[RE-wrenches] NEC 2014 690.12 Rapid Shutdown

Dave Click daveclick at fsec.ucf.edu
Tue Apr 15 08:18:02 PDT 2014 

Nathan, 690.12 only applies to "PV system circuits installed on or in 
buildings" so that might be your answer. You'd only be affected by 
690.12 if you're running to an interior inverter. So- your strategy of 
exterior conduit to wall-mounted inverters on the exterior of a building 
won't be subjected to the 690.12 requirement.

On 2014/4/15, 11:09, Nathan Charles wrote:
> 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 
> <mailto: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 <tel: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>
>>     [mailto:re-wrenches-bounces at lists.re-wrenches.org
>>     <mailto: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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