Another question, this time about lightning

sub3marathonmansub3marathonman Posts: 300Solar Expert ✭✭✭
I've tried to search the past answers about lightning protection, but I'm still pretty confused.

First, if lightning hits the panels, with the ground wire running inside the conduit aren't you just sending the electricity down into the rest of the system and your house, instead of sending it straight down outside? One electrician said to have a second ground tied in and straight down to the main ground. But then you've got two paths to the same place, one straight and one round-about through all the PV equipment, and I'm not sure how that would work. I do understand about the problem if you use another separate grounding rod and thus have a difference between the two rods.

Second, what happens with the conduit? Is it energized during the strike too? That would seem to be bad. And what about the ground wire inside. Should it be a bare wire to help ground the conduit, or insulated to prevent galvanic corrosion between the copper and the conduit metal?

Or do you just follow the instructions and hope things are never put to the test?

Is there someplace that has a good explanation about this? Some of the answers are way above what I can understand, and some of the theory seems to be debated too. On one post I seem to remember not setting up the grounding wire in a ring, or something to that effect, why would that be?
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Comments

  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Another question, this time about lightning
    Or do you just follow the instructions and hope things are never put to the test?

    Yep--that is usually the best way if you have no other knowledge or experience to work with.

    Your electrician's idea is not bad... Lightning is a "high frequency" phenomenon. So, it is not just "DC Resistance" that governs the flow of lightning current/energy.

    Solid wire has a higher impedance than stranded wire (look up "skin effect"--basically at high frequencies, the current flows on the "skin" of the wire--more strands, more surface area).

    Lots of sharp bends vs few, large diameter bends--again, the few/large diameter bends, has a lower impedance--hence the lightning induce current will follow the lower impedance paths.

    Since they both would end up at the same grounding rod/location, the energy is being "dumped" to the correct place.

    Regarding corrosion impeding lightning flow--The lightning just came through several miles of air--a tiny amount of corrosion is not going to affect the lightning path at all.

    Many times, a direct strike is going to cause extensive damage--no matter what... Proper (usually) single point grounding (or "star connected grounding" where the "ground point connection to the home/equipment is in the center of the star) helps prevent damage from nearby strikes causing equipment damage inside of your home.

    A good place to look for detailed discussions... Look for Lightning + Ham radio web sites. In some ways, very similar problems vs that faced in solar RE (metal "things" up high that attract lighting that are connected to devices inside of our home).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 7,967Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    I'm going to ignore code here - this is what I would do, having read all the Ham manuals for years, and living in a low strike area (So Calif).

    The fast pulse lighting strike is something like a toy "slot car" It does not like to change direction. I would follow the conduit down from the roof, and most likely at the "bend" or box, where it changes direction, I would supply a BETTER conductor down to the earth, where I would pound in a "copper plated" steel ground rod. This keeps the pulse outside, rather than directing the strike inside, thru your inverter and to the power meter's ground wire.

    But code is different, and after the inspector leaves, I doubt he's coming back.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
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  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Another question, this time about lightning

    Also a warning... I agree that sometimes code can cause worst problems with respect to lightning (the NEC was sometimes terrible with respect to DC systems too).

    However, sometimes you can do worse by mixing suggestions from different techniques... And end up with a worst solution by combining parts from two different methods vs following a weaker single methodology.

    My suggestion, rather than asking general questions about lightning--give a real setup (10 panels on roof with GT and AC mains on rocky ground with 5 panels + 40' wind turbine on an off-grid backup system in Florida -- lighting capital of the US, if not the world).

    Solar Guppy is in the middle of Florida--and he has some very interesting ideas about lightning control... And, from what I have read, his theory is strong and demonstrated by good results (no lightning damage to his systems/home). SG's lightning amelioration practices are just about the exact opposite of NEC's best practices code requirements.

    Sub--Give an example of the problem you would like to solve--then everyone can give their suggestions/experience.

