I’ve had this happen many times with Enphase micro inverters. I’ve actually had them burn the back of a PV module. The cause was an internal short circuit which tripped the strings circuit breaker, when I cycled the breaker and turned it back on...... instant trip. I would put someone up on the roof to visually and audibly confirm which micro inverter was causing the short, it was typically very obvious to the naked eye.
Michael D Nelson MD Electric & Solar, Inc. 707-684-0064 mobile 707-884-1862 office www.mdelectricsolar.com www.facebook.com/mdelectricandsolar > On Jul 3, 2018, at 12:45 PM, Jason Szumlanski > <ja...@floridasolardesigngroup.com> wrote: > > > 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: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org >
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