Electrical installation earthing

The Electrical Installation Equipment Manufacturer s Association (UK). Earth Leakage Circuit Breaker. 

Earth connections for electrical installations as well as process units, storage tanks, pipelines, and gas lines handling inflammable materials shall be as per instmetions/standard practice. 

Earthing is the connection of the exposed conductive parts of an electrical installation to the main protective earthing terminal of the installation. 

Let us first define some of the words we will be using. Chapter 54 of the lET Regulations describes the earthing arrangements for an electrical installation. It gives the following definitions ... 

Extraneous conductive parts - the structural steelwork of a building and other service pipes such as gas, water, radiators and sinks. They do not form a part of the electrical installation but may introduce a potential, generally earth potential, to the electrical installation. 

The installation earthing arrangements are indicated by the second letter, where T means the exposed conductive parts are connected directly to earth and N means the exposed conductive parts are connected directly to the earthed point of the source of the electrical supply. 

Result of short circuit or short circuit to earth because of faults in electrical installations... 

P. Thurnherr, Electrical installations design, selection, erection and inspection, in lECEx International Conference Kuala Lumpur, Malaysia, 2014-L.C. Towle, A Definitive Guide to Earthing and Bonding in Hazardous Areas, The MTL Instruments Group Pic, May 1997. TP1121—1. 

Section 3.2 of Chapter 3 of the lET Electrical Installation Design Guide tells us that the basic design intent is to use standard final circuits wherever possible to avoid repeated design. Provided that earth fault loop impedances are below 0.35 ohm for TN-C-S supplies and 0.8 ohm for TN-S supplies the standard circuits can be used as the basis of all final circuits. 

In your own words, state the meaning of earthing and bonding. What types of cables and equipment would an electrician use to achieve earthing and bonding on an electrical installation ... 

An electrical earth system comprises the provision on the supply system of an earth connection to facilitate earth fault current flow, the connecting of all exposed metalwork within the installation to a common grounding terminal and the connection of this terminal to earth. For a complete installation the principal factors which need to be considered, are ... 

TT system All exposed conductive parts of an installation are connected to an earth electrode, which is electrically independent of the source earth. 

If the positive potential changes are very small and confined to a few points on a small unprotected structure, it may be practicable to reduce the potential at these points by installing reactive anodes. The anodes will probably be most effective if they can be buried between the two structures. In some circumstances a similar screen of zinc, aluminium or steel may be installed between the structures. The screen must be electrically connected to the unprotected structure since it is installed with the object of providing an electrolytic path to earth for the interaction current. 

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