"Rapid Shutdown" of a system

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MechEdetour

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Location
NY, USA
Well, I've held off for a little while but figured I'd have to break the seal eventually as far as making my first post is concerned.

I understand this clause in the NEC is probably going to undergo some changes/adjustments in the near future, along with being incorporated into standards, etc. But I am curious how the case would apply to:

Say I have a string of arrays going into DC combiner, which is then feeding an inverter (oversimplified system but should suit the question I'm asking). Theoretically the DC combiner designed with a contactor, along with a remote control station should have the ability to satisfy the requirements of 690.12. However, in the case where the inverter cannot satisfy 690.12(2) due to say discharging capacitors, then the DC combiner "assembly" that can function as a solution to rapid shutdown no longer does because of the inverter that its being used with. And vice versa. An inverter that discharges in the required time, will still have live conductors feeding it if the DC combiner does not have a rapid shutdown feature.

To me it seems like the rapid shutdown requirements are heavily dependent on the integration of all the components. Is it not? In the system I presented, the DC combiner AND the inverter would need to be designed to satisfy the requirement. Additional to this it seems like a combiner or inverter can't be listed to satisfy the requirement of 690.12 in a PV system. How would this be incorporated into a standard so that just a combiner that meets rapid shutdown requirements doesn't create the illusion that the entire system will satisfy the requirement as well. Does it all come down to the installer satisfying 690.12 and not the manufacturer of listed equipment?

I guess I'm just looking for a discussion.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Well, I will start with the observation that adding a relatively small bleeder resistor on the inverter side of the Rapid Shutdown disconnect will probably be good enough to discharge any input capacitors in the inverter within 10 seconds.
Internal capacitors farther down the path, which by the circuit configuration cannot feed DC back onto the DC input wires, do not, IMHO, count as their stored energy is confined to the inside of the inverter.

Your observation that a listed Rapid Shutdown disconnect may not by itself kill all DC downstream in an interesting one. I wonder whether any GTIs actually have capacitors directly on the DC input?
 

SolarPro

Senior Member
Location
Austin, TX
To me it seems like the rapid shutdown requirements are heavily dependent on the integration of all the components.

Correct. That's certainly the case today. In the future, we'll have an actual product safety standard and tighter Code requirements, which will both tend to drive product development toward standardized off-the-shelf components.

FWIW, I'm aware of at least one company with a rapid shutdown combiner that incorporates a capacitor discharge circuit:

http://www.innovativesolarinc.com/rapid-shutdown.html

Also, SolarPro and IAEI magazines have both published detailed articles about complying with NEC 2014 rapid shutdown requirements:

http://solarprofessional.com/articles/design-installation/rapid-shutdown-for-pv-systems

http://iaeimagazine.org/magazine/2015/01/22/rapid-shutdown-of-pv-systems/
 

MechEdetour

Member
Location
NY, USA
Your observation that a listed Rapid Shutdown disconnect may not by itself kill all DC downstream in an interesting one. I wonder whether any GTIs actually have capacitors directly on the DC input?

Correct. That's certainly the case today. In the future, we'll have an actual product safety standard and tighter Code requirements, which will both tend to drive product development toward standardized off-the-shelf components.

Are there any standards being worked up to address rapid shutdown at the moment? Earlier today I was searching through the PV forum for topics regarding Rapid Shutdown and I thought I came across a comment that a standard was being developed and should be published within a month or so. . . and that was dated Feb of this year. I believe current UL1741 is 2010? So no Rapid Shutdown in there. . .

And good articles for sure.
 

MechEdetour

Member
Location
NY, USA
Bringing this back to life. Few things have evolved since I initially asked some questions.

One of the things that I gather from NEC Rapid Shutdown requirements is that "690.12(5) Equipment that performs the rapid shutdown shall be listed and identified." After reading the articles (again) and comparing the language to other sections of 690 that require listed equipment, it is clear that equipment does not have to be specifically listed for rapid shutdown. It just needs to be listed/identified for whatever purpose it serves (disconnection, initiation, etc.).

Considering that a CRD has been published that addresses some new definitions, construction requirements, and testing requirements for Rapid Shutdown (that can potentially end up in UL1741), will this inadvertently lead the AHJ to think that equipment used to fulfill 690.12 requirements must be specifically listed for rapid shutdown (ie listed to UL1741)?

Thoughts?
 

SolarPro

Senior Member
Location
Austin, TX
Yes, there is confusion regarding this distinction. It is also the case that requirements for equipment listed specifically for rapid shutdown are coming soon:

Labeled vs. identified. The NEC 2017 requirements for “listed and labeled” rapid-shutdown equipment meaningfully revises NEC 2014, which requires “listed and identified” equipment. Article 100 defines the term identified as “suitable for the specific purpose, function, use, environment, application, and so forth.” By contrast, the definition of labeled in Article 100 “indicates compliance with appropriate standards or performance in a specified manner.” The latter is more prescriptive and narrowly defined than the former.

In practice, this means that installers can use off-the-shelf electrical components to meet NEC 2014 rapid-shutdown requirements so long as the conditions of use are consistent with the equipment ratings. For example, under NEC 2014, you could locate a contactor combiner at the edge of a PV array and use this to meet Section 690.12 as long as the combiner was rated for the outdoor environment and the PV voltage and current characteristics. NEC 2017 will require that this contactor combiner be specifically listed to a rapid-shutdown PV array standard and labeled accordingly. Revised language in 690.12(D) states: “Equipment that performs the rapid-shutdown functions, other than initiation devices such as listed disconnect switches, circuit breakers or control switches, shall be listed and labeled for providing rapid-shutdown protection.”

