ground bar

ws9876
ws9876 Solar Expert Posts: 448 ✭✭✭
in Off Grid Solar & Battery Systems #1
I have an inverter and controller mounted on wood.I put a small buss bar below them to connect all the chassis grounds to.It is screwed into the wood with 2 screws but there is a piece of plastic under the bar.So there is a small connection from the bar to the wood by the 2 screws.Is this ok???
another thing...I have Romex coming out of the inverter and was going to tie the ground wire from the Romex to the bar as well..ok??
The bar will be tied to an outside ground rod. I wanted to have a separate rod for the solar system because it is not tied into the grid system at all. Different outlets totally.But it will take 60 ft of grounding wire to run to the new ground rod.So I was thinking that
I might use the ground for the grid AC system because its only a 35 ft run to it with that solid ground wire 6 gauge.
But that would mean that in a small way the 2 systems would be tied together.Its only a ground but the ground wire does go back into the AC mains...is this ok??? eventually I think I will put in the new ground rod anyway but for now it would be good to use
the other AC rod.. thanks for info...
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    Re: ground bar
    ws9876 wrote: »
    But that would mean that in a small way the 2 systems would be tied together.Its only a ground but the ground wire does go back into the AC mains...is this ok??? eventually I think I will put in the new ground rod anyway but for now it would be good to use
    the other AC rod

    With the distances you mention, you should have both ground rods (or plates, or whatever) connected to each other (through a trench) with heavy bare copper wire.

    When you have two ground rods and lightning strikes in your neighborhood, your two grounds can be 1000s of volts apart. Current will want to flow from one ground to the other. That means the two separately grounded systems in your house may be 1000s of volts apart. Sparks may fly between the two systems.

    By bonding the two grounds through a trench, you provide a better path for the current. btw, consider some lightning arresters.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #3
    Re: ground bar

    My understanding is that it is easier / simpler to use the same ground rod that the house AC is using. But if you want a 2nd one, as vtMaps says, you MUST connect them together, lighting strikes or not.

    As I was told by a engineer, only go for a 2nd ground rod if you really must / have to.
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: ground bar

    Reiteration time.

    First of all grounding of a system is not for lightning protection. I don't know why people can not understand this. Electrical Safety Ground and lightning protection are two different things.

    Second, single point grounding is the 'goal' but is not strictly necessary depending on how the system(s) are arranged. If you have two separate power system in one location that have no ties for hot, neutral, or any DC then their grounds do not have to be connected either; they can be separate. The ESG is there to provide a low resistance path to trigger high current and trip circuit protection in the event of energizing some portion of the system that is not supposed to be (such as hot coming in contact with the metal case of component). The idea here is that someone would be in no danger of creating and alternate power path through their body if they touch something.

    I do not understand the reasoning for this second ground rod on the OP's system. If it is 60' away and thus requires a lot more wire to connect to there seems no point in adding it. Just as two systems may have two separate rods they do not need to have two separate rods. There is no advantage to it.

    Ground and grounding system are not the primary wiring affected by lightning strikes. Two separate systems in one house are no more likely to become energized from lightning than if it were your's and your neighbour's systems which would be separate and possibly even less than 50 feet apart. Dual grounding rods become problematic when they are tied together above ground, thus creating a ground loop which includes the resistive qualities of the actual Earth conducting between rods. This is why a multiple rod single point ground requires all connections, including ground wire and clamps, be subsurface; so that to the one above ground connection to the ground wiring the multiple rods and connections between them 'appear' as one Earth contact point.

    Lightning protection is a matter of directing the high Voltage, high frequency RF type energy that occurs in air around strikes to Earth. It will be picked up by the non ground wiring primarily, especially any long runs outside such as PV wiring or grid hook-up or even a power line to an outbuilding. These sorts of wires literally act as antennas and attract the SV. The important thing is to give a low resistance path from these wires to ground before the energy has a chance to find its own way which may include traveling through your charge controller (for example) and frying it to a crisp. Thus the use of lightning arrestors on these lines. They provide a path to ground which is near infinite resistance at low Voltage and near zero resistance at high Voltage.

