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Thread: PV Panel Grounding and the NEC?

  1. #1
    gregmk Guest

    Question PV Panel Grounding and the NEC?

    I'm doing a ground install, with 36 Sharp panels mounted on galv. steel UniStruts, which in turn are strapped onto 1.5" galv. pipe rails teed onto the same type pipes cemented into the ground.

    I could put grounding lugs onto the holes provided in the panels, but I'd like to just put a bolt with star washers through the grounding holes and bolt directly to the UniStruts for a good ground. This would provide a ground path throughout the panels, struts, and pipes. Then attach a 8gauge solid copper wire from the pipes to a grounding rod, thereby grounding the entire system. Does this sound just as reasonable as using grounding lugs? It seems to me simpler and less costly.

    The Sharp Manual says: " Each photovoltaic module has a hole in the side frame for either a bolt, nut and washer grounding the module to the frame, a ground lug fastened by bolt or screw, or an appropriate screw (hardware not
    provided). Installation for wiring shall be in accordance with the NEC and grounding method shall comply with the NEC, article 250."

    The first option mentioned sounds like what I'd like to do. Does anyone know if that's consistent with the NEC's article 250? I can't find that article on the internet, so I'm not sure what it requires.
    Thanks all.
    Greg

  2. #2

    Lightbulb Re: PV Panel Grounding and the NEC?

    You may find John Wiles' discussion on this very topic to be of interest. See: http://www.nmsu.edu/%7Etdi/pdf-resou...PENDIX%20G.pdf

    And, here's a link to the lugs and additional info: http://store.solar-electric.com/gbdbtsopagrl.html

    HTH,
    Jim / crewzer
    120618: System off-line for a while...

  3. #3
    gregmk Guest

    Default Re: PV Panel Grounding and the NEC?

    I read John Wiles article about grounding, and it doesn't sound like the use of grounding lugs is required. My thinking is that roof-mount systems typically use lugs because there may not be a consistent grounding on the racking system. With a ground-mount system made of steel, it would be easy to bolt through the grounding hole of the panel (using a star washer to score the panel) directly to the steel struts to have continuity through the whole mounting system (which then need to be grounded via a grounding wire to the grounding electrode. I just don't see why I should buy 36 grounding lugs at $5 a piece and maybe 150 feet of grounding wire when the mounting structure itself serves to provide the continuous ground. Any thoughts out there?

  4. #4
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    Default Re: PV Panel Grounding and the NEC?

    NEC code requires each and every panel have its own ground bond, mounting hardware does not meet that requirement as the panels are coated frames.

    Ground bonds use screws that dig into the frame for contract, nut and bolts used for racking are not a NEC approved for grounding as they may not perice the coating.

  5. #5
    gregmk Guest

    Default Re: PV Panel Grounding and the NEC?

    Hey, Solar Guppy:
    I understand what you're saying, but there's a couple things...

    >>Ground bonds use screws that dig into the frame for contract, nut and bolts used for racking are not a NEC approved for grounding as they may not perice the coating.<<

    The Sharp 216W panels, according to their manual, have a grounding hole that's large enough that it requires a bolt and nut with a star washer to score the panel, even when using a grounding lug. Apparently, that star washer is the only electrical connection between the panels and the grounding lug - via the bolt (since the grounding lug is against the panel coating).

    >>NEC code requires each and every panel have its own ground bond, mounting hardware does not meet that requirement as the panels are coated frames.

    If the bolt with the star washer pierces the coated framing for the grounding lug, wouldn't it do the same if the bolt was bolted directly to the UniStrut (instead of the grounding lug)?

  6. #6
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    Default Re: PV Panel Grounding and the NEC?

    In a previous life, the NEC/NRTL's would not allow mounting hardware to double as safety grounds. Their argument was that they wanted the person to have to physically undo the safety ground rather than "accidentally" undo the safety ground during normal servicing operations (for example, I have a ground wire coming in from the cord to a power supply and I want to use the PS mounting screw as the safety ground--NEC/NRTL's will not allow).

    So no matter how many screws and washers I had holding things together, I still had the "silly" ground wire bolted to a piece of sheet metal.

