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  • Ground Tutorial

    Grounding and Bonding are the most misunderstood subject in the electrical profession. Many engineers, technicians, and electricians do not understand the subject. The inside joke is NEC was made to confuse the Communist and DYI's. Unfortunately the result is it even confuses pros. In reality it is very simple, and likely everything you think you know is wrong. The following is strictly limited to Solidly Grounded Electrical Systems used in conventional residential wiring systems. I am not going to cover Corner, Delta, Impedance, Ungrounded, and Lightning Protection systems as each is a book in itself.
    Terms are defined in NEC article 100 and 250.2. Section 250.4 defines the performance requirements of article 250. There are few I will use here you need to know.

    Grounding or Ground is an intentional planned connection to earth or a body in place of earth like the frame of your car. Keep in mind Ground does not necessarily mean dirt. If that were the case a plane, spaceship, and your car electrical system would not be safe.

    Bonding is the intentional electrical connection between two or more conductive bodies like equipment, rods, pipes or wires. It is either planned or unplanned.

    Grounded System means to intentionally bond one of the current carrying circuit conductors to ground to facilitate operation of Over Current Protection Devices (OCPD)like fuses and breakers. This connection is only allowed to be at one point only. In an AC system this is done at the Service Entrance Disconnect means usually located inside the Meter Can or your Main Breaker Panel. In an AC system the Grounded Circuit Conductor aka Neutral. In a DC system is called Bat Return and can be either be the positive or negative terminal post of your battery. 99% chance you have no choice and it will be the Negative battery term post. Open the hood of your car and look at your battery. You will see one large conductor bonded to the frame of your car usually located on the engine block near the starter or firewall.

    Ground Electrodes (GE) is pipes, rods, wire, rings, concrete encased rebar, or anything metallic buried in the dirt. In a Car or RV is the frame.

    Ground Electrode System (GES) are ground electrodes and Bonded together to form a GES. All GEs available shall be used. If you do not have any GE's you must make them and the minimum requirement is two 8-foot 5/8 inch diameter UL approved copper cladded steel rods separated by at least 6-feet. Note here that is the minimum requirement and if you use two or more rods, best practice is to separate them be at least twice the rod length to be effective for lightning. You cannot use Isolated GE's like one for DC and another for AC. That can get you killed and wreak havoc on your electrical system.

    Ground Electrode Conductor (GEC) is the conductor that Bonds the GES to the Grounded Circuit Conductor aka Neutral or Battery Return.

    Main Bonding Jumper (MBJ) is one of the most critical elements of a Grounded System that allows your OCPD to operate effectively. It is the Planned Fault Path for ground fault currents to return to the source (battery, utility, generator etc). Without it your fuses and breakers will not work. This conductor is the wire between the grounded circuit service conductor, and EGC. In some case, the MBJ and GEC is the same conductor.

    Equipment Ground Conductor (EGC) the EGG or today called Equipment Bonding Conductor (EBC) is the conductor used to ground the noncurrent-carrying metal parts of equipment. Its function is to keep your equipment as close as possible to ground potential and provide a safe path for ground-fault current to flow. In an AC system it will be the 3rd wire (usually green) and must be ran with and closely coupled to the Circuit Conductor. In a DC system it can be separated from the circuit conductors. It can be bare, solid, or stranded, and if Insulated must be GREEN. Without it like the MBJ, your OCPD's are useless.

    Grounding and Bonding is crucial inside a structure. Without it, if something goes wrong like the HOT conductor (ungrounded circuit conductor) were to come in contact with exposed metallic parts of the system, you can be electrocuted. It provides a planned fault path back to the source to clear faults by operating the OCPD. So what does Ground have to do with this? ABSOLUTELY NOTHING. You heard me NOTHING. It is forbidden to use ground as a CIRCUIT CONDUCTOR in any NEC application. Dirt is worthless as a conductor with low voltage. Low voltage is not likely what you think it is. 480 volts is Low Voltage. Only utilities can use earth as a conductor because they operate at high voltages a completely different subject.

    Lets bust the biggest myth and lie taught in many text books. It has two versions and is one of the main sources of confusion. They go something like this.
    1. Electricity takes the path of least resistance.
    2. Electricity takes the path of least resistance to ground.
    Both are blatant lies and slap Kirchhoffs Law in the face. Many folks have been electrocuted, injured, killed, and billions of dollars lost in property damage from this myth. Like I said, it was made up to kill communist and DIYs.

