At present, due to the limitation of structure and material selection, the insulation between dangerous live parts and accessible conductive parts in some audio power amplifier products does not meet the standard requirements, mainly in the following three situations:
Situation 1: The secondary conductor passes through the surface of the primary dangerous live parts, which easily leads to the insulation between the dangerous live parts and the secondary conductors connected with the touchable conductive parts not meeting the standard requirements.
Standard Interpretation: For a class of equipment, if the secondary conductor is connected with the protective grounding conductor, the insulation between the primary Dangerous Live point components and the secondary conductor can only meet the corresponding basic insulation resistance strength and insulation impedance requirements; if the secondary conductor is not connected with the protective grounding conductor, the dangerous live parts and components are connected with the protective grounding conductor. The insulation between secondary conductors needs to meet the relevant requirements of thickness, insulation impedance and resistivity for strengthening insulation or double insulation; for second-class equipment, the insulation between dangerous live parts and secondary conductors should meet the relevant requirements of thickness, insulation impedance and resistivity for strengthening insulation or double insulation.
Solutions: In product design, secondary conductors should be avoided from passing through the surface of primary dangerous live components; if the structure is not allowed, secondary conductors with basic insulation requirements should be insulated to withstand the corresponding resistance and insulation impedance test; secondary conductors with double insulation or enhanced insulation requirements should be insulated. It is required that its insulation can withstand the corresponding electrical resistance and insulation impedance test, and meet the insulation thickness requirements. Because the damage of the insulation of the conductor will cause danger in the standard sense, it is necessary to fix the conductor. When applied with 2N force, the conductor will not suffer from abrasion and extrusion such as sharp edges, moving parts and components, nor will it touch parts whose temperature exceeds the allowable temperature of the insulation of the conductor.
Circumstances 2: The pins of dangerous live parts on the back of the power supply board are too close to the metal shell connected with the electrical conductivity of the accessible parts, which results in the insulation between the dangerous live parts and the accessible conductive parts can not meet the requirements of the standard.
Standard Interpretation: There should be effective isolation between dangerous live parts and metal enclosures connected with electrical conductivity of touchable parts. For one type of structure, basic insulation requirements should be met; for the second type structure, strengthening insulation or double insulation requirements should be met. Each type of insulation should bear the corresponding electrical resistance and insulation impedance test, and meet the corresponding insulation thickness and fire protection requirements. Structural design should prevent components pins from wearing and extruding insulation.
Solution: Insulating gaskets or increasing the distance between dangerous live parts and metal housing. Insulating gaskets need to meet the following requirements: Insulating gaskets need to completely cover dangerous live components, and can meet the corresponding electrical strength, insulation impedance, insulation thickness and fire protection requirements. If the distance between them is increased, the shortest distance needs to meet the creepage distance and electrical gap of the strengthened insulation. It is suggested to improve the production process, control the pin length of components, and prevent live components from entering the above areas.
Circumstances 3: The large size of the opening on the side of the equipment shell leads to unqualified electrical clearance and creepage distance, and foreign body enters the equipment through the opening.
Standard Interpretation: The design of equipment housing should make it possible to insert metal test needle or standard test finger into the side opening of the equipment housing, not to touch dangerous live parts and foreign objects through the opening to enter the equipment interior.
Solution: The dimension of the side opening of the shell is controlled within 4 mm. It ensures that the dangerous live parts can not be touched after the relevant insertion test with the test finger. The shape of the opening is designed as shutters to ensure that foreign bodies can not enter the equipment through the opening.