| Résumé | Earthing systems play an essential role in electrical systems in terms of safety for people in the vicinity against the hazard of electric shocks as well as protection and proper operation of equipment during the incidence of faults. Both are achieved by providing a low-impedance path that can dissipate fault currents to the conductive mass of Earth. One of the first steps in the design of an earthing system is estimating the total resistance to earth and determining the proper size and basic layout of the earth electrode required. Engineers must design adequate earthing systems that comply with international standards and national regulations, which in fact incorporate a variety of earthing methods and various formulae to obtain the design parameters, especially the earthing resistance. The effects of using the varied formulae for each earthing technique are ambiguous and entail considerable risks, and thus require comprehensive compilations and critical examinations. This paper reviews many of the earthing design formulae available in widely used international standards and published scientific papers for a comparative analysis of their differences. The results of a rigorous survey for each earthing type, based on respective electrical resistances’ calculations evaluated for a specified range of resistivities, are presented in line graphs to show precise trends. A recommended list of the most conservative formulae from a safety perspective, based on the results obtained, is outlined as a basis for computing the earthing resistance for designing effective earthing systems. This provides a beneficial compact reference to facilitate the revision and provision of international earthing standards agreement. |
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