    I too live in a low lightning area--so I have no direct experience testing my theories vs direct strikes (although, I never heard of any problems with my telephony/network system designs from the field--but a good lighting control "system" would keep the energy from my equipment).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EcnerwalEcnerwal Posts: 101Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    There used to be a very good treatise about lightning and solar systems on this very site, but it's gone now, or moved and well hidden. WindSun? It was under the not very obvious page name "test.html" according to my bookmark for it.
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    Search Solar Guppys posts. If memory serves he wrote the treatise.

    Tony
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Another question, this time about lightning

    Here is one Solar Guppy "oldie but goodie" post on grounding:
    Living in the lightning capital of the US, I never understood the concept of grounding the PV frames, that's a couple hundred square feet of lightning attraction that at best will vaporize the ground wire and at worst cause your home to burn to the ground.

    PV cells don't touch the frame, the Jbox or MC box doesn't touch the frame, there is no way a panel defect can energize the frame.

    One of the nice things about regulations, is that is ALWAYS up to the local inspectors to what is acceptable, regardless of what the NEC has written.

    In all my installations, with full written approval of the local inspectors my frames are left un-bonded to anything. the last thing I want is to be waving a flag at the next bolt of lightning to say HIT ME HERE and that is exactly what grounding the frames do.

    Each and every year I get about 20-30 hits within a few hundred feet of my home. Last year the street light got nailed and took out 2 inverters by backfeeding in the mains. That street light is less than 30 ft from the solar panels .. so I think its safe to say my preference saved my array/house from a direct hit!

    I'm not sure how John Wiles became an expert in lighting issues and best practices of wiring to write regulations for the NEC, but where he lives I doubt he see the activity in his lifetime I see in one rainy season here in central Florida.

    Part of a long thread discussing "What the Heck is NEC doing?"...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: Another question, this time about lightning

    Sub,

    If your getting permitted from polk county, Jim Legee is the head electrical guy and is the one that signed off on me NOT grounding the frames. He is a very smart, down to earth type and understands exactly the issue I was avoiding

    If you haven't yet, setup a meeting with him to review you PV plans , you can contact him at the Bartow office of the building department ( polk county ). He is the one that will approve the application and will be the one for final sign off on the permit. When I expanded my system in 2007, he brought all the inspectors out to check things out ... 4-5 inspectors milling my about my solar stuff was fun :)

    The system is in its 6th year, with hundred or so strikes near by every year, never once has the house or panels been hit, while many nearby objects at similar or lower heights have been.

    My home is well exposed as well, I'm near the top of a 120 foot hill ( mountain in Florida ), I can see 30 miles to the east so its not exactly a low profile area lightning wise.

    SG
  • n3qikn3qik Posts: 741Solar Expert ✭✭
    Re: Another question, this time about lightning

    I also went against NEC code. I have 2 groups of panels, one on the house and a second on a shed 120 feet from the house. Per NEC, I needed a ground wire from the shed to the house that would have to be in a conduit to be tied at my house panel. Now if there was a strike at the shed, it would also enter the house via the ground wire.:cry:

    What I did was to ground the frames only at the shed to a local rod at the shed. This would keep most of the strike at the shed. Same with the ones on the house. I am using Unisolar panels, the thin-film cells are at if not under the frames. With the cells this close, there is a good chance if the frames get hit it will arc over to the cell and then on to the charge controller. If using Si panels, there is a larger gap so Solar Guppy's way would work.

    Also, I am using 2 Delta DC surge protectors to slow the sting down.

    This is for near strikes only, if a direct strike, all bets are off for what ever you do.
  • WindsunWindsun Posts: 1,164Solar Expert ✭✭
    Re: Another question, this time about lightning
    Ecnerwal wrote: »
    There used to be a very good treatise about lightning and solar systems on this very site, but it's gone now, or moved and well hidden. WindSun? It was under the not very obvious page name "test.html" according to my bookmark for it.

    http://www.windsun.com/Photovolaic_Systems/Lightning_Protection.htm

    I took it off line to update it with a bunch of new info, and never got it finished. I put it back up for now, but bear in mind that it was written pretty much only for off-grid systems, and (2) it needs some updating with new info.