    In some cases, we could get away with using a mounting stud also as a safety ground, but it had to be "double nutted"--For example, the first nut held down the power supply board and the second nut only held down the green wire.

    In the end, the local inspector may or may not notice (or even care about) the "alternate grounding". But no matter what the inspector approves (by the way, the inspector is never liable for "faulty" inspections), your exposure is (typically) with home owner's insurance--if there is ever a problem (lighting strike/fire/damage, somebody gets shocked/injured/killed) and the insurance investigator is looking for a reason not to payout the claim... You can bet your bottom dollar that they will be reviewing your installation with a fine toothed comb.

    -Bill

  7. #7

    Default Re: PV Panel Grounding and the NEC?

    Greg,

    I apologize for not really reading your OP. NEC Article 250.136(A) considers electrical equipment secured to grounded metal supports i/a/w NEC 250.134 to be “effectively grounded”. So, it seems to me that what you’re proposing can be done.

    Unfortunately, 250.134 cross-references so many other NEC Articles (i.e., 250.32, 250.102, 250.118, 250.140, 250.142, 250.168 ) that it’s beyond the scope of a post like this to go into all of them.

    The following links to additional articles by Wiles might be useful. It might also be worth your while to visit your local library and peruse through NEC 250.134, 250.136, and the ensuing thorny paths.

    http://www.nmsu.edu/~tdi/pdf-resources/CC102.pdf
    http://www.nmsu.edu/~tdi/pdf-resources/CC103.pdf

    HTH,
    Jim / crewzer
    120618: System off-line for a while...

  8. #8
    gregmk Guest

    Default Re: PV Panel Grounding and the NEC?

    Hi, Bill:
    <<Their argument was that they wanted the person to have to physically undo the safety ground rather than "accidentally" undo the safety ground during normal servicing operations>>

    That makes perfect sense, Bill. I can see the point.

    So, another question I have would be related to the type of grounding lug. Home depot has aluminum grounding lugs with a steel set screw. It looks exactly like the typical solar grounding lugs that sell for nearly $5 a piece. Home Depot's, however, are only about a buck a piece. Any reason why those won't due? I see the typical solar ones are tin plated. I find that odd, as tin is one of the worst metal conductors. Aluminum is much farther up the list, in terms of conductivity. I considered electrolysis being an issue, but bolting an aluminum lug to an anodized aluminum panel negates that. And the copper wire going through the lug shouldn't be any more dissimilar than copper going through the tin plate.

  9. #9
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    Default Re: PV Panel Grounding and the NEC?

    "Pure" Aluminum has a very nasty habit of forming an oxide layer that is both gas/water impermeable (good--prevents corrosion) and electrically insulating (bad--poor connections). Aluminum also "cold creeps" (moves away from high stress points like physical connections).

    Regarding surface materials, you have to look at the potential of the different metals to see if they are compatible or not (I have tossed all my stuff that had the standard metals and their electro-negative potentials). Typically, you did not want to select two metals that had large potentials (<0.2 volts?) so that when joined together, they don't act like a battery and force corrosion.

    NEC might have a list of the potentials for common metals--the UL regs did. Copper to Aluminum is probably not a good match. You would need a "grease" anti-corrosive compound, high pressures, and hopefully weather sealed to get a "reliable" safety connection.

    -Bill

  10. #10

    Default Re: PV Panel Grounding and the NEC?

    Home Depot's, however, are only about a buck a piece. Any reason why those won't due?
    From the first Wiles reference I cited above:

    "The ILSCO GBL4 DBT, the Burndy CL50-DB-T, and equivalent lugs are tin-plated, lay-in lugs made of solid copper with a stainless-steel screw. They accept a 4 AWG to 14 AWG copper conductor. They are listed for direct burial use (DB) and outdoor use and can be attached to aluminum structures (the tin plate allows this). The much cheaper ILSCO GBL4 lug and the Burndy equivalent look identical but are tin-plated aluminum, have a plated screw, and are not listed for outdoor use."
    HTH,
    Jim / crewzer
    120618: System off-line for a while...

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