Jason - Thanks for sharing - this is a good lesson for all Wrenches. Years ago we had a dual string inverter installation where the DC positives and negatives were mixed between the two interters. String 1 positive went to inverter 1, string 1 negative went to inverter 2 and vice versa. The inverters tested out and ran for about two weeks and then one of them literally caught on fire. Since then, we implemented a policy of checking wiring coming from the roof down individually. In the case of microinverter branch circuits, this means checking each branch circuit voltage on the roof with the other breakers off one branch at a time.
Not to get too far off on a tangent, but as we're installing more and more energy storage with lots of onsite wiring work, it is clear that fully testing wiring is of utmost importance. We have a procedure for checking voltage at each piece of equipment (such as a backup loads panel, etc) prior to turning on branch breakers. We've run into a couple of scenarios where hots and neutrals were mixed up causing 240 v to go to a 120 v circuit. Not good. August On Wed, Jan 22, 2020 at 2:58 PM Jason Szumlanski < [email protected]> wrote: > I discovered the issue I believe, so I thought I'd update all of you who > gave me ideas on what to look for (thank you). > > And this is something that I stress the importance of all the time... > > The branch circuit pairs were not properly paired up! All of the L1 > conductors went to L1 on the bus and all of the L2 to L2. However, for > example, circuit 1 L1 and circuit 2 L2 were on a single 2-pole breaker. And > circuit 2 L1 and circuit 1 L2 were on another breaker. Everything worked > because it was electrically connected to the right bus bar. However, when > there was a previous fault one of the breakers probably didn't trip when it > should have as a result of the improper pairings. It was reset a few times > and just kept heating up and heating up. > > This isn't conclusive, but it sure makes sense. It wasn't fun tracking > this down with 5 strings and 5 junction boxes on the roof, but once we > started continuity testing and finding strange results, it became clear. > > Jason Szumlanski > > > > On Tue, Jan 21, 2020 at 12:10 PM Jason Szumlanski < > [email protected]> wrote: > >> (System installed by another contractor...) >> >> I have been tasked with assisting in the investigation of damage in a >> subpanel used to combine inverter output circuits (5 strings of >> microinverters). There appears to be no damage to conductors or other >> system components. It looks like the damage started at the stabs of the bus >> bar where the breakers connect. Picture attached. Here are a few clues: >> >> - Monitoring indicates that damage occurred overnight a few weeks >> ago. That night we had rain as a winter front came through Florida, >> possibly lightning. The prior day everything was fine. >> - The next morning, only 2 of 5 strings started producing power, but >> 4 of 5 strings were reporting data to the Envoy. The two strings that were >> reporting but not producing power reported 0Vac and Voc on the DC side of >> the microinverters. >> - A couple of weeks later, 1 of the 2 strings that was producing >> power quit doing so, but continued reporting data. >> - Customer discovered damage yesterday. >> - About a week before the initial damage apparently manifested >> itself, another contractor installed a whole house generator transfer >> switch on the line side of the PV interconnection. The generator has never >> been run (there is not even a LP fuel source on site yet). I pointed out >> that the solar interconnection, which was previously on the supply side, >> would need to be moved to the supply side of the generator transfer >> switch's main breaker before operation. During the transfer switch >> installation, the contractor also switched line 1 and line 2, but that >> shouldn't really matter, except for Enphase consumption monitoring, which >> was messed up by the swapping of the lines. >> >> So I'm looking for ideas. I'm wondering if the OCPD would be a likely >> place for lightning damage to manifest itself. I can't visually detect any >> other damage anywhere else. I can't imagine that the transfer switch >> installation would have anything to do with it, but the timing is >> interesting. Other than replacing the subpanel and OCPD and firing it back >> up (no pun intended), I'm not sure how to approach further investigation. >> >> Jason Szumlanski >> Florida Solar Design Group >> >> >> _______________________________________________ > 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 > >
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