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Thread: Ungrounded PV systems

  1. #1
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    Ungrounded PV systems

    So I'm about to install my first ungrounded PV system, and I have a pretty basic question. Are there any specific labelling requirements on the DC side? I'm running under the assumption that each conductor has some potential to earth ground, therefore is "hot". I certainly won't be marking anything white or grey, I know, but is a simple (+) and (-) sufficient to satisfy NEC PV source circuit labelling requirements?

    Oh, and I'm just talking about terminations, not the labelling of DC cables or conduits.

  2. #2
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    Quote Originally Posted by c_picard View Post
    So I'm about to install my first ungrounded PV system, and I have a pretty basic question.
    I have a pretty basic question -- why would you ever do such a thing?
    Julie in Austin

    Born to brew, forced to work ...

  3. #3
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    As far as the why .......... why not?


    This is from the 2008 NEC, be sure to check the 2011 as you are a MA guy.

    690.35 Ungrounded Photovoltaic Power Systems. Photovoltaic
    power systems shall be permitted to operate with
    ungrounded photovoltaic source and output circuits where
    the system complies with 690.35(A) through (G).

    (A) Disconnects. All photovoltaic source and output circuit
    conductors shall have disconnects complying with 690,
    Part III.

    (B) Overcurrent Protection. All photovoltaic source and
    output circuit conductors shall have overcurrent protection
    complying with 690.9.

    (C) Ground-Fault Protection. All photovoltaic source and
    output circuits shall be provided with a ground-fault protection
    device or system that complies with (1) through (3):

    (1) Detects a ground fault.

    (2) Indicates that a ground fault has occurred

    (3) Automatically disconnects all conductors or causes the
    inverter or charge controller connected to the faulted
    circuit to automatically cease supplying power to output
    circuits.

    (D) The photovoltaic source conductors shall consist of the
    following:

    (1) Nonmetallic jacketed multiconductor cables

    (2) Conductors installed in raceways, or

    (3) Conductors listed and identified as Photovoltaic (PV)
    Wire installed as exposed, single conductors.

    (E) The photovoltaic power system direct-current circuits
    shall be permitted to be used with ungrounded battery systems
    complying with 690.71(G).

    (F) The photovoltaic power source shall be labeled with the
    following warning at each junction box, combiner box, disconnect
    disconnect,
    and device where energized, ungrounded circuits
    may be exposed during service:

    WARNING
    ELECTRIC SHOCK HAZARD.
    THE DC CONDUCTORS OF THIS
    PHOTOVOLTAIC SYSTEM ARE UNGROUNDED
    AND MAY BE ENERGIZED.

    (G) The inverters or charge controllers used in systems
    with ungrounded photovoltaic source and output circuits
    shall be listed for the purpose.

  4. #4
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    I know the code allows ungrounded systems, but I haven't been able to find a listed inverter (in the US) that is ungrounded.

    I'm responding to an RFP now that asked for ungrounded PV, but I have to tell them they can't have it, because the AHJ will not allow non-UL listed stuff in his jurisdiction.
    Ron

  5. #5
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    Here's a link to a Solar Edge letter of compliance...

    http://www.solaredge.com/files/pdfs/...e-products.pdf

    It's an ETL listing, but still valid.

    This is a small residential job, here's an article about the potential benefits of the Solar Edge system.http://www.solaredge.com/files/pdfs/...-interview.pdf

    As stated, this is a first for me, but seems interesting...I was a bit baffled the first time I looked at the electrical diagram and saw 20 modules in series!

  6. #6
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    Quote Originally Posted by iwire View Post
    This is from the 2008 NEC, be sure to check the 2011 as you are a MA guy.
    Actually, I just looked and there were no changes to 690.35 in the 2011 cycle.

  7. #7
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    Quote Originally Posted by c_picard View Post
    Here's a link to a Solar Edge letter of compliance...
    I was a bit baffled the first time I looked at the electrical diagram and saw 20 modules in series!
    I gather you are using Solar Edge optimizers. I don't know much about these things, but I'm a little unclear as to what it is about using these that requires an ungrounded system.

  8. #8
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    Quote Originally Posted by c_picard View Post
    As stated, this is a first for me, but seems interesting...I was a bit baffled the first time I looked at the electrical diagram and saw 20 modules in series!
    If the NEC would allow 1,000 VDC strings, you'd see longer. I've worked on a number of projects where there were a dozen or more panels in a string, and the only reason there were that few is the 600 volt limit.
    Julie in Austin

    Born to brew, forced to work ...

  9. #9
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    Yeah, I haven't seen documentation just yet, and I'm not sure why the main inverter is set up ungrounded.
    I gather the whole grounding thing is pretty unique to the U.S. Solar Edge is Israeli I think.

    ...a little background; I'm not used to seeing strings of more than 12 likely because it get's so damned cold up here in New England! That and because most of the inverters I've used were limited in their input voltages, for example PV Powered's limit is well below 600Vdc. This job coming up maxes out at 550Vdc, cutting it mighty close.

    I'll post any info I come across, so long as it's not "Confidential and Proprietary"

  10. #10
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    690.47(B), 250.169

    Evidently this is the first SolarEdge inverter installed in the US, so I don't feel so bad about not knowing the specifics on ungrounded systems.

    We got some questionable intel from tech support today when we asked about a GEC requirement....we were told one wasn't needed. We installed one anyhow, and I just looked over 690.47(B), seems like we made the right call.

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