Reinforced concrete used for the basement of building generally has a certain electrical conductivity and a large contact area with the soil. Hence it can be used for earthing purpose. ln order to use the building basement as earthing electrode，it is necessary to confirm that the earthing is below resistance 2Ω prescribed in Ministerial Ordinance of Technical Standards for Electrical Facilities Interpretation article 22. To estimate the earthing resistance by calculation，the building basement is generally replaced by ah hemisphere electrode having the same surface as the basement. In this paper，earthing resistance obtained by three kinds of calculation methods are compared and discussed.

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