Lightning - tis the season?

SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
Had a bit of a scare.
Normally we are lucky to see only 3 or 4 instances of distant lightning and some thunder each year. However, last night we were in the thick of things with some very loud flashes with big bangs shortly thereafter (1/2 to 1 second?). We are 1000' up a 1500' mountain, it seemed close.

I have a grounded PV array. The ground wire goes from the array to my Midnite combiner on the roof (the combiner has a Midnite surge protector), and then directly to the ground rod without entering the building.

When the lightning was on top of us (not knowing what else to do) I flipped the "PV IN" breaker on my flexpower panel to off. This probably did not confer any additional protection to my PV equipment, but I didn't know what else to do.

I also thought about disconnecting the + and - PV IN wires that are connected to the charge controller & flexpower panel. But didn't do this - seemed a little risky with all those flashes and bangs. I also flipped the house AC breaker to off (again, don't know if this would have protected any house appliances).

In the end the storm passed after an hour & all the PV & AC equipment seems to be fine. But I felt sort of helpless - and I was thinking about all those posts I read in NAWS about (even indirect) lightning damaging inverters and other PV gear.

Is there anything else I could have done to protect ourselves better from such an encounter? Any additional gear to install? Thanks!
Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    when a storm is that close or already on top of you there's not a whole lot you can do except to do what you did. try not to let the "loud flash" happen before you are able to flip breakers and such, but i think you did quite well being the strike was within about 1000ft. if it didn't hit your array, the emp did. i would look things over to see if there's any evidence of a hit. odds are everything functioned as it should and diverted whatever energies were present from the strike to the ground. being the breakers and such weren't flipped until afterward, i think i would credit the spd and keeping all ground wires outside for saving your system.

    odd as i am typing this on a new pc as it replaces one that blew out from lightning surge.:confused:
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Lightning - tis the season?

    You did basically what I do. We've been very fortunate here, very little lightening last few years, but when it does come, I pull all the switches, including panels to controller, controller to batteries, batteries to inverters, and where possible, inverters to house, leaving only the ground wires connecting the various items. Of course this wouldn't protect in the event of a direct hit, but really, what else CAN you do beyond that, other than sit back and hope for the best.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    when one isn't at home to flip those things is when murphy said it will storm. i think you have succeeded in preventing most possibilities of damage between the spd and keeping the grounds outside, but i'm sure you have seen it out of me here on the forum that lightning does whatever it wants to no matter what you've done to thwart it.
  • SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
    Re: Lightning - tis the season?
    niel wrote: »
    if it didn't hit your array, the emp did. i would look things over to see if there's any evidence of a hit. odds are everything functioned as it should and diverted whatever energies were present from the strike to the ground. being the breakers and such weren't flipped until afterward, i think i would credit the spd and keeping all ground wires outside for saving your system.

    Yes, you are right I should climb up to the roof to see how the Midnite SPD fared:

    From the Midnite SPD Manual: "Both LED’s in the SPD should glow blue as a sign that voltage is present in system, SPD is connected correctly and working and the system is protected. Note. LED’s will only be on when voltage is present. In PV circuits the lights will go out at night because arrays are not producing voltage."

    Another thought when I go up there, I have a #10 ground wire going from my panels to the combiner box and then a #6 going to ground. The #10 was a matter of convenience when the panels were being wired up - my panel lugs were having great difficulty accepting the stiffer #6. Any thoughts on this as well? Is 10 reasonable?
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    sure if not taking on a strike. even the large wire sizes may have great difficulty staying together with a full strike, but it should be ok in general. often times a good ground can dissipate the static precharges better often avoiding a strike. i saw first hand when a ground wire for an antenna of mine was severed and the 2 pieces were now separated by about a foot so precharges weren't able to dissipate. a side branch of lightning did hit the antenna and i saw the resulting beam of electrical energy jump from the end of the cable (disconnected from the radio) and literally went 6ft to the nearest outlet where it was able to go to ground. i have to figure that most of the energy went and jumped that 1ft gap on the ground wiring outside and there was still a high enough potential to cause that 6ft jump inside the house to the wall outlet. if memory serves it is about 1000v per inch of jump in air.

    deviated a bit.:-) anyway if the pv wires themselves are larger than the #10 wire then i would suggest matching or exceeding the wire used for the pvs. for example if you use #4 for the pv wiring to the combiner from each string then use #4 or better for the ground wire. the pv wire size between the combiner and cc does not matter for that combiner is the point where you are grounding at. most pv strings use either #12 or #10 initially, but if you went with a bigger wire size to the combiner for the pv leads then you need to match the ground leads to at least that size.

    in addition to inspecting the spd, inspect all of the pv frames as well for a strike would show up as possibly a discoloration or burned spot or possibly even a melted spot.
  • SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
    Re: Lightning - tis the season?
    niel wrote: »
    in addition to inspecting the spd, inspect all of the pv frames as well for a strike would show up as possibly a discoloration or burned spot or possibly even a melted spot.

