AC disconnect on grid tie parts list

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Dave Angelini
Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
in Grid Tie and Grid Interactive Systems #1
I am checking a parts list and I see that there is an AC disconnect switch included in a California grid-tie system. Is this needed if there is a 20 amp backfed circuit breaker connecting AC to the inverter? Thanx!
"we go where power lines don't" Sierra Nevada mountain area
   htps://offgridsolar1.com/
E-mail offgridsolar@sti.net

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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #2
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    AC disconnects are required if the system inverter does not meet rapid shut down.
    Very few string inverters meet the requirement for rapid shut down, micro inverters do.
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  • Ampster
    Ampster Registered Users Posts: 174 ✭✭✭
    #3
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    SolarPowered wrote: »
    AC disconnects are required if the system inverter does not meet rapid shut down.
    Very few string inverters meet the requirement for rapid shut down, micro inverters do.
    In addition different cities have their own requirements. I my little beach town a roof AC disconnect is required as well as one near the panel. I have Enphase inverters, which presumably have rapid shutdown. The requirement for the roof disconnect comes from the fire department which has made that into the code or the rules that the building inspectors follow.
    8 kW Enphase micros AC coupled to a SolArk 12K
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #4
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    Thanks the inverter is an SMA TL series. Ground mount array with a DC disco outside. If this needs the AC disco it is outside I would think.....
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • Ethan Brush
    Ethan Brush Solar Expert Posts: 235 ✭✭
    #5
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    SolarPowered wrote: »
    AC disconnects are required if the system inverter does not meet rapid shut down.
    Very few string inverters meet the requirement for rapid shut down, micro inverters do.

    There is no reason that a GTI mounted within 10 feet of an array would not be rapid shut down. From an earlier thread, I believe we are in agreement but you always word it like there is something special about microinverters meeting the 690.12 requirements and and sting inverters not. Perhaps you mean something like, " since string inverters are often mounted further than 10 feet from the array, they often do not meet the rapid shut down requirements."
    Every manufacturer I have seen states that their inverters meet the rapid shut down requirements if mounted within 10 feet of an array. The equipment performing the rapid shut down must be listed and identified, but it does not have to be specifically listed and identified for the purpose.

    What would a AC disconnect have to do with rapid shut down anyway? Typically we are talking DC conductors within that 10 feet distance, so the rapid shut down equipment would be a switch and a combiner/contactor type of product like the one SMA makes.

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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #6
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    My application that I am checking has the array on the ground 300 feet away from the TL series Inverter.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
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    Dave Angelini wrote: »
    My application that I am checking has the array on the ground 300 feet away from the TL series Inverter.
    In which case any AC disconnect, at or after the inverter, will be of no use whatsoever with respect to the DC Rapid Shutdown required by the 2014 NEC. The question is what version of the NEC will be affecting any particular ongoing or new installation.
    If the 2014 NEC applies and you have your inverter outside the 10 foot limit from the array boundary, then a rather expensive Rapid Shutdown DC combiner box may be needed to meet the Rapid Shutdown requirement.
    SMA SB 3000, old BP panels.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #8
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    Ethan Brush wrote: »

    There is no reason that a GTI mounted within 10 feet of an array would not be rapid shut down. From an earlier thread, I believe we are in agreement but you always word it like there is something special about microinverters meeting the 690.12 requirements and and sting inverters not. Perhaps you mean something like, " since string inverters are often mounted further than 10 feet from the array, they often do not meet the rapid shut down requirements."
    Every manufacturer I have seen states that their inverters meet the rapid shut down requirements if mounted within 10 feet of an array. The equipment performing the rapid shut down must be listed and identified, but it does not have to be specifically listed and identified for the purpose.

    What would a AC disconnect have to do with rapid shut down anyway? Typically we are talking DC conductors within that 10 feet distance, so the rapid shut down equipment would be a switch and a combiner/contactor type of product like the one SMA makes.

    Yes you are correct. I am being short with my language.

    String inverter manufacturers should be calling this out in the installation language in order not to confuse the installer, whether or not an AC disconnect is applicable.

