This is not a knock on microinverters, but information to potentially help save the next guy a bunch of time... This is not specific to any brand, but for purposes of explaining I will mention it was an Enphase IQ6+ system.
One of the great advantages of microinverters, even over optimizers, in my mind is how when a single unit fails the rest of the string just keeps on running. I recently ran into a tripping breaker. My first diagnostic step was to swap the string with another string's breaker to eliminate the breaker itself as a source of the problem. That wasn't it. It just popped the other breaker. So I probably had a dreaded wiring fault. Knowing that pulling wires out of this particular conduit would be a nightmare, I hoped to disconnect the string at the j-box on the roof and crossed my fingers that the problem wasn't in the pipe. I was delighted to find out that there was no fault in the home run wiring, so I suspected the trunk cable. To check that I tested continuity line to line and line to ground. Nothing. Next stop was the string terminator just to double check because I have seen intermittent faults from a poorly installed terminator. It looked great. I checked the waterproof caps on a couple of unused drops. Looked good. I carefully inspected for any cuts and scuffs in the cable. No luck. But I was convinced it was a trunk cable issue. I was just about to cut the trunk cable in half to isolate the issue to one half of the trunk cable when I decided to just try turning on the breaker once more. Pop, sizzle, boom, smoke. Found the problem. It was a microinverter with an internal fault. Fortunately, it tripped the breaker and damage was isolated to that unit, which was swapped out and everything was fine. Problem solved. It got me thinking about my approach to diagnosing this issue. I think next time I will start with disconnecting the string in the junction box just like I did this time, then test and reconnect it. My next step will be to disconnect every micro in the string from the trunk cable and test again by turning on the breaker. Then if it's not the trunk cable or home run wiring I can narrow down the offending microinverter by plugging in subsets of the string. I just got lucky because it finally failed catastrophically when I had the modules off. The owner had reset the breaker several times before and the system ran for hours or days without issue. There must have been an intermittent AC fault within the bad micro that finally just manifest itself in a more demonstrative way. So a single point of failure can result in taking down a whole string. That's the first time I've had that happen other than a straight-up wiring fault. Jason Szumlanski
_______________________________________________ List sponsored by Redwood Alliance List Address: [email protected] Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
