[RE-wrenches] NEC 2014 690.12 Rapid Shutdown

Nathan Charles ncharles at paradiseenergysolutions.com
Tue Apr 15 08:09:53 PDT 2014


Hi All,

I have a follow up to this discussion.  What's the proper way to think
through this regarding ground mounts?  It seems to me that if the goal is
to protect firefighters then running a conduit underground and coming up to
outdoor wall mounted inverters is keeping in the spirit of things, but I'm
not sure if the language of 690.12 supports this.  Am I mistaken?  Do you
have any best practice advice for this scenario?

Best regards,
-N


On Tue, Jan 21, 2014 at 12:36 PM, Drake <
drake.chamberlin at redwoodalliance.org> wrote:

>
> Bill,
>
> It is good to see that energized conductors are going to be disconnected
> near the arrays. I've been an advocate of disconnecting these conductors by
> ground fault sensing equipment since ground fault detection was first
> implemented in the code. If contactors are to be installed on roofs, it
> likely won't be long before both ground faults and arc faults are
> automatically cleared.
>
> When the requirement for AC arc fault branch circuit protection was first
> put in the NEC, it was postdated to allow time for the electrical industry
> to adapt. This new remote disconnecting requirement does not provide any
> lead time.
>
> As the 2014 NEC is adopted in various jurisdictions, inspectors may feel
> that it is necessary to disallow systems without the newly required
> disconnect feature. This may result in serious problems for solar companies
> and customers, as well as manufacturers.
>
> The protection of firefighters is essential. The implementation of
> renewables is essential also. Insurance claims for weather related, global
> warming-triggered climatic disasters are rising exponentially. Extreme
> weather related events result in major loss of life and billions of dollars
> in property damage. Atmospheric CO2 levels continue to climb from the
> burning of fossil fuels. This is a crisis of global proportions.
>
> My request for code writers is to please take into account the effect that
> inserting new rules into the NEC may have on the stability of renewable
> energy, and implement new requirements in a way that will allow for a
> smooth interface.
>
> Thank you,
>
> Drake
>
> Drake Chamberlin
>
>
>
>
>
> *Athens Electric LLC OH License 44810 CO License 3773 NABCEP Certified
> Solar PV 740-448-7328 <740-448-7328> *http://athens-electric.com/
>
>
> At 12:45 PM 1/16/2014, you wrote:
>
> Content-Type: multipart/alternative;
>          boundary="----=_NextPart_000_0F94_01CF129F.BCC65BD0"
> Content-Language: en-us
>
>
> Jeffrey,
>
> Sounds like you need to get involved in the code making process since you
> have so many good ideas on how to improve the language. I like
> confrontational discussions as long as they lead to a better understanding
> and constructive outcomes.
>
> About 30 people worked on this language, so it is definitely not perfect.
> However, I don’t think it is quite as bad as you make it out to be. I
> wanted to jump in since some of your conclusions were not correct.
>
> This is a circuit requirement, not a disconnecting means requirement,
> since it has to do with shock hazard of PV circuits in and around a
> building. This is for firefighter safety. 30V is the international standard
> for touch safe in a wet location. 240VA is to set a limit on the available
> power on a circuit. Contactor combiners, which would be part of a compliant
> solution, have 24V control circuits. The other reasoning for 240VA is that
> internally, 72-Cell PV modules can be divided into segments of this power
> level for the foreseeable future (more on that another day).
>
> If the conductors stay outside, you have 10’ from the array to place your
> shutdown device. On large central systems, this would likely be a contactor
> combiner­most manufacturers sell these. If the conductors are going
> immediately into the building, as with residential and integrated systems,
> a shutdown device would have to be within 5’ of entering the building. If
> goes outside for a while, then inside the building, the total length could
> be no more than 10’ and no more than 5’ inside the building­this is not
> additive. Remember, all this is for firefighter safety.
>
> As Brian Mehalic and others have pointed out, the language does not
> specify where the shutdown initiating device is to be located. The lack of
> detail is more for flexibility than it is to give an AHJ license to make an
> installer do anything they want.
>
> With grid-tie only systems (no battery backup), it would be most
> convenient and cost effective to have a system that initiates the shutdown
> on loss of utility. In this way, a firefighter can do what they normally
> do, shut down utility power to the building, and the rapid shutdown would
> automatically initiate. This does not necessitate an additional
> disconnecting means for a load-side PV connection. The main breaker could
> be the initiating device. For a supply-side connection, the NEC already
