To realize effective insulating measures with high efficiency at a low cost.
The maximum voltage of an external insulation path L3 (the path of a ground point P3 to a ground 5 for customers to a metal sheath 3-2 for distribution line or a stringing 3-2' for distribution line, a metal sheath 4-2 for communication drop line or a stringing 4-2' for communication line to a CP pole 15 to a ground line 10 to a drop line 3-1 for distribution to an outlet P1 for distribution line: when there is no GW 19) between the outlet P1 for distribution line and a ground point P3 at the time of dielectric breakdown is determined. The breakdown voltages of an internal insulation path L1 between the outlet P1 for distribution lines and a outlet point P2 for distribution line, and an internal insulating path L2 between the outlet P1 for distribution line and the ground point P3 are set, so as to be higher than the maximum voltage in dialectic breakdown.
MAKINO HIRONORI
AOKI OSAMU