    Fact is electricity takes every path available back to the SOURCE. and the source of your power is not dirt, earth, or ground. The Source is things like a battery, generator, inverter, or utility. The only time Earth or dirt is a Source of power is lightning and static electricity. Those are two things you do not want to invite inside to live with you.

    So what protects you and your wiring? It is simple OCPD and a Reference to Ground. Again Ground does not necessarily mean dirt. It can be the frame of your car or an imaginary point in space and time. So lets makes this crystal clear all Ground means is a REFERENCE POINT. Nothing more, nothing less.
    So how does an OCPD work? Very simple when too much current flows, an OCPD heats up if it is a thermal device. A fuse melts, and a breaker is on bimetallic or dissimilar metals so when heated up contracts and expands tripping itself open. There are other types but is not important for you to understand right now. In order to operate an OCPD like a fuse or breaker very quickly, ideally we want to induce a fault current at least 6 times the device rating. At 6 X the OCPD operates instantly clearing the fault. Example a common 20 amp OCPD we want to induce 120 amps through it to make it operate instantly.

    So how do we make that happen? Simple with a green insulated or bare piece of wire we call an EGC of the proper size. To Induce 120 amps on a 120 volt circuit requires a maximum 1 Ohm of total circuit resistance. That includes the Hot Line or ungrounded circuit conductor, connections, and the breaker resistance itself. So the ground resistance has to be .5 Ohms or less. Got 12 volts? Now we are talking .05 Ohms or less.

    While it is possible to obtain a .5 Ohm earth ground resistance providing your budget is limitless and you own a copper mine. What will it take to trip your Main 100 or 200 Amp Main Breaker? There is not enough money or copper in the world you could bury in dirt. It is all but impossible and no reason to do so. So lets look at a simple circuit. One that points out why you cannot have isolated ground rods or use earth as a conductor. On average if you drive an 8-foot rod in the dirt you obtain roughly 500 Ohms, Look at the circuit below is what you get if you used dirt as your ground conductor and obtain 5 Ohms with each rod. I use 5 Ohms in the circuit because this is a slide I use in lectures and conferences to bust the 5-Ohm requirement Telecom myth that is still exist today.

    Picture is worth a thousand words. Unfortunately many people even pros make the mistake above. It can get you killed. So how do we fix it and do it right? Look below.

    See how darn easy that is? Does dirt have anything to do with it? Nope it does not, it is just a Reference Point. All the reference does is establish a 0-Volt reference point So under normal operating condition eliminates touch potential difference between earth and the chassis of the equipment so when you touch it, there is no voltage difference. Remember it can be your mobile home or RV. Ground does not mean dirt or earth.

    More later.
    Last edited by Sunking; 01-18-2017, 09:09 PM.
    MSEE, PE

  • #2
    OK lets put what we have learned into a RV, Camper, and Mobile 12 volt application. I am showing a 1000 watt Inverter, the largest one should ever use at 12 volts. Any higher than that just gets real dangerous and almost impossible for a DIY to terminate properly. So take note just because I am showing 1000 watts does not mean you should use a Inverter that large.

    In mobile applications you need to consider wire type, in particular the Insulation and strand construction. To keep it short, you want use Marine Battery Wire (#4 AWG and larger), and Marine Primary Wire (6 AWG and smaller). It is expensive but well worth it. The insulation is good to 105 degrees C, and can be used in wet locations exposed to grease, gasoline, and diesel. The insulation is also resistant to salt air, UV, abrasion/cut resistant, easy to bend, and get through tight spots. The wire inside if fine stranded and tinned. This makes the wire resistant to corrosion and easy to work with. I strongly recommend you buy the cable from a vendor who also makes cable to your specs so you do not have to terminate the compression connectors.

    OK below is a very simple common RV/Camper setup with just an Inverter. No fuses are required or needed between the panels and controller. Panels do not produce enough current to damage the wire. You can use up to 2 parallel strings before a fuse is required.
    Please take a look at the battery and note there are two fuses installed right on the battery term post. One fuse facing the controller and another fuse facing the Inverter. It is extremely important to install your fuses and breaker right on the battery term post. Fuses are used to protect the wiring, and the minimum wire size is dependent on the fuse size. You might be asking why two. Real simple the battery is the source of power, not the panels. If for any reason the wire between the Controller and Battery were to fault to ground from say a pinched wire, you would have a dead short on the battery causing to wire to vaporize and a possible battery explosion.

