Abstract
With the developments of the society in Information Technology in recent years，electrical equipment for the home is becoming more and more advanced. More electrical appliances for the home are of greater capacity using 200V of single-phase 3 wires and there is more internet enabled information technology equipment. Protective earthing is required for these home electrical appliances to prevent electric shock and functional earthing to ensure the operation of electronic appliances. Furthermore，there is a trend to equip the panel board with a surge protective device（SPD）for the protection of the electric power line against lightning surges. Earthing is indispensable to this SPD as well. When we consider the future proliferation of electrical and computerized homes，equipment earthing is critical. This equipment earthing can be used as an earthing electrode. This approach is defined in Electricity Utilities Industry Law Interpretations and the Japanese Industrial Standard （JlS-A-4201）in our country as “Structure Earthing”，and it is implemented. As for Germany，reinforced concrete of housing is specifically used as earthing electrode. However，in our country，there is no example where housing foundation is put to practical use as an earthing electrode substitution. Hence，this paper examined the estimation of earthing resistance of housing foundation used as a substitute earthing electrode，considering the size and form of the foundation.