    Hi Niel,
    Went up at noon yesterday. The one bue LED was lit. I think that's OK. Per the SPD's manual......

    5. Both LED’s in the SPD should glow blue as a sign that voltage is present in system,
    SPD is connected correctly and working and the system is protected. Note. LED’s will only be on when voltage
    is present. In PV circuits the lights will go out at night because arrays are not producing voltage. This does not
    indicate that the SPD is broken. If voltage is present and the blue LED’s are off, the SPD needs repair. When
    connecting one half of the SPD to PV- and ground, the PV- led will not light. The circuit is protected, but there
    is normally no voltage between PV- and ground.


    No charring, melting or burning. Everything looked good.

    I will still change the panel ground wire to #6 (and this time no excess ground wire coiled up under the last panel;)). I'll also order another SPD, just to have a backup.

    Regarding the latter. When I called Midnite to order the first SPD I was advised to get the 115 model. My record incoming PV volatage at the CC (coldest temperature) is 108v, typically it maxes out in the high 80's or 90's. Can you confirm that the 115 is still OK to get, or do you think the 300 is better.

    I don't think the original advice was off, but the below helpful video (cued to the right spot) made by Ryan made me think twice.

    http://www.youtube.com/watch?feature=player_detailpage&v=-B64V_FZBFQ#t=25s

    Cheers, SP
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    i think you are good to go with that 115v spd, but it is cutting it close before needing the next size up spd. a spare is ok, but imo not necessary. now doubling up on the connected spds will just add more to the path of dissipating the emp. maybe overkill, but certainly doesn't hurt and does increase your odds.

    that is good that you see no indications of a strike anywhere. it must have been just a nearby strike with its associated emp.

    now you did not say what size wire each pv string is using for the + and - power leads. if they are #6 then yes, change the ground lead to #6. come to think of it i believe #8 is the minimum ground wire size from the nec if memory serves. others can confirm or deny that. in any case the heavier wire is desirable if you've already got it. like i said a direct hit on your setup the wire may not be able to handle and could literally explode apart be it #6 or #10. it would most likely follow the path of the ground wire even if it has been vaporized by said strike as the lightning had already chosen that path. larger wiring will increase your odds of survivability though.

    now i don't know what wiles would have to say about what i'm about to say, but here goes anyway. the ground lead going down to the ground rod could be beefed up by doubling the #6 wire from the combiner to the rod. this would do better than the indicated dc equivalent resistant to a #3 wire would do because 2 #6 wires would have more surface area and could send the rf content of a strike better to ground. some like to use braid because of this characteristic, but braid is susceptible to breaking easier and the finer strands could rot through faster than a solid wire. braid also tends to be expensive. now i'm not telling you to do this stuff as i believe you will be fine running the all #6 wire, but this stuff is worth mentioning. even the use of multiple ground rods tied electrically underground and physically separated by at least 8ft with bare #6 copper wire or better is another good way to improve ones protection by lowering the resistance to the ground in this manner too. it's a game of odds and you can have very little in protection and wind up surviving and the guy that went all out with protections got everything fried. it does what it wants to do and all we can do is try to defeat it.
  • SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
    Re: Lightning - tis the season?

    Neil,
    I appreciate your feedback. Although the NEC does not apply in my case, I appreciate the practical advice from folks on this forum who have a great deal of working knowledge. I also realize lightning's randomness and "all bets off" when it comes to a direct hit.
    niel wrote: »
    now you did not say what size wire each pv string is using for the + and - power leads. if they are #6 then yes, change the ground lead to #6

    Yes, my PV + and - are both #6, and the ground wire going from the Combiner box to the 4' copper ground rod outside is also #6. What I plan to do is replace the #10 going from my panels to the combiner box with #6. Everything will be #6 then. However, this does mean that I have to get larger lugs for my panels in order to fit the thicker #6 though. Seeesh.:p

    "...even the use of multiple ground rods tied electrically underground and physically separated by at least 8ft with bare #6 copper wire or better is another good way to improve ones protection by lowering the resistance to the ground in this manner too"

    I realize that I only have a 4' earth rod (it was all our little hardware store had at the time). Then again I am located in moist deep soil. I think I can ship in a longer rod, but I also have another 4 footer that I can pound in & tie to the existing rod. Sounds like you recommend that. My instinct, though, is that the rods should be close to each other. But you say that I would have to connect the two rods by at least 8' of copper wire (no bare copper wire here:cry:). Is this 8' a rod separation length, or just a wire length?

