Electric appliances, due to the protection against electric shock, are divided into four classes: 0, I, II and III.
Class 0 includes devices, where only basic insulation is used (working). They are characterized by the lack of a terminal intended for connection with the protective conductor.
Class I includes devices, where only basic insulation is used, and they are equipped with protective terminals to connect the conductive parts accessible with the protective conductor of the network system.
Class II includes electrical equipment, in which all accessible conductive parts are separated from live parts (belonging to an electrical circuit) double insulation or reinforced insulation. These devices do not have a protective terminal and should be marked with the symbol ?
Class III includes electrical equipment, which can only be operated with very low voltage SELV or PELV.