[RE-wrenches] Inverter Output Circuit OCPD Meltdown

[Chris Sparadeo]

Jason,

Have you calculated your back-fed amapacity allowance to confirm it
complies with the 120% busbar rule as per 705.12?

Best,
Chris

On Tue, Jan 21, 2020 at 12:40 PM August Goers <august at luminalt.com> wrote:

> Hi Jason -
>
> It certainly appears that there was some sort of surge or short. We've had
> a few cases where microinverter branch circuit end termination caps were
> left off or fell off and shorted out during rain storms. You might want to
> double check that those are all in place. We've also had cases were
> microinvers themselves developed internal shorts. This third comment is
> only anecdotal - I've been in touch with a couple of other installers that
> have had back-fed breaker issues specifically with Eaton brand breakers
> burning up the bus stabs. Our company has had one unexplained issue where
> the inverter output breaker bus stabs were burned up with Eaton breakers. I
> have no idea whether the breakers were faulty or what, but thought I'd just
> mention it in case there is a pattern.
>
> Best, August
> Luminalt
>
>
> On Tue, Jan 21, 2020 at 9:10 AM Jason Szumlanski <
> jason at floridasolardesigngroup.com> 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
>>
>>
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-- 
Chris Sparadeo


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