    And BTW, any corrections or comments on it are welcome.

    Solar Guppy and I differ on the grounding of panel frames. Almost every off grid system we have seen with a blown inverter has had ungrounded or poorly grounded (or in one case, grounded per NEC...).
    Per NEC, I needed a ground wire from the shed to the house that would have to be in a conduit to be tied at my house panel. Now if there was a strike at the shed, it would also enter the house via the ground wire.:cry:

    ...Is a recipe for disaster IMO.

    One possible reason that we differ with Guppy is that where he lives, you can actually get a good ground in most cases. Here in the SW (where that article was mostly written for), it is often very difficult. Our own system on our remote house has 4 10 foot ground rods, and still would not meet current specs it it had to meet specs.
  • sub3marathonmansub3marathonman Posts: 300Solar Expert ✭✭✭
    Re: Another question, this time about lightning
    Windsun wrote: »
    http://www.windsun.com/Photovolaic_Systems/Lightning_Protection.htm


    Solar Guppy and I differ on the grounding of panel frames. Almost every off grid system we have seen with a blown inverter has had ungrounded or poorly grounded (or in one case, grounded per NEC...).


    ...Is a recipe for disaster IMO.

    One possible reason that we differ with Guppy is that where he lives, you can actually get a good ground in most cases. Here in the SW (where that article was mostly written for), it is often very difficult. Our own system on our remote house has 4 10 foot ground rods, and still would not meet current specs it it had to meet specs.

    That is what makes things so confusing! And it looks like some advice is great where it rains but terrible for the desert. But a novice has a tough time figuring out what is right. And, a wrong decision could be financial disaster.

    I did wonder, and Solar Guppy commented on it, whether or not a lightning strike would melt some little copper wire out there. It seems like you would need the biggest cable you could get to really protect things. And, from what everybody says, even then it is questionable.

    Solar Guppy has been a great help to me, especially since we live close by, so when he's saying something I'm really listening. But still, it just seems so counterintuitive to leave something ungrounded.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: Another question, this time about lightning
    Solar Guppy has been a great help to me, especially since we live close by, so when he's saying something I'm really listening. But still, it just seems so counterintuitive to leave something ungrounded.

    Does one ground roof shingles? how about the vents stacks for the plumbing, or how about a fireplace vent/chimney?, what about the ridge vent, roof vents or drip edge which circles the entire home?

    No to all of the above ... so what makes PV frames any different? Answer, some guy named John Wiles ...

    One needs to understand, grounding of the frames is a NEC thing and it has zero factual field data to support "its" reasoning , which has been described as IF the frames somehow become energized AND someone touches the frames there is some hazard. There is no possible way the frames can become energized by a fault in the PV panel and it would require double faults on the wiring AND a path from the person touching the fault to ground ...

    Lightning doesn't think, its simply follow the path with the least resistance to ground. If someone wants to paint a bulls-eye on there house, then follow the the NEC code on frame grounding, I choose to use my education an knowledge and explained this to the building inspector, he agreed and I'm permit approved on all my solar.

    What people may not know is the NEC is written by only a few people, its geared toward safety, not performance or any other concerns and has NO, read ZERO input for things like lightning suppression.

    Most importantly the NEC is only a GUIDE, not a requirement, to assist local building inspectors in permitting and approving safe electrical systems. Municipal, county and city building departments and trumping them all the local Fire chief have the actual authority for approving a permitted project, if one has some time look into what it takes to get something approved for NewYork City, they literally have there own rules on just about everything
    Windsun wrote: »
    http://www.windsun.com/Photovolaic_Systems/Lightning_Protection.htm
    Solar Guppy and I differ on the grounding of panel frames. Almost every off grid system we have seen with a blown inverter has had ungrounded or poorly grounded (or in one case, grounded per NEC...).


