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Electrical Earthing System Guidance for Installation and Maintenance

Author: Apogeeweb Date: 1 Mar 2021  993

why do we need earthing

Introduction

Earthing (also known as grounding) refers to the process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire, for safety and functional purposes. Generally, the "ground" of electronic equipment has two meanings: one is to connect to the "earth". Taking the earth as the zero potential, connecting the metal shell of electronic equipment and the circuit reference point to the earth can protect the safety of equipment and personnel, such as protective earthing, lightning protection earthing, etc. In addition, the earthing in the weak current system does not necessarily mean the ground connected to the earth in the true sense. It has the effect of improving the stability of the system, shielding and protecting the electromagnetic compatibility of the system, and it can also be connected to the "earth" when necessary.

What is Electrical Earthing?

Catalog

Introduction

Ⅰ Earthing Basic

1.1 Electrical Earthing

1.2 Earthing Symbols

Ⅱ What Are the Types of Earthing?

Ⅲ Why Is Electrical Earthing Important?

Ⅳ Earthing Q&A You Should Know


Ⅰ Earthing Basic

1.1 Electrical Earthing

An earthing system (UK and IEC) or grounding system (US) connects specific parts of an electric power system with the ground. Earthing is a therapeutic technique that involves doing activities that “ground” or electrically connect you to the earth. In modern earthing concepts, for line engineers, the meaning of this term is usually a reference point of line voltage; for system designers, it is often a cabinet or rack; for electrical engineers, it is safe earthing or connecting to the earth. A more general definition is a low impedance path for current to return to its source. Note that the requirements are "low impedance" and "path".

1.2 Earthing Symbols

PE, PGND, FG: Protective ground or chassis
BGND or DC-RETURN: Power supply (battery) return
GND: Work ground
DGND: Digital ground
AGND: Analog ground
LGND: Lightning protection ground

power system earthing

Ⅱ What Are the Types of Earthing?

There are many types of earthing, including single-point earthing, multi-point earthing and mixed types of earthing. Among them, single-point earthing is divided into series earthing and parallel earthing. Generally speaking, single-point earthing is used for simple circuits, such as earthing distinctions between different functional modules, and low-frequency (f<1MHz) electronic circuits. When designing high frequency (>10MHz) circuits, multi-point earthing or multilayer boards (complete ground plane) should be used. The following are four specific earthing methods.

1. Earth Floating
In electronic design, a commonly used method is floating technology. In this method, the signal ground of the circuit board is not connected to the external public ground, thereby ensuring good isolation of the circuit. The circuit is well isolated from the external ground system and is not easily affected by the interference on the external ground system. However, static electricity is easy to accumulate on the circuit and cause electrostatic interference, which may generate dangerous voltage.
Small-scale low-speed (<1mhz) equipment can use earth floating, a single-point connection to the ground by the metal shell.

2. Single-point earthing in Series
This kind of earthing method is relatively simple, and there is no need to pay so much attention to the circuit board design. So it will be used more. However, this kind of circuit will have common impedance coupling, causing each circuit module to affect each other.

3. Single point earthing in Parallel
This method of earthing, although getting rid of the common impedance coupling problem of series single-point earthing, but in actual use, it will introduce too much earthing wire annoying, as to which one needs to be comprehensively evaluated in the actual process. If the circuit board area allows, use the parallel mode, and if the connection between the various circuit modules is kept simple, then use the series mode. In general, there are power modules, analog circuit modules, digital circuit modules and protection circuit modules in the downloaded board. In this case, I use a parallel single-point earthing method.

