[RE-wrenches] Rapid shutdown questions

[boB at midnitesolar.com]

[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