Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This document is developed in accordance with the rules given in GB/T 1.1-2020 Directives for standardization—Part 1: Rules for the structure and drafting of standardizing documents.
This document is Part 31 of GB 3836 Explosive atmospheres. The following parts of GB/T 3836 have been issued:
——Part 1: Equipment—General requirements;
——Part 2: Equipment protection by flameproof enclosures “d”;
——Part 3: Equipment protection by increased safety “e”;
——Part 4: Equipment protection by intrinsic safety “i”;
——Part 5: Equipment protection by pressurized enclosure “p”;
——Part 6: Equipment protection by oil immersion “o”;
——Part 7: Equipment protection by powder filling “q”;
——Part 8: Equipment protection by type of protection “n”;
——Part 9: Equipment protection by type of protection “m”;
——Part 11: Material characteristics for gas and vapour classification—Test methods and data;
——Part 12: Material characteristics for combustible dusts—Test methods;
——Part 13: Equipment repair, overhaul and reclamation;
——Part 14: Classification of areas—Explosive gas atmosphere;
——Part 15: Electrical installations design, selection and erection;
——Part 16: Electrical installations inspection and maintenance;
——Part 17: Equipment protection by pressurized enclosure “p” and artificially ventilated room “v”;
——Part 18: Intrinsically safe electrical systems;
——Part 20: Equipment with equipment protection level (EPL) Ga;
——Part 21: Application of quality systems for equipment manufacture;
——Part 22: Protection of equipment and transmission system using optical radiation;
——Part 23: Group I, category EPL Ma equipment intended to remain functional in atmospheres endangered by firedamp and/or coal dust;
——Part 24: Equipment protection by special protection “s”;
——Part 25: Requirements for process sealing between flammable process fluids and electrical systems;
——Part 26: Electrostatic hazards—Guidance;
——Part 27: Electrostatic hazards—Test;
——Part 28: Non-electrical equipment for explosive atmospheres—Basic method and requirements;
——Part 29: Non-electrical equipment for explosive atmospheres—Constructional safety “c”, control of ignition source “b”, liquid immersion “k”;
——Part 30: Equipment and components in explosive atmospheres in underground mines;
——Part 31: Equipment dust ignition protection by enclosure “t”;
——Part 32: Intrinsically safe systems with electronically controlled spark duration limitation;
——Part 33: Equipment in adverse service conditions;
——Part 34: Equipment assemblies;
——Part 35: Classification of areas for explosive dust atmospheres;
This document replaces GB/T 12476.5-2013 Electrical apparatus for use in the presence of combustible dust—Part 5: Protection by enclosures “tD”, and the following main technical changes have been made with respect to GB/T 12476.5-2013:
——Type A and Type B have been deleted (see Clauses 5 to 9 of Edition 2013);
——Three levels of protection “ta”, “tb” and “tc” and their requirements have been introduced (see Clause 4);
——The structural requirements have been modified (see Clause 5 of this standard; Clauses 4, 6, 7 of Edition 2013);
—The requirements for inspections and tests have been modified (see Clause 6 of this standard; Clause 8 of Edition 2013);
——The requirements for marking have been modified (see Clause 7 of this standard; Clause 9 of Edition 2013);
This document is not equivalent to IEC 60079-31: 2013 Explosive atmospheres—Part 31: Equipment dust ignition protection by enclosure “t”.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This document was proposed by the China Electrical Equipment Industry Association.
This document is under the jurisdiction of SAC/TC 9 National Technical Committee on Explosion Protected Electrical Apparatus of Standardization Administration of China.
The previous editions of this document are as follows:
——It was first issued as GB 12476.5-2013 in 2013;
——This edition is the second revision, which is included in GB/T 3836.
