Electrical grounding or ? Grounding ? originally began as a safety measure used to help prevent people from accidentally coming in contact with electrical hazards. Think of your refrigerator. It?s a metal box standing on rubber feet with electricity running in and out of it. You use magnets to hang your child?s latest drawing on the metal exterior. The electricity running from the outlet and through the power cord to the electrical components inside the refrigerator are electrically isolated from the metal exterior or chassis of the refrigerator.
If for some reason the electricity came in contact with the chassis, the rubber feet would prevent the electricity from going anywhere and it would ?sit?, waiting for someone to walk up and touch the refrigerator. Once someone touched the refrigerator, the electricity would flow from the chassis of the refrigerator and through the unlucky person, possibly causing injury. Grounding is used to protect that person. By connecting a wire to the metal frame of the refrigerator, if the chassis inadvertently becomes charged for any reason, the unwanted electricity will travel down the wire and out safely into the earth; and in the process, trip the circuit-breaker stopping the flow of electricity. Obviously, that wire has to connect to something that is in turn connected to the earth or ground outside.
The process of electrically connecting to the earth itself is often called ?earthing?, particularly in Europe where the term ?grounding? is used to describe the above ground wiring. The term ?Grounding? is used in America to discuss both earthing and grounding. While grounding may have originally been considered only as a safety measure, with today?s advances in electronics and technology, grounding has become an essential part of everyday electricity. Computers, televisions, microwave ovens, fluorescent lights and many other electrical devices, generate lots of ?electrical noise? that can damage equipment and cause it to work less efficiently. Proper grounding cannot only remove this unwanted ?noise?, but can even make surge protection devices work better.
An electrode is anything placed into the ground that is used to provide an electrical connection to the earth. The most common electrode is the copper-clad driven grounding rod. This grounding rod is essentially an 8 or 10-foot long shaft of mild-steel, thinly coated with copper and driven into the earth. The process of installing an electrode would be called ? earthing ?. Other electrodes included concrete-encased electrodes, ground plates, water pipes, building foundations, and electrolytic grounding rods, to name a few.
Each electrode has its own unique advantages and disadvantages. In the case of the copper-clad driven rod, it is very inexpensive to purchase, but can be overly labor-intensive and time-consuming to install. It also has some poor electrical properties. On the other hand, electrolytic rods while cost prohibitive, out perform any other grounding electrode on the market today.
The most common performance criteria or specification used today is Resistance-to-Ground or commonly called ?ground resistance?. In the electrical world, resistance is anything that opposes the flow of electricity. Do you remember all the hype about ?super conductors? that has been in the news for the last decade or so? With super conductors, Scientists are trying to develop a material with zero resistance to electricity. They have yet to succeed at any practical level.
It turns out, that all known materials have an electrical resistance at some level, even copper. So as you can imagine, dirt, rock and sand have varying resistances, and based on the particular composition of the soil, the resistance to electricity that your particular part of the earth provides can be very different. In fact, the resistance of the soil (per cubic meter) can vary from location to location by thousands of ohms (ohms is a unit of measurement used for resistance) and that can make a big difference in how effective your grounding will be. Resistance-to-Ground (or ground resistance) is a measurement of the actual resistance of the electrodes in the grounding system. The measurement is made in ohms with a target level of 25-ohms or less being mandated by the National Electric Code. * Technology companies commonly require a target of 5-ohms or less to maintain valid warranty requirements.
* The National Electric Code (NEC) has a series of rules and exceptions regarding this target, and should be referenced directly for further information.
We can measure the electrical resistance of almost anything, including soil. Understanding the resistance to electricity that the soil provides enables engineers to draft and design grounding systems to meet engineering specifications. The difference between resistance and resistivity is relatively simple. Resistivity is resistance placed in terms of weight or volume, such as, ?the resistance of a pound of copper? or ?the resistance of a gallon of water ? In the case of soil, we want to measure a particular volume, typically a cubic meter. So, the resistivity of soil is given in ohmmeters.
It is impossible to get the resistance of <10 with individual electrodes in all areas. All standards of repute including IS, BS, IEEE80 etc categorically state, the resistance of the electrode depends on soil resistivity.
Yes, you can install earth electrode without back fill compound. As you are aware that earth resistance value depends on soil characteristics which varies from place to place with seasonal variation, the earth pit without back fill compounds may exhibit different resistance value at different places in different soil conditions.
To overcome these problems, use of mixture coal and salts are recommended by different national and international standards. The salts and moisture present in the earth pits reduces the soil resistivity and coal that absorbs and retain the moisture around the earth pipe, thus helps in maintaining low earth resistance value. Similarly, we also recommend and suggest the use of Back Fill Compounds inside the earth pit, instead of conventional mixture of salt & coal as the use of Back Fill Compounds reduces the possibility of fast corrosion of earth pipe. The Back Fill Compounds which is a mixture of eco-friendly minerals reduces the rate of corrosion of the earth electrodes. The BFCs suggested by us has all the requisite quality that an ideal back fill compounds should have. Nevertheless, you as per your requirement and understanding, are free to use any suitable back fill compounds that are available in the market in different name.
The JEF ECOSAFE earth pit can definitely be closed with concrete / tiles etc.. However, if any garden / lawn / rain water harvesting facilities are in the vicinity, they will be useful in increasing the moisture content in the surrounding soil which relies the resistance.
In some UPS systems which have an isolation transformer, a separate neutral is derived on the output side through a dedicated earth pit. No other connections shall be made to this earth pit apart from UPS neutral. However, this earth pit shall be connected to the general earth grid underground to achieve equi-potential.
