimes a few hours later but it's almost always in the morning usually only once. For some reason a couple days ago it went ape sh*t and tripped several times more in the morning than it usually does. This has been an issue for the past ~4 years. We've tried improving the grounding, contacting SMA, contacting the local utility.... nothing. I doubt it's the inverter but we haven't really ruled that out. Nothing else in the house cares about what ever is causing the inverter to fault. My hypothesis is it's his transformer(s). On his street there are 3 15kVA transformers in parallel on the 240v side so they form several loops with the HV side. I've never seen that before. I think it's possible that the parallel transformers are establishing some kind of weird resonance when load is juuuuust right in the mornings. This would explain how erratic the tripping events are. I'm hoping to try to convince the utility to isolate his transformer. Anyone with electrical experience think this is the issue? Has anyone seen parallel transformers before?