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.
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