Clause 3 – How to understand the definition of “class III appliance”
class III appliance: appliance in which protection against electric shock relies on supply at safety extra-low voltage and in which voltages higher than those of safety extra-low voltage are not generated.
NOTE basic insulation may be required in addition to supply at SELV. Refer to 8.1.4.
To understand this, you need to first understand what is safety extra low voltage(SELV). Please refer to the definition and explanation of SELV. This type of product is generally powered by an adapter, USB, or a low-voltage power supply in a car. When this type of product is sold, it will not be equipped with a device that converts 100-240V AC power into the needed low voltage, because if it is equipped with such a conversion device, such as an adapter, then the adapter and the appliance form a whole, and the protection level of the whole is determined by the adapter. The adapter is usually a class II construction, so the adapter and the appliance are defined as a class II appliance. Because the power supply voltage of this type of appliance is relatively low, it sometimes leads to the inability to complete some specific electrical functions, so it is necessary to use a boost circuit to increase the voltage to achieve some special functions of the appliance. For example, the function of a negative ion generator requires a boost operation. This type of appliance with a similar negative ion generator or a boost operation (voltage value higher than the SELV) cannot be determined as a Class III appliance.
The word “safety” is included in the four words “safety extra low voltage”, but this does not mean that SELV is safe, and it is not necessarily safe to touch directly. Only safety extra low voltage circuits that meet the requirements of standard 8.1.4 can be touched directly. We will specifically analyze and explain this when analyzing clause 8.1.4.
The fan shown in the figure below can be defined as a class III appliance. However, this fan has two ears, which makes it not compliant with clause 22.44. We will explain the details later.