    ...Is a recipe for disaster IMO.specs.

    My references to frame grounding relate to roof mounted arrays, not ground mount. As to inverters being fried, that's an entirely different topic, at least from this EE prospective.

    The most likely cause of failure is IMP induced voltages in wiring, I get that every year. Any length of wire that's 50+ feet or more, especially if its in a conduit in the ground is going to be a pick-up and inject large voltage transients into what ever is connected to the wire.

    I loose something every year, usually something on the RS232 or Ethernet connections within the house. At my last home, the wiring from the front gate would blown up the controller 1-2x year when ever there is a near by strike. Frame Grounding will have zero migration on this as when the hit happens, the area near the strike is for a few milliseconds raised in voltage and the wiring running in the ground get coupled into the wiring.

    Poor soil ( grounding wise ) of the southwest will make this even more of an issue and while traveling in the ground will find the path to ground may be the inverters inputs ( wiring to the array ) is much better than the rocky soil its bouncing around and thru.
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    SG,

    You pose an interesting question. We live in a very high lightning area and have very difficult grounding issues. We always would ground things (antennas) with a wire directly from the antenna into the lake! (these are off grid buildings) The generators were (are) also bonded with a wire sent into the lake.

    When I built my new house someone suggested that that was a very poor idea because in the event of a strike IN the lake near me, the strike would find that wire, and return up the ground into the building. We have used this system for ~60 years and have never had a problem. In the new house, I sent a ground wire from the PV frames, to the steel chimney, since it sticks up way higher than any surrounding metal, picking up the radio antenna pole, down the side of the building, picking up the breaker box neutral/ground and then 100' of bare copper laying on the ground, terminating on a ground rod driven into a small gravel bed. (We are on a granite island, covered with a few inches of duff, with boulders and small pockets of gravel,, driving a ground rod is almost impossible).

    I have been inclined to undo the roof top panels and let them float. I would keep the chimney bonded, but cast loose the breaker box ground. The idea would be that a lightning strike near the chimney would transfer down the wire to ground and would not have the path to the breakers. I would then run a separate, ( and separated!) ground wire from the breaker panel,, either into a similar ground pit, or into the lake.

    Any opinions?

    Tony

    PS You are right, we don't ground gutters, or flashings or skylight frames, or any other metal on our roofs. Or how about standing seam steel or copper roofing? Many of my buildings have steel roofs.
  • WindsunWindsun Posts: 1,164Solar Expert ✭✭
    Re: Another question, this time about lightning
    Does one ground roof shingles? how about the vents stacks for the plumbing, or how about a fireplace vent/chimney?, what about the ridge vent, roof vents or drip edge which circles the entire home?
    All mine are plastic, tile, or wood, so they don't ground very well ;)
    One needs to understand, grounding of the frames is a NEC thing and it has zero factual field data to support "its" reasoning , which has been described as IF the frames somehow become energized AND someone touches the frames there is some hazard. There is no possible way the frames can become energized by a fault in the PV panel and it would require double faults on the wiring AND a path from the person touching the fault to ground ...

    What people may not know is the NEC is written by only a few people, its geared toward safety, not performance or any other concerns and has NO, read ZERO input for things like lightning suppression.

    I have never understood the purpose of grounding frames from an NEC perspective. But these are the same folks that gave us MC4 connectors, and those 18-inch appliance cords back a decade or two ago...
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Another question, this time about lightning

    Historically, isn't lightning protection for a home/building based on installing lightning rods to intercept the energy and direct it way from the structure? Then it would not matter if gutters, roof vents, etc. are then less of an issue.

    In our trip around the southwest last fall--every major structure (museum, visitor centers, etc.) stuck out in the middle of nowhere (on top of a hill, etc.), was bristling with pointed rods tied together with copper cable.