    As always there is absolutely nothing that can protect you from a direct hit. Lightning goes where it wants to and destroys whatever it hits.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: ground bar

    ws9876,
    the earth is the ultimate ground and for electricity it should ideally be a solid resistanceless conductor. why do you think they call it "ground"? because it is all of the earth. that means the ground your neighbor uses should be the same ground you use. the ground rods are only your means of connecting to the ground. in reality the ground has resistance so it is best to send all of your ground connections to 1 point of connection to the ground. that 25ft between your rods (if i've got that right) qualifies in my book as needing the underground connection for most soils in the case of multiple rods to make it better appear as 1 rod. for 60ft it is optional as even utility companies find it unnecessary to tie between poles which is a much larger distance than 25ft and has ground resistances that are higher due to distance. it doesn't matter if it is your grid ground or your cc ground or pv frame ground as they should be tied to the same single point when close together. this is not to be confused with a chassis ground as that really isn't a ground, but is a common point of connection that takes on the appearance of ground without actually being connected to the ground. your car is a perfect example of this with all negative connections going to the chassis. guess where the terminology came from. in reality it does not normally go to the ground, but i suspect they used the term ground so as to make people visualize it as a single common point of connection going no further than the chassis.

    it is true the voltage differentials can manifest between 2 rods of a small distance apart and could cause problems. usually lightning differentials are the biggest problem, but ground loops of current between the rods can also develop because the ground is not resistanceless. with larger distances, like several hundred feet and higher, the resistance is higher and could be enough to suppress any significant voltages and currents from doing any harm. all of this is with the picture of lightning hitting the ground and traveling through the ground. that's quite a bit of energy going through the soil.

    for the benefit of some who tried to educate me on a subject i made them aware of in the first place, lightning emp is different just to make that distinction as it is only a strong byproduct of the initial stroke that can also still do damage. lightning emp is weaker and can be dissipated from a device like an spd through a separate ground rod say 25ft away from the main ground rod as in the case of a separate building with no bad results. it still should ideally be interconnected at that 25ft distance, but spd's don't carry the full stroke of lightning and aren't designed to. they are only designed to carry the emp and are not critical to the initial wiring or functioning of the electrical circuits in place. they are only a low resistance path to the ground when voltages are high enough.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
    Re: ground bar
    niel wrote: »
    ws9876,
    the earth is the ultimate ground and for electricity it should ideally be a solid resistanceless conductor. why do you think they call it "ground"? because it is all of the earth. that means the ground your neighbor uses should be the same ground you use. the ground rods are only your means of connecting to the ground. in reality the ground has resistance so it is best to send all of your ground connections to 1 point of connection to the ground. that 25ft between your rods (if i've got that right) qualifies in my book as needing the underground connection for most soils in the case of multiple rods to make it better appear as 1 rod. for 60ft it is optional as even utility companies find it unnecessary to tie between poles which is a much larger distance than 25ft and has ground resistances that are higher due to distance.

    This is perpetuating the fallacy of ground as a perfect fault current return path simply because it minimizes the role of what is in practice the most important part of the "ground" connection. That is the resistance between your ground electrode (rod, pipe, concrete encased electrode or whatever) and the great mass of the earth around it.
    In practice, it is unlikely that the resistance from a typical driven ground rod and "earth" is lower than 10 ohms, and it is quite possible for it to be more than 25 ohms.
    That means that even if the utility end of the connection is perfect (approximated by tens or hundreds of ground rods in parallel with wires connecting them as well as other incidental grounds such as water pipes bonded at individual users' main panels) the fault current flowing into a ground rod with no direct connection back to the utility neutral wire will probably not even trip a branch circuit breaker.
    Take a 120V 20A circuit, and make a deliberate connection from the hot side to an isolated driven rod. The current is likely to be less than 12A and may well be as lower than 5A. That will not trip the 20A breaker, and will leave the full voltage of 120V open to touch on the ground rod and the soil near it.

