Class I: In the primary to secondary aspect, the basic insulation structure is used to prevent electric shock protection from dangerous voltages. In addition, a grounding protection that meets the grounding impedance regulations is required.
When the basic insulation fails, the ground protection will withstand the dangerous voltage to the ground.
Class II: In the primary to secondary aspect, the structure of reinforced insulation or double insulation is used to prevent electric shock protection from dangerous voltages. The reinforced insulation or double insulation can have a protection function when there is no ground protection in the single failure