<html>
<body>
Hello Robin and boB.<br><br>
Ryan’s 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. <br><br>
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. <br><br>
A very nice feature of today’s lower module prices is that many people
who <u>really want PV</u>, but have never been able to afford it, can now
have a system. New requirements are eroding this new found ability. <br>
<br>
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. <br>
<br>
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?<br>
<br>
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? <br>
<br>
<br>
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
<a href="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.</a> How many people were killed by
solar electric systems that year? <br>
<br>
How about an exemption for residential systems under 12 kW? This size
system has a power potential of 1/200<sup>th</sup> of that of the wire
that runs 10 feet over your back yard with no protectionwhich you can't
shut off! <br>
<br>
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. <br>
<br>
Drake <br><br>
<a name="_MailAutoSig"></a>Drake Chamberlin<br>
<i>Athens Electric LLC<br>
OH License 44810<br>
CO License 3773<br>
NABCEP Certified Solar PV <br>
740-448-7328<br>
</i><a href="http://athens-electric.com/">http://athens-electric.com/</a>
<br><br>
<br><br>
At 03:16 PM 8/28/2014, you wrote:<br><br>
<blockquote type=cite class=cite cite="">[Robin chiming in,
below]<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
Robin Gudgels<br><br>
<br><br>
On 8/27/2014 8:45 AM, Dan Fink wrote:<br>
<blockquote type=cite class=cite cite="">Hi Mac, all;<br>
Since Colorado just adopted NEC2014 July 1, I have not heard any AHJ
stories yet. But look at 690.12 (1):<br>
"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."<br>
(my emphasis on "OR")<br><br>
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"<br><br>
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.<br><br>
All thoughts appreciated, still puzzling this out.<br><br>
Dan Fink<br>
Buckville Energy<br>
Otherpower<br>
NABCEP / IREC / ISPQ accredited Continuing Education Providers<br>
970.672.4342</blockquote></blockquote></body>
</html>