Clause 3 – How to understand the definition of “class III construction”

class III construction: part of an appliance for which protection against electric shock relies upon 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.
NOTE 2 If the main part of the appliance operates at SELV and is delivered together with a detachable power supply unit then this main part of the appliance is considered to be of class III construction in a class I appliance or class II appliance as appropriate.

Here again, emphasis is placed on a part of the appliance. The explanation of Note 1 is more rigorous, because the definition here stipulates safety extra-low voltage, but safety extra-low voltage is only a part that can be touched if it meets the requirements of 8.1.4.

The appliance is powered by a pluggable adapter (without protective earthing), and the adapter and the appliance are delivered to the user together. The adapter and the appliance are together judged to be Class II appliances. Because the adapter is Class II, this determines the class of protection against electric shock. However, the appliance – fan alone is a Class III construction, that is a Class III construction in a Class II appliance.

Of course, there is another situation, that is, a switch power supply PCB is embedded in the appliance, and this switch power supply PCB can provide a SELV circuit. Then, the SELV circuit part constitutes class II construction.