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

[William Miller]

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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