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Thread: Aux electrode

  1. #1
    Join Date
    Jun 2018
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    Glen bunie, md, us
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    Aux electrode

    Still using NEC 2014 not at NEC 2017 yet. Read and saw youtube videos that nearby lightning strike current may be traveling in low impedance path from rooftop solar aux electrode to bldg electrode via EGC. NEC 2014 690.14(d) refers to solar array aux electodes shall be installed in accordance with NEC 250.54. Why cannot one use the exception to aux electrode of nec 2014 250.54 earth shall not be used as effective ground fault current path to not install or discourage aux electrode solar array rooftop since low impedance path maybe created when lightning or I am not interpreting that correctly?

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  2. #2
    Join Date
    Dec 2006
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    Chapel Hill, NC
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    I believe what 250.54 is talking about is that the earth (ground rod, etc) cannot be used as a mechanism to clear faults. In other words, you cannot exclude the equipment grounding conductor and just use a ground rod as a means to clear faults. I think that is the case.

    However, it can work in reverse using this exception. Not sure if 690 disallows this or not

    250.121 Use of Equipment Grounding Conductors. An
    equipment grounding conductor shall not be used as a
    grounding electrode conductor.


    Exception: A wire-type equipment grounding conductor installed
    in compliance with 250.6(A) and the applicable requirements
    for both the equipment grounding conductor
    and the grounding electrode conductor in Parts II, III, and
    VI of this article shall be permitted to serve as both an
    equipment grounding conductor and a grounding electrode
    conductor.
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  3. #3
    Join Date
    Jun 2018
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    Glen bunie, md, us
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    Ok. However, Nec 690.47(d) says shall be installed in accordance with nec 2014 250.54. Nec 250.54 says one or more grounding electrodes shall be permitted to be connected to EGC.

    So I am not sure where one would get understanding that NEC 2014 690.47(D) requires the solar arrary aux electrode?

  4. #4
    Join Date
    May 2011
    Posts
    4,688
    It's a little hard to tell exactly what you're asking without more punctuation, but let me say this....

    690.47(D) is a misguised, unnecessary code requirement. Don't try to make logical sense of it in terms of physics or electrical theory. It's been taken out of the 2017 NEC as a requirement because there's no good reason for it.

    I have no problem advising you to ignore this code requirement unless the AHJ makes you follow it. In that case, you'll pretty much have to just ask the AHJ exactly what they want. Try starting from what is easiest to install and ask them 'Does that meet your requirement?' And if the answer is 'no' suggest the next easiest thing, and so on.

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