William, If you swap strings, does the fault stay with the string, or with the input? and if you do run without the string for a while can you determine that the arc faults stop? Just figure it is worth making 100% sure the fault is actually in the DC side of that one string you have isolated, and not something internal to the inverter or on the AC side.
Cheers, Dave On Mon, Jun 19, 2023 at 5:30 PM Kirk Herander via RE-wrenches < re-wrenches@lists.re-wrenches.org> wrote: > 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@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 >> >> >> >> >> _______________________________________________ >> List sponsored by Redwood Alliance >> >> Pay optional member dues here: http://re-wrenches.org >> >> List Address: RE-wrenches@lists.re-wrenches.org >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> There are two list archives for searching. When one doesn't work, try the >> other: >> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> http://www.members.re-wrenches.org >> >> > > -- > > *Kirk Herander / **kirkh@vermont.solar <kirkh@vermont.solar>* > > *Owner|Principal, VT Solar, LLC* > > *Celebrating our 32st Anniversary 1991-2023!!* > > dba Vermont Solar Engineering > > 802.863.1202 > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > > -- [image: Logo] <https://www.sungineersolar.com/> Dave Tedeyan, P.E. Owner | Sungineer Solar p: he | him | his a: 1653 Slaterville Rd. | Ithaca, NY 14850 w: www.sungineersolar.com <http://www.sungineersolar.com/> c: (607) 270-0370
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