Earthing is an essential aspect of any electrical installation. It is a system designed to protect people, equipment, and structures from electric shock and other hazards by providing a low-resistance path for electrical currents to flow to the earth. There are three commonly used earthing systems known as the TT, TN, and IT systems. In this article, we will discuss these earthing systems in detail.
TT System
In the TT system, the earthing electrode is connected to a local earth source, such as a rod or plate, and each piece of equipment is also connected to the same local earth. This system provides a low-resistance path for fault currents to flow to the earth, and is commonly used in areas where the soil resistivity is high.
The TT system is considered to be the safest earthing system, as it provides a high level of protection against electric shock. It is also relatively easy to install and maintain, as each piece of equipment is connected to the same local earth source. However, the TT system can be more expensive than other earthing systems, as it requires the installation of additional earth electrodes.
TN System
In the TN system, the earthing electrode is directly connected to the power supply neutral. The TN system can be further subdivided into three types: TN-S, TN-C, and TN-C-S.
TN-S System
In the TN-S system, the power supply neutral is directly connected to the earthing electrode, and each piece of equipment is connected to the same earthing electrode. This system provides a low-resistance path for fault currents to flow to the earth.
The TN-S system is commonly used in low-voltage electrical installations, as it is simple to install and provides a high level of protection against electric shock. However, this system can be less effective in areas where the soil resistivity is high, as the earth resistance can be too high to provide adequate protection.
TN-C System
In the TN-C system, the power supply neutral and the earthing conductor are combined into a single conductor, known as the combined neutral and earth (CNE) conductor. Each piece of equipment is then connected to the CNE conductor, providing a low-resistance path for fault currents to flow to the earth.
The TN-C system is also known as the combined system, as the neutral and earth are combined into a single conductor. This system is commonly used in low-voltage electrical installations, as it is simple to install and provides a high level of protection against electric shock. However, this system can be less effective in areas where the soil resistivity is high, as the earth resistance can be too high to provide adequate protection.
TN-C-S System
The TN-C-S system is a combination of the TN-S and TN-C systems. In this system, the power supply neutral is connected to the earthing electrode, and the CNE conductor is used to connect each piece of equipment to the earthing system.
The TN-C-S system is commonly used in low-voltage electrical installations, as it provides a high level of protection against electric shock and is relatively easy to install and maintain. However, this system can be less effective in areas where the soil resistivity is high, as the earth resistance can be too high to provide adequate protection.
IT System
In the IT system, the power supply neutral is not directly connected to the earth. Instead, each piece of equipment is isolated from the earth and connected to an isolated earthing transformer, which in turn is connected to the earthing electrode. This system provides a high level of safety against electric shock, as the fault current is limited by the impedance of the transformer.
The IT system is commonly used in high-voltage electrical installations, as it provides a high level of protection against electric shock and is relatively easy to install and maintain. However, this system can be more complex and expensive than other earthing systems, as it requires the installation of an isolated transformer and additional earthing electrodes.
Advantages and Disadvantages of Each System
Each earthing system has its advantages and disadvantages, and the choice of system depends on a variety of factors, such as the type of installation, soil resistivity, and level of protection required.
The TT system provides the highest level of safety against electric shock, but it can be more expensive to install and maintain, especially in areas with high soil resistivity.
The TN-S system is simple to install and provides a high level of protection against electric shock. However, it can be less effective in areas with high soil resistivity.
The TN-C system is also simple to install and provides a high level of protection against electric shock. However, it can be less effective in areas with high soil resistivity, and there is a risk of electric shock if the CNE conductor is damaged.
The TN-C-S system combines the advantages of the TN-S and TN-C systems and is commonly used in low-voltage electrical installations. However, it can be less effective in areas with high soil resistivity.
The IT system provides a high level of safety against electric shock, but it can be more complex and expensive to install and maintain.
Earthing is an essential aspect of any electrical installation, as it provides a low-resistance path for fault currents to flow to the earth, protecting people, equipment, and structures from electric shock and other hazards. There are three commonly used earthing systems: the TT, TN, and IT systems.
The choice of earthing system depends on a variety of factors, such as the type of installation, soil resistivity, and level of protection required. Each system has its advantages and disadvantages, and it is important to choose the system that provides the highest level of protection while also being cost-effective and easy to install and maintain.