Introduction
GB/T 3836 Explosive atmospheres aims to establish the basic technical requirements for equipment used in explosive atmospheres and related aspects of its application, covering the design, manufacture, inspection, type selection, installation, inspection, maintenance, repair and site classification of equipment used in explosive atmospheres. It adopts the form of one part for one standard, including but not limited to the following parts:
——Part 1: Equipment—General requirements;
——Part 2: Equipment protection by flameproof enclosures “d”;
——Part 3: Equipment protection by increased safety “e”;
——Part 4: Equipment protection by intrinsic safety “i”;
——Part 5: Equipment protection by pressurized enclosure “p”;
——Part 6: Equipment protection by oil immersion “o”;
——Part 7: Equipment protection by powder filling “q”;
——Part 8: Equipment protection by type of protection “n”;
——Part 9: Equipment protection by type of protection “m”;
——Part 11: Material characteristics for gas and vapour classification—Test methods and data;
——Part 12: Material characteristics for combustible dusts—Test methods;
——Part 13: Equipment repair, overhaul and reclamation;
——Part 14: Classification of areas—Explosive gas atmosphere;
——Part 15: Electrical installations design, selection and erection;
——Part 16: Electrical installations inspection and maintenance;
——Part 17: Equipment protection by pressurized enclosure “p” and artificially ventilated room “v”;
——Part 18: Intrinsically safe electrical systems;
——Part 20: Equipment with equipment protection level (EPL) Ga;
——Part 21: Application of quality systems for equipment manufacture;
——Part 22: Protection of equipment and transmission system using optical radiation;
——Part 23: Group I, category EPL Ma equipment intended to remain functional in atmospheres endangered by firedamp and/or coal dust;
——Part 24: Equipment protection by special protection “s”;
——Part 25: Requirements for process sealing between flammable process fluids and electrical systems;
——Part 26: Electrostatic hazards—Guidance;
——Part 27: Electrostatic hazards—Test;
——Part 28: Non-electrical equipment for explosive atmospheres—Basic method and requirements;
——Part 29: Non-electrical equipment for explosive atmospheres—Constructional safety “c”, control of ignition source “b”, liquid immersion “k”;
——Part 30: Equipment and components in explosive atmospheres in underground mines;
——Part 31: Equipment dust ignition protection by enclosure “t”;
——Part 32: Intrinsically safe systems with electronically controlled spark duration limitation;
——Part 33: Equipment in adverse service conditions;
——Part 34: Equipment assemblies;
——Part 35: Classification of areas for explosive dust atmospheres;
Protection by enclosure “t” is an important type of protection of explosion-proof electrical equipment for explosive dust atmosphere. In terms of standardization of this technology, China adopted IEC 61241-1 to formulate GB 12476.5-2013 in 2013. Since issuance and implementation of the above standards, type of protection “t” technology has experienced certain new development. In terms of international standards, the adopted standard IEC 61241-1 has been incorporated into IEC 60079, and the current edition is IEC 60079-31: 2013. Its technical content has changed greatly, and is being revised for a new edition. At present, GB 12476 is being revised and incorporated into GB/T 3836. In order to adapt to the development of explosion-proof technology and industry, and coordinate with the revision of China's standard series, it is necessary to revise GB 12476.5 and incorporate it into GB/T 3836.
This revision refers to IEC 60079-31: 2013, while taking into account the revisions of GB/T 3836 and IEC standards. As a part of special type of protection, this standard supplements and modifies the general requirements of GB/T 3836.1.
Explosive atmospheres—Part 31: Equipment dust ignition protection by enclosure “t”
1 Scope
This standard specifies the requirements for design, construction and testing of Ex equipment and Ex components dust ignition protection by enclosure “t”.
This standard is applicable to electrical equipment protected by enclosure and surface temperature limitation for use in explosive dust atmospheres.
This standard does not apply to dusts of explosives, which do not require atmospheric oxygen for combustion, or to pyrophoric substances.
This standard does not apply to Ex equipment or Ex components intended for use in underground parts of mines as well as those parts of surface installations of such mines endangered by firedamp and/or combustible dust.
This standard does not take account of any risk due to an emission of flammable or toxic gas from the dust.
This standard supplements and modifies the general requirements of GB/T 3836.1. When a requirement of this standard conflicts with a requirement of GB/T 3836.1, the requirement of this standard takes precedence.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 197 General purpose metric screw threads—Tolerances (GB/T 197-2018, ISO 965-1: 2013, MOD)
ANSI/ASME B1.20.1 Pipe threads, general purpose(inch)
ANSI/UL 248 (all parts) Standard for low-voltage fuses
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 3836.1, as well as the following definitions, apply.
