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Thread: NEC Article 705.12(D)(3) “Exception”

  1. #1
    Join Date
    Mar 2018
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    Carlsbad California USA
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    NEC Article 705.12(D)(3) “Exception”

    I am having trouble interpreting NEC Art 705.12(D)(3) “Exception” specifically the Exception.


    the following code: 2011 NEC 705.12(D)(3) Exception: “Connection shall be permitted to be made to the load side of ground-fault protection provided that there is ground-fault protection for equipment from all ground-fault current sources. Ground-fault protection devices used with supplies connected to the load-side terminals shall be identified and listed as suitable for backfeeding.”


    I have a 480V/277V Solar Switch Switch Board rated 1600A, which has a 1600A Bolted Pressure Switch with a GFP device.
    The Long time setting of the Switch is 1000A.


    The Switchboard has 10 -100A interactive utility connection (solar Inverters from solar arrays) which are connected on the load side of the BP Main GFP sensor.


    The exception permits this stating “provided that there is ground-fault protection for equipment from all ground-fault current sources. Ground-fault protection devices used with supplies connected to the load-side terminals shall be identified and listed as suitable for backfeeding.”


    My interpretation of the exception, is that the 10-100A breakers would also have to provide a level of GFP and the breaker and GFP sensor within the downstream load side connected Branch feeder breakers be listed for back feeding.


    This would provide the switchboard from Ground fault protection from the solar arrays (other than Utility ground fault current sources).


    Is this correct?


    Currently the 10-100A installed breakers are molded case fixed curved breakers that do not have GFP capability.




    The contractor’s argument is that due to the fact the inverters shutdown on a loss of Utility then the switchboard would be protected by the inverters GFCI devices. I do not agree with this due to the fact that the inverter (ungrounded inverters) GFCI devices sense current on the DC side of the inverter only.


    The EOR has written a letter stating that he has designed the system to code and excepts the installation as is.


    Please respond ASAP if possible and help us understand this Article.




  2. #2
    Join Date
    May 2011
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    4,128
    (First, you're still on the 2011 code in California? It doesn't make much difference since most of this is now in 705.32, but one piece of language that went away is "Ground-fault protection devices used with supplies connected to the load-side terminals shall be identified and listed as suitable for backfeeding.")

    My interpretation of the exception, is that the 10-100A breakers would also have to provide a level of GFP and the breaker and GFP sensor within the downstream load side connected Branch feeder breakers be listed for back feeding.
    I think this is pretty much in agreement to what has been said on this forum in the past. My understanding is that the typical approach is to connect on the supply side of any GFP device. A less typical approach is to add some type of additional GFP device to the inverter output(s). The only thing I would quibble with is that you said the 10 100A breakers would have to provide GFP, but it's conceivable that those outputs could have GFP devices distinct from the breakers.

    The contractor’s argument is that due to the fact the inverters shutdown on a loss of Utility then the switchboard would be protected by the inverters GFCI devices. I do not agree with this due to the fact that the inverter (ungrounded inverters) GFCI devices sense current on the DC side of the inverter only.
    I believe you have this correct.

  3. #3
    Join Date
    Nov 2015
    Location
    CA, USA
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    Quote Originally Posted by Zbailey View Post
    I am having trouble interpreting NEC Art 705.12(D)(3) “Exception” specifically the Exception.


    the following code: 2011 NEC 705.12(D)(3) Exception: “Connection shall be permitted to be made to the load side of ground-fault protection provided that there is ground-fault protection for equipment from all ground-fault current sources. Ground-fault protection devices used with supplies connected to the load-side terminals shall be identified and listed as suitable for backfeeding.”


    The contractor’s argument is that due to the fact the inverters shutdown on a loss of Utility then the switchboard would be protected by the inverters GFCI devices. I do not agree with this due to the fact that the inverter (ungrounded inverters) GFCI devices sense current on the DC side of the inverter only.


    The EOR has written a letter stating that he has designed the system to code and excepts the installation as is.

    I'm not sure why you are referencing the 2011 NEC in CA now, but I'll roll with it.

    NEC 240.13 requires GFP on 480/277V systems 1,000A and greater, and 230.95(A) states that the GFP setting has to be 1,200A or less. So the answer is that as long as the main breaker GFP setting plus about 1.1 times the inverter rated current is less than 1,200A the system is protected. The idea of GFP is to limit equipment damage in the event of a ground fault, meet that requirement and you have met the code.

  4. #4
    Join Date
    Mar 2018
    Location
    Carlsbad California USA
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    4

    Thank you both for your interpretations

    Apologize for the 2011 quotes, the projects in question are using the 2014.

    thank you both very much for your interpretations though.

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