ground rods

Discussion in 'Electrical Forum discussion & Blog' started by jwelectric, Mar 30, 2011.

  1. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Per Randy's request


    What is the purpose of installing the grounding electrodes on a wiring system?

    First just what is a grounding electrode? Most people will think of ground rods. A rod is just one of several different grounding electrodes. In 250.52(A) of the NEC is the outline of the different electrodes.
    (1) Metal Underground Water Pipe.
    (2) Metal Frame of the Building or Structure.
    (3) Concrete-Encased Electrode.
    (4) Ground Ring.
    (5) Rod and Pipe Electrodes.
    (6) Other Listed Electrodes.
    (7) Plate Electrodes
    (8) Other Local Metal Underground Systems or Structures.
    The metal water pipe is required to be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8) and the rod, pipe, or plate shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8).

    250.50 mandates that where any or all of these electrodes are present they must be bonded together to make one grounding electrode system.

    What is the purpose of this grounding electrode system? There are four reasons to install this electrode system and four reasons only. The electrode system is not for letting any current flow to earth. The reasons are outlined in 250.4(A) (1) Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

    Lightning can strike a transmission line several miles away and be carried on these lines to our homes. This connection to earth gives lightning a path to travel to where it is trying to go in the first place, earth.
    Line surges can and do come from many different places with lightning being one. A short between the primary and the secondary of a transformer could be another.
    Unintentional contact with higher voltages can come from the primary over head conductors falling down and hitting the lower voltage lines.
    Then we have the stabilization during normal operation which seems to be a great confusion. The phrase “stabilize the voltage to earth during normal operation†has been in the code for many years. In any system the voltage between any two ungrounded (hot) conductors will be regulated by the source. The voltage between any ungrounded (hot) conductor and a conductor that is connected to earth will be regulated by the source. On a system where no connection is made to earth the voltage between the ungrounded conductors and ungrounded metal parts can be from zero to infinite and considered to be unstable. The grounding or connection to earth keeps the voltage stable.

    On any circuit there is no need for grounding in order for the circuit to work. When the circuit is working properly all current is being carried on the conductors installed for that circuit.
    In the event of an overload all current is being carried on the conductors installed for that circuit. This overload can be due to much of a load or due to voltage drop but grounding plays no role at all.
    In the event of a short circuit all the current is being carried by the conductors installed for the circuit and no grounding is needed.
    In the event of a ground fault grounding is not needed. All current will be carried back to the main bonding in the service equipment and then to the source via the neutral conductor.
    Many proposals have been submitted to have the name of the equipment grounding conductor changed to the equipment bonding conductor. The substantiation for these proposals in most cases had been the confusion about the job of the equipment grounding conductor.

    In 250.4(A)(2) we are told that the purpose of connecting noncurrent carrying metal parts to earth is to limit the voltage to ground on these materials.
    In 250.4(A)(3) it states; Normally non– current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground fault current path.

    This connection of noncurrent carrying metal parts to the source (the neutral in the service equipment) is what is discussed in 250.4(A)(5) to establish a low resistance path back to the source in order to trip the breaker or blow the fuse.

    (5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

    The last sentence of this section tells us that the earth shall not be used as a fault path simply because the resistance of dirt is too high for the voltage to push the current through it back to the source.


    In every case outlined above the earth grounding plays no role what so ever in the circuit. In every case outlined above the circuit over current device be it fuse or breaker will protect the circuit and people.

    Earth grounding is for four reasons and four reasons are outlined in 250.4(A)(1) and has no role in how the circuits works in any type of premises wiring system.

    The grounding electrode system or the equipment grounding conductor does not take current from the system and dump it into earth. In the event of a hot coming in contact with a metal object that is bonded to the equipment grounding conductor that current is carried back to the service equipment where it then travels back to the transformer via the grounded neutral conductor which will draw a high current that trips the breaker or blows the fuse.

    Ground rods installed at swimming pools, outdoor hot tubs, ornamental pools, fountains, wharves, docks, boat houses, and piers are installed for the same four reasons outlined in 250.4(A)(1). The installations or grounding electrodes at any remote building or structure be it a storage building, work shop, detached garage, barn, or dock is for the same four reasons.
    There is a big misconception that grounding electrodes installed at places around water is to relieve stray voltages. These grounding electrodes are installed for the same four reasons as any other grounding electrode as outlined in 250.4(A)(1).

    If these rods removed stray voltages at buildings and structures around water would they not remove the stray voltages found around our out building and structures as well as our homes?
    Are not plumbers troubled by stray voltages doing work on metallic piping systems all the time? This proves that the grounding electrodes installed at the service does not mitigate stray voltages.