3.1
dust ignition protection by enclosure “t”
type of protection for explosive dust atmospheres where electrical equipment is provided with an enclosure providing dust ingress protection and a means to limit surface temperatures
4 General
4.1 Levels of protection
Type of protection “t” is divided into three Levels of Protection based on the risk of the Ex equipment becoming an ignition source in an explosive dust atmosphere. Equipment with dust ignition protection by enclosure “t” shall be either:
——Level of Protection “ta” (EPL “Da”), or
——Level of Protection “tb” (EPL “Db”), or
——Level of Protection “tc” (EPL “Dc”).
The construction and marking requirements apply to all electrical equipment, and in addition, Ex equipment with Level of Protection “ta” shall meet the requirements given in 4.3 and Ex equipment with Levels of Protection “tb” and “tc” shall meet the requirements given in 4.4.
Failure modes as defined in the industrial standard for particular components shall be taken into account when considering applicable fault conditions.
For metal film or wire wound structure, short circuit faults are not considered when the current is limited by the resistance. The rated voltage of the resistor shall not be lower than the maximum rated voltage of the equipment.
4.2 Equipment groups and ingress protection
The relationship between the Level of Protection, the group, and ingress protection (IP) required is shown in Table 1.
Table 1 Level of Protection, equipment group and ingress protection relationship
Level of Protection Group IIIC Group IIIB Group IIIA
“ta” IP6X IP6X IP6X
“tb” IP6X IP6X IP5X
“tc” IP6X IP5X IP5X
4.3 Requirements for Ex equipment with Level of Protection “ta”
4.3.1 Fault current
Ex equipment not marked according to Clause 7 shall only be connected to a circuit with a prospective short circuit current of not greater than 1.5 kA.
4.3.2 Maximum surface temperature
The requirements for maximum surface temperature for Ex equipment with Level of Protection “ta” modify and supplement the requirements of GB/T 3836.1.
The maximum surface temperature shall be measured on the surfaces of the internal components in accordance with 6.1.2. The highest of the measured temperatures shall be the basis for the maximum surface temperature marking. If the equipment contains a supplementary enclosure inside, the temperature shall be measured on the external surface of the supplementary enclosure.
Note 1: For equipment with Level of Protection “ta”, the thermal test shall take into account the potential rare failure of partial fracture of the external enclosure.
Note 2: The heat dissipation of equipment with Level of Protection “ta” is limited, and the maximum power dissipation under normal conditions is usually limited to a few watts.
4.3.3 Overpressure
A positive internal pressure of 4 kPa shall be applied to the enclosure in accordance with 6.1.1.3 prior to the dust exclusion test.
4.3.4 Dust exclusion
Dust exclusion by enclosure shall be carried out in accordance with 6.1.1.
4.3.5 Protective devices
4.3.5.1 General
If the EX equipment is capable of exceeding the marked maximum surface temperature as a result of the temperature test of 6.1.2 in the event of expected failure or rare failure, a protective device is required. The protective device may be directly integrated into the Ex equipment or be external to the Ex equipment.
Where the external protective device is not provided by the manufacturer as part of the Ex equipment, the certificate marking shall include the symbol “X” in accordance with GB/T 3836.1, and the Specific Conditions of Use shall detail the required ratings and characteristics of the protective device. The protective device shall be capable of interrupting the maximum current of the circuit in which it is installed. If the Ex equipment contains a cell or batteries, only sealed cell or sealed batteries shall be used. The control device can also be considered as a protective device, provided it also protects the complete Ex equipment from exceeding the maximum surface temperature.
4.3.5.2 Thermal protective devices
The Ex equipment shall be protected by one or more integral thermal protective devices. Thermal protective devices shall not be of a self-resettable type and shall be duplicated unless conforming to GB/T 9364 (all parts), GB/T 9816.1, or ANSI/UL 248 (all parts), in which case only one device is necessary.
Alternatively, if it can be demonstrated that an overcurrent protective device can be used to provide thermal protection, such a device may be used. When an overcurrent protective device is not used as a thermal protective device, it is permissible for the overcurrent protective device to be located outside the enclosure of the Ex equipment. In this case, the certificate marking shall include the symbol “X” in accordance with GB/T 3836.1, and the Specific Conditions of Use shall detail the required overcurrent protective device.
The response time of the thermal protective devices should be taken into account and be adequate for the necessary over-temperature protection.
