Earthing has been accomplished through bonding of a metallic system to earth

21 Mar 2022

Earthing equipment refers to various devices used for transferring electricity directly to the earth’s plate. Some of the commonly used earthing equipment includes low resistance cables, insulated operating rods, pruning heads, clamp sticks, specialist and earth clamp application heads and operating rod bags. These components connect buildings with a conductive surface placed inside the earth or at a neutral point in the soil for enhanced safety. They provide protection from significant electrical disturbances, such as lightning strikes and power surges and aid in minimizing the risk of electric shock from current leaking from uninsulated metal parts of electrical devices. As a result, they are commonly used in commercial and residential buildings and industrial plants.

Earthing Equipment Market Trends:

Rapid industrialization, along with significant growth in the construction industry in recent years, represent as the key factors creating a positive outlook for the market. With the increasing construction of commercial and residential buildings, roads, tunnels, manufacturing plants and railways tracks, especially in developing nations, there is a growing requirement for efficient earthing equipment. This, in turn, is contributing to the market growth. Earthing is essential in buildings to protect residents, machinery and appliances from electrical surges and dissipate short circuit current. Additionally, various technological advancements, such as the integration of consumer electronics with artificial intelligence (AI) and the Internet of Things (IoT), are acting as other growth-inducing factors. This has resulted in the increasing utilization of smart devices, such as televisions and refrigerators, which require constant earthing, thereby creating a positive outlook for the market. Other factors, including the increasing product demand from automobile manufacturers, along with the reconstruction of the existing power grids, are anticipated to drive the market further.

The purpose of earthing is to minimize risk of receiving an electric shock if touching metal parts when a fault is present. Generally green wire is used for this as a nomenclature. Under fault conditions the non-current carrying metal parts of an electrical installation such as frames, enclosures, supports, fencing etc. may attain high potential with respect to ground so that any person or stray animal touching these or approaching these will be subjected to potential difference which may result in the flow of a current through the body of the person or the animal of such a value as may prove fatal then they may get shocked. The earthing discharges the leakage current to the earth and hence avoid the personnel from the electric shock. It also protects the equipment from lightning strokes and provides the discharge path for the surge arrester, gap and other devices. 

 To avoid this non-current carrying metal parts of the electrical system are connected to the general mass of earth by means of an earthing system comprising of earth conductors to conduct the fault currents safely to the ground. Earthing has been accomplished through bonding of a metallic system to earth. It is normally achieved by inserting ground rods or other electrodes deep inside earth. Earthing is to ensure safety or protection of electrical equipment and human by discharging the electrical energy to the earth. The earthing is achieved by connecting the parts of the installation to the earth by using the earth conductor or earth electrode in intimate contact with the soil placed with some distance below the ground level.

The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire is known as the electrical earthing. The electrical earthing is done by connecting the non-current carrying part of the equipment or neutral of supply system to the ground. Mostly, the galvanised iron is used for the earthing. The earthing provides the simple path to the leakage current. The short-circuit current of the equipment passes to the earth which has zero potential. Thus, protects the system and equipment from damage.

The earthing mat or electrode under the ground level have flat iron riser through which all the non-current-carrying metallic parts of the equipment are connected. When the fault occurs, the fault current from the equipment flows through the earthing system to the earth and thereby protects the equipment from the fault current. At the time of the fault, the earth mat conductors rise to the voltage which is equal to the resistance of the earth mat multiplied by a ground fault. The contacting assembly is called earthing. The metallic conductors connecting the parts of the installation with the earthing are called electrical connection.

What is a solidly earthed system?

A device or a system can be said to be solidly earthed if it is electrically connected to an earth electrode without the intention of additional resistance or impedance in earth connection, and this system can protect the device from over-voltages.

What are the objectives of earthing?

It can provide an alternative path for the fault current so the fault current can travel in that path without damaging the equipment or endanger the user. The conductive parts which are exposed won’t reach a dangerous potential. Voltage can be maintained in an electrical system by preventing over current and excessive voltages. Low impedance path will be provided to the fault current and by this; it can ensure the correct operation of protective devices.

