[RE-wrenches] Rapid shutdown questions

Drake drake.chamberlin at redwoodalliance.org
Sun Aug 31 14:21:14 PDT 2014


Hello Robin and boB.

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.

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 today’s 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20140831/07940064/attachment-0002.html>


More information about the RE-wrenches mailing list