    . it's a game of odds and you can have very little in protection and wind up surviving and the guy that went all out with protections got everything fried. it does what it wants to do and all we can do is try to defeat it.

    Amen

    I read your doubling up idea with interest. We only get braided, insulated copper wire here (I think that is what we get). For example, my combiner box to ground run is pretty stiff 7 strand stuff. Basically it's about 175us for me to add another run. I will first get my panel ground sorted out and then think about the latter.

    A side note: I have a concrete block house built with a ton of rebar, large footings also with rebar. I have a metal roof, metal rafters, metal purlins, all tied into the rebar that goes all the way down to said footers. The rebar is not in every CMU cell in the house, but at least 40%. I am still going to ground my PV according to best practices, but perhaps it can be said that I kind of live in a sort of 'Faraday cage'?
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Lightning - tis the season?
    Surfpath wrote: »
    ... but perhaps it can be said that I kind of live in a sort of 'Faraday cage'?

    It can and should be said. But only to the extent that:
    1. All of the metal parts are deliberately or incidentally bonded together in a way that can carry high current.
    2. Openings like windows, door, chimneys, are small enough, and most important,
    3. You do not invite the lightning to come in through the cage on your wiring!

    The last point is the one you have the most control over, and is also an argument for a good surge suppressor between incoming ungrounded wires and ground. Not for direct strikes but for the near misses.
    SMA SB 3000, old BP panels.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    inetdog is correct as every piece of roofing, perlins, rafters, etc. would need bonded together electrically. i believe you already stated that you did not bring the ground wire into the house so you did not negate it that way. i would not trust the rebar to stay as a good electrical conducting ground if it is already, which i doubt. what you could do is parallel a wire going to a proper ground rod just outside the perimeter of the slab. if the rebar fails you have the ground rod and if the rebar stays good then you have extra ground conductivity.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Lightning - tis the season?
    niel wrote: »
    i would not trust the rebar to stay as a good electrical conducting ground if it is already, which i doubt.

    Depends on the rebar, how the rods are tied together and how the concrete interfaces to the earth.

    NEC states, I believe, that 20 linear feet of 1/2 inch rebar, or smaller pieces wire bonded together at contact points totaling 20 feet makes a suitable ground IF the concrete the rod is imbedded in is in contact with earth. No membrane, crushed rock, foam insulation, etc. underneath it. And the concrete should include foundation or footings (deeper in the earth), not just slab.

    The electrical conductivity of concrete is surprisingly high, and the amount of surface area involved, compared to a simple thin ground electrode rod, makes it perform far better.

    You also need to make sure that you use a suitable clamp or cadweld to connect the Ground Electrode Conductor to the exposed rebar.
    SMA SB 3000, old BP panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Lightning - tis the season?

    BTW there's stuff used in civil engineering to coat rebar so that it doesn't corrode. Guess what it does to the electrical properties? Yep; just like insulation.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    i may do a search, but concrete is basically like stone and the only possibility for conduction of electricity is for metallic impurities or moisture in it. under the strain of a lightning strike you will see conduction from the sand content in the concrete temporarily and the sand would be turned into glass afterward.

    i did find this pertaining to the resistivity of the concrete and what happens to the rebar. it's under "relation to corrosion".

    http://en.wikipedia.org/wiki/Electrical_resistivity_measurement_of_concrete

    that means the better ground it is the faster the rebar corrodes and it is soon to be no good due to rust.

    ftr, on yahoo answers one guy said about 10k ohm per cm. that's terrible.

    http://answers.yahoo.com/question/index?qid=20090313025719AAtX0R5
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Lightning - tis the season?
    niel wrote: »
    i may do a search, but concrete is basically like stone and the only possibility for conduction of electricity is for metallic impurities or moisture in it. under the strain of a lightning strike you will see conduction from the sand content in the concrete temporarily and the sand would be turned into glass afterward.
    ...
    that means the better ground it is the faster the rebar corrodes and it is soon to be no good due to rust.
    ...
    ftr, on yahoo answers one guy said about 10k ohm per cm. that's terrible.
    Just like kW versus kWH is important, keep in mind that resistivity is measured in Ω-cm, not in Ω/cm. To get resistance from resistivity in the simple case of two parallel plates, you divide by the plate area and multiply by the distance between them. So (Ω-cm divided by cm2) times cm = Ω.

