In the United States, the rule for grounding appliances is governed by the National Electrical Code (NEC), which is maintained and published by the National Fire Protection Association (NFPA). The NEC sets the standards for electrical installations to ensure safety and prevent electrical hazards.
According to the NEC, most appliances with metal cases or external metal parts that are likely to become energized must be grounded. Grounding serves as a safety measure to protect users from electric shock in the event of a fault or malfunction. Grounding involves connecting the metal parts of the appliance to the earth or a grounding conductor, typically through the appliance's power plug and the electrical system's grounding conductor.
Some appliances are exempt from the grounding requirement under specific conditions. Appliances that are designed in a way that provides an equivalent level of safety may be allowed to use a two-prong (ungrounded) plug. These are typically referred to as "double-insulated" or "Class 2" appliances. They have an additional layer of insulation that prevents contact between the internal electrical components and the external metal case, reducing the risk of electric shock even if the case becomes energized.
Common examples of appliances that are often exempt from grounding requirements and use two-prong plugs include:
Small kitchen appliances: Toasters, blenders, food processors, coffee makers, etc., are typically double-insulated and do not require grounding.
Personal care appliances: Hair dryers, electric shavers, and similar items are usually double-insulated.
Audio and video equipment: Many audio and video devices, like TVs, DVD players, and stereos, are designed as double-insulated.
It's important to note that although some appliances may be exempt from grounding requirements, they must still meet other safety standards and should be used with care. Always follow the manufacturer's instructions and, if in doubt, consult a qualified electrician to ensure proper electrical safety in your home.