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

Comments

  • crewzercrewzer Posts: 1,830Registered Users, Solar Expert
    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-resources/pdf%20version%20divided%20PV:NEC/APPENDIX%20G.pdf

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

    HTH,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    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?
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    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.
  • System2System2 Posts: 6,290 admin
    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)?
  • BB.BB. Posts: 25,042Super Moderators admin
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Posts: 1,830Registered Users, Solar Expert
    Re: PV Panel Grounding and the NEC?

    Greg,

    I apologize for not really reading your OP. :blush: 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. :roll:

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

    HTH,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    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.
  • BB.BB. Posts: 25,042Super Moderators admin
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Posts: 1,830Registered Users, Solar Expert
    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
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?

    Nice info, guys. Thanks!
    There's always more to this stuff than meets the eye, isn't there?
    I'm grateful for forums like this. Keeps me in line. :-)
    Greg
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?
    "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."

    Does anyone know where to purchase the ILSCO GBL4 DBT or the Burndy CL50-DB-T ground lugs without having to pay an arm and a leg for them? :confused:
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: PV Panel Grounding and the NEC?

    try our forum host at:
    http://store.solar-electric.com/gbdbtsopagrl.html
    it's on sale too!:D
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?

    The cheapest place I found so far is here:

    http://www.backwoodssolar.com/

    They have 10 for $35 dollars but that is still kind of expensive for some lugs. :roll:
  • icarusicarus Posts: 5,070Super Moderators admin
    Re: PV Panel Grounding and the NEC?

    It seems that sitting down and having lunch with your inspector, or a beer after hours can pay big dividends. I'm not advocating bribery here, buy my relationships with inspectors over the year has been great because we spent the time getting to know each other(s) and learning to toss ideas off one another to come to compromises over the years that meet the spirit of codes if not the letter.

    In this case, a conversation with the inspector, to convince him why grounding through the frames and the unistrut is acceptable. In my mind the suspect parts are always the bolts, nuts, screws etc that are making up the bonds.

    In smaller, lower voltage arrays I don't see what the big life safety issue is. The life safety issues should always be the primary concern. I'm not competent to comment on higher voltage arrays. Protection of the hardware very secondary. Every once in a while I came across a real conflict between the two in the building business.

    Just my two cents worth.

    Icarus
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?
    icarus wrote: »
    In smaller, lower voltage arrays I don't see what the big life safety issue is.
    Just my two cents worth.

    Icarus

    My thoughts exactly with my 12 volt non-grid-tie system.
    I have everything well grounded, but it's in hope of preventing lightening damage, not out of concern for someone getting electrocuted from touching a panel frame. Of course I have the inverters and their AC outputs etc all tied in to the same ground, both for personal safety and lightening protection. :)

    Wayne
  • BB.BB. Posts: 25,042Super Moderators admin
    Re: PV Panel Grounding and the NEC?

    The theory with UL type safety codes was that grounding connections had to be only for grounding--and could not be "incidental safety grounding" from, for example, mounting hardware.

    UL did not want the safety ground to be "accidentally" lifted while taking something apart. We could share a safety ground with other grounds--but it had to be double nut'ed... The safety ground plus nut, then more wires and nuts--so the safety ground was the last to be removed--and it required a separate operation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?

    Interesting - - and makes sense. Thanks BB.
    My "equipment" ground cable goes right into the earth and is bonded underground, along with the 4 PV grounds (one off each of the 4 lowest points of the single, all heavy industrial, non-anodized aluminum, one piece welded rack and go straight down into the earth), to two separate ground plates which are also bonded together underground. All stainless fasteners throughout. Surely that should be enough for a 12 volt system ??
  • BB.BB. Posts: 25,042Super Moderators admin
    Re: PV Panel Grounding and the NEC?

    Wayne,

    There is really no such thing as non-anodized aluminum.

    Low alloy and pure Aluminum "self anodizes" or corrodes at surface and creates a very hard water and oxygen resistant surface. (high alloy aluminums also corrodes at the surface, but instead does not create a sealed surface--so requires chemical anodizing to create the protective layer).
    Aluminium oxide is an electrical insulator but has a relatively high thermal conductivity (40 W/m K). In its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools.[3]
    Aluminium oxide is responsible for metallic aluminium's resistance to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin passivation layer of alumina quickly forms on any exposed aluminium surface. This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as aluminium bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. The alumina generated by anodising is typically amorphous, but discharge assisted oxidation processes such as plasma electrolytic oxidation result in a significant proportion of crystalline alumina in the coating, enhancing its hardness.

    So, in terms of getting a good 12 volt DC electrical connection with aluminum--it is pretty iffy. Unless you use hardware designed for the task (and maybe some protective compounds at each joint to keep out oxygen/water)--I would guess that the joints will eventually go high resistance.

    But--if you are doing this for lightning protection--then it should have high enough voltage to punch through the oxide layer and pass to ground.

    I am not sure from your post---Do you have aluminum in direct contact with the ground? If so, perhaps you should dig into the ground a bit around the aluminum and see if you have any electrolytic corrosion...

    If so, you should probably look at zinc or magnesium sacrificial anodes to protect the aluminum structure.

    Aluminum buried with copper ground wire/rods is setup for a nice battery--with the aluminum being the sacrificial material (probably a lot of the issue will depend on the chemistry of your soil).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?

    Sorry, what I meant was aluminum not anodized at the factory and after 9 months out in the weather, still shiny bright. All cables and wires are copper and the ground plates are CSA. All gnd connections to the aluminum rack are through stainless, nothing but stainless coated with no-ox touches the aluminum. I expect that in time I'll have to rework the connections, but so far so good and keeping a close eye on them. So far, FLUKE 75 showing resistance at the gnd connections too low to reliably measure. But for sure I will be keeping an eye on then.
    Thanks for your comments, they are appreciated. It's always good to share information and ideas.
    By the way, no aluminum anywhere is in direct contact with earth or soil, as it's mounted high on south side of shed.
    Wayne
  • BB.BB. Posts: 25,042Super Moderators admin
    Re: PV Panel Grounding and the NEC?

    Sounds like you did it 100% right Wayne!

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?

    Thanks a lot Bill, I always appreciate your comments, always helpful.
    I've learned so much from this form, it's awesome!
    Cheers
    Wayne
  • System2System2 Posts: 6,290 admin
    Re: PV Panel Grounding and the NEC?
    "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."

    Guys, about the lugs themselves, does anyone know where to purchase the ILSCO GBL4 DBT or the Burndy CL50-DB-T ground lugs without having to pay an arm and a leg for them? :confused:
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: PV Panel Grounding and the NEC?

    adiel,
    why are you being so concerned of a possible few dollar savings on the proper connectors in light of spending huge amounts for the pvs, etc.? it's one thing to shop around, but i think your quest may be a bit redundant in the overall picture. what's worse is you expect us to pursue your quest for you. if we knew we'd have said so in the beginning when you already asked that question. it may be possible it may not be found too much cheaper than you have already found it to be to make any real difference.
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