4.3.6 Internal supplementary enclosure
Where normally arcing and sparking parts are incorporated in the equipment, these parts shall have a supplementary enclosure inside the main enclosure. In accordance with 4.3.2, the marked maximum surface temperature of the equipment shall be measured on the external surface of the supplementary enclosure.
When internal components that may generate heat are encapsulated inside a supplementary enclosure, the marked maximum surface temperature of the equipment shall be measured on the external surface of the supplementary enclosure in accordance with 4.3.2.
The supplementary enclosure shall meet the following requirements with the modifications to GB/T 3836.1.
——A COT of at least equal to the lower specified ambient temperature and at least 20 K greater than the maximum service temperature applies for non-metallic materials;
——Resistance to impact test is performed in accordance with 6.1.1.2 with no hot and cold impact testing required;
——After the impact test without hot and cold impact testing, IP6X is required for the level of protection as specified in GB/T 4208.
4.4 Requirements for Ex equipment with Levels of Protection “tb” and “tc”
4.4.1 Fault current
The maximum short-circuit current shall be determined for the Ex equipment with Level of Protection “tb” or “tc” that is used to connect to the power supply and presents the on-off malfunction current greater than 10 kA. The test shall be performed in accordance with 6.1.1.1, and marked in accordance with Clause 7.
4.4.2 Maximum surface temperature
The maximum surface temperature shall be measured on the external surfaces of the enclosure for Ex equipment with Levels of Protection “tb” and “tc” in accordance with 6.1.2 under normal operating conditions.
4.4.3 Overpressure
A positive internal pressure of 2 kPa shall be applied to the enclosure in accordance with 6.1.1.3 prior to the dust exclusion test, except where the design of the electrical equipment is such that gaskets or seals are physically constrained from moving, e.g., an “O” ring in a groove.
Foreword i Introduction iv 1 Scope 2 Normative references 3 Terms and definitions 4 General 5 Construction 6 Verification and tests 7 Marking Annex A (Nominative) Supplementary requirements for glands
Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This document is developed in accordance with the rules given in GB/T 1.1-2020 Directives for standardization—Part 1: Rules for the structure and drafting of standardizing documents.
This document is Part 31 of GB 3836 Explosive atmospheres. The following parts of GB/T 3836 have been issued:
——Part 1: Equipment—General requirements;
——Part 2: Equipment protection by flameproof enclosures “d”;
——Part 3: Equipment protection by increased safety “e”;
——Part 4: Equipment protection by intrinsic safety “i”;
——Part 5: Equipment protection by pressurized enclosure “p”;
——Part 6: Equipment protection by oil immersion “o”;
——Part 7: Equipment protection by powder filling “q”;
——Part 8: Equipment protection by type of protection “n”;
——Part 9: Equipment protection by type of protection “m”;
——Part 11: Material characteristics for gas and vapour classification—Test methods and data;
——Part 12: Material characteristics for combustible dusts—Test methods;
——Part 13: Equipment repair, overhaul and reclamation;
——Part 14: Classification of areas—Explosive gas atmosphere;
——Part 15: Electrical installations design, selection and erection;
——Part 16: Electrical installations inspection and maintenance;
——Part 17: Equipment protection by pressurized enclosure “p” and artificially ventilated room “v”;
——Part 18: Intrinsically safe electrical systems;
——Part 20: Equipment with equipment protection level (EPL) Ga;
——Part 21: Application of quality systems for equipment manufacture;
——Part 22: Protection of equipment and transmission system using optical radiation;
——Part 23: Group I, category EPL Ma equipment intended to remain functional in atmospheres endangered by firedamp and/or coal dust;
——Part 24: Equipment protection by special protection “s”;
——Part 25: Requirements for process sealing between flammable process fluids and electrical systems;
——Part 26: Electrostatic hazards—Guidance;
——Part 27: Electrostatic hazards—Test;
——Part 28: Non-electrical equipment for explosive atmospheres—Basic method and requirements;
——Part 29: Non-electrical equipment for explosive atmospheres—Constructional safety “c”, control of ignition source “b”, liquid immersion “k”;
——Part 30: Equipment and components in explosive atmospheres in underground mines;
——Part 31: Equipment dust ignition protection by enclosure “t”;
——Part 32: Intrinsically safe systems with electronically controlled spark duration limitation;
——Part 33: Equipment in adverse service conditions;
——Part 34: Equipment assemblies;
——Part 35: Classification of areas for explosive dust atmospheres;
This document replaces GB/T 12476.5-2013 Electrical apparatus for use in the presence of combustible dust—Part 5: Protection by enclosures “tD”, and the following main technical changes have been made with respect to GB/T 12476.5-2013:
——Type A and Type B have been deleted (see Clauses 5 to 9 of Edition 2013);
——Three levels of protection “ta”, “tb” and “tc” and their requirements have been introduced (see Clause 4);
——The structural requirements have been modified (see Clause 5 of this standard; Clauses 4, 6, 7 of Edition 2013);
—The requirements for inspections and tests have been modified (see Clause 6 of this standard; Clause 8 of Edition 2013);
——The requirements for marking have been modified (see Clause 7 of this standard; Clause 9 of Edition 2013);
This document is not equivalent to IEC 60079-31: 2013 Explosive atmospheres—Part 31: Equipment dust ignition protection by enclosure “t”.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This document was proposed by the China Electrical Equipment Industry Association.
