1) Class I equipment for the protection of electric shock not only rely on the basic insulation, but also rely on some auxiliary safety measures, that is, the equipment can be touched by the conductor for the protection of the ground, to prevent the basic insulation failure, can be touched by the conductor will not bring the hazardous voltage to the human body. Basic insulation + protective grounding
2) Class II equipment for the protection of electric shock depends not only on the basic insulation, but also rely on reinforced insulation and double insulation and other additional safety measures, these measures do not have protective grounding. Basic reinforced double insulation + no protective earth
3) Class III equipment for protection against electric shock not only rely on basic insulation, but also the use of medical extra-low voltage power supply. Basic insulation + extra-low voltage supply