    Keep the Frame/Chassis ground wires short as possible. Make sure they are tapped into structural steel like a frame member. DO NOT tap to sheet metal. Be sure to remove all paint, grease, and debris to shiny metal. Use locking hardware like Dragon Tooth lock washer and apply anti-oxidant grease to mating surfaces. Also be sure to bond the Charge Controller and Inverter as shown.

    OK the second drawing is just an expansion of the first to include DC Distribution. Nothing has really changed except to use a larger wire and fuse from the Battery to the Distribution Block. Again Marine supply distributors offer a variety of DC distribution blocks like Blue Sea.

    Final comments are you can use larger wire than shown, just do not use smaller wire. I also show a Battery Isolator in each drawing. This allows your vehicle alternator to do most of the charging. Panels are really just for show and spending your dough. The Isolator is also a power source, thus why you see it fused on both ends.

    Hope this helps.
    Last edited by Sunking; 01-22-2017, 12:39 AM.
    MSEE, PE


    • #3
      OK last installment. We are taking the system inside to your home. I really hesitated doing this because there is a lot more involved. All the rules change, and some I am certain most of you are not aware of. To start Inverters completely change. You cannot use mobile Inverters inside your home if you interconnect them to the Premise Wiring System. I bet you a dollar right now you had no idea It requires a different Inverter. It has everything to do with Grounding. Lets start with what you know. A Mobile Inverter has receptacles you can plug a cord in, and an Inverter made for Premises wiring does not. Inverters made for you home has a Hardwired Terminal along with a Main Breaker. For a small Inverter of say 24 volt @ 2000 watts will have a 20 amp GFCI Breaker. That gets connected to your Main AC Breaker Panel. Largest you will most likely run into for you guys operating at 48 or more battery voltage can see up to a 60-Amp Breaker on a 6000 watt Inverter. Do no task about 12 volt Inverters. They should not be used in your homes. Bottom Lin eif your Inverter does not carry a UL-1741 certification, you cannot use it. You can spot a Mobile Inverter a mile away or just see a picture of it. If it has receptacles, it is MOBILE.

      First thing that changes is Lightning comes into play, and with panels on your roof brings Lightning into play. In an RV or Truck you are immune to Lightning, but now that you connected to earth electrically (ground) or Grounded makes you a target. You are now asking for it. So look below and see how we handle it. All the panels and the TVSS if you use one are connected to a DOWN CONDUCTOR. The Down Conductor will hurt your wallet. Per code for a structure less than 75 feet requires a minimum 2 AWG with minimum strand size of 17 AWG if you use stranded wire and you should to stand a remote chance of terminating it properly. It can be bare, stranded, insulated or bare. It should be tinned or else you are just wasting your time and money as corrosion will do every connection in you do not use timed. Only way around it is use what the pros use, exothermic welding never fail connections. The Down Conductor runs straight down an outside wall nearest the final point of connection to the panels. Ideally it goes down the side where your PV Panels enter your home along with all utilities like phone, water, CATV, and commercial AC, That alone Is enough to keep lightning outside where it belongs. When you bring services in from different locations around your home Invites Lightning in and have a look around inside and see what you have to eat. Lightning has to have a point to enter, and a point to leave. Bring everything in from a Single Point called a Ground Window. A Ground Window is an imaginary zone within 3-feet of the Ground Window. In other words a ground bar or Ground Bonding Point on an outside wall to bond all services to and the services are within 3 cable feet of the Ground Point.

      Next you now see Over Current Protection Devices (OCPD), fuses/breakers installed on each string of panels. The reason is simple when there is 3 or more strings of panels requires OCPD. None are required or needed with just 1 or 2 strings. Panels are current sources, not voltage. As a current source maximum current is limited called Isc or Current Short Circuit. All panels have an Isc rating to be used in calculations. The highest Isc you are going to see on a solar panel is not going to be more than 9 amps. A panel with a 9 amp Isc uses 12 or 14 AWG wire. Example a 14 AWG wire with 90 degree insulation in free air can safely handle 30 amps all day and night. So if a single or two strings fault, the fault current is 9 and 18 amps respectively, and again a 14 AWG can safely handle 30 amps. So you cross a line with the 3 or more strings.

