APPLICATION The items has small size, light weight,novel structure and excellent performance. They are mounted in the illumination distribution board and used in guesthouses, block of flats,high buildings, squares,airports, railway stations,plants and enterprises etc, in AC circuits 50HZ for protection of overload, short circuit and for circuit change-over in lighting system. Working environment 1. The altitude not exceeding 2000m. 2. The ambient temperature is from +40°Cto -5°C. 3. The relative humidity is blow 90%（+25°C）. 4. Mounting gradient not exceeding 5°. 5. Mounted no notable shock and strike. 6. Ambient environment freeing from explosive danger and air or dust which may cause corrosion of metal or weakness of insulation. 7、 Ambient environment freeing from erosion of rain or snow.