Why do we need earthing?

Earthing is done for the safety of humans, equipment, and property and if there is no effective
earthing then it could lead to the loss of property and lives.

It can ensure the safety of property and lives.  It can prevent insulation breakdown by keeping the system voltage under limits when a fault condition occurs. It can provide an equipotential platform where electronic equipment can be operated. Electrical noise in the cable can be reduced by providing an alternating path for induced current. It can minimize arcing faults.

What is the difference between system earthing and equipment earthing?

System earthing is done by considering the protection of electrical equipment, by stabilizing voltages with respect to ground. Whereas the equipment earthing is done for the protection of the personnel by maintaining the potential of non-current carrying equipment at or near earth potential. Mostly the system earthing is done by earthing the neutral of the supply system. In case of fault conditions the non-current carrying conductors of the electrical installations such as frames, enclosers, fencing could attain high potential with respect to ground so it would be dangerous to the person who comes in contact with it, to avoid this equipment earthing is done by connecting the non-current carrying conductors of the electrical system to the earth, it is done by the earthing system which consists of earth electrodes which conduct the fault current safely to ground.

Why coal and salt is added in earth pits

Coal is added to earth pits because it is a bad conductor; it is made up of burning wood. It has a property of absorbing water because it is porous. Salt is added to earth pits because it is basically sodium chloride and when it comes in contact with water it breaks into ions and helps in electrical conduction.

Aim of Earthing:

The earthing system is essential for any electrical installation to avoid dangers associated with fault currents and lighting strikes. A properly designed common earthing system is used for both electrical system and lighting protection system. An earthing system comprises of protective earthing conductor, equipotential bonding bars, connectors and earthing electrode. A good earthing system aims as:

Protect installations and equipment by providing a low impedance path for fault current.

Ensures that all exposed conductive parts do not reach a dangerous potential. Avoid the risk of fire in electrical installation system. Provide security for people by limiting step and touch voltages – by providing an alternate path for the fault currents to flow. Provide safe path to dissipate lighting and short circuit currents. The earthing provides the easiest path to the flow of short circuit current even after the failure of the insulation. Improve the quality of the signal by equal signal reference and minimize electromagnetic noise. Provide stable platform for operation for sensitive electronic equipments i.e. to maintain voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the equipment.

Earth Electrodes

 In general horizontal ring earthing combined with vertical earth electrodes shall be used. In horizontal earth electrode, copper coated steel round solid conductor of 10 mm size shall be used. Horizontal earth conductor shall have minimum number of joints. The minimum length between joints shall be greater than 20 meters. Vertical earth electrodes shall be of copper coated solid steel with minimum coating thickness of 250 microns. Each electrode shall be 1 meter long with suitable coupling mechanism between roads so that multiple rods can be driven deep in soil.

Conductive concrete based earth enhancing materials shall be used for back filling the augured earthing hole after inserting the vertical earth electrode. Approximately 25 kg’s earth material shall be used for a three meter road inserted in a 100 mm augured whole in a slurry form. The earth enhancing material shall not contain Bentonite content. All joints under soil shall be exothermically welded. Joints with SS clamps and SS bolts are allowed only in exposed area. If one earth electrode does not provide required value, additional rods shall be installed ideally two rod lengths apart, but as a minimum at 1 rod length apart. The more electrodes used, better will be the electrical connection to the earth. Connect all vertical electrodes together with a horizontal earth conductor and finally to the equipotential bonding but at the shelter’s power entry panel.

When the ordinary earth electrode provides a poor earth resistance and value is not stable throughout the year, particularly in places with rocky soil, chemically charged electrodes can be used. The chemically charged electrodes shall be 3 meters long, made of copper pipe with minimum external diameter of 55 mm and thickness of 2.5 mm. The chemicals filled inside the charged electrode leaches into the nearby soil and provide a low resistance value. Care should be taken while providing the earth electrode under the ground:

The earthing electrode should not be placed near the building whose installation system is earthed more than 1.5 m away. The resistance of the earth wire should not be more than 1 ohm. The wire use for electrode and circuit should be made up of the same material. The electrodes should be placed in vertical position so that it can touch the layers of the earth.