This is an important distinction. Some jurisdictions— including New Jersey, New Mexico and Washington—have misinterpreted NEC 2014 requirements and asked installers and vendors to prove that rapid-shutdown solutions comply with a rapid-shutdown safety standard. As of today, no such standard exists. Until the NEC 2017 is adopted, there is no requirement that equipment used for rapid shutdown be listed and labeled specifically for the rapid shutdown of PV arrays. Installers can use any listed equipment to provide rapid shutdown, so long as they field the equipment in a manner consistent with the product listing.

Source: NEC 2017 Updates for PV Systems by Bill Brooks
 

Carultch

Senior Member
Location
Massachusetts
Yes, there is confusion regarding this distinction. It is also the case that requirements for equipment listed specifically for rapid shutdown are coming soon:



Source: NEC 2017 Updates for PV Systems by Bill Brooks


What if you meet the requirements of rapid shutdown, without rapid shutdown specific equipment? Is it still permissible to satisfy this requirement with microinverters, or inverters within the length limit from the array?
 

pv_n00b

Senior Member
Location
CA, USA
There are a couple of TIAs in the pipe for RSS in the 2014 NEC. One will change the 10 second time to 30 seconds to bring the controlled conductors below the cutoff voltage and the other is to clarify the listing requirements for RSS equipment since some AHJs have misunderstood the current language. The RSS equipment is just supposed to be listed electrical equipment and not listed and identified for RSS usage. While this is a known distinction to most some AHJs and installers still struggle with the NEC language and misapply it.

The new language for NEC 2017 will require equipment to be listed, labeled, and identified for RSS usage. The standard will be included in UL 1741 and has just been finalized by the technical committee that was developing it, next it will be sent to the 1741 STP for evaluation. When it actually will be approved and published is anyone's guess. UL moves at it's own speed. In my opinion the new requirements are a bit overkill but that is what the committee came up with.

There is a distinction in the standard between packaged systems that provide all the RSS functions needed to shut down the controlled conductors and single components that are part of an RSS but will not provide full functionality. If a manufacturer makes a component that is only part of an RSS, such as a DC contactor, they will have to clearly state in the installation manual that other components are required to have a fully functional RSS.

Unfortunately from what I have seen there is a general dismissal of the time requirement in the 2014 NEC and installers and AHJs are often accepting systems that only have a DC disconnect close to the PV array. While this is better than nothing the DC conductors will take too long to discharge with this type of system.

Micro-inverters are inherently compliant with RSS standards out of the box, DC-DC converters at the module are not for most. If you can get an inverter inside the controlled conductor zone you are good to go. SolarEdge has a kit that makes their systems RSS ready. There are a number of DC contactor type systems being marketed as RSS compliant that are not due to the inverter contribution not being addressed, but there are a couple that include discharge resistors that are supposed to provide a full RSS. Just make sure the inverter manufacturer has approved the equipment as working with their inverters. No random mixing and matching if you like your inverter warranty.
 

MechEdetour

Member
Location
NY, USA
There are a couple of TIAs in the pipe for RSS in the 2014 NEC. One will change the 10 second time to 30 seconds to bring the controlled conductors below the cutoff voltage and the other is to clarify the listing requirements for RSS equipment since some AHJs have misunderstood the current language. The RSS equipment is just supposed to be listed electrical equipment and not listed and identified for RSS usage. While this is a known distinction to most some AHJs and installers still struggle with the NEC language and misapply it.

The new language for NEC 2017 will require equipment to be listed, labeled, and identified for RSS usage. The standard will be included in UL 1741 and has just been finalized by the technical committee that was developing it, next it will be sent to the 1741 STP for evaluation. When it actually will be approved and published is anyone's guess. UL moves at it's own speed. In my opinion the new requirements are a bit overkill but that is what the committee came up with.

There is a distinction in the standard between packaged systems that provide all the RSS functions needed to shut down the controlled conductors and single components that are part of an RSS but will not provide full functionality. If a manufacturer makes a component that is only part of an RSS, such as a DC contactor, they will have to clearly state in the installation manual that other components are required to have a fully functional RSS.

Unfortunately from what I have seen there is a general dismissal of the time requirement in the 2014 NEC and installers and AHJs are often accepting systems that only have a DC disconnect close to the PV array. While this is better than nothing the DC conductors will take too long to discharge with this type of system.

Micro-inverters are inherently compliant with RSS standards out of the box, DC-DC converters at the module are not for most. If you can get an inverter inside the controlled conductor zone you are good to go. SolarEdge has a kit that makes their systems RSS ready. There are a number of DC contactor type systems being marketed as RSS compliant that are not due to the inverter contribution not being addressed, but there are a couple that include discharge resistors that are supposed to provide a full RSS. Just make sure the inverter manufacturer has approved the equipment as working with their inverters. No random mixing and matching if you like your inverter warranty.

Thanks for the info. I was actually reading through the CRD that addresses the requirements for RS and they sure go above and beyond.

However, even with all the extensive requirements, I still feel as though issues will arise in the field where an AHJ deems an installation compliant with 690.12 because of listed and labeled RS equipment that is present. For example, what I mean by this is that the contactor/relay/switch that will be listed for RS, but then combined with an inverter that discharges in well above 10 or 30 seconds, will no longer fulfill the requirements of 690.12. Hopefully the equipment that will now (likely) be listed for RS will not reduce the attention the system needs to ensure it meets all the requirements.
 
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