    There are many things that one can do to reduce the induction of electrical energy into electronic equipment--basically all of the same things that are done to reduce radio frequency interference.

    Keeping wire runs (+/-, hot/neutral) parallel (or even twisted a few times per foot ideally), running crossing wire runs at 90 degrees (say house wiring hear lightning grounding cable), putting everything in a metal shield (conduit, braid, metal cabinets) to prevent energy entering in--and also, surprisingly--10'+ of the capacitance of braid (and conduit?) does a pretty good job of knocking out the higher frequencies. Avoid circular runs of wire--if slack must be stored, make the bundle in a figure "8".

    Keep wire terminals close together. Avoid turning common differential signals (such as +/- or Hot/Neutral pairs) into common mode (don't ground one lead such as the "-" or the "neutral" wires).

    Don't multiple reference/ground a system... Don't run your negative lead from the battery shed and ground it both at the shed and the wind turbine tower. Your two points will turn a nearby strike into high energy induce into the negative lead (you are picking up the voltage gradient across the 100' of earth from the tower to the shed from the dissipation of energy through the earth).

    I would guess, much of the above can help with nearby strikes... However, nothing much helps with a direct hit--basically just replace the blown components.

    And what do you do with a huge array of "metal plates" that must be open to the sun--and therefore susceptible to lightning... I do not know... I could guess and suggest that I would:
    • install lightning rods every 10-20 feet near the array (no shadows)
    • ground the frames, float the +/-, run the DC feed to the inverter or charge controllers through at least 10' of grounded conduit/metal jacket
    • keep all +/- pairs tied together... Don't run a "big open circle" when connecting all of the panels together (may take more wire to run this way).
    • run a pair of lightning surge suppressors at the DC input to the Inverter (inverter, suppressors, and conduit should be right at the "entrance of the building" and "away" / cross at 90 degrees from all other in-building cabling to reduce the chance of lightning energy from entering the building and getting "in" other cabling--power, network, phone, etc.).
    My theory is to 1) divert the energy away from my wiring/exterior devices, 2) capture/divert the energy away from the first "in building" device (surge suppressors), and 3) limit damage to the first isolation device (GT Inverter) and avoid damage/hazards to the occupants of the building and other in-building devices.

    The above highlights what I humbly believe to be a serious flaw in every DC Solar Charge Controller / DC Off-Grid system out there (again, in my very humble opinion).

    With a DC Charge Controller (PWM, MPPT, etc.--at least all those I am aware off)--there is no isolation. So the NEC requirements of grounding the negative battery lead (or the "-" of a Grid Tied Inverter Input), should make it more likely to get lighting damage in/around the system. And even if you use surge suppressors, there still will be a pulse of energy sent through the system because there is no isolation after the suppressors (which probably need hundreds of volts to "fire"). And why I like to use a good TSW inverter between the DC and AC devices--to provide better isolation (vs going with DC only devices).

    I "love" GT Inverters because they have electrical isolation (at least 1,800 volts AC IIRC) between their "dangerous" DC input and the relatively benign AC wiring of the home (I don't like the NEC requirement for "ground fault" referencing/wiring of the panels). This makes it much easier to address the excess voltage and current issues on the DC side of the GT inverter (surge suppressors, capacitive coupling of conduit, everything is differential mode signal/power--which is easier to protect against high frequency surge and dump the common mode energy from the lightning to earth through a proper grounding system).

    My two cents for discussion purposes only--not a recommendation for anyone to go out there and violate NEC and Building Codes based on the above.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • homerramirezhomerramirez Posts: 102Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    Solar Guppy has a lot of experience on this subjet and yet I disagree with his opinion, attic fans , gutters, roof shingles do not produce electricity, solar panels do, in my short experience with solar panels, after installed my panels on the roof I notice lot of dirt on the panels glass, (we do not live in high dust area), so I knew that it was STATIC what made dust particles stick to the glass, I had to run to Home Depot and got #6 wire to ground my roof mounted panel to a 8ft. ground rod , I do not want to share it with grid tied ground rod. since I ground the panels dust on that magnitude is not an issue.

