Feedback from City of Berkeley [RE-wrenches]

[Matt Lafferty]

RE: External DC Service Disconnect for inverters with "integral" DC
Disconnects.

Like it or not, we MUST INSIST on external service disconnects for our
inverters if we are going to be responsible. 

I've replaced too many inverters to count. Witnessed one on fire and have
replaced close to a dozen that caught fire. I know of quite a few more that
I didn't personally get involved with.  That's just on the residential side.
I've also seen a few commercial, central inverters after they've burned up
on the DC side. Generally in the DC Disconnect/Contactor area... 

Every single one of these examples had integral AC & DC disconnects. I know
I didn't want to walk up to the inverter I happened to witness as it caught
on fire.  I'm sure nobody else will, either, but that's not the whole story.
Try explaining to a customer who has had their inverter flame out that
you're going to put the same thing back in while they're looking at soot
marks on their wall...

I believe it is important to note that, in my direct experience, ignition
did not extend beyond the inverter enclosures.  For what it's worth, most
(but not all) of the residential inverters mentioned above were discontinued
several years ago. 

In at least two of the cases I had to work on, the entire array was pulled
into a short circuit. One of those was 100+ KW. Hate to break the news, but
it ain't all fun and games all the time. The only thing that's going to shut
the current off is the rotation of the earth. The least we can do is make
sure that we can isolate it to a reasonable degree of safety if something
does go wrong. Somebody may not have time to wait for darkness!

I believe that external disconnects are too valuable to be left out of any
of our systems. AC & DC for that matter.  AC disconnect can be a breaker, of
course. It's about time that got squared away... 

$0.020001 (Two cents with inflation...)

Matt Lafferty 


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