To prevent the electric breakdown of an electric facility within a structure struck by lightning, and to see that lightning damage may not extend to other structures.
This excessive voltage prevention device 10 comprises a grounding electrode 22 which is connected with the casing 20A of an electric facility 20 provided within a consumer's structure, a distribution line 16 for supplying power to the electric circuit 20B of the electric facility 20, a surge protection device 26 which is connected between the distribution line 16 and the grounding line 22, a surge protection device 34 whose one end is connected with the distribution line 16, and a grounding electrode 32 which is connected with the other end of the surge protection device 34 and is provided, at such a distance that a current does not flow from the grounding electrode 22, away from the grounding electrode 22, and has such a grounding resistance value that the potential of the distribution line 16 is under the estimated dielectric strength of the electric facility within other consumer's structures when a current flows to the grounding electrode 34 via the surge protection device 26 and the surge protection device 34.
Kato Kazunori
Katsuichi Nishimoto
Hiroshi Fukuda