Hello Robin and boB.
Ryans Midnite video of the Birdhouse and rapid
shutdown disconnects is amazing. It does look
like you are producing a means of implementing this new code rule.
In many situations, the rapid shutdown
requirement certainly makes sense. In a large
system where high voltages and currents are
present over large areas of solar array, major
safety features need to be in place. The extra
cost of the rapid shutdown equipment and its
installation likely wouldn't produce much of an
obstacle to the budget of a major commercial installation.
A very nice feature of todays lower module
prices is that many people who really want PV,
but have never been able to afford it, can now
have a system. New requirements are eroding this new found ability.
I would like to suggest the use of hazard-based
criteria to decide if rapid shutdown is to be
required. A small cabin system with 750 W of PV,
a Kid charge control, and a couple of L-16
batteries should clearly be excused from any
rapid shutdown requirement. The system is easy to
understand, and can be disabled quickly.
The requirement should be applied only to systems
that have a large amount of power. The level of
hazard could be evaluated for different
scenarios. What is the demonstrated hazard of a
9.6 kW system feeding a pair of Classics and a
fused battery bank? How many problems have been
reported with properly installed systems of this
size? What is the arc potential?
Please keep in mind that a standard 120/240 V
grid connection can have an open wire running 10
feet above the yard, which can run as much as 25
feet down the side of a house, in unprotected
Service Entrance Cable. This wire may have a
10,000 Amp (or greater) short circuit current at
240 Vand this wire can't be shut
off. Therefore, 2,400 kW is available! Why can't
a few kW of PV be run down the side of a house in metal conduit?
What are the statistics that demonstrate that
small PV systems are significant safety hazards?
Are there real statistics, rather than anecdotal
events? There were an estimated
<http://www.thecarconnection.com/news/1090330_early-estimate-35200-traffic-deaths-in-2013-a-drop-of-3-from-2012>32,500
traffic deaths in 2013. How many people were
killed by solar electric systems that year?
How about an exemption for residential systems
under 12 kW? This size system has a power
potential of 1/200th of that of the wire that
runs 10 feet over your back yard with no protectionwhich you can't shut off!
Given the good safety record of PV, maybe we can
keep existing standards for smaller systemsones
that won't add unnecessary expenses that keep
these systems from ever being built.
Drake
Drake Chamberlin
Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV
740-448-7328
<http://athens-electric.com/>http://athens-electric.com/
At 03:16 PM 8/28/2014, you wrote:
[Robin chiming in, below]
Dan, The 2014 690.12 is worded poorly. That is
why there is so much confusion. MidNite Solar is
sitting on the NEC2017 690.12 committee. There
are a lot of smart people in this group. The
2017 version says ALL PV SYSTEMS, not just on or
in buildings. The 10 foot space gets reduced to
1 foot like it always should have been.
There will be a lot of other clarifications too.
The systems that use shunt trip breakers [with
Remote Trip coil] and contactors are for string
inverters. Shunt trip breakers will be used for
battery based systems and grid tie inverters
with an AC outlet like the SMA TL series. Micro
inverters do not require anything like what our
system is. They can use the existing backfed
breaker in the main distribution box as long as
it is labeled accordingly. Solar Edge has a
system that meets the Rapid Shutdown requirement also.
The UL standard for Rapid Shutdown has been
written. It is going to go out to a task force
for review, comment and changes soon. MidNite
Solar will be on that task force. The MidNite
Birdhouse is going through UL now and is being
evaluated to this new standard. All of our
disconnecting combiners and SOBs are already ETL
listed. UL is modifying the new Rapid Shutdown
Draft standard as they come upon things in the
Birdhouse that the standard didn't consider. One
of the biggies that has not been sorted out is a
requirement for feedback. Contactors, power
supplies and a switch will meet the requirement
for 2014. The issue with this type of system is
that when you push the button to turn off the
contactors, there is no way to tell that they
actually opened up. Without feedback that
verifies that the contactors are actually open,
you are taking a chance with people's lives.
600VDC contactors can weld themselves closed. If
first responders don't trust the Rapid Shutdown
system, they are going to let the house burn. We
do have feedback on the birdhouse system.
Contactors do not have feedback. It is not
simple to add this feature to a contactor based system.
Installing a switch 15 feet up on the side of a
building or on the roof is not the intent of
690.12. This will not be allowed in 2017. The
exact placement of the initiating device
(Birdhouse) is not cast in concrete due to the
differences in where main panel boards are
located, but it will not allow things like
mentioned here 15 feet up in the air or in the attic or on the roof.
Battery based systems are the most complicated
to meet 690.12. The NEC committee is deferring a
lot of this to MidNite as we are already doing
it and have gone over all the different ways
things can go wrong. We started designing our
system right after the Bakersfield fire 5 years
ago. The Bakersfield fire is what got the NEC to
require disconnecting combiners. We couldn't
imagine why a fire fighter would want to get up
on the roof of a burning building to look for a
combiner? This is why we started the birdhouse
project way before anyone ever thought of the
words Rapid Shutdown. Turns out this was a good
thing since battery backed up systems make the
issue ten times more complicated. We spent years
working out issues and there were lots of them
that required a start from scratch approach numerous times.
AC coupling to a battery based inverter does not
automatically meet 690.12 as someone mentioned
in this thread. That battery based inverter must
also be shut off. The micro inverters would of
course shut off when the utility is shut down,
but the battery based inverters job is to keep
things powered up when the grid is down. So the
battery based inverter has to be shut down also.
It would also make sense to shut off an auto
start generator with the Rapid Shutdown button.
Some generators are designed to start up upon
loss of grid. Once the first responders have
the meter pulled, that could start up a
generator and cause risk of shock. If the
generator is designed to start on low battery,
it could start a day later when the fire has
been put out, but that also poses risk of
electrical shock when unexpectedly the part of
the house that is left all of a sudden comes live with juice.
The cost for a Rapid Shutdown system will vary a
lot depending on what you want to shut down. You
do not need to run conduit to all the boxes and
switches. There is 600V Cat5e 90C USE-2 cable
available that will suffice. I don't see a
system being installed for less than $1500 though.
Robin Gudgels
On 8/27/2014 8:45 AM, Dan Fink wrote:
Hi Mac, all;
Since Colorado just adopted NEC2014 July 1, I
have not heard any AHJ stories yet. But look at 690.12 (1):
"Requirements for controlled conductors shall
apply only to PV system conductors of more than
5 ft in length inside a building, OR more than 10 ft from a PV array."
(my emphasis on "OR")
I interpret this to mean that if a ground mount
array is more than 10 ft from the building,
then any PV circuits that run up the outside of
the building from their trench (for example to
penetrate the wall to the power center on the
inside) must be controlled because they are
"on" the building. And even if you penetrated
right from the trench into the crawl space,
then up to the power center on the inside wall,
with less than 5 ft distance, still needs to be
controlled if the array is more than 10 feet
from the building because of that "OR"
The logic and safety advantage of this for
firefighters is another topic entirely. As a
first-arriving firefighter, I would spot the PV
racks on the ground, walk over to them, and
throw the disconnects on the nicely-labeled
combiner boxes located within 10 feet of the array.
All thoughts appreciated, still puzzling this out.
Dan Fink
Buckville Energy
Otherpower
NABCEP / IREC / ISPQ accredited Continuing Education Providers
970.672.4342
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