Clause 3 – How to understand the definition of “clearance”

clearance: shortest distance in air between two conductive parts or between a conductive part and theaccessible surface. Clearance is a very important concept. In order to understand clearance, we need to say it again that no substance is completely insulated, and air can also conduct electricity. When the voltage is very high, the current will…

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…

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…

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

The emphasis here is on a part of the construction on the appliance, which can meet the requirements of double insulation or reinforced insulation. Therefore, a class I appliance will also contain a class II construction .Example: The oven shown in the figure below uses a metal shell and a plastic switch knob. When the…

Clause 3 – How to understand the definition of “class II appliance”

class II appliance: appliance in which protection against electric shock does not rely on basic insulation only but in which additional safety precautions are provided, such as double insulation or reinforced insulation, there being no provision for protective earthing or reliance upon installation conditions. NOTE 1 Such an appliance may be of one of the…