Tweet
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.
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.
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.
- Electricity takes the path of least resistance.
- Electricity takes the path of least resistance to ground.
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.
Comment