    However, in the case of lightning, the voltage of the strike is in the 100KV + range and the impedance of the lightning protection down conductor (inductive at the high frequencies of a lightning strike) can be in the 1000 ohm plus range. Under than condition, a 25 ohm resistance of a ground rod will not even be noticed by the lightning strike. Although it may jump to an even better path if one is available.

    Grounding, as in attempting to connect to earth, is NOT a major feature in electrical safety at voltages below about 480 volts. What is needed instead is a solid wire or conduit return path back to the POCO neutral.
    Having multiple ground rods tied together at a single point by a wire network will certainly reduce the total ground electrode resistance, but it still may not be good enough to trip a circuit breaker.
    (In our 120V 20A example, you would need a total electrode resistance of less than 3 ohms to reliably trip the 20A breaker in a time that would minimize injury or property damage.)
    ... they are only a low resistance path to the ground when voltages are high enough.
    And there, buried in an aside at the end, is the critical point for general electrical safety.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: ground bar

    Although we are skipping that the neutral in our split-phase AC system is tied to ground to render its Voltage zero in respect to ground making it "safe to touch" because we will not be a better path to Earth than the ground wiring already in place. If something is wrong with that grounding then all bets are off.

    This has a reciprocal which inetdog was trying to explain: it means the metal casings of everything grounded are connected to neutral so if the hot does short to he case it not only shorts to ground but to its opposite pole as well, thus ensuring sufficiently low resistance to induce a momentary surge in current capable of tripping the over-current protection.

    And there is that wonderfully vague description of what constitutes proper Earth ground. For some people since you can buy a 5' rod and pound it in that's enough. In some places it may be. Others are burdened with dry, sandy soil which will have very high resistance. That's when they start talking about trying to find a depth that is damp in dry weather.

    If you've done it wrong you probably will never know until it's too late.

    Understanding the purpose of the ground wiring is one thing. Determining the best way to achieve the desired result can be quite another.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #8
    Re: ground bar
    Cariboocoot wrote: »

    And there is that wonderfully vague description of what constitutes proper Earth ground. For some people since you can buy a 5' rod and pound it in that's enough. In some places it may be. Others are burdened with dry, sandy soil which will have very high resistance. That's when they start talking about trying to find a depth that is damp in dry weather.

    If you've done it wrong you probably will never know until it's too late.

    Understanding the purpose of the ground wiring is one thing. Determining the best way to achieve the desired result can be quite another.

    That is why UFER grounding is so acceptable in the desert southwest.

    http://en.wikipedia.org/wiki/Ufer_Ground
    During World War II, the U.S. Army required a grounding system for bomb storage vaults near Tucson and Flagstaff, Arizona. Conventional grounding systems did not work well in this location since the desert terrain had no water table and very little rainfall. The extremely dry soil conditions would have required hundreds of feet of copper rods to be inserted into the ground in order to create a low enough impedance ground to protect the buildings from lightning strikes.

    In 1942, Herbert G. Ufer was a consultant working for the U.S. Army. Ufer was given the task of finding a lower cost and more practical alternative to traditional copper rod grounds for these dry locations. Ufer discovered that concrete had better conductivity than most types of soil. Ufer then developed a grounding scheme based on encasing the grounding conductors in concrete. This method proved to be very effective, and was implemented throughout the Arizona test site.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
    Re: ground bar

    inetdog,
    i'm not arguing what constitutes a good ground or a perfect ground, but i'm arguing the spd does not need to tie to the same ground when some distance away. please read my intent with my post and do not pose to educate me as someone else tried to do as the spd going to a separate rod really has no bearing on the rest of the proper ground or its operations with the hots. an spd poses a good path to ground only when voltages rise above a preset level and is only capable of emps being sent to ground. i have no argument in him tying the rods together and he should up to a certain reasonable distance to get a better ground. you won't teach me anything i don't already know.