    There are instances however, some local jurisdictions do require a AC disconnect for service means, incase jurisdictions are locked out of the service main. So it is probably more important to read jurisdiction language if it is in fact applicable.
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  • Ethan Brush
    Ethan Brush Solar Expert Posts: 235 ✭✭
    #9
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    inetdog wrote: »
    In which case any AC disconnect, at or after the inverter, will be of no use whatsoever with respect to the DC Rapid Shutdown required by the 2014 NEC. The question is what version of the NEC will be affecting any particular ongoing or new installation.
    If the 2014 NEC applies and you have your inverter outside the 10 foot limit from the array boundary, then a rather expensive Rapid Shutdown DC combiner box may be needed to meet the Rapid Shutdown requirement.

    My understanding of 690.12 is that it applies to buildings, so in a ground mount situation, the only conductors that would require rapid shut down would be PV system conductors that extend more than 5 feet inside a building. The 10 feet from the array figure is for arrays on buildings. I agree the wording is a bit ambiguous, but when you consider the intent of this whole thing, I dont think they care about an underground feed from an array to a house.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #10
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    Ethan Brush wrote: »

    My understanding of 690.12 is that it applies to buildings, so in a ground mount situation, the only conductors that would require rapid shut down would be PV system conductors that extend more than 5 feet inside a building. The 10 feet from the array figure is for arrays on buildings. I agree the wording is a bit ambiguous, but when you consider the intent of this whole thing, I dont think they care about an underground feed from an array to a house.

    A good point to think about.
    The racking itself that supports the array is a structure under the NEC definition, but not necessarily a building. But it is not clear that the Rapid Shutdown provisions apply only to arrays on buildings.
    The intent to protect fire fighters and other first responders seems clear from the context of the new requirement.
    SMA SB 3000, old BP panels.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #11
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    The code that the AHJ is looking at is definitely not 2014 and that is why I asked if the AC disconnect was specified as " just in case ". With the ground mount arrays 300 feet underground run to an outside the building DC disconnect, I would think that is all a fireman would want. The TL series has it's own internal DC disco and so my client was deciding weather to buy another DC disco for outside and the supplier specced them an AC disco.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #12
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    Dave Angelini wrote: »
    The code that the AHJ is looking at is definitely not 2014 and that is why I asked if the AC disconnect was specified as " just in case ". With the ground mount arrays 300 feet underground run to an outside the building DC disconnect, I would think that is all a fireman would want. The TL series has it's own internal DC disco and so my client was deciding weather to buy another DC disco for outside and the supplier specced them an AC disco.

    Yes, but if the manufacturer has the language in the installation notes that it is meant for rapid shut down, you can design around rapid shut down.

    The reason why I say this is that many jurisdictions, some follow code back as 2008, but if the installation language is inclusive of rapid shut down then, it would be recognized by that AHJ. Reason why I use micro inverters is because that language "rapid shut down" is recognized in both enphase, and ABB's notes, whereas most string inverter manufacturers don't incorporate the language, so therefore it isn't recognized by the jurisdiction.

    All that matters is what the jurisdictions planner or engineer approves, according to the notes provided. You could possibly even get a page from SMA internal docs, stating the equipment is for rapid shut down and they would more than likely approve it.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #13
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    In the case of SMA, the inverter would have to be within 10 feet of the edge of the array for any Rapid Shutdown feature in the inverter to qualify. No simple string inverter is capable of telling the PV panels to stop putting out voltage.
    The SolarEdge string inverter, on the other hand, can command the optimizers at each of the panels to shut down, regardless of the separation between them. Older SolarEdge optimizers and some microinverters may need to have a modification fitted to discharge the internal capacitors more quickly when the unit is shut down.
    SMA SB 3000, old BP panels.
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  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    #14
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    Early grid tie requirements frequently required an external AC disconnect switch. Its a leftover from large generator requirements. The utility wanted a switch that they could throw and lock out. This requirement has been removed from most small grid tie requirements. I do remember at one point that one of the electrical unions in CA were arguing with their management and were locking opening the disconnects and locking them out as a negotiating ploy. My original inverter required one and I now have all three of my systems outputting through that switch.
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