4. Multi-point Earthing
Multi-point earthing is used more in daily circuit design, especially in multi-module circuit design. This earthing method can effectively reduce high-frequency interference problems, but it is also prone to cause earthing loops. This point must be fully considered in the design to improve the circuit stability. The working ground of small high-speed (>10MHz) equipment should be grounded at multiple points with its metal casing. The distance between earthing points should be less than 1/20 of the wavelength of the highest operating frequency, and the metal casing should be connected to the ground at a single point.
In short, in the design of electronic circuits, the most important point is to reduce the loop area of the circuit, to improve the stability of electronic design and the EMC design of electronic systems. In the actual design, have comprehensive evaluation of the above various earthing technologies to achieve the purpose of improving system stability.

electrical earthing system installation parts

Ⅲ Why Is Electrical Earthing Important?

As for earthing function, the introduction of earthing technology was originally a protective measure to prevent electrical or electronic equipment from being struck by lightning. The purpose was to introduce the lightning current generated to the ground through the lightning rod, thereby protecting the building. At the same time, earthing is also an effective means to protect personal safety. When the phase line touches the equipment shell caused by some reason (such as poor insulation of wires, aging of wiring, etc.), the equipment shell will have dangerous voltages. The generated fault current will flow through the neutral line to the ground, thereby playing a protective role. 
With the development of electronic communication and other digital fields, it is no longer sufficient to consider only lightning protection and safety in the earthing system. For example, in a communication system, the interconnection of signals between a large number of devices requires each device to have a reference ground as the signal reference ground. And with the complexity of electronic equipment, the signal frequency is getting higher and higher. Therefore, in the earthing design, special attention must be paid to electromagnetic compatibility issues such as mutual interference between signals. Otherwise, improper earthing will seriously affect the reliability of system operation. Also, the concept of "earthing" has also been introduced in the high-speed signals return technology.

 

Ⅳ Earthing Q&A You Should Know

The following questions relay on electrical earthing science and grounding physics to explain how electrical charges from the earth can have huge effects on our life. And how do you discharge the electrical energy directly to the earth by earthing technology. Also these Q&A give you considerable attention for the earthing system design and installation.

earthing system for electric shock

1. What is the difference between earth earthing and electrical earthing?
The earth is an object with very low resistance and very large capacitance. It has the ability to absorb infinite charge, and meanwhile can maintain the potential unchanged. Therefore, it is used as the reference potential of a system electrically, that is electrical earthing. In addition, in electronic equipment, when transmitting current and signal conversion at various levels of circuits, a reference potential is required to prevent interference from external signals. This potential is called logical ground or floating ground.

2. What is the difference between the ground potential and the logical ground potential?
Since the earth can absorb infinite electric charge, the potential of the earth looks macroscopically zero. Due to the influence of the natural electric field and the artificial electric field in the earth, the potential of each point of the earth is different. In engineering, 20m away from the artificial electric field is regarded as zero potential (earthing potential). The electrical ground potential is related to the current injected into the ground by the electrical system. When a large current flows into the electrical ground, the electrical ground potential may reach a very high voltage, especially when the lightning current flows into the electrical ground. The instantaneous potential of the electrical ground can reach 100,000 volts. Therefore, a separate lightning protection earthing point cannot be located in a place where have pedestrians.

3. What is the shell?
Due to the damage of the insulation layer of the wire, the phase wire is in contact with the outer shell of the electrical equipment, which is called a bumping shell. If the insulation of the phase wires and the enclosure of the electrical equipment does not meet the specified requirements, the equipment cannot be put into use. The reason for the insulation drop may be moisture or damage to the insulation layer, which can be analyzed according to the environment in which the circuit equipment is used.

4. What is the step voltage?
When an electrical device has a short-circuit fault to the ground, the fault current flows from the fault ground to the ground electrode and returns to the power source. Therefore, an electric field is generated around the ground of the fault point and the ground electrode, which is away from the ground of the fault point or the ground of the ground electrode. The closer, the higher the potential, and the farther, the lower the potential. When the distance between the two feet of a person is about 0.8 meters, standing in this electric field, because the two feet are at different potential points, there will be a potential difference. This potential difference is called the step voltage.