This document is under the jurisdiction of SAC/TC 9 National Technical Committee on Explosion Protected Electrical Apparatus of Standardization Administration of China.
The previous editions of this document are as follows:
——It was first issued as GB 12476.5-2013 in 2013;
——This edition is the second revision, which is included in GB/T 3836.
Introduction
GB/T 3836 Explosive atmospheres aims to establish the basic technical requirements for equipment used in explosive atmospheres and related aspects of its application, covering the design, manufacture, inspection, type selection, installation, inspection, maintenance, repair and site classification of equipment used in explosive atmospheres. It adopts the form of one part for one standard, including but not limited to the following parts:
——Part 1: Equipment—General requirements;
——Part 2: Equipment protection by flameproof enclosures “d”;
——Part 3: Equipment protection by increased safety “e”;
——Part 4: Equipment protection by intrinsic safety “i”;
——Part 5: Equipment protection by pressurized enclosure “p”;
——Part 6: Equipment protection by oil immersion “o”;
——Part 7: Equipment protection by powder filling “q”;
——Part 8: Equipment protection by type of protection “n”;
——Part 9: Equipment protection by type of protection “m”;
——Part 11: Material characteristics for gas and vapour classification—Test methods and data;
——Part 12: Material characteristics for combustible dusts—Test methods;
——Part 13: Equipment repair, overhaul and reclamation;
——Part 14: Classification of areas—Explosive gas atmosphere;
——Part 15: Electrical installations design, selection and erection;
——Part 16: Electrical installations inspection and maintenance;
——Part 17: Equipment protection by pressurized enclosure “p” and artificially ventilated room “v”;
——Part 18: Intrinsically safe electrical systems;
——Part 20: Equipment with equipment protection level (EPL) Ga;
——Part 21: Application of quality systems for equipment manufacture;
——Part 22: Protection of equipment and transmission system using optical radiation;
——Part 23: Group I, category EPL Ma equipment intended to remain functional in atmospheres endangered by firedamp and/or coal dust;
——Part 24: Equipment protection by special protection “s”;
——Part 25: Requirements for process sealing between flammable process fluids and electrical systems;
——Part 26: Electrostatic hazards—Guidance;
——Part 27: Electrostatic hazards—Test;
——Part 28: Non-electrical equipment for explosive atmospheres—Basic method and requirements;
——Part 29: Non-electrical equipment for explosive atmospheres—Constructional safety “c”, control of ignition source “b”, liquid immersion “k”;
——Part 30: Equipment and components in explosive atmospheres in underground mines;
——Part 31: Equipment dust ignition protection by enclosure “t”;
——Part 32: Intrinsically safe systems with electronically controlled spark duration limitation;
——Part 33: Equipment in adverse service conditions;
——Part 34: Equipment assemblies;
——Part 35: Classification of areas for explosive dust atmospheres;
Protection by enclosure “t” is an important type of protection of explosion-proof electrical equipment for explosive dust atmosphere. In terms of standardization of this technology, China adopted IEC 61241-1 to formulate GB 12476.5-2013 in 2013. Since issuance and implementation of the above standards, type of protection “t” technology has experienced certain new development. In terms of international standards, the adopted standard IEC 61241-1 has been incorporated into IEC 60079, and the current edition is IEC 60079-31: 2013. Its technical content has changed greatly, and is being revised for a new edition. At present, GB 12476 is being revised and incorporated into GB/T 3836. In order to adapt to the development of explosion-proof technology and industry, and coordinate with the revision of China's standard series, it is necessary to revise GB 12476.5 and incorporate it into GB/T 3836.
