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Thread: 690.47 Grounding Electrode System

  1. #1
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    690.47 Grounding Electrode System

    I'm a bit confused by 250.97 ('11 Code).
    Is it permissible to ground my DC system by a grounding conductor from my DC system to my AC grounded conductor or must I have a grounding electrode on the DC circuit ?
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  2. #2
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    Quote Originally Posted by augie47 View Post
    must I have a grounding electrode on the DC circuit ?
    I find it a bit confusing too.
    Answer as I see it, it depends on the inverter.
    Isolated = grounded = yes.
    Non-isolated = ungrounded = no.

    Here's the latest list:
    http://solarprofessional.com/article...specifications
    ---
    Ungrounded system diagram (last one on list):
    https://www.homepower.com/articles/s...ded-pv-systems
    ---
    If you’re using an ungrounded inverter, your system will still have a grounding electrode, an equipment ground, a GEC, an AC system grounding point, and a grounded AC conductor. It is only missing the DC system grounding point and the grounded DC conductor.
    https://www.homepower.com/articles/s...s-pv-grounding
    ---
    And the other option (#1):
    https://www.homepower.com/articles/solar-electricity/design-installation/code-corner-more-system-grounding



  3. #3
    Join Date
    May 2011
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    3,552
    Answer: yes, you can use the same electrode for DC and AC requirements. That's regardless of inverter type. If you have an ungrounded DC system then UL doesn't care about having a DC GEC, but the 2011 code still requires it. A lot of AHJs I worked with did not require it because inverter manufacturers put out white papers about UL standards. Equipment grounding is still required of course.

  4. #4
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    "must I have a grounding electrode on the DC circuit"

    I misspoke previously- when I said (Isolated = grounded = yes) I meant an electrode is required FOR the DC circuit, *not*- "on the" or "at the".

    ----
    Over the past few Code cycles, the changes to 690.47 have been dramatic. In the 2011 Code, the changes made to 690.47 seemed well-received by the PV community, primarily due to the deletion of the most difficult and controversial requirement, 690.47(D), which called for additional electrodes for array grounding. The 2011 NEC’s 690.47 has three subsections, with the third being the most widely used. The first two are for systems that exclusively produce and use DC or AC. The third subsection, 690.47(C), applies to systems that have both DC and AC electrical requirements—the majority of PV systems installed today. That third subsection is divided into three additional subsections for different installation scenarios.

    All three of 690.47(C)’s subsections require that the DC grounding system be connected to the AC system’s grounding electrode. For grid-direct PV systems, this is generally the existing grounding electrode—a ground rod, water pipe, concrete-encased electrode, etc. A new DC grounding system connection to earth can be accomplished by:


    • Establishing a new DC GE and bonding the new electrode to the existing AC GE.
    • Connecting a new DC GEC from the inverter to the existing AC GE.
    • Using a combined DC GEC and AC EGC (in one wire) from the inverter to the grounding bus bar in the associated AC equipment.

    Each of these provisions has its own unique set of rules to follow. Grounding and bonding is always a complicated case.
    https://www.homepower.com/articles/s...bonding-part-2
    ---

    Wow, so this issue has been around since 1989.
    Of course, this bolded means not grounding it to an electrode on/at the DC side.

    In view of the prevalent practice, with apparent success, among European designers of not grounding the
    dc system,
    the quasi-axiomatic practice by U.S. designers of multiple-point grounding should be re-examined,
    and
    a dialogue initiated between the two parties.
    https://www.nist.gov/sites/default/f...otovoltaic.pdf

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