    Most stray voltages come from the utility which uses the earth as a fault path. The distribution lines are of high enough voltage to push the current through earth to clear any fault currents. In most cases across America the primary voltages at the transformer supplying our homes is 7200 volts and at these voltages is enough to drive over 200 amps through earth and open the fuse supplying the transformer. Most of the fuses supplying our transformers at our homes will be 15 amps or less.

    On water where boats and ships cannot earth ground the fault current path must be established through the water craft. This fault current path sometimes is the water therefore giving stray voltages to the water. In these cases the earth grounding at our piers and docks will not remove these voltage gradients. This is accomplished by equal bonding grids and planes which brings the water and anything we come into contact with to the same potential therefore no current flow.

    If you find this post informative and useful then please post and let me know that my time was not wasted.
    Also if you disagree please post and list the information which disproves anything posted.
    Or just post you comment
    Last edited: Mar 30, 2011
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

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    sorry I didn't mean to make it a sticky note
  3. Randyj

    Randyj Master Plumber

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    The one thing I do not see addressed here is the voltage drop in wires to earth ground or the differences in remote earth ground potential voltage. I'll be thinking about the rest of it...
  4. ActionDave

    ActionDave Electrician

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    What are you talking about?
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

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    There is no such thing as you have posted
  6. ballvalve

    ballvalve General Engineering Contractor

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    Last edited: Mar 31, 2011
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

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    This site is for lightning rods that go on top of a building.

    I don’t see the equipment grounding conductor melting during a lightning strike any more than I see the conductors in the link you posted melting.
  8. ballvalve

    ballvalve General Engineering Contractor

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    You may be aware that most ground rods often cannot be driven to their full depth due to rocks. In this area its a given that you might get 4 or 6 feet, then its cut it off and beat it with a hammer to make it look like it went in. A very few might add a second rod to obtain the length.

    Would it be permissable or better to lay the rod horizontally in a trench 2 or 3 feet deep and bend it up at the pole?
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

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    First you must try up and down, if this doesn’t work then lean it to 45 degree angle and if it still won’t go then bury it 30 inches deep. No need to bend it up
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Way back when, when I was in the army, the communications chief at Ft. Bliss, El Paso, Tx said that when they went out on a field excercise to the desert, in order to get a good ground (necessary for some radio communications) they had to prepare long in advance with help of the cooks. They had them order lots of extra salt. Then, when they needed to go out on the exercise, they drove their ground rods/array then mixed up lots of salt water, and then poured it on the ground periodically for the duration of the exercise. This gave them a decent ground plane for the antennae and operation of the radios. Now, how does this apply to a conventional home - not much except to realize that grounds, returns, neutrals, and power is a lot more complicated than most people realize. There are lots of smart people out there that have spent lots of time trying to figure out how to make the things we take for granted work properly. Not following the defined rules can make the whole thing start to fall apart, giving unexpected results, some of which can kill you.
  11. Randyj

    Randyj Master Plumber

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    Jim,
    in the area where I live the dirt is so full of minerals that it is no problem to get a current to travel through the ground. As far as voltage, I get as much voltage through my ground rod as I do through my neutral.... and it's 200 ft to the transformer. A magnet will pick up all kinds of small rocks in my yard. Of course, we're not all that far from Birmingham which is known for it's iron ore and this is coal country too.
  12. ActionDave

    ActionDave Electrician

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    That means nothing other than your voltmeter is working.
  13. LLigetfa

    LLigetfa DIYer, not in the trades

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    LOL

    Ja, a volt meter deliberately has a high impedance so as not to affect the circuit under test. Decades ago I paid hundreds of dollars for my B&K VTVM for that very reason.

    If Randyj knew his Ohm's law, he wouldn't make such a statement unless he were simply trolling.
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Here are some inserts from a study done by Institute of Electrical and Electronics Engineers over a five year period between 1988 and 1993 for driven rods for utility power stations and communication companies where low resistive earth grounding is imperative.

    What is a transient voltage? As defined; 2: (physics) a short-lived oscillation in a system caused by a sudden change of voltage or current or load

    Transient voltages can be introduced by the magnetic field between the high voltage transmission lines and earth.

    Solar flares which flex earth’s magnetic field can introduce transient voltages. (one weber [100 million lines of flux] for one second equals one volt)
  15. LLigetfa

    LLigetfa DIYer, not in the trades

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    As I mentioned before in another thread, I worked on a project for Ontario Hyydro where we were improving the grounding of their lattice towers for lightning protection. In some cases we had as many as 50 ground rods on a single tower.