This revision refers to IEC 60079-31: 2013, while taking into account the revisions of GB/T 3836 and IEC standards. As a part of special type of protection, this standard supplements and modifies the general requirements of GB/T 3836.1.
Explosive atmospheres—Part 31: Equipment dust ignition protection by enclosure “t”
1 Scope
This standard specifies the requirements for design, construction and testing of Ex equipment and Ex components dust ignition protection by enclosure “t”.
This standard is applicable to electrical equipment protected by enclosure and surface temperature limitation for use in explosive dust atmospheres.
This standard does not apply to dusts of explosives, which do not require atmospheric oxygen for combustion, or to pyrophoric substances.
This standard does not apply to Ex equipment or Ex components intended for use in underground parts of mines as well as those parts of surface installations of such mines endangered by firedamp and/or combustible dust.
This standard does not take account of any risk due to an emission of flammable or toxic gas from the dust.
This standard supplements and modifies the general requirements of GB/T 3836.1. When a requirement of this standard conflicts with a requirement of GB/T 3836.1, the requirement of this standard takes precedence.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 197 General purpose metric screw threads—Tolerances (GB/T 197-2018, ISO 965-1: 2013, MOD)
GB/T 3836.1 Explosive atmospheres—Part 1: Equipment—General requirements (GB 3836.1-2021, IEC 60079-0: 2017, MOD)
GB/T 9364 (all parts) Miniature fuses [IEC 60127 (all parts)]
GB/T 9816.1 Thermal-links—Part 1: Requirements and application guide (GB/T 9816.1-2013, IEC 60691: 2002, MOD)
ANSI/ASME B1.20.1 Pipe threads, general purpose(inch)
ANSI/UL 248 (all parts) Standard for low-voltage fuses
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 3836.1, as well as the following definitions, apply.
3.1
dust ignition protection by enclosure “t”
type of protection for explosive dust atmospheres where electrical equipment is provided with an enclosure providing dust ingress protection and a means to limit surface temperatures
4 General
4.1 Levels of protection
Type of protection “t” is divided into three Levels of Protection based on the risk of the Ex equipment becoming an ignition source in an explosive dust atmosphere. Equipment with dust ignition protection by enclosure “t” shall be either:
——Level of Protection “ta” (EPL “Da”), or
——Level of Protection “tb” (EPL “Db”), or
——Level of Protection “tc” (EPL “Dc”).
The construction and marking requirements apply to all electrical equipment, and in addition, Ex equipment with Level of Protection “ta” shall meet the requirements given in 4.3 and Ex equipment with Levels of Protection “tb” and “tc” shall meet the requirements given in 4.4.
Failure modes as defined in the industrial standard for particular components shall be taken into account when considering applicable fault conditions.
For metal film or wire wound structure, short circuit faults are not considered when the current is limited by the resistance. The rated voltage of the resistor shall not be lower than the maximum rated voltage of the equipment.
4.2 Equipment groups and ingress protection
The relationship between the Level of Protection, the group, and ingress protection (IP) required is shown in Table 1.
Table 1 Level of Protection, equipment group and ingress protection relationship
Level of Protection Group IIIC Group IIIB Group IIIA
“ta” IP6X IP6X IP6X
“tb” IP6X IP6X IP5X
“tc” IP6X IP5X IP5X
4.3 Requirements for Ex equipment with Level of Protection “ta”
4.3.1 Fault current
Ex equipment not marked according to Clause 7 shall only be connected to a circuit with a prospective short circuit current of not greater than 1.5 kA.
4.3.2 Maximum surface temperature
The requirements for maximum surface temperature for Ex equipment with Level of Protection “ta” modify and supplement the requirements of GB/T 3836.1.
The maximum surface temperature shall be measured on the surfaces of the internal components in accordance with 6.1.2. The highest of the measured temperatures shall be the basis for the maximum surface temperature marking. If the equipment contains a supplementary enclosure inside, the temperature shall be measured on the external surface of the supplementary enclosure.
