[RE-wrenches] Enphase String Breaker Heating Up

Jason Szumlanski jason at floridasolardesigngroup.com
Fri Aug 5 01:29:40 PDT 2022

I did visually inspect the bus and it appears like new. The current was
well under 16A on all circuits when tested at peak conditions. I'm certain
the circuits are not overloaded (I cut and installed the trunk cable
personally). This enclosure is not located in direct sunlight.

When I first got the call I expected to see melted wire insulation and
loose wires connections causing the tripped breakers. I was surprised to
find the load side of the breakers absolutely perfect. There are no visual
indicators as the the cause. I'm thinking the hot breaker in the IR image
has been failing internally but never tripped, and that heated up the bus
and surrounding breakers enough for them to trip and ultimately fail after
multiple resets.

I'll replace the remaining hot breaker and see if that solves the issue.

Thanks for all of the ideas.


On Thu, Aug 4, 2022, 11:11 PM Darryl Thayer via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> 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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