[RE-wrenches] AFCI tripping on SB 4000US-12

[Kirk Herander]

Hi William,
Modules can be meggered individually in or in series strings (with a
caveat). I've done it many times and discovered internal module shorts
between positive and gnd,or neg and gnd.

I once took the customer's garden house up on the roof, and meggered a
string, while trickling water on panels individually. When a short
occurred, I knew that the respective soaked panel was internally
compromised (old Sanyo 190's BTW). .

The caveat with meggering a string is that you have to be sure the series
string voltage plus the megger voltage (i.e. V scale you are measuring with
on the meter) does not exceed the max. voltage rating of the panels.
Obviously most new modules have at least a 1000vdc rating these days, who
knows what Shell SQ's rating is/was. For modern mods rated @ 1000v, I use
the meggers 500vdc scale.

And with Solaredge, you can megger straight through their optimizers if
necessary. There's an app note on their site with directions.

On Mon, Jun 19, 2023 at 2:11 PM William Miller via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Friends:
>
>
>
> We installed a bunch of Shell SQ-150-PC modules on a ground mount almost
> 20 years ago.  The original SB2500 inverters died so we upgraded to
> SB4000US-21 inverters.  We had some ground fault or AFCI issues a number of
> years ago so we replaced all homeruns with PV wire which resolved the
> problem.
>
>
>
> These panels have J-boxes which we interconnected with 1/2” NMLT.  The
> home runs are with PV wire with absolutely no splices and the inter-panel
> jumpers are THWN.
>
>
>
> Recently we started getting AFCI disturbances on one inverter.  We
> isolated the fault to one string.  We opened every pull box and panel J-box
> and all of the wiring looks dry, clean and tightly connected.  We inspected
> every panel front and back and see no hotspots or visible corrosion.
>
>
>
> I have a megger I have never used.  The homerun is kind of long so maybe
> it has insulation problems.  I could isolate the homerun and megger those
> leads.  I am researching if I can megger PV modules.  It looks like this is
> commonly done.  That looks like my next step.
>
>
>
> Does anyone have any ideas on what I should do next? I suppose I could
> start swapping each of the 10 modules in the problem string with panels in
> the non-problem strings, but that seems like a lot of work.
>
>
>
> Thanks in advance.
>
>
>
> William Miller
>
>
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com
>
> CA Lic. 773985
>
>
>
>
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-- 

*Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*

*Owner|Principal, VT Solar, LLC*

*Celebrating our 32st Anniversary 1991-2023!!*

dba Vermont Solar Engineering

802.863.1202
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