Based on function, plugs can be categorized into: headphone plugs, DC plugs, audio plugs, USB plugs, video plugs, microphone plugs, charger plugs, mobile phone plugs, and others. Internationally, household appliances are classified into three main categories:
Class I: Appliances featuring only a single layer of insulation. These appliances require the installation of a residual current device (RCD) and grounding protection (meaning they must utilize a three-pin plug). Examples include air conditioners, machine tools, and electric motors.
Class II: Appliances featuring double-layer insulation. While they require the installation of a residual current device (RCD), they do not require grounding protection (meaning they can utilize a two-pin plug). Examples include televisions, electric fans, desk lamps, induction cookers, and ceramic cookers.
Class III: Appliances that operate on safety extra-low voltage (SELV)-typically within the 12–36V range. Examples include mobile phones and laptop computers.