5. What is contact voltage?
When the insulation of electrical equipment is damaged and a short-circuit occurs to the shell, people who touch the electrical equipment will have the risk of electric shock. To define the degree of danger, the potential of the equipment 0.8 meters away from the horizontal direction of the electrical equipment when it fails is measured. The potential difference between the two is called the contact voltage.

6. What is the earthing resistance difference between the earthing electrode and the equipment?
The ratio of the earthing voltage to the earthing current is called the earthing resistance of the earthing electrode. When measuring the earthing electrode resistance in a project, an ac voltage is artificially applied to the earthing electrode, and then the current flowing into the earthing electrode is measured. The ratio of the two is the earthing resistance. The earthing resistance of the equipment is the sum of earthing wires resistances.

7. What are the classifications of earthing functions?
Generally divided into two categories: protective earthing and functional earthing
1) Protective earthing can be divided into the following 4 types:
Protective earthing: earthing the exposed conductor part of the equipment is called protective earthing. Its purpose is to prevent electrical equipment insulation damage or leakage, which may cause electric shock when people touch it.
Lightning earthing: Lead lightning into the earth to prevent electric shock or other property damage.
Anti-static earthing: Introduce static charges into the ground to prevent the accumulation of static electricity from causing harm to the human body and equipment.
Anti-corrosion earthing: Bury a metal body underground as a sacrificial anode or cathode to protect the metal body connected to it, such as a metal oil pipeline.
2) Functional earthing can be divided into the following 4 types:
Working earthing: In order to ensure the operation of the power system, earthing is done at an appropriate place in the power system, which is called working earthing. In an AC system, this point is generally a neutral point.
Logic earthing: To obtain a stable reference voltage, the appropriate metal parts in the electronic equipment are used as the reference zero potential, and the electronic parts that need to obtain the zero potential are connected to this metal part. This method is called logic earthing.
Shield earthing: Ground the metal shell or the metal net to protect the electronic equipment in the shell or the net from external electrical interference, or prevent the electrical equipment in the shell or the net from causing interference to external electronic equipment.
Signal earthing: A earthing method set to ensure that the signal has a stable reference potential.

8. What is working ground?
In order to ensure the safe operation of the electrical device, the earthing of any point (usually the neutral point of the power supply) of the device conductive part is called the working ground.

9. What is the relationship between the safety voltage and the use environment?
The safety voltage is to prevent personal electric shock. The degree of electric shock is related to the impedance of the human body, and the impedance of the human body has a great relationship with the contact condition. Under different conditions, it is different.
The relationship between human body impedance and contact conditions is usually divided into three categories:
1) High impedance: dry skin, dry environment, high impedance ground
2) Low impedance: moist skin, humid environment, low impedance ground
3) Zero impedance: for example, the human body is immersed in water

10. What is the difference between short circuit and ground fault?
The electrical connection between mutually insulated live conductors due to insulation damage is called a short circuit. For example, between phase wires of different phases, or between a phase wire and a neutral wire, exist an electrical connection, there may be a short circuit. The electrical connection error between the live conductor and the earth is called a ground fault. In addition, live conductors refer not only to the phase line, but also the neutral line. The ground refers to the metal shell of grounded electrical equipment, non-electrical metal pipes and the earth.

11. What parts of the earthing device consist of?
earthing device is a general term for earthing electrode and earthing wire.
The earthing electrode is a conductor buried in the soil or concrete foundation for dissipating current. It can be divided into two types: natural earthing electrode and artificial earthing electrode.
There are several types of natural earthing electrodes: the underground metal plumbing systems, the metal structure of the building and the reinforced concrete structure.
The artificial earthing electrode should adopt horizontally laid round steel, flat steel, metal earthing plate, and vertically laid angle steel, steel pipe, round steel, etc.

