[RE-wrenches] Inverter Output Circuit OCPD Meltdown

[Jason Szumlanski]

(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
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