    Let's put that into a different perspective. It is most useful to compare the performance of a ground rod in soil to a concrete encased electrode (also called a Ufer ground after the guy who first studied and advocated them.)

    The other source at the Yahoo Answers link includes tables taken from a reference work that suggest that values under 2000 ohm-cm are common. Even though a resistivity of 10,000 ohm-cm is not great, just look at what it should be compared to:
    The soil resistivity value is subject to great variation, due to moisture, temperature and chemical content. Typical values are:
    Usual values: from 10 up to 1000 (Ωm)
    Note that one Ω-m is equal to 100 Ω-cm, so the range for soil is 1000 to 100,000 Ω-cm. This makes concrete look a lot better by comparison, given that you have a minimum of 20 feet of rebar, and often more like hundreds of feet, compared to the 8-10 foot length of a ground rod.
    And for typical soils a 10 foot ground rod will often end up with a resistance under 25 Ω.

    (The moist rust on a corroded rebar will not be a very good insulator, unless it dries out. )

    BTW, I think that one reason the the US uses Ω-cm as the unit of resistivity is that we break out laughing when anybody talks about resistivity measured in ohmmeters. :-)
    SMA SB 3000, old BP panels.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    1st of all any rotted out metal is no good. you might just as well stick the end of the ground wire into the soil rather than connect to the rotted rebar.

    2ndly you talk of the concrete like you are putting the rebar into the soil. you aren't as this is extra resistance between the conductors and the soil.

    3rdly the better the conductivity of the concrete the worse the concrete is strength-wise.

    4thly i agree an 8-10ft rod is often not sufficient enough, but would be better than rotted rebar through concrete and then to the soil.

    5thly as i said before one strike will turn the silicon from a semiconductor to glass making it an insulator from that point on and needing replaced.

    6thly cracks even if hairline in the concrete as it ages will vastly increase the resistance due to blocked paths.

    bottom line here is i think using rebar and concrete stinks as a ground and was orchestrated to make life easy on construction costs. i think things were bent to suit if not people being outright paid off.
    btw there are more points too like the rebar is basically a limited contact surface plate encased in cement, while a ground rod penetrates deep into the soil and below. i have said before that much of the nec is ok, but some areas you know it is far from right.
  • mike95490mike95490 Solar Expert Posts: 9,359 ✭✭✭✭✭
    Re: Lightning - tis the season?
    niel wrote: »
    ...

    bottom line here is i think using rebar and concrete stinks as a ground and was orchestrated to make life easy on construction costs. i think things were bent to suit if not people being outright paid off.
    btw there are more points too like the rebar is basically a limited contact surface plate encased in cement, while a ground rod penetrates deep into the soil and below. i have said before that much of the nec is ok, but some areas you know it is far from right.


    The UFER concrete grounding was designed for dry desert usage, where the large amount of mildly conductive concrete WAS
    effective for grounding munition bunkers. Rebar in concrete should have a 50 year life, and the rebar needs to be tied together to all the segments, not just one stick. And the alkaline nature of concrete preserves the steel rebar.

    AFIK the situation, I've seen nasty concrete jobs where the rebar was too close to the edge and is breaking through the concrete, at that point, it 's a major mistake.
    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 ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mike95490mike95490 Solar Expert Posts: 9,359 ✭✭✭✭✭
    Re: Lightning - tis the season?

    Most "ground rod" is a steel bar, with a flash of copper on it, lifetime is way less than rebar in concrete. Most of the copper gets scratched off when the rod is pounded in.
    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 ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Lightning - tis the season?

    One grounding problem I have encountered more than once in my travels is much what Niel describes: varying conditions causing the actual effectiveness of the ground rod to change over time or season. Too often the code is written with the assumption that dirt is the same everywhere when it is not. Damper soil conducts better, but also increases corrosion. This is no surprise when you consider that electrical conductivity is a chemical reaction by nature. So a steal rod driven into the ground may start out fine, but as it slowly rusts away it becomes a lousy conductor.

    I suppose we could always drill 50' 3/4 holes in the ground and sink very long and expensive copper down them. But it's probably better to periodically test the ground function and service it when it fails. That is highly unlikely to happen in the average home. Whole-house GFCI anyone? Spare me!
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Lightning - tis the season?
    mike95490 wrote: »
    The UFER concrete grounding was designed for dry desert usage, where the large amount of mildly conductive concrete WAS
    effective for grounding munition bunkers. Rebar in concrete should have a 50 year life, and the rebar needs to be tied together to all the segments, not just one stick. And the alkaline nature of concrete preserves the steel rebar.