    The company I work for now is a NUG and has hydro generation as well as biomass cogeneration facilities. We also have communication towers and a tall smokestack that frequently gets hit by lightning. Equipment can be affected by induced voltages from the EMP even if not hit directly. We have a truck scaling operation where we needed to take extraordinary measures with bonding due to the efficiency of the grounding with the amount of buried metal.
  16. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Basic Electricity 101 we learn that the voltage drop across one resistor in series will be equal to the applied voltage.
    From your service back to the transformer through earth would be one resistor in series no matter how many rocks you magnetic will pick up.

    It is not a matter of how much voltage is present it is a matter of how much current will travel through this resistor (earth).

    Check the resistance of your rod using the three point resistance test for ground rods but the equipment is very expensive. You could use a clamp-on resistance tester but they aren’t very accurate.
    This will tell you the amount of current that will travel throung earth at your house.
  17. Randyj

    Randyj Master Plumber

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    Let's not have another bash Randy day... if anyone notices, I did qualify that statement by saying "as far as voltage goes". Just because you guys are big time in the discipline of electricity does not mean that I don't know diddly about ohm's law. Had I thought there was no change to current then I would not have qualified that statement. The fact that there is such a high ferrous mineral content here does make this dirt a much better conductor than dirt with little salt or conductive ability. I do know that I've used the same method of checking voltage and found that current to ground rods had around 64 volts. This is one thing I've referred to in the other thread. I found this where someone had swapped or confused their neutral with ground at some point in old house wiring. All the person who did this knew is that his/her light bulb still worked so "they" let it go and thought everything was fine... until something else got plugged in and suddenly there was a problem, something burned out quickly... or didn't work at all. I wouldn't call giving examples and asking questions honestly to be trolling....
  18. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Randy,

    First no one is bashing you but you must take the statements as posted for the information in our response. You make the comment in your statement that;
    Here you clearly make the statement that there is no problem to get current go travel through the ground. Did you mean to imply that where you live current will travel through earth or did you mean something else?
    Based solely on what you said what I think you meant was the potential was the same on the earth ground as the neutral not that current was traveling through earth.

    Earlier you make this statement;
    What would the voltage drop in wires to earth ground have to do with anything? Just what is a remote earth ground potential voltage? No one or at least I don’t have a clue to what you are saying.

    Then in your last post you say;
    Current is measured in amperage not voltage. Voltage is the amount of pressure and amperage is what is flowing. They are two separate things and mean two separate things.

    You say;
    If you had a full understanding of Ohm’s Law then you wouldn’t keep saying that while you were checking voltage you found current to the ground rods. You would understand that while checking voltages you were looking at the difference in potential and current was not in the picture.

    The only tools that the other posters as well as I have to work with are those you are giving us yourself.

    Please understand that no one is bashing you but trying to help you to better understand. It is your own post and the terms you use that we are responding to.
    The one thing that no one here or anywhere else will ever be able to do is help you to understand your mistakes until you are willing to listen.

    Based solely on these few statements I have quoted here anyone would believe that you don’t understand current flow. if you did you would stop making the statement that while you was checking voltage you found current flowing of 64 volts.
    What you are saying in reality is that while you were checking voltage you found a difference in potential of 64 volts but this doesn’t mean that any current was flowing.

    Please understand that it is not my intent to belittle, condescend, distain, ridicule, mock, or bash you in any way. It is my intent to help you to understand that the earth ground plays absolutely no role what so ever in how a circuit works. It does not let current bleed off or make someone coming in contact with exposed metal any safer. This is accomplished through bonding back to the source at the service equipment.
  19. LLigetfa

    LLigetfa DIYer, not in the trades

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    Randy,
    I did not make the trolling accusation without careful consideration and it is not my intention to bash you. I've been following your threads and the bit of jousting between you and JW. Now, JW does like to take things very literally and it is my humble opinion that he will jump on your incorrect use of nomenclature even if he knew what you meant to say. Of course I cannot prove that just like I cannot prove that you use the wrong nomenclature deliberately to elicit a reaction.

    When I was a child, I would hang onto the literal meaning of words. I still do at times. One time my father told me to stop pulling the cat's tail. Being the smart ass that I was, I pointed out that the cat was pulling his own tail, that I was merely holding it. It still got me a cuff in the ear.
  20. ActionDave

    ActionDave Electrician

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    This is worth repeating, so I did.
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