      Everything remains the same until we get into the AC Breaker Panel you use to distribute power in your home wiring aka Premises wiring. This is where the Inverter comes into play and determines what Bonding is required. In the drawing below, look at the AC breaker panel and the Main Bonding Jumper connected between Ground and the Grounded Circuit Conductor aka Neutral. This bond does the exact same thing as the bond to the Battery Negative Terminal Post does. It provides the planned Fault Current Path back to the source which is now the Inverter. Here is the kicker. You may or may not need to wire it as shown in the first drawing but rather the second drawing. See the difference? The AC panel is not required to be bonded directly to dirt. It comes from the Inverter in drawing 2.

      Why the difference. The answer lies in the Inverter. Some Inverters make that N-G bond inside and is hardwired. You have no choice but to use it because you CANNOT bond N-G again downstream. So in drawing 2 the N-G bond is inside the Inverter. Now you may ask; What is the problem with bonding the Grounded Circuit Conduct more than once? Answer is real simple, if you did would force normal load currents to flow Ground Conductors because you just put the Ground Conductor in parallel with a circuit conductor. Load current would split and flow on both conductors. You now have exposed voltage on chassis and frame you can come in contact with and get electrocuted. Current flowing through wire resistance develops voltage. All exposed metal parts of the system you want to hold at earth potential so if you touch it there is no voltage difference. If you run load current through ground conductors, you develop voltage.

      OK in the drawings I show 2 or three ground rods. Code minimum is 2 Ground rods plus bonding any water pipes, structural steel or any electrode available. Takeaway here is you use all electrodes available, especially copper water pipe in your home. So if you use a well with metal piping, It must be Bonded. If this is a Trailer house the frame will need to be bonded. The minimum is 2 rod separated by at least 6 feet (best practice is separated at least 2-times ground rod depth), and bonded together to form a common GES.

      OK to wrap up hopefully you noticed fuses and wire sizes did not change much if any at all. You use roughly the exact same size fuses, breakers, wire sizes despite the fact Inverter sizes range from 1000 to 4000 watts. A 80 Amp MPPT Controller has limits with respect to Panel Input Wattage vs Battery Voltage. But the current does not change. 80 amps is 80 amps at any voltage. With an 80 amp Controller you are restricted to the maximum panel input wattage vs battery voltage.
      1000 watts @ 12 volts
      2000 watts @ 24 volts
      4000 watts @ 48 volt.

      Battery AH capacity does not change with respect to minimum/maximum AF capacity. Assuming you are running full power input on the controller, all battery voltages will use the exact same AH capacity. At 80 amps of charge current minimum battery size is 640 AH for C/18, and maximum is 960 AH for C/12. Ideal size if 800 AH for C/10.

      Additionally there is no reason should ever need a fuse larger than 100 to 125 amps from the battery to load using 4 AWG wire. Connect the dots here, that means at 100 amps at 12 volts is a 1000 watt Inverter or load, 2000 watts @ 24 volts and 4000 watts @ 48 volts. How many ignorant people out there have a 12 volt 2000 watt Inverter? If I struck a nerve, I am talking about YOU. Take away this rule, it will keep you safer and sleep better at night. Inverter size should be no larger than your panel wattage. Keep your Inverter wattage less than or equal to your Panel wattage. Another issue is battery capacity, if you intend to run max power of 1000, 2000, or 4000 watts you had better have at least 640 AH of battery capacity.
      12 volts / 100 to 500 watts.
      24 volts / 501 to 1500 watts.
      48 volts / 1501 to 4000 watts.

      How many of you have that 2000 watt 12 volt Inverter with a 12 volt 100 AH Marine Battery? You are playing with a loaded gun my child. Look down the barrel so you can see what happens when you pull the trigger.

