Class I tool
Tool in prevent to get an electric shock the protection of depends not only on the basic insulation, and it also contains an additional safety precaution, its method is palpable electrically conductive parts and installed in the fixed line protection (ground) wire connected, in such a way to make palpable electrically conductive parts in the basic insulation damage accident not be charged body.
II class tool
Its rated voltage more than 50 v. Tool in prevent to get an electric shock the protection of depends not only on the basic insulation, and it also provides double insulation or reinforced insulation additional safety precautions and without protective earthing of or reliance on the measures of installation conditions. This kind of tool shell has a metal and nonmetallic two kinds, but hand part is nonmetal, non-metallic place has "back" symbols.
Class III tool
Its rated voltage not more than 50 v. The very low voltage power supply, tools internal do not produce than security very low voltage high voltage. This kind of tool shell are all plastic