Spending more time on the roof, while putting more equipment and parts to meet MLPE, means more trips up the ladder, which increases, not decreases the #1 worker safety danger: Falls. Please correct me if I have somehow misunderstood this, but MLPE is not making installers safer based on OSHA information provided.   Also after installation, which system is more likely to require workers to return to work on the roof, pulling up modules, trying to find problem equipment?  More connections is More safe?  Really?  I haven't had to climb back up on the roof on any of my older, lower voltage off grid work in almost a decade.

Once again, MLPE has its place, (larger systems, multiple subarrays, higher voltage) but we should have sensible exemptions as have been mentioned already.  We are endangering ourselves and our employees needlessly, to comply with 690.12.

Ray Walters
Remote Solar
303 505-8760

On 5/6/20 8:41 PM, drake.chamber...@redwoodalliance.org wrote:

Interestingly enough, the data on the link <https://www.osha.gov/pls/imis/AccidentSearch.search?p_logger=1&acc_description=&acc_Abstract=solar&acc_keyword=&sic=&naics=&Office=All&officetype=All&endmonth=05&endday=05&endyear=2002&startmonth=05&startday=05&startyear=2021&InspNr=> provided shows accidents from gas explosions, falls, health problems and  industrial injuries. None of these incidents could have been prevented by module level power electronics. This is typical of the data that I've seen so far.

---


On 2020-05-06 17:22, Martin Herzfeld wrote:

There could be an issue of encouraging MLPE for worker safety?
1.  This is data involving incidents with workers in the OSHA Fatalities and Catastrophe Investigation Summaries found here:
https://www.osha.gov/pls/imis/AccidentSearch.search?p_logger=1&acc_description=&acc_Abstract=solar&acc_keyword=&sic=&naics=&Office=All&officetype=All&endmonth=05&endday=05&endyear=2002&startmonth=05&startday=05&startyear=2021&InspNr=
2.  In the past I've observed an arc fault at the module level with traditional string systems without a listed arc-fault circuit interrupter NEC/CEC 690.11. The function in NEC/CEC 690.12 would be - to _reduce the shock hazard _- for /emergency responders/ or /firefighters? (NEC 2020)./  However, I've observed thermal events in the panelboard with plans and workmanship issues. On the other hand, falls are the #1 reason for incidents in the construction industry.
All the best,

Martin Herzfeld, Interstate Renewable Energy Council (IREC) Certified Master Trainer ™ for Photovoltaics (PV) Installation Professional #IREC 10037
Contract Training Provider (CTP)
Adjunct Professor, Energy

California Solar & Electrical Contractor License #00833782  C46, C10, D56, D31, C-7 - Since 2004 Solar, Electrical, Trenching, Pole Installation & Maintenance, Instrumentation

Contract Solar (PV) Technical Inspector - 3rd Party Inspections
Underwriters Laboratories (UL) Certified PV Installer #17, OSHA 30
OSHA-Authorized Construction Trainer #32-0105338
CompTIA Certified Technical Classroom Trainer (CTT+) #T3NSZCNBBKB4QTQG

* Professional Member, International Association of Electrical Inspectors  #7035507 - Since 2006 * Accredited and Registered North American Board of Certified Energy Practitioners (NABCEP) Continuing Education (CE) Training Provider

On Thu, Apr 30, 2020, 8:29 AM <drake.chamber...@redwoodalliance.org <mailto:drake.chamber...@redwoodalliance.org>> wrote:


    I would like to see real data on the fire risk of string
    inverters. Anecdotal problems are not data.
    The industry is definitely heading toward MLPE due to the rapid
    shutdown requirements. In many cases MLPE makes sense, in other
    cases it doesn't.
    Systems that are more cost effective and reliable can often be
    built by using string inverters.
    ---


    On 2020-04-29 22:05, Jason Szumlanski wrote:

        "Rapid Shutdown does not prevent fires."

        Not true. If the effect of RS is to steer the market to MLPE,
        I believe it has a significant impact on reducing fire risk.
        As one who has watched a DC conductor fire smolder out of
        control, I am sold on an AC module or microinverter
        architecture. While RS on a DC array doesn't necessarily
        reduce fire risk within the array, it still has the potential
        to reduce severity and spread. Nothing is going to prevent
        all fires. I get that. We're talking about risk mitigation
        when it comes to RS.
        As for "dependable string inverters," the one dependable
        feature is failure at least once in the module lifetime,
        accompanied by a shocking repair bill.
        I'm not a shiny object following kind of guy, but the writing
        is on the wall. MLPE is the future. Modular, serviceable,
        disposable if you will. Like it or not, Edison is going to
        lose this battle to Tesla (Tom vs Nikola). And I live less
        than 5 minutes away from Tommy E's winter home in Fort Myers,
        FL. And I "grew up" in the industry living off-grid in DC
        power. But AC distribution wins for safety at various scales.



        On Wed, Apr 29, 2020, 9:42 PM
        <drake.chamber...@redwoodalliance.org
        <mailto:drake.chamber...@redwoodalliance.org>> wrote:

            Rapid Shutdown does not prevent fires; it was originally
            drafted to allow firefighters to vent a roof without
            being hindered by energized PV arrays. This rule was
            expanded to include other DC wiring from PV sources.

            As for PV safety, I'd like to see some significant,
            statistical evidence that shows there is a major fire
            danger from PV relative to other sources. A fire from a
            solar array gets a lot more press than one from a gas
            leak, bad wiring or an ash tray emptied into a wastepaper
            basket.

