Interesting. I'd like to get a hold of those test results. It is not always practical, but I have never had an issue using opaque black-out type tarps (of course - testing for voltage is a critical safety step). The flimsy blue stuff will definitely not work. At one time I had a sports field cover, but it was too heavy to manage. Then again, we deal with low-slope roofs around here, making roofs easily walk-able. I challenge the assertion that it's ineffective and unreliable. Practical? Judgment call. How effective is a disconnect at de-energizing the conductors between the array and the disconnect itself?
There are many module and inverter manufactures that prescribe opaque covers while conducting wiring operations in their manuals. Here are some other resources that point to this same method for "shutting down a PV system" including: Home Power http://www.homepower.com/articles/solar-electricity/equipment-products/pv-safety-and-firefighting Fire Engineering: http://www.fireengineering.com/articles/print/volume-162/issue-5/features/solar-electric-systems-and-firefighter-safety.html On Thu, Sep 24, 2015 at 2:19 PM, Lloyd Hoffstatter < lhoffstat...@sunstruckconsulting.com> wrote: > 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> 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> 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> > 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 > > > > > > [image: Gradient Cap_mini] > Lic 773985 > millersolar.com <http://www.millersolar.com/> > 805-438-5600 > > > > _______________________________________________ > List sponsored by Redwood Alliance > > 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 > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > _______________________________________________ > List sponsored by Redwood Alliance > > 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 > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Redwood Alliance > > 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 > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > >
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