    When I put the new building up that is how they set up the sub panel grounding per the code monkey. All the rebar had to be tied together for the whole structure. We were going to put in a proper ground rod or run it back to the main panel ground and he nix both of those. Install approved, no fighting with those guys.

    BTW he was OK with us using the sub-panel cable to the main ground as well, its a long ways away, over 100ft. Personally I didn't like the idea of having another ground path at all.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?
    solar_dave wrote: »
    When I put the new building up that is how they set up the sub panel grounding per the code monkey. All the rebar had to be tied together for the whole structure. We were going to put in a proper ground rod or run it back to the main panel ground and he nix both of those. Install approved, no fighting with those guys.

    BTW he was OK with us using the sub-panel cable to the main ground as well, its a long ways away, over 100ft. Personally I didn't like the idea of having another ground path at all.

    if you are talking about a ground lead in the air then i don't blame you, but if it is to be buried back to the main rod it is no longer just another path. it literally becomes part of the ground itself rather than a path to it. it is like an extension of the ground rod in the soil and the only electrical path is into the soil.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Lightning - tis the season?
    niel wrote: »
    if you are talking about a ground lead in the air then i don't blame you, but if it is to be buried back to the main rod it is no longer just another path. it literally becomes part of the ground itself rather than a path to it. it is like an extension of the ground rod in the soil and the only electrical path is into the soil.

    Nope it is air/conduit on the way back to the main panel. Just very weird for them to force that. The PVC conduit runs under ground for about 15 ft, then up thru the back of a closet then it is in the 4 conductor cable from the main panel in the attic.
  • SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
    Re: Lightning - tis the season?

    Hi Folks,
    Interesting discussion about concrete reinforced rebar & conductivity. Even though my house is structurally built like a -connected- metal cage, I'm still using a (traditional?) panel to rod ground wire. I figure it's better to create a path than to wait & see where lightning may want to go.

    On a related note, I brought up the issue of having only one 4' ground rod (currently). I was hoping this was OK. If the consensus is that another rod would be prudent, I was hoping someone could advise me regarding the installation. Here is my original question:

    "I realize that I only have a 4' earth rod (it was all our little hardware store had at the time). Then again I am located in moist deep soil. I think I can get a [6' rod], but I also have another 4 footer [stored in my solar room] that I can pound in & tie to the existing rod.....[If I should install the 2nd] my instinct is that the rods should be close to each other. But you say that I would have to connect the two rods by at least 8' of copper wire (no bare copper wire here). Is this 8' a rod separation length, or just a wire length?"

    Just to clarify, my one 4' rod in the ground is the "single point ground" for my AC house panel, the solar equipment (ie my Flexpower panel), and the aforementioned combiner to ground wire.

    All three #6 wire grounds are connected to the rod with one of those brass 'acorn' looking clamps. It is rare that the soil around the ground is not wet or moist.
    -SP
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Lightning - tis the season?

    4ft rods are no good as you need at least 8ft in length. i don't even know why they sell them that small. as to the 8ft i was referring to physically separating them by 8ft as this spreads out the ground coverage, but you still need about 8ft+ of bare copper wire to tie 2 underground rods with and that is to be buried deep enough so that it may not be disturbed easily. i always said at least a foot, but i believe this came up that about 18in or so should be utilized, but don't count on my memory as it is still back in the pentium days and is failing a bit short these days.:p
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Lightning - tis the season?
    niel wrote: »
    2ndly you talk of the concrete like you are putting the rebar into the soil. you aren't as this is extra resistance between the conductors and the soil.
    If the conductivity of the concrete is better than the conductivity of the soil it is resting on, it is not extra resistance it is lowered resistance. Once you have gotten a large enough surface area, the resistance of the interface between rod and soil or concrete and soil does not matter much, nor is it nearly as important to get to a great depth. If you cannot drive a rod 8' deep because of rocky soil, you are allowed to bury it horizontally instead. It is the surface area that matters once you have reached moist dirt. And a foundation of concrete sealing out the air will help keep the dirt nice and moist.
    SMA SB 3000, old BP panels.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Lightning - tis the season?
    inetdog wrote: »
    If you cannot drive a rod 8' deep because of rocky soil, you are allowed to bury it horizontally instead.

    I wonder what you would do if you had a solid rock?
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Lightning - tis the season?
    NorthGuy wrote: »
    I wonder what you would do if you had a solid rock?

    Unfortunately, I think you are required to drill into it unless you can find a qualifying alternate electrode. A Ufer would be acceptable, I think, even it the concrete were resting on solid rock. The resistance might be a little high, but.....
    SMA SB 3000, old BP panels.
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