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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