Note 1: For equipment with Level of Protection “ta”, the thermal test shall take into account the potential rare failure of partial fracture of the external enclosure.
Note 2: The heat dissipation of equipment with Level of Protection “ta” is limited, and the maximum power dissipation under normal conditions is usually limited to a few watts.
4.3.3 Overpressure
A positive internal pressure of 4 kPa shall be applied to the enclosure in accordance with 6.1.1.3 prior to the dust exclusion test.
4.3.4 Dust exclusion
Dust exclusion by enclosure shall be carried out in accordance with 6.1.1.
4.3.5 Protective devices
4.3.5.1 General
If the EX equipment is capable of exceeding the marked maximum surface temperature as a result of the temperature test of 6.1.2 in the event of expected failure or rare failure, a protective device is required. The protective device may be directly integrated into the Ex equipment or be external to the Ex equipment.
Where the external protective device is not provided by the manufacturer as part of the Ex equipment, the certificate marking shall include the symbol “X” in accordance with GB/T 3836.1, and the Specific Conditions of Use shall detail the required ratings and characteristics of the protective device. The protective device shall be capable of interrupting the maximum current of the circuit in which it is installed. If the Ex equipment contains a cell or batteries, only sealed cell or sealed batteries shall be used. The control device can also be considered as a protective device, provided it also protects the complete Ex equipment from exceeding the maximum surface temperature.
4.3.5.2 Thermal protective devices
The Ex equipment shall be protected by one or more integral thermal protective devices. Thermal protective devices shall not be of a self-resettable type and shall be duplicated unless conforming to GB/T 9364 (all parts), GB/T 9816.1, or ANSI/UL 248 (all parts), in which case only one device is necessary.
Alternatively, if it can be demonstrated that an overcurrent protective device can be used to provide thermal protection, such a device may be used. When an overcurrent protective device is not used as a thermal protective device, it is permissible for the overcurrent protective device to be located outside the enclosure of the Ex equipment. In this case, the certificate marking shall include the symbol “X” in accordance with GB/T 3836.1, and the Specific Conditions of Use shall detail the required overcurrent protective device.
The response time of the thermal protective devices should be taken into account and be adequate for the necessary over-temperature protection.
4.3.6 Internal supplementary enclosure
Where normally arcing and sparking parts are incorporated in the equipment, these parts shall have a supplementary enclosure inside the main enclosure. In accordance with 4.3.2, the marked maximum surface temperature of the equipment shall be measured on the external surface of the supplementary enclosure.
When internal components that may generate heat are encapsulated inside a supplementary enclosure, the marked maximum surface temperature of the equipment shall be measured on the external surface of the supplementary enclosure in accordance with 4.3.2.
The supplementary enclosure shall meet the following requirements with the modifications to GB/T 3836.1.
——A COT of at least equal to the lower specified ambient temperature and at least 20 K greater than the maximum service temperature applies for non-metallic materials;
——Resistance to impact test is performed in accordance with 6.1.1.2 with no hot and cold impact testing required;
——After the impact test without hot and cold impact testing, IP6X is required for the level of protection as specified in GB/T 4208.
4.4 Requirements for Ex equipment with Levels of Protection “tb” and “tc”
4.4.1 Fault current
The maximum short-circuit current shall be determined for the Ex equipment with Level of Protection “tb” or “tc” that is used to connect to the power supply and presents the on-off malfunction current greater than 10 kA. The test shall be performed in accordance with 6.1.1.1, and marked in accordance with Clause 7.
4.4.2 Maximum surface temperature
The maximum surface temperature shall be measured on the external surfaces of the enclosure for Ex equipment with Levels of Protection “tb” and “tc” in accordance with 6.1.2 under normal operating conditions.
4.4.3 Overpressure
A positive internal pressure of 2 kPa shall be applied to the enclosure in accordance with 6.1.1.3 prior to the dust exclusion test, except where the design of the electrical equipment is such that gaskets or seals are physically constrained from moving, e.g., an “O” ring in a groove.
Contents of GB/T 3836.31-2021
Foreword i
Introduction iv
1 Scope
2 Normative references
3 Terms and definitions
4 General
5 Construction
6 Verification and tests
7 Marking
Annex A (Nominative) Supplementary requirements for glands