      If you have questions, please start a thread.
      Last edited by Sunking; 02-03-2017, 04:28 PM.
      MSEE, PE


      • #4
        Thanks for doing this. It was a good addition to the QRZ forums when you did something similar over there. If you can sometime, maybe in another thread, I'd be interested in knowing what we should look for in a ground rod as far as its ability to dissipate static and lightning, since that's all it does. In other words if the tests we do are even meaningful since they are done at power frequency.
        Steve Dold
        Say NO to useless over-quoting


        • #5
          Originally posted by sdold View Post
          Thanks for doing this. It was a good addition to the QRZ forums when you did something similar over there. If you can sometime, maybe in another thread, I'd be interested in knowing what we should look for in a ground rod as far as its ability to dissipate static and lightning, since that's all it does. In other words if the tests we do are even meaningful since they are done at power frequency.
          Thanks Steve. I assume you mean on QRZ? LPS is way beyond the scope here on this forum. Hell it is over the heads of hams. How many hams do you know that advocated their RF grounds be Isolated from the service ground? You know where I am going with that.

          Like we spoke on the phone you can take a 10-foot section of 750 MCM, about the length of any GEC, and its Impedance at lightning frequencies is well over 10 K-Ohm. Put that in series with a 5-ohm copper mine buried out side and you have a 10 K-Ohm plus to dirt. As you said we measure the 5 Ohms at extremely lower power frequencies. Care to guess what happens at HF and RF? You know where this is heading. Even 5 Ohms is meaningless and would not operate a low voltage 20 amp fuse. .

          But here is a clue. Lightning travels on the surface. You need good capacitance coupling to dirt. How do you do that? Do Flat Strip Radials going out and away from the protected structure sound good? Crow Foot! How about Parallel RC circuit? What happens as freq goes up in a parallel RC circuit. Rods are the R, Radials are the C.

          See we just lost 99% of the readers.

          Last edited by Sunking; 01-20-2017, 05:19 PM.
          MSEE, PE


          • #6
            I can answer you here here Steve, once I get Part Two done the thread will be locked and all replies deleted. Like any electrodes codes require to be at least 18 inches below surface, plus another 12-inches below frost line. Little foggy on depth? Straps lower Inductive coupling and increase capacitive coupling. Exactly what the doctor ordered for lightning. However you do not see it used much except for really critical stuff like DOD, FAA, and KFAQ (formerly home of KVOO AM Radio and Paul Harvey) in Tulsa OK.

            One trick I forgot to mention in our conversation is using Bentonite Clay to dope and backfill with. Bentonite is aka Drillers Mud, and used in most women's make-up. Yes ladies you cover your face with MUD. Bentonite has a unique electrical characteristic and takes on a negative charge when moist and does not shrink of crack on your face ladies. It reacts with copper and minerals in the soil which have a positive charge. In fact if you ever use a chemical ground rod it is required to backfill the hole you core out, place the rod down the hole and backfill with a Bentonite slurry.
            MSEE, PE


            • #7
              Originally posted by J.P.M.

              I'm a bit out of my element here, but when the copper oxidizes, what does the reduced conductivity of copper oxide do the design of a grounding system, if anything ?
              If oxidation rates are a consideration, does the drillers' mud reduce those oxidation rates ?
              When is tinning of copper recommended, if at all?
              When, if at all, besides for rigidity, is strip thickness of any consideration with respect to surface area/volume ?
              Inspection requirements (for coatings) if used ?

              Inquiring minds want to know.

              Q1 Simple tinned conductors. Also common in Substations is to back fill with Bentonite clay as it is neutral PH. If not every women's faces would be burned off.
              Q2 The cross sectional area still must meet minimum circular mills requirement. Like I said not many use it. Think military communication and EMP.
              Q3 Not required by code, best practice.
              Last edited by Sunking; 01-22-2017, 12:29 AM.
              MSEE, PE


              • #8
                Mike Substation grounds are a grid usually constructed with 250 MCM tinned copper. Keep in mind a Substation ground does two things. Lightning discharge and more importantly protect workers and equipment from HV utility fault. Example at switch or cabinet locations inside the yard you will raised steel decks for employees to stand on during switch operations. The steel plates are bonded to the Ground Grid.

                Rods are used and will be at least 20 feet up to 40 foot rods. Grid Spacing will be 2 x rod length. Power Frequencies do go deep in earth and outward, and lightning travels along the surface. The grid extends 7 feet outside the fence perimeter. If you look around you can find test videos using a dummy with a long 10-foot piece of conduit or rods. The dummy worker is holding the conduit at one end, and the other end is touch the ground. Then they induce a HV fault, and the dummy goes up in flames. Good ole Step Potential Gradient at work here. Both Lightning and HV does this. That is why you see steel platforms. The distance betwee your feet is enough to kill you during a HV fault from utility or lightning striking nearby.

