[RE-wrenches] Enphase String Breaker Heating Up

[Darryl Thayer]

Hello, breakers are thermal-magnetic the current heats the breaker; if the
current is high enough for long enough, a solder pot inside melts; this
current and excessive heat causes other breakers to open  Are you sure the
string current is less than 80% of the breaker rating and the wire
connecting to the breaker is ampacity 120 percent of the current?  I have
seen several of these events when the cabinet is in the sun or in other hot
locations.  Also, excessive breakers in a panel board can cause heat
build-up and premature breaker tripping.  If a breaker trips from heat
several times, the bus bar clip can soften or distort, this can damage the
bus.
I hope this has some value.

On Thu, Aug 4, 2022 at 1:12 PM Jason Szumlanski via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> I have a commercial 208 volt job where four of 11 fully populated strings
> of IQ7A had breakers that were tripped as reported by the client. They were
> able to reset two of them. They also reported that the two they were not
> able to reset we're very hot. The other two were warm.  By the time I got
> to the site, all four breakers had permanently failed.
>
> Once I got replacements, I was able to install them and they turned on
> without any faults. I gave it about 15 minutes and then put my infrared
> camera on it. To my surprise, the breaker immediately above two of the
> failed breakers and across from the other two failed breakers was clearly
> hot. I'm thinking this might have been the bad breaker all along causing
> the heat issue on the bus bar which made adjacent breakers fail. But this
> hot breaker did not fail.
>
> Does this seem like a plausible scenario, and if so, any ideas on what
> might have caused it? All of the breaker bolts were tight, but a couple
> were not torqued to spec. I just find it strange that one breaker that
> didn't fail would cause other adjacent breakers to heat up enough to fail.
>
> Flir image attached. This was after I replaced the four failed breakers.
>
> Jason Szumlanski
> Florida Solar Design Group
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