Types of Electrical Earthing

The electrical equipment mainly consists of two non-current carrying parts. These parts are neutral of the system or frame of the electrical equipment. From the earthing of these two non-current carrying parts of the electrical system earthing can be classified into Neutral Earthing and Equipment earthing. In neutral earthing, the neutral of the system is directly connected to earth by the help of the GI wire or GI strip. The neutral earthing is also called the system earthing. Such type of earthing is mostly provided to the system which has star winding. For example, the neutral earthing is provided in the generator, transformer, motor etc.

Equipment type of earthing is provided to the electrical equipment. The non-current carrying part of the equipment like their metallic frame is connected to the earth by the help of the conducting wire. If any fault occurs in the apparatus, the short-circuit current to pass the earth by the help of wire. Thus, protect the system from damage.

Grounding:

Grounding means connecting the live part (it means the part which carries current under normal condition) to the earth for example neutral of power transformer. Grounding is done for the protections of power system equipment and to provide an effective return path from the machine to the power source. For example grounding of neutral point of a star connected transformer. Grounding refers the current carrying part of the system such as neutral (of the transformer or generator). Because of lightening, line surges or unintentional contact with other high voltage lines, dangerously high voltages can develop in the electrical distribution system wires. Grounding provides a safe, alternate path around the electrical system thus minimizing damage from such occurrences. Generally Black wire is used for this as a nomenclature.

In grounding, the current carrying parts are directly connected to the ground. The grounding provides the return path for the leakage current and hence protect the power system equipment from damage. When the fault occurs in the equipment, the current in all the three phases of the equipment become unbalance. The grounding discharges the fault current to the ground and hence makes the system balance. The grounding has several advantages like it eliminates the surge voltage and also discharge the over voltage to the ground. The grounding provides the great safety to the equipment and improves the service reliability.

All electrical/electronic circuits (AC & DC) need a reference potential (zero volts) which is called ground in order to make possible the current flow from generator to load. Ground is may or may not be earthed. In electrical power distribution it is either earthed at distribution point or at consumer end but it is not earthed in Automobile (for instance all vehicles’ electrical circuits have ground connected to the chassis and metallic body that are insulated from earth through tires). There may exist a neutral to ground voltage due to voltage drop in the wiring, thus neutral does not necessarily have to be at ground potential.

In a properly balanced system, the phase currents balance each other, so that the total neutral current is also zero. For individual systems, this is not completely possible, but we strive to come close in aggregate. This balancing allows maximum efficiency of the distribution transformer’s secondary winding.

Basic difference between Grounding and Earthing:

In grounding the current carrying part is connected to ground whereas in earthing the body of the equipment is connected to ground. Grounding is the link between the neutral of the equipment and ground whereas earthing is the link between the equipment body and earth pit which is placed under the earth surface. Grounding protects the power system equipment whereas earthing protects the human from electric shock. Grounding provides the return path to the current whereas earthing discharges the electrical energy to the earth.

Three types of grounding generally used in electrical network namely Solid grounding, Resistance grounding and Reactance grounding. Types of earthing used in electrical system/network are Pipe earthing, Plate earthing, Rod earthing, earthing through tap and strip earthing. Grounding indicated by black color and earthing indicated by green color. Grounding use for balancing the unbalance load whereas earthing use for avoiding the electrical shock. Neutral of generator and power transformer is connected to ground. The enclosure of the transformer, generator, motor etc. is connected to the earth.

The grounding wire is placed between the neutral of the equipment and the earth whereas in earthing the earth electrode is placed between the equipment body and the earth pit which is placed under the ground. In grounding the equipment is not physically connected to the ground, and the current is not zero on the ground, whereas in earthing the system is physically connected to the ground and it is at zero potential.