    the posed scenario i secondarily referred to was from kento on midnite forum that at some distance out (like a separate building quite far away) the spd should be on the neutral too. i agree with this because the wire's resistance at a distance allows it to pick up lightning emp. it becomes above ground when dealing with radio frequencies which are richly present in lightning emps. the quickest way is straight through the spd to a ground rod there. it won't adversely affect anything else and its being sent to the ground there will prevent it from having to travel back to the neutral/ground tie point at the main cb box which everybody was arguing it can just tie to the neutral over there. traveling along the hots with an emp going back along the neutral will also inductively place the emp back into the hots. an spd is not required to be handled quite as the rest of the electrical neutral/ground is for it is not part of the normal operations of electrical circuit usage. it can go to a separate ground rod not tied to the rest of the ground rods as its only function would be the lightning surge to the ground there and has 0 to do with the other grounds which are much farther away.
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  • ws9876
    ws9876 Solar Expert Posts: 448 ✭✭✭
    #10
    Re: ground bar

    good info all around. thanks. I am going to do a separate ground system for my PV...no connection to my house ground due to 50 ft outside distance.
    It just works better that way.
    My solar ground is going to be 2/ 5 ft copper rods driven down under and connected underground 6 ft apart.Not perfect but good enough. I am not worried.
    I hardly ever have lightning here in the high prairie/desert.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: ground bar

    What Niel says is absolutely true.

    You can run a separate ground wire to a separate ground rod to provide surge protection (i.e. lightning arrestor) because this function is not the same as the ESG function. Without the SPD you don't have SV protection just because you have a ground wire.

    Basically you are picking up any of the SV occurring on outdoor power lines (AC or DC) and giving it a low resistance (for the higher than operating Voltages) path to ground, which is what it wants anyway. Doing this without introducing it to the interior of the house is generally looked upon as good, except by some people who have written the code the wrong way.

    So running some mutli-strand copper from the array frame/mount to an above ground connection on an independent ground rod and using this same wiring as the ground connection for the SPD of the positive and negative array wires is not only viable but in some cases much preferred to alternate grounding methods.

    Might have to explain this many different ways 'til we find one that slots in to everyone's minds.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
    Re: ground bar

    ws9876,
    sounds like a good plan to me except the rods need to be 8ft minimum by code.
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  • DanS26
    DanS26 Solar Expert Posts: 269 ✭✭✭
    #13
    Re: ground bar
    ws9876 wrote: »
    good info all around. thanks. I am going to do a separate ground system for my PV...no connection to my house ground due to 50 ft outside distance.
    It just works better that way.
    My solar ground is going to be 2/ 5 ft copper rods driven down under and connected underground 6 ft apart.Not perfect but good enough. I am not worried.
    I hardly ever have lightning here in the high prairie/desert.

    Your approach is sane and code compliant.

    My only concern is that a lightning strike or high voltage event at your home may see your low impedance ground at your array as a much better place to discharge. If that happens, the high voltage will use your inverter, connecting wires and solar panels as the path to ground and causing much destruction in between. Also vice versa, a strike at your array could see your home as a better place to discharge........

    IMHO keep everything at the same electrical potential. Yes, 50 ft of #6 copper is expensive, but it is some insurance.
    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: ground bar
    DanS26 wrote: »
    Your approach is sane and code compliant.

    My only concern is that a lightning strike or high voltage event at your home may see your low impedance ground at your array as a much better place to discharge. If that happens, the high voltage will use your inverter, connecting wires and solar panels as the path to ground and causing much destruction in between. Also vice versa, a strike at your array could see your home as a better place to discharge........

    IMHO keep everything at the same electrical potential. Yes, 50 ft of #6 copper is expensive, but it is some insurance.

    That is the reason for putting the SPD on the array at the array combiner and connecting its grounding lead to the array ground wire. For paranoid protection you can put another SPD on the incoming wires and connect it to the other ground wire.

