William and Wrenches, I have pondered situations like this one and wonder the following: If a high voltage DC solenoid were placed at the PV array and the coil was controlled by an arc fault detector along with a means of manually disconnecting, would that not work to satisfy shut down requirements and safety concerns?
We have been using 350A, 800 volt solenoids from Gigavac in our lithium battery system on both the positive and negative terminals (controlled by a CPU) to provide 100% disconnect if case of any battery fault. Larry On Sep 23, 2015, at 2:26 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 <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 <image002.jpg> Lic 773985 millersolar.com <http://www.millersolar.com/> 805-438-5600
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