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Classification of Electrical and Electronic Equipment with regard to Protection against Electric Shock
This standard was developed by reference to the international standard IEC 536 (1976) Classification of Electrical and Electronic Equipment with regard to Protection against Electric Shock.
1 Subject Content and Application Scope
This standard specifies the classification and definition of low-voltage electrical and electronic equipment intended for connection to an external power supply, with regard to protection against electric shock in the event of an insulation failure.
This standard is applicable to electrical and electronic equipment with rated voltage not exceeding 660V AC r.m.s. If necessary, there is possibility of using it for higher voltages and other purposes in the related standard.
This standard is applicable to electrical and electronic equipment for use by the general public in homes, offices, workshops, schools, farms and the like, and for medical and dental purposes.
This standard is applicable to open-type equipment, that is to say equipment itself not provided with the protection against contact with live parts.
2 Normative References
GB 2900.1 Electrotechnical Terminology - Fundamental Terms
GB 3805 Safety Voltage
GB 4208 Degrees of Protection Provided by Enclosure
GB 4776 Electrical Safety Terminology
3 Terms
3.1 basic insulation
insulation applied to live parts to provide basic protection against electric shock
3.2 supplementary insulation
independent insulation applied in addition to basic insulation in order to provide protection against electric shock in the event of a failure of basic insulation
3.3 double insulation
insulation comprising both basic insulation and supplementary insulation
3.4 reinforced insulation
a single insulation system provides a degree of protection against electric shock equivalent to double insulation
Note: the term "insulation system" does not imply that the insulation must be one homogeneous piece. It may comprise several layers which cannot be tested singly as supplementary or basic insulation.
3.5 safety impedance
an impedance connected between live parts and accessible conductive parts, of such value that the current, in normal use and under likely fault conditions in the equipment, is limited to a safe value, and which is so constructed that the reliability is maintained throughout the life of the equipment
3.6 safety extra-low voltage (SELV)
a voltage which does not exceed 50V AC r.m.s. between conductors, or between any conductor and earth, in a circuit which is isolated from the supply mains by means such as a safety isolating transformer or converter with separate windings
Notes:
① Limitation to SELV in different industries is specified in the related professional standard.
② See GB 3805 for the limitation to voltages when direct contact with live part is involved.
③ The voltage limit shall not be exceeded either at full load or no-load, but it is assumed, for the purpose of this definition, that any transformer or converter is operated at its rated supply voltage.
4 Classes of Equipment
The class numbers are not intended to reflect the safety level of the equipment, but only the means by which the safety is obtained.
According to this classification, the protection against electric shock is provided by surrounding environment, equipment itself or power supply system. See Table A1 of Annex A.
Equipment protection not against electric shock is specified in other national standard, e.g. degree of protection provided by enclosure is detailed in GB 4208.
4.1 Class 0 equipment
Equipment in which protection against electric shock only relies upon basic insulation; this implies that there are no means for the connection of accessible conductive parts, if any, to the protective (earthing) conductor in the fixed wiring of the installation, reliance in the event of a failure of the basic insulation being placed upon the environment.
4.2 Class I equipment
Equipment in which protection against electric shock does not rely on basic insulation only, but which includes an additional safety precaution in such a way that means are provided for the connection of accessible conductive parts to the protective (earthing) conductor in the fixed wiring of the installation.
Notes:
① For equipment intended for use with a flexible cord or cable, this provision includes a protective (earthing) conductor as part of the flexible cord or cable.
② Where relevant standards permits, any component is at least subject to basic insulation and equipped with earthing terminal, but the power cord is not equipped with earthing conductor and the plug is not equipped with earthing pin, so it cannot be introduced to the power socket with earthing contact, provided that the protective conductor is not connected with the protective (earthing) conductor in fixed wiring, the protection is then equivalent to that of Class 0, but the earthing provisions of the equipment in all other respects shall fully comply with the requirements of Class I.
1 Subject Content and Application Scope
2 Normative References
3 Terms
4 Classes of Equipment
Annex A (Informative Reference) Table for Principal Characteristics of Equipment and Precautions for Safety
Additional Explanation