                So if you get trapped outside in the open during a lightning storm. put your feet together. Not kidding, utility workers are trained to do that during switching operation if not standing on a steel plate. .
                MSEE, PE


                • #9
                  Originally posted by Sunking View Post
                  One trick I forgot to mention in our conversation is using Bentonite Clay to dope and backfill
                  We're going to be boring a hole through the concrete floor of the building in a couple of weeks to drive a ground rod for a powdercoating booth. I think I have some of the stuff you mentioned, by the way I believe it's spelled "Betonamit" according to the container. I'll backfill the hole in the floor with plenty of it and maybe a little water to be sure we get the best ground possible.
                  Last edited by sdold; 01-23-2017, 03:00 PM.
                  Steve Dold
                  Say NO to useless over-quoting


                  • #10
                    Originally posted by sdold View Post
                    We're going to be boring a hole through the concrete floor of the building in a couple of weeks to drive a ground rod for a powder coating booth.
                    Dang you, I just spewed Dr Pepper all over my keyboard from laughing. You owe me a new one. Let me guess some manufacture requires that huh? All I can say is gig them with a good ole fashion extremely high Invoice for that silliness and to buy me a new keyboard. Sounds just like the CNC idiots. Just be dang sure you run the EGC so it will work and be safe.

                    Originally posted by sdold View Post
                    I think I have some of the stuff you mentioned, by the way I believe it's spelled "Betonamit" according to the container.
                    Yep same stuff repackaged with the price jacked up. Don't feel bad, your wife and Daughter pay $10 for the same stuff in a Compact and makeup. Less than a penny worth of bentonite with a label that says Cover-Girl.
                    Last edited by Sunking; 01-23-2017, 03:32 PM.
                    MSEE, PE


                    • #11
                      Originally posted by Sunking View Post

                      [FONT=comic sans ms]Dang you, I just spewed Dr Pepper all over my keyboard from laughing.
                      You were supposed to spew Dr. Pepper for a different reason! We use it to break big rocks at radio sites.

                      I thought the current just made negative ions at the gun and those extra electrons went back to the power supply through the "ground" wire attached to the part. I don't know how a ground rod would help. Am I right, or is there a real reason for a ground rod? Other than to electrocute the operator during a nearby lightning strike. The rod was a salesman's recommendation.
                      Last edited by sdold; 01-23-2017, 03:33 PM.
                      Steve Dold
                      Say NO to useless over-quoting


                      • #12
                        Originally posted by sdold View Post
                        I thought the current just made negative ions at the gun and those extra electrons went back to the power supply through the "ground" wire attached to the part. I don't know how a ground rod would help. Am I right, or is there a real reason for a ground rod? Other than to electrocute the operator during a nearby lightning strike. The rod was a salesman's recommendation.
                        Does that answer your question? Must be the same salesman that sells CNC machines.

                        By code you can add as many Supplemental Rods as you want and can afford. However it does not permit you from excluding the EGC. That EGC just gave Lightning a path right through your electrical system inside the plant.

                        Powder coating is really simple. You can buy a unit for your home that uses 120 VAC. You have a Power Supply, than converts AC to HVDC using a transformer. You connect that wirty dord Ground (positive) lead to the object you are applying power to, and the negative terminal is inside the spray head nozzle surrounded by plastic tubes. As the powder passes by through the nozzle is charged up with negative charge and when it hits the object you are painting is a positive charge and sticks like glue. The EGC provides the protection. The EGC bonds the positive output of the rectifier, which is connected to the object with a Clamp. The paint sprayer head is also bonded to the EGC. Only the Nozzle is charged up. Touch the nozzle with the switch on and you get a nice spark of static electricity that will make you jump and piss in your pants.

                        If that is what the customer wants, give it to them. Just mo momey in your and the salesman pockets, and the customer does not need to know. The salesman just gave you plausible denial.

                        Almost forgot, Yes Steve you are right.
                        Last edited by Sunking; 01-23-2017, 04:02 PM.
                        MSEE, PE