12. What are the measures to prevent direct electric shock?
Insulate charged objects
Use shields or barriers to block the human body from charged objects
Use leakage switch as additional protection

13. What are the measures to prevent indirect electric shock?
Set up automatic power-off device
Equipment with double insulation
Take ungrounded local potential connection
Electrical isolation

14. What are the types of earthing systems for high-voltage systems?
1) Direct earthing, that is, the neutral point of the transformer or generator is connected to the earthing device directly or through a small resistance (such as a current transformer). This kind of earthing method has a large earthing current when a single-phase earthing short circuit occurs, so it is also called the large current earthing system.
2) Ungrounded, the neutral point of the transformer in this system is not grounded or connected to earthing equipment such as arc suppression coils, large resistances, and the earthing device.

15. Can the natural earthing electrode be used for the earthing of DC electrical devices?
The earthing of AC electrical installations should make full use of the natural earthing electrode buried in the ground. For the earthing of DC electrical installations, it is not allowed to use the natural earthing electrode as the PE wire, earthing wire and earthing electrode of the current pattern. The earthing device is connected to the natural earthing. The distance between earthing devices and AC electrical devices shall not be less than 1m to avoid electrical corrosion.

16. What is the function of total equipotential bonding?
The function of total equipotential bonding (MEB) is to reduce the contact voltage of indirect contact electric shock in the building and different metal parts with different potential, which eliminate the dangerous fault voltage introduced from outside the building through electrical lines and various metal pipes.

17. What is supplementary bonding?
The two conductive parts are directly connected with wires to make the contact voltage of the fault drop below the contact voltage limit, which is called supplementary or additional equipotential bonding (earthing). When the earthing device fails, the indirect contact protection conditions for automatically cutting off the power supply cannot be met, supplementary bonding should be set. It should also be installed in places with special requirements such as bathrooms, hospitals, and swimming pools.

18. What is local equipotential bonding?
Local equipotential bonding (LEB) refers to the connection of multiple supplementary equipotential bonding through the bonding terminals in a local board, which is called local equipotential bonding.

19. How to check the conductivity of equipotential bonding?
1) Welding quality inspection
2) Bolt connection quality inspection
3) Measure resistance between branch and trunk

20. What are the characteristics of arc short circuits?
There are two forms of short circuit and ground fault: metallic and arc short. The current of metallic short circuit is very large, which can make the overcurrent protector (circuit breaker or fuse) act in time and the fault is not easy to go on. The short circuit point of arc short circuit has arc or electric spark and the impedance is large, therefore, the short circuit current is small. So overcurrent protection will not take effect. However, the temperature of the arc short-circuit point is very high, which can reach thousands of degrees Celsius locally. It is very easy to ignite the substances around the short-circuit point and cause a fire.
Arcing short circuit not only occur in electrical and earthing faults, but poor connections between wires can also cause it. For example, cause flickering of incandescent lamps or interference for TV sets. At this time, you must check whether the connection point of the line is reliable.

 

Frequently Asked Questions about Electrical Earthing System Basics

1. What is elecrical earthing and types of earthing?

Earthing is the first step towards electrical safety. ... Earthing is done to provide safety to user from electric shock. It is a set of conductors connected in series or in parallel in order to dissipate the potential difference immediately into the ground. The wire connected from equipment to earth called earthing wire.

 

2. What is difference between earthing and grounding?

The key difference between earthing and grounding is that the term “Earthing” means that the circuit is physically connected to the ground which is Zero Volt Potential to the Ground (Earth). Whereas in “Grounding” the circuit is not physically connected to ground, but its potential is zero with respect to other points.

Difference between Earthing and Grounding

 

3. Is grounding the same as earthing?

The key difference between earthing and grounding is that the term “Earthing” means that the circuit is physically connected to the ground which is Zero Volt Potential to the Ground (Earth). Whereas in “Grounding” the circuit is not physically connected to ground, but its potential is zero with respect to other points.

 

4. What is the purpose of earthing?

Earthing is used to protect you from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth. It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault.

 

5. Which wire is used for earthing?

copper wires
Earthing Lead or Earthing Joint
Eventhough copper wires are generally used as earthing lead, copper strips are preferred for high installation as it can carry higher values of fault current due to its wider area.

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