[RE-wrenches] Rapid shutdown questions
Dave Click
daveclick at fsec.ucf.edu
Fri Aug 29 10:08:26 PDT 2014
While I share Robin's optimism, I should also note the "NEC 2017 690.12
committee" referred to is not the code making panel. While it does have
(at least) one firefighter representative among a majority of PV
industry personnel, there's no guarantee that the Code Making Panel
approves this committee's proposal. There could very well be a competing
proposal from firefighters that requires cell-level shutdown every time
a red truck drives within 1/4 mile of an array, because "SAFETY!"
DKC
On 2014/8/28, 15:16, boB at midnitesolar.com 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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