    An actual strike will fry everything anyway no matter what you do.
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  • DanS26
    DanS26 Solar Expert Posts: 269 ✭✭✭
    #15
    Re: ground bar
    Cariboocoot wrote: »
    That is the reason for putting the SPD on the array at the array combiner and connecting its grounding lead to the array ground wire. For paranoid protection you can put another SPD on the incoming wires and connect it to the other ground wire.

    An actual strike will fry everything anyway no matter what you do.

    Talk about "paranoid protection". I live in a lightning prone area. Every year I was losing equipment to voltage spikes...microwave, stereo system, speakers, TV's, fence chargers, etc. That was years ago before I installed a proper grounding system...a system that had the same electrical grounding potential at all buildings served by the REMC transformer. On top of that I had REMC put a SPD at the can, then another at the meter, then I put another at the main disconnect. Point of use SPD's at sensitive electronics. Additional SPD's at the inverters and AC combiner.

    Yes it was expensive, but I have not lost a piece of equipment since. Anecdotal maybe, but I'm a believer.
    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
    Re: ground bar

    at the pvs there's no sensitive equipment to blow out. i only mentioned about the spd for a branch circuit at another building where an spd is warranted. is it paranoia to put one there though? not really as i see it as just adding more movs to handle large surges with. that was the concept of why midnite put so many in there spd in the first place so i guess you feel they are paranoid. more of them certainly does not hurt anything and if done outside rather than inside it could prevent some of that energy from making it inside.

    2 5ft rods are not to code as they would say 8ft minimum even though 2 5ft rods would essentially have 2 more ft of rod exposure than 1 8ft rod would. not the real subject matter here, but how i view it.

    do i think ws can benefit from an spd at both ends of the pv wires. yes as that one in a million could happen. is it required? no and odds are it won't happen. if he does use an spd it would be first at the equipment inside, but he does not have to use one and he feels he gets little enough lightning that he will take the chance.
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #17
    Re: ground bar
    Cariboocoot wrote: »
    Might have to explain this many different ways 'til we find one that slots in to everyone's minds.

    A LOT of people are getting lost between a) all the acronyms, more often than not b) due to misunderstanding what is written here because of different frameworks of reference, c) having never done anything like this ever and d) so many different opinions and experiences from all over the world.

    Imho best thing is to get as much info here and then get professional help so that you can ask the right questions for where you are in the world to ensure that the person advising you, does appear to have knowledge on the matter. A collective as found here on this forum, is the best place to start.

    To sum up generally:
    - If you have a ground rod already for your house, use it. It probably would be installed to regulations for your area.
    - If not, min 8 feet (2.5m) of rod is required in wet ground and if you are in a dry area, then encased it in concrete.
    So a 8 feet rod encased in concrete is probably the way to go to make as sure as you can for all the non-experts?

    And lest we forget. Most houses are insured, so if there is a lighting or related issue, in case of disaster, your equipment is normally covered under your household section. Just check with your insurer that it is and / or what they need in order to have your equipment insured.

    And if you are not insured, or cannot get insurance, then get a professional to install it for you IF you have the smallest inkling of getting a feeling to form a thought that you would want to start getting an idea that maybe, just maybe you are ever so slightly unsure about anything on this subject. :-)
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
    Re: ground bar

    a if you want clarification on something then ask. we can't talk on a primal basis for those that aren't familiar all of the time.

    b that was my doing as i initially answered ws and vt in the same post. my reference to vt was not meant for ws or the rest of you, but i got challenged anyway as usual and they really had no clue what the whole story was to educate me on it as is typical. but i tried anyway to clarify.

    c don't worry about your inexperience as you can ask and it can be done via pm to eliminate sidechatter when necessary.

    d yes, you will get that, but don't think that is all that is here as many here have degrees. now none of us write nec rules (local to the u s), but it would probably be better if we did as we have more common sense, and knowledge in the area pertaining to solar, than the idiots that do write them.
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