PURPOSE: To prevent intrusion of effective lightening surge by forming a connective conductor in connection with common ground Cu bar bus bar or a grounding bus bar in a circular arc, thereby fixing to the grounding bus bar, and by making grounding perfect.

CONSTITUTION: The right end of a power grounded bus bar 1 is extended to outdoors and connected to a buried grounded electrode, and another power grounded bus bar 6 is furnished at the top, whose other end is also connected with outdoor grounded electrode. To this the two ends of each indoor common ground Cu bar bus bar 2-2" are bent and connected by connective conductors 4-4'' and 7-7'' Also by connective conductors 8-8'', coupling conductors 5, 5' are bent and connected to approx. center of the indoor common ground Cu bar bus bars 2-2''. Thereby intruded lightening voltage and current are discharged to the ground divergently to lead to enlargement of the anti-discharge amount.