> requires that the PV disconnect switch be located adjacent to the service
> disconnecting means (article 230).
>
> The biggest issue with string inverters (central inverters) is that there
> is a need to shutdown the capacitor input side of the inverter since that
> stays energized for 5 minutes or more. The 10 seconds was to provide a
> means to rapidly discharge the capacitors rather than requiring a relay or
> tripping device. Doing something other than a relay will require a test
> laboratory to evaluate the function­guess what?­we don’t have a standard
> yet to evaluate those products. Sounds like you might want to work on that
> committee.
>
> It is more complicated for battery backup systems. Midnite Solar’s
> birdhouse products are the best I have seen so far to address this concern.
> Since dc and ac circuits are not differentiated, battery backup systems
> need to have a shutdown process that works independently of a utility
> outage for obvious reasons, and it must shutdown both the dc circuits and
> the backup ac circuits. A separate switch, like the birdhouse, would be
> necessary that only controls these functions in an emergency situation.
>
> Is the language not detailed­possibly. This was done to provide
> flexibility rather than create problems. Fire departments have been
> requiring rooftop disconnects for years in California. These disconnects
> are nearly worthless from a shock prevention point of view since capacitors
> in the inverter stay charged or there are multiple disconnecting means
> feeding each other. We have been trying to hold the fire community off of
> rooftop disconnect requirements so we could work on a solution that
> actually does what they want it to do. There is a long discussion on this
> in the appendix of my “Understanding the CalFire Guidelines” document on
> the SolarABCs website.
>
> The 2014 NEC language was a compromise worked out with the solar industry
> (yes string inverter companies as well) in response to the first version of
> the proposal which was to require module-level shutdown. This is not
> module-level shutdown, it is PV output circuit shutdown (combiner box
> shutdown is another way to look at it). However, the 2017 NEC cycle is this
> year and there was a lot of talk about requiring module-level shutdown this
> time around.
>
> I hope this helps. I will be writing articles for IAEI journal and other
> periodicals on this subject since it was a very far-reaching and
> potentially confusing new requirement in the NEC. Thanks for your interest
> and let’s keep the constructive dialogue going on the subject. It is time
> to get involved in the NEC update process again.
>
> Bill Brooks.
>
> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org<re-wrenches-bounces at lists.re-wrenches.org>]
> *On Behalf Of *Jeffrey Quackenbush
> *Sent:* Thursday, January 16, 2014 1:09 AM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] NEC 2014 690.12 Rapid Shutdown
>
> Wrenches,
>
> There is no guidance in the Code text for where the shutdown should take
> place. (1) says: "Requirements for controlled conductors shall apply only
> to PV system conductors of more than 1.5m (5') in length inside a building,
> or more than 3m (10') from a PV array."
>
>
> So, the provisions *apply if* the circuit 10' from the array and 5'
> inside a building, but no mention is made of where the shutdown actually
> needs take place in the circuit. In the video Bill Brooks suggests that the
> shutdown mechanism should also be placed within this 10'/5' boundary but
> that is just an inference -- nowhere in the text is this actually
> specified. If that was the intent of the Code committee, then they've done
> a poor job actually expressing it in English.
>
> I'm concerned that some AHJs will interpret this to exclude all central
> inverter systems (without the addition of cost-inducing secondary DC-DC
> converters like Tigo) because the combiner or junction box can be many feet
> from the actual beginning of a home run under the array. Alternately,
> permissive AHJs could allow this function to be fulfilled anywhere, meaning
> that the implementation won't meet the intent of the writers.
>
> I'm also concerned, as Isaac mentioned, that there are no requirements for
> how the shutdown be initiated, or that it contains of the accessibility and
> grouping requirements that are always included for disconnects. I really
> think this should be treated and categorized as a disconnect requirement,
> not a circuit requirement, because that is the ultimate function that's
> intended.
>
> I'm surprised none of the inverter manufacturers have chosen to comment
> here, as this could dramatically impact the sales of central inverters.
>
> Jeffrey Quackenbush
>
>
>
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-- 
Nathan Charles
Engineer
NABCEP Certified PV Installation Professional #042013-20
Paradise Energy Solutions
(717) 283-2021 direct
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