    The fact is , static on the air atracts electricity (lightning) , About 5 yrs. ago I'd wach a tv program on PBS about lightning, there was some teen girs in an open area on a cloudy day recording, suddently her hair was sticking up, and what they thought was funny end up in tragedy....

    Again , static atracts electricity, lightning will take the shortest path to ground.

    P.S. sorry about the story but happen as shown on PBS.
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Another question, this time about lightning

    Remember too that the earth has a natural electrostatic field that is around a couple hundred volts per meter...

    In theory, stick panels on a 2 story roof (~10 meters), that could charge ungrounded (insulated) metal upwards of 2,000 volts with respect to ground.

    And you can get ~50,000 volts per meter under a thunderstorm (in theory--500,000 volts on ungrounded metal structures).

    So, you are between a rock and a hard space here...

    If you are working on your ungrounded array framework, you could get shocked by several thousand volts (powered by the capacitance of the frames). Won't kill you--but could give you a nasty surprise.

    On the other hand, in a lighting storm, grounding the frames 10 meters up just put a big "strike me" sign on the metal frames because they are now 500,000 volts of "opposite charge" with respect to the local earth field.

    Floating the DC Panel connections vs earth grounding now becomes an issue--if you ground them, they are 500,000 volts below earth potential when on the roof. Float them, then what is the common mode voltage offset... To offset static charge, I have always used 10-20 megOhm resistors--That will certainly bleed off any charges to ground--but then it pulls the panels to ground reference--making them a nice lightning target.

    So--what are peoples opinions about placing multiple lightning rods (heavily grounded pointed rods) above the "north" side of the arrays and grounding the array frames?

    Solar Guppy's practice of not earth grounding (and if I remember correctly), unplugging the arrays when lighting is in the area would seem to reduce the entire potential for lightning strikes or damage...

    However, IIRC, SG's arrays are either ground mounted (which is probably framed grounded to earth through the metal/concrete mounting structure) or on a 1 story roof (probably "insulated" by wood and composite roof--which would be debatable insulation when the roof is wet).

    Vs. those people with solar panels on multistory buildings--which would seem to be much more susceptible to strikes/damage.

    Just to put the earth's field into prospective, helicopters carrying external loads beneath them on cables can draw upwards of a 12" electric spark if the loads/cable end is not grounded before a ground crew starts manipulating the load/hook. That is, very roughly, upwards of 700,000 volts in dry air.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    this does become a touchy subject and the nec is going far in their quest to address everything and they windup splitting hairs that they have no business splitting. i respect sg's opinions on the matter and we have discussed them before, but i too lean on grounding. if that grounding isn't good or compromised in some ways even though within wiles' rules on the matter, it could be worse than no ground at all. i contend that if a ground requirement rule makes it a worse condition of safety, that i will not honor their rule on it. wiles is by no means a lightning expert and i too addressed him prior to the latest nec update. he made it worse, in my opinion, than having no ground at all and many here saw my thoughts on the subject matter.
    a static discharge can blow out one's sensitive electronics in a solar setup and that static can draw a lightning strike so i elect to directly ground my us64 frames, but not the +/- wires themselves. with my controller my battery - is not to be directly connected to my pv -, but if i wanted to i could use methods of piping excessive voltages from those leads to ground with diodes (due to peak inverse voltage) or with movs and gas discharge methods. as mine is presently, i use a diode across both the pv + and - leads. as it is, any reverse v differential between those pv leads that exceed 50v are somewhat shorted out to each other, but i don't have them connected to ground. my system isn't up high on the house and isn't large so i'm not going to worry about it too much. i also have my large grounding system that would draw off most of anything present as well because of my many antennas/lightning rods.
    wiles tries to oversimplify and categorize everything and he can't. many cities and towns make the nec, and thusly wiles, law for their place for the lack of something better from somebody better qualified and this one size fits all ADVICE from the nec can be dangerous to follow at times even if one interprets it as it was intended. nothing is simple or identical in all cases as wiles tries to make it, even beyond if one argues its necessity. symbolically, i see what he does as having a cop outside your locked front door while leaving full access to the thief from the open backdoor he requires you to have.
  • System2System2 Posts: 6,290 admin
    Re: Another question, this time about lightning

