FN7- 12R(L) model indoor AC HV load break switch-fuse combination apparatus is developed and designed based on international technology and national power supply requirement, it passed all type tests and trial-operation inspections. The apparatus conforms to IEC420: AC LOAD BREAK SWITCH AND FUSE COMBINATION APPARATUS(1990 EDITION) Compared to international product it keeps up with technical level with small volume and light weight. It is applicable in ring main unit and prefabricated substations as well as 12kv line and power distribution system. The product realizes three working positions: power making. power breaking and earth. It applies to power system of rated voltage 6- 12kv, 50/60HZ breaking load current over load current and short-circuit current.