Wrenches, UL has done testing on various materials for use as array covers, and lists their results. While perhaps not too practical as a means of shutting down a working system, this can be one of firefighters’ only effective methods when a fire has occurred and has damaged modules until PV pros arrive to disable system (UL tests have also shown destroyed modules still can produce high voltage).
Regards, Lloyd Hoffstatter NABCEP PV Installer NY-Sun instructor From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Thursday, September 24, 2015 1:06 PM To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Subject: Re: [RE-wrenches] Rooftop DC disconnects Brian: I agree 100%. Handling a tarp on a roof is impractical, ineffective and unreliable. Wind and slope are just two factors that increase danger and reduce reliability. William On Sep 24, 2015, at 9:12 AM, Brian Mehalic <br...@solarenergy.org<mailto:br...@solarenergy.org>> wrote: I disagree about tarps. We've tested fully covered arrays (and small ones at that) and still had what would be considered lethal levels of current and voltage, even when using heavy, reflective tarps. And it can be very difficult to ensure they stay in place, plus it's impractical for larger arrays. Brian On Sep 24, 2015, at 6:31 AM, Jason Szumlanski <ja...@floridasolardesigngroup.com<mailto:ja...@floridasolardesigngroup.com>> wrote: "In this scenario, there is no safe way to replace either of the two Morningstar controllers." The BEST rooftop disconnect remains... a big thick tarp. Not totally practical in an emergency situation, but it is pretty fail safe. Unfortunately for emergency responders, that does not take care of the AC circuits in a microinverter or AC module system, but ideally the building main is shut down anyway, and the risk is the same as any other 240V equipment/appliance circuits. Jason Szumlanski On Wed, Sep 23, 2015 at 4:26 PM, William Miller <will...@millersolar.com<mailto:will...@millersolar.com>> wrote: Dear Fellow Wrenches Below is a design conundrum that may resonate with some of you: We are finalizing a design for an off-grid residential system. The customer insist the PV should be on the roof and pre-installed a 1-1/4” PVC conduit from his roof to a crawl space, in anticipation of a solar install. This created real problems, because we all know we can’t pull PV source or output circuits in (or now, on) the envelopes of habitable buildings. There was no practical way to replace the PVC. We contrived a method to sleeve ¾” liquid-tight through the 1-1/4” PVC to the crawl space, continuing on with EMT. This is the largest metallic conduit we could fit. The distance was greater than 10 feet so we couldn’t use EMT. Due to the conduit size restriction, we upgraded to Morningstar 600 volt charge controllers, allowing us to reduce conductor size. (As a sidebar, although the Morningstar is listed as a 600 volt charge controller, we have found no circumstance were we could take advantage of that high a voltage. With the currently available high wattage modules, by the time we added enough in series to get to 600 volts, we were well beyond the wattage capabilities of the controller. For sake of design considerations, I suggest one regard these units as ~300 volt charge controllers.) We now have plans for 300 volt PV feeders running down an interior wall and under the house, with no roof-top disconnecting means. It is my understanding none are required. I am not comfortable with this. In this scenario, there is no safe way to replace either of the two Morningstar controllers. Should someone drill through or damage the EMT in the wall or under the floor, there would be no way to turn off the feeder. I don’t like putting HU361RBs on a roof. They must remain vertical and so they stick up too high and are hard to provide mounting for. Sola-deck units are another option, but they require integrating with shingles, not practical on this job or many others. I finally settled on a DC-Sunvolt PV-X16A-4X-RG disconnect as a possible solution. At $216 it is not out of range. The unit will provide means to turn off the feeders for service. I will report back on my impressions of the unit. To distill this scenario, I don’t believe the code requires a disconnect, but I feel morally obligated to install one. I’d be interested in verification of the code interpretation and others response to similar situations. I found no other options for rooftop disconnecting means that would be small, reasonably priced and not present a high profile. If there are products I don’t know about, I would be most grateful to receive your input. While researching the hardware I stumbled upon this article, linked below. It seems to present a real dilemma, but I am not convinced. Please remain skeptical as you read. It appears all of the links direct you to the same source. https://www.linkedin.com/pulse/greatest-debacle-solar-pv-australias-rooftop-dc-isolator-lucas-sadler Thanks again to all of you for helpful advice and expertise. I learned about Sunvolt here, just one of many great suggestions. Sincerely, William Miller [Gradient Cap_mini] Lic 773985 millersolar.com<http://www.millersolar.com/> 805-438-5600<tel:805-438-5600> _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org> _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org>
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