    Just a little tidbit about lightning rods. Lightning rods have sharp points on them. The points act as a collector to deionize the charged air around them which decreases the conductivity of the air near the rods. The air that is farther away from the lightning arrestors is still ionized and a better conductor so if lightning strikes it will tend to go where the air is more conductive and stay away from the lightning arrestors. If you take a vandegraff generator that is shooting sparks all over the place and approach it holding a sharp pin in your hand, you can touch it with the pin with no arcing because the sharp point discharges the air between the genrator and you until your pin makes contact with the generator. If you don't have a pin and just touch the generator with your hand, you are in for a shocking experience.
    This has been a very interesting thread. Running ground wires between everything seems like it will be hard on equipment during a lightning storm.

    George
  • KamalaKamala Posts: 452Solar Expert
    Re: Another question, this time about lightning

    I have been wrestling with this issue for some time. That issue being, how to eliminate the threat of damage (in a range of a few hundred dollars to DEATH!) from extreme weather phenomena. I have come to the conclusion that this goal CANNOT be achieved. The threat can only be mildly ameliorated.

    Extreme weather events such as hurricanes, blizzards, and thunderstorms can do much damage. They are somewhat predictable. A thunderstorm can spawn less predictable, yet even more catastrophic phenomena, such as lightning and, the king of absolute localized destruction, tornadoes.

    Occasionally, earthquakes might be more destructive than tornadoes. In my estimation, the predictability of either occurring is almost equal. But "quakes" are relatively infrequent compared to tornadoes. The problem being, how does one prepare for all the potential destruction that the Earth may send your way?

    Hurricane: board up, run away.
    Blizzard: store fuel and food. hunker down.

    Earthquake: architects.

    Tornadoes: hole in the ground.

    Lightning: Something higher than you to take the strike. Then curl up, probably KYAGB, to prevent ground currents from taking a long resistive path through your body ( think I^2*R) and relax.

    Tony, tall trees around your place will take the hit. The problem is how that energy might be dispersed on the ground. I think that's why your lake ground has worked for so long. Big mass.

    Just rambling.

    K
  • russruss Posts: 593Solar Expert
    Re: Another question, this time about lightning

    Earthquake - The building code here in Turkey is quite strict (if followed). There is more reinforcing steel in my house than industrial structures many places.

    The inspection system is strong - again if it is adhered to. İn the case of big construction companies they often have a sister company to do the inspection. İf the intent of the company is good then all is well. İf they are shysters then you have a problem.

    For our project (5 homes in a group) the inspection company did a good job which İ am thankful off.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    from kamala,
    "I have come to the conclusion that this goal CANNOT be achieved. The threat can only be mildly ameliorated. The problem being, how does one prepare for all the potential destruction that the Earth may send your way?"

    although higher in price that $200 i think one of these may suffice for all of those possibilities if properly grounded at all 4 corners. then again some diy could possibly bring that inline with that price goal if some materials are on hand.;)
    http://www.tornadosaferoom.com/2person.html
    now i admit it won't do much good if a volcano erupts near it.:cry::p
  • rsl360rsl360 Posts: 14Registered Users
    Re: Another question, this time about lightning

    I'll probably regret jumping into this.

