Earthing System for Industrial Installations

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Earthing System for Industrial Installations

Earthing System for Industrial Installations- A system consists of an electrical installation and its supply. According to I.E.E regulations, an earthing system can be classified into three or four alphabetic names. The explanation of these characters is as follows;

(i). The first alphabet reflects the supply earthing system

T= Represents the direct earthing of one or more supply places.

I = Denotes that supply has either not been earthed altogether or it has been earthed through the fault limiting impedance.

(ii). The second alphabet represents earthing of the installation;

T = All exposed carrying metal parts have been earthed directly.

N = All exposed recipient metal parts have been connected directly with an earthed supply conductor

(iii). The third and fourth alphabet reflects the arrangement of the earthed supply conductor;

S = Represents isolated neutral and earth conductors

C= Represents a combination of neutral and earth into one single conductor

The afore-mentioned explanation can also be described as follows;

T.I System

This system represents the supply earthing system. The first alphabet in T.I system i.e., “T” represents the direct earthing of one or more spots of a supply, whereas the other character “I” denotes that supply has not been earthed at all, or it has been earthed through a fault limiting impedance.

T.N System

This system represents an arrangement of earthing for installation. The alphabet “T” in the T.N system means that all exposed conductive metal parts have been earthed directly, whereas “N” means that all exposed conductive metal parts have been connected to the directly earthed supply conductor.

S.C System

This system represents an arrangement of the earthed supply conductor. The alphabet “S” in the S.C system denotes isolated neutral and earthed conductor, whereas “C” signifies that neutral and earth have been joined together into a single conductor or used as a single conductor.

Based on the aforementioned arrangements, or with the help of the above–mentioned groups, the following earthing systems are devised for industrial installations;

TT – Systems

According to I.E.E regulations 514–7 and 542–4, the majority of installations providing electricity through overhead supply, are provided protection by means of this system. In other words, the T.T system is such a standard arrangement for most of the installations fed via overhead supply, through which these installations are provided security (i.e., installations are provided safety). The earth and neutral conductor are isolated or separated from each other in the installation, and the supply company does not provide any earthing terminal. All exposed conductive parts installed within this system are connected together through an earth electrode, which remains independent of the earth source. This has been illustrated in figure 8.1.

Figure 8.1

TN – S System

The earthing of all those installations which are provided supply through an underground cable is carried out under this type of system. This system is most commonly used nowadays, i.e., this system has become very popular and its application is widespread. In this system, the armor of a supply cable or an isolated safety conductor (PE) is used. Under this system, all exposed conductive parts of a consumer’s installations are connected to the protective conductor i.e., PE through earthing terminal. This has been illustrated vide figure 8.2. In other words, all exposed conductive parts of a consumer’s installation or earthing terminals, are connected to the power supplier’s protective conductor (PE) in this system.

Figure 8.2

TN – C System

According to I.E.E regulation 524 – 5, protective earth and neutral conductors are connected together to form a combination of protective earth and neutral conductors i.e., PEN which is used both in supply as well as installation. This system has been illustrated in figure 8.3.

Remember that this system is not used directly on any public supply, but rather used under certain specific conditions e.g., private plants, etc.

This system is also known as protective multiple earthing. In this system, a neutral conductor, as well as a protective conductor, are joined together to form a PEN conductor, or a combined neutral earth (CNE) conductor. A separate conductor is used as a protective conductor in the installation. This has been illustrated in figure 8.4. This system actually is a combination of the TN – C, and TN – S system (as the name of this system implies) and contains merits or advantages of both these systems.

Figure 8.3

Figure 8.4

TI – System

According to IEE regulations 542 – 7 and 542 -4, this earthing system is not used in public supply, rather this system is used in mines, etc., under certain specific circumstances. All exposed parts in this system are joined with the earth electrode, whereas the supply is earthed through an impedance. This has been illustrated in figure 8.5, or it is made independent of earth.

Figure 8.5