[RE-wrenches] Rooftop DC disconnects

[Jason Szumlanski]

"​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 <william at 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
>
>
>
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