    Over some time, I've seen that there seem to be two contradictory points of view on how lightning works. One is that big heavy conductors and lightning rods will carry lightning away, but also attract lightning. Related to this is the thought that big metal objects attract lightning. The other is a little more complicated, but comes down to the idea that pointy objects, (lightning rods), dissipate static, which prevents the attraction of the leaders that lead to lightning strokes. This second theory is the one that led to the idea of the fuzzy lightning preventers, which look somewhat like a bottle brush. I've seen a lot of these in Florid on top of power lines. By now there should be some data as to how well they work. (or don't) Sailing forums have some opinions on this as well, they also cannot come to a consensus.

    rsl
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    you are correct in that metal lightning rods can attract as well as dissipate even if it becomes a full stroke. we are going on the assumption that there's already a great deal of metal high up (pvs and associated wires). the fact that the metal is there can bring the leaders to it as well as the full stroke. as such i am in the opinion that a ground is needed to attempt to direct this energy should it strike being that it is already attracted. the real cure would be no metal up high, but that's most likely not going to happen for those of us keeping pvs in the best view of old sol as we can.

    as to the fuzzyness of those arrestors, they are attempting to have as much contact with the air as is possible. think of it as many little pointed lightning rods. some use a metal ball instead. it's the extra contact area with the surrounding air they hope to achieve.
  • solar_davesolar_dave Posts: 2,335Solar Expert ✭✭✭✭
    Re: Another question, this time about lightning

    Hmm interesting discussion, Now I get a hint as to what the code guys were talking about with all the heavy grounding they required the installers to use over and above the NEC requirements. They required a huge ground cable to be installed into the incoming water system copper pipe. Still this discussion of not having the panels grounded in compliance with NEC might invalidate any claim I might have to make against the insurance company in the event of a strike. Mostly because it was part of the original design and the code approval.

    Rock and a Hard Place?
  • LostinSpaceLostinSpace Posts: 97Registered Users ✭✭
    This is an old thread, but quite relevant to me. It is one of the better discussions I've come across trying to figure out what to do about lightening on my brand new first time DIY solar system. But I'm still lost. Here is a question in case anyone is still following this thread...

    My ground mount panels are about 50' from the building housing the inverter/cc. That equipment connects to a local ground rod that I drove in next to the building.

    Whether or not I choose to ground my panels, I have installed a lightening arrestor at the combiner box attached to the panel mounts. The arrestor is wired to a ground rod I drove in at the panels.

    QUESTION: Do I run a ground conductor between the two ground rods? Again, 50' apart.


    Qty 24 Sharp 153W poly panels, Midnite MNPV6 combiner, Magnum MS-4448-PAE inverter with RC50 remote, Magnum MMP Mini panel, Midnite Classic 150 charge controller, Qty 32 LiFePO4 72AH cells in 2 string 48V array. BMS.
  • mike_smike_s Posts: 56Registered Users ✭✭
    edited July 2017 #27
    BB. said:

    Solid wire has a higher impedance than stranded wire (look up "skin effect"--basically at high frequencies, the current flows on the "skin" of the wire--more strands, more surface area).
    That only applies to Litz wire. For ordinary stranded wire, there's not much difference between solid and stranded, because all the strands are shorted to each other.

    Edit: I just noticed this is a 7 year old thread which was dragged up. 
  • jonrjonr Posts: 1,102Solar Expert ✭✭✭✭
    IMO, yes.  All ground points should be bonded together.
  • vernonturnervernonturner Posts: 1Registered Users
    I have lightning rod on adjacent building so I hope that lightning strike wil avoid me  :D
    I'm just started to use solar panels and it is very useful and necessary thing. I hope that here I will find useful information about these panels
  • SolraySolray Posts: 246Registered Users ✭✭
    The strike is not the issue most times, it's the charged ions in the air accumulating on components.
  • jonrjonr Posts: 1,102Solar Expert ✭✭✭✭
    > I have lightning rod on adjacent building so I hope that lightning strike wil avoid me

    Figure about a 45 degree from the tip zone of protection.    And even if it diverts a strike, ground potential rise may get you.
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