The grounding gives the path to an unwanted current and hence protects the electrical equipment from damage, whereas the earthing decreases the high potential of electrical equipment which is caused by a fault and thus protects the human body from the electrical shock.

Functional difference between earthing & Grounding:

There is no major difference between earthing and Grounding, both means “Connecting an electrical circuit or device to the Earth”. This serves various purposes like to drain away unwanted currents, to provide a reference voltage for circuits needing one, to lead lightning away from delicate equipment. Even though there is a micro difference between grounding & earthing.

Balancing the Load Vs Safety:

Ground is a source for unwanted currents and also as a return path for main current some times. While earthing is done not for return path but only for protection of delicate equipments. It is an alternate low resistance path for current. When the neutral for a three phase unbalanced connection take out and send it to ground, it is called grounding. Grounding is done to balance unbalanced load. While earthing is used between the equipment and earth pit so as to avoid electrical shock and equipment damage.

Equipment Protection Vs Human Safety:

Earthing is to protect the circuit elements whenever high voltage is passed by thunders or by any other sources while Grounding is the common point in the circuit to maintain the voltage levels.  Earth is used for the safety of the human body in fault conditions while Grounding (As neutral earth) is used for the protection of equipments.

Earthing is a preventive measure while Grounding is just a return path:

The ground conductor provides a return path for fault current when a phase conductor accidentally comes in contact with a grounded object. This is a safety feature of the wiring system and it would never expect to see grounding conductor current flow during normal operation. Do not Ground the Neutral Second time When It is grounded either at Distribution Transformer or at main service panel of consumer end. Grounding act as neutral. But neutral cannot act as ground.

System Zero Potential Vs Circuit Zero Potential:

Earthing and Grounding both is refer to zero potential  but the system connected to zero potential is differ than Equipment connected to zero potential .If a neutral point of a generator or transformer is connected to zero potential then it is known as grounding. At the same time if the body of the transformer or generator is connected to zero potential then it is known as earthing.

The term “Earthing means that the circuit is physically connected to the ground and it is Zero Volt Potential to the Ground (Earth) but in case of “Grounding” the circuit is not physically connected to ground, but its potential is zero(where the currents are algebraically zero) with respect to other point, which is also known as “Virtual Grounding.” Earth having zero potential whereas neutral may have some potential. That means neutral does not always have zero potential with respect to ground. In earthing we have Zero Volt potential references to the earth while in grounding we have local Zero Volt potential reference to circuit. When we connect two different Power circuits in power distribution system, we want to have the same Zero Volt reference so we connect them and grounds together. This common reference might be different from the earth potential.

Illegal Practice of interchange Purpose of Grounding & earthing wire:

Neutral wire in grid connections is mandatory for safety. Imagine a person from 4th floor in a building uses Earth wire (which is earthed in the basement at Basement) as neutral to power his lights. Another Person from 2nd floor has a normal setup and uses neutral for the same purpose. Neutral wire is also earthed at the ground level (as per USA practice Neutral is Grounded (earthed) at Building and as per Indian Practice it is Grounded (earthed) at Distribution Transformer). However, ground wire (Neutral wire) has a much lower electrical resistance than Earth Wire (Earthing) which results in a difference of electrical potential (i.e. voltage) between them. This voltage is quite a hazard for anyone touching a Earth wire (Metal Body of Equipment) as it may have several tens of volts.

The second issue is legality. Using ground wire instead of neutral makes you an energy thief as the meter uses only the Phase and neutral for recording your energy consumption. Many Consumers make energy theft by using Earthing wire as a Neutral wire in an Energy meter.

Conclusion:

The Earth Resistance measurement could be carried out at selected points along its route. The Earth Resistance profile varies between 10 Ohms and 20 Ohms. Soil identifications as well as programmed intensive field measurements of soil resistivity and earthing system at selected sites proves that soil resistivity values’ depend on the type of soil. In rocky areas, the resistance could be lowered by a buried network of well-designed earth mat or by a network of buried counterpoise earth wire in order to reduce the effect of lightning stroke. For better earthing of electrical systems the soil resistivity should be improved for effective earthing of system.