            Large public buildings should have all the protection
            that is available. Does one size fit all?

            Would it be reasonable to allow residential installations
            under 12 kW, with 1/4 of the roof adjacent to the array
            available for venting, to be excepted from 690.12? What
            about sparsely occupied commercial buildings with ample
            roof area open for ventilation?

            Many of us have chosen to work with renewable energy
            technology to lessen the harms caused by fossil fuel
            extraction and combustion. The need for non-carbon based
            energy sources has become extremely clear.

            The old string inverters still chug along year after
            year, with little or no maintenance. Someone must pay for
            the ongoing maintenance of module level electronics.
            Dependable string inverter systems should be allowed
            unless statically significant danger can be demonstrated.

            Drake

            ---


            On 2020-04-29 16:01, Jason Szumlanski wrote:

                I have been to several PV fires for string inverter
                systems, both commercial and residential, and have
                seen many DC systems at serious risk of fires or in
                various stages of melted insulation and connectors.
                Most of these systems have exhibited good to
                excellent workmanship. Things just went wrong. Some
                were traceable to animal damage, wind, or other
                unmitigated factors, and some were unexplained. I
                disagree that there isn't justification for rapid
                shutdown.
                In my opinion, what we need is some additional
                innovation and competition in the MLPE space.
                Reliability is clearly a key factor, but there is no
                denying that MLPE has added safety benefits among
                other benefits. And if you do enough volume and set
                up your business for efficiency (standardization of
                product offerings), MLPE isn't much more expensive.
                It becomes a negligible cost relative to the benefit.
                The value proposition is easy to convey. There are
                limits to this, but for the majority of residential
                and small commercial installations, MLPE has become
                the de facto standard around here. String inverters
                are dinos, and replacing 8-12 year old transformer
                based inverters is many times more annoying than some
                MLPE swaps. I will admit that the roofs around here
                are pretty easy to walk, so that is a factor that
                might not apply to you.
                If you go under due to manufacturer product failures,
                you are not writing your contracts right or not
                charging enough for service issues beyond your
                control. I believe that's a red herring. You might
                suffer some reputation damage, but for someone that
                has been installing MLPE for over a decade, that is
                totally manageable. Consumers find a service call to
                replace MLPE a LOT more palatable than a surprise
                inverter replacement that could cost thousands of
                dollars. People just don't plan for that.
                Regarding rapid shutdown devices, I have also come
                across a few that "someone" has bypassed around here.
                I don't know if they were never installed properly or
                disabled/bypassed due to failure. It seemed
                suspicious to me at the time. I remember that it made
                me wonder what good is a rapid shutdown device if it
                is easily defeated? That's another argument for MLPE.
                It has pretty failsafe MLPE functionality.
                Jason Szumlanski
                Florida Solar Design Group

                On Wed, Apr 29, 2020 at 10:59 AM
                <drake.chamber...@redwoodalliance.org
                <mailto:drake.chamber...@redwoodalliance.org>> wrote:

                    Clearly, rapid shutdown increases cost and
                    reduces reliability. Given the excellent safety
                    record of PV, prior to rapid shutdown being
                    required, it is unnecessary. The few anecdotal
                    incidents of PV fires were not enough to justify
                    the requirement, especially on smaller systems.

                    According to a friend who worked for a local
                    installation company that went under, a big part
                    of the reason for their failure was the chronic
                    replacement of microinverters and optimizers.

                    What steps can be taken to create some balance in
                    the rapid shutdown requirements that are in the NEC?


                    ---


                    On 2020-04-29 07:27, Sky Sims wrote:

                        So far rapid shutdown has been a nightmare.
                        It's added a lot of cost for no measurable
                        benefit.
                        Using always off devices like midnight solar
                        and Tigo makes it impossible to test open
                        circuit voltages. Which opens the door to
                        tons of problems when commissioning systems.
                        Also we've been trying out midnight Solar's
                        product and have had an absurd failure rate.
                        Which means lots of truck rolls and
                        troubleshooting and system downtime. They
                        send replacement product but they aren't
                        paying for the lost weeks of productivity.
                        We have Tigo product in hand and are deciding
                        which project to try it on. But our big
                        concern about using it is not only the
                        inability to confirm open circuit voltage of
                        the strings but also the way panels bypass if
                        the device doesn't allow the panel to connect
                        properly. Both of these features are a recipe
                        for problems and potential troubleshooting
                        nightmares. The warranty from Tigo doesn't
                        cover our expense if the product fails. And
                        that's really what our reservations about the
                        product boil down to right now. If we're on a
                        job with 50 units and one fails, the
                        contractor or the homeowner will be the ones
                        eating the expense of finding it and
                        replacing it. There has to be a better option.

                        Sky Sims
                        Https://EcologicalSystems.biz

                            On Apr 28, 2020, at 7:46 PM, Corey
                            Shalanski <coreso...@gmail.com
                            <mailto:coreso...@gmail.com>> wrote:

                            Now that 690.12 of the /NEC/ 2017 has
                            been in effect for several years, I am
                            curious how designers and installers are
                            meeting the associated requirements with
                            string inverter-based systems (*not*
                            considering microinverters or DC
                            optimizers). I am generally a fan of the
                            KISS principle, and as best I can
                            determine the /Tigo/ TS4-F device is one
                            of the simplest options currently
                            available on the market. What are others
                            finding?
                            I'd love to hear about favored options
                            for complying with rapid shutdown. Any
                            success stories? or better yet, any early
                            failures?
                            --
                            Corey Shalanski
                            Jah Light Solar
                            Portland, Jamaica
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