The type of metal used has no significance on the earth electrode resistance. None of the formulae given in any of the international standards factor in the type of metal in calculation of the earth resistance. However, it is to be noted that the copper electrode has a higher current handling capability as compared to the GI / steel electrode. Also in highly corrosive areas, use of GI / Steel electrode may not be appropriate. Copper or copper coated electrodes have a better resistance to corrosion and hence are better suited in such areas.
With the increased degree of sophistication in all equipments, the grounding system needs to be reliable over a long term to ensure safety and proper working of these equipments. Besides, all industries are facing a shortage of manpower and as such they are not watered regularly . Also, it may not be possible to test the Earth Pits frequently. Also, in a lot of cases the Earth Pits may not be accessible after a few months / years due to various reasons. Further, in a running unit, disconnecting some Earth connections may warrant Shutdown. This coupled with the fact that the equipments are far more sensitive today makes a clear case for adopting maintenance free earthing solutions in all scenarios.
The BS-7430 ? 2011 provides a formula vide Clause No.9.5.7 Page 40 which is as below:
• P is the resistivity of soil, in ohm metres (?);
• Pc is the resistivity of infill material, in ohm metres ?);
• d is the diameter of electrode, in metres (m);
• D is the diameter of infill (Backfill), in metres m);
• L is driven length electrode, in metres (m);
The above formula specifically gives a weightage to the resistivity of the in-fill material. The lower the resistivity of the in-fill material, lower will be the overall earth resistance (this fact is mentioned in all standards like IS-3043, BS-7430 and IEEE-80 .The resistivity of our backfill material is less than 0.1 O Mtr and thus , by using our special Backfill, the reduction in resistance between 30 to 60% over conventional earthing systems can be obtained for a given site conditions.
As mentioned in all the standards like IEEE & BS etc, the inner shell of soil closest to the electrode comprising the bulk of the electrode ground resistance to remote earth. As per the Table given in IEEE No 9,The first 100 mm around the electrode accounts approximately for 38 to 50% of the total resistance. Hence by having a highly conductive compound, the electrode in a 4 inches (100 mm) dia bore hole, upto 30 to 60% of the total resistance can be controlled. This is the reason why a 4? bore hole filled with our Backfill compound offer lower resistance to the tune of 35 to 50%. Bore sizes beyond this will not be cost effective.
In that case, we suggest you have the earthing tested. The traditional earthing methods have been plagued with corrosion and low conductivity problems for decades. The conventional earthing system methods have a very short service life. They become ineffective and are as good as no earthing at all.
Our earthing systems have proven over the last decade that a circular cross section is the best suited design for equal & fast dissipation of current through the electrode and into the earth. We have carried out developmental work on the plate ? in ? pipe design earlier, but dropped it as it was inefficient and prone to long term problems.
Since the earthing system works underground, lot of environmental factors come into play to decide the life of the earthing system. They include
• Soil conditions
• Moisture content
• Climate changes
• Soil resistivity
• Types of soil (normal, sandy, semi rocky, rocky etc.)
• Acidity levels of the soil
• Basic maintenance schedule
Apart from the above, it is very crucial that the installation of the earthing system is done as per specifications, non adherence will not only drastically reduce service life of the system but also hinder earth resistance results.
We can offer a variety of solutions for rocky areas like counterpoise earthing, radial earthing, Mat earthing, Satellite earthing , deep bore earthing etc. Depending on the site conditions and the requirements / applications, the right solution can be adopted. Our team will be happy to help you in suggesting a right method once all the required inputs are shared with us.
The resistance can be lowered only by altering the medium adjacent to the electrode. The IEEE80, IS3043 and BS 7430 have all mentioned as under: ?To obtain overall low resistance, current density should be as low as possible for the MEDIUM ADJACENT TO THE ELECTRODE which should be so designed to cause the density to decrease rapidly with distance from the electrode.? The IEEE80 has also mentioned that the soil around the electrode should be modified to obtain a low earth resistance. Thus the most important factor for obtaining low resistance value is SOIL TREATMENT i.e. the material around the electrode ? which is the backfill material and not the electrode itself.
The basic objective of good earthing is to ensure the safety of life and property from shock and fire. Lightning, Surges or Unintentional contact between an energized electric conductor and the metal frame or structure that encloses it or an insulation failure in electrical equipment etc., can cause dangerously high voltages in the electrical distribution system. Under such circumstances, grounding provides an alternative low impedance path and thereby minimizes damages. A good and an efficient earth ensures that all parts of apparatus other than the live parts shall be at earth potential, i.e. zero at all times.
Anyplace where electricity is used, earthing is important for safety of life and property. This can include
• Telecommunication towers
• Power transmission towers & HT/LT lines
• Power generation plants
• High rise buildings
• Production plants
• Windmills etc.
Unfortunately, our electrical ecosystem is not perfect. It is constantly attacked by high voltages, fault currents,surges, short circuits & lightning all of which can turn deadly. So, any structure which has electricity running through it needs earthing for the protection of property and life.
As explained earlier in Point No. 13 the earth resistance largely depends on the resistivity of the soil (Mother Earth) at site. This soil resistivity changes seasonally and will vary through the year depending on the weather and other extraneous conditions. As such, the earth resistance also will vary in tandem with variations in soil resistivity. Further, it has also been recorded by various agencies like CBIP etc, that the soil resistivity in a given place changes over time. Consequently, the earth pit resistance will also change over the years. However, it is to be noted that this variation will be generally limited to a bandwidth of around 25%.
While Bentonite clay is effective in certain areas, it cannot be of help in all / dry areas. As per the IEEE 80 ?Bentonite has a resistivity of 2.5 Ohm Mtr at 300% moisture. It may not function well in a dry environment because it may shrink away from the electrode increasing the electrode resistance.