Shenzhen ZhongNuo Testing Technology Co., Ltd. is based in South China and specializes in explosion-proof certification and coal safety certification application consulting services, offering a one-stop explosion-proof technology consulting service.
Limitation requirements for surface resistance of non-metallic shells of explosion-proof equipment
In hazardous areas with explosive dust or gases/vapors, such as coal powder and flour, static electricity may cause fires or explosions, posing significant risks. Therefore, it is advisable to minimize the use of insulating materials in explosive hazard areas. When selecting electrical insulating materials, consider maintaining low insulation resistance to prevent discharges when non-metallic components come into contact with charged components. For non-metallic insulating materials, the antistatic ability of the equipment can be assessed by measuring the surface resistance of the equipment's housing.
Surface resistance, measured in ohms (Ω), refers to the resistance between two electrical contacts on the measuring surface.
In accordance with the requirements of the IEC 60079 series standards:
In Category II explosive gas environments, when the surface area of a non-metallic enclosure of an electrical equipment exceeds a certain limit (as shown in Table 1), a surface resistance test of the non-metallic material is required to verify that: by selecting the material, the surface resistance meets at least one of the following requirements during measurement according to IEC 60079-0 26.13:
At ≤1 GΩ, (505)% relative humidity;
At ≤100 GΩ, (305)% relative humidity.
2. In environments with Class III explosive dust, if the surface area of the non-metallic housing of electrical equipment does not exceed 500 mm², the risk of static electricity can be disregarded; if it exceeds this limit, a surface resistance test must be conducted for verification. The criteria for assessment are the same as those for the surface resistance test limits in Class II gas environments. For fixed installation equipment that cannot meet the surface resistance limits, an "X" can be added after the "Explosion-proof" symbol, a corresponding warning sign should be placed on the equipment, and the user should be informed in the user manual.

What documents are required for applying for explosion-proof certification?
1. Product Documentation: When an enterprise applies for a certification of explosion-proof compliance for intrinsic safety electrical equipment, it should provide assembly drawings, circuit diagrams, printed circuit board diagrams, silk-screened diagrams, component material lists, and label drawings, among others. For non-intrinsic safety electrical equipment, the technical documents submitted for inspection should include drawings that reflect the sample's explosion-proof performance (including assembly drawings and component drawings). If the overall drawing can clearly indicate the product's explosion-proof parameters and structure, only the overall drawing needs to be submitted for inspection.
2. Technical Documentation: Includes corporate standards/technical requirements. The corporate standards/technical requirements for products should be written in the prescribed format, and their content should not only include performance requirements of the product but also cover防爆-related aspects: such as basic parameters, explosion-proof markings, environmental conditions for use, explosion-proof performance requirements, relevant tests for explosion-proof performance, and markings related to explosion-proof.
3. Additional Information: For products with adhesive bonding or casting, provide the model names, performance descriptions, and relevant process documents for the adhesives and casting agents. For products with plastic casings, include the material of the plastic and corresponding performance documents. Battery-operated products require the provision of relevant battery specifications.

Certification standards for explosion-proof equipment used in explosive gas environments:
GB/T 3836.1-2021 Explosive Atmospheres, Part 1: Equipment, General Requirements
GB/T 3836.2-2021 Explosive Atmospheres, Part 2: Equipment protected by explosion-proof enclosures "d"
GB/T 3836.3-2021 Explosive Atmospheres, Part 3: Equipment protected by an intrinsic safety "i" type
GB/T 3836.4-2021 Explosive Atmospheres Part 4: Equipment protected by intrinsic safety "i"
GB/T 3836.5-2021 Explosive Atmospheres Part 5: Equipment protected by an “p” pressure housing
GB/T 3836.6-2017, Part 6: Equipment protected by immersion-type "o" in explosive atmospheres
GB/T 3836.7-2017 Explosive Atmospheres, Part 7: Equipment protected by filling with sand of type “q”
GB/T 3836.8-2021 Explosive Atmospheres, Part 8: Equipment protected by "n" type protection
GB/T 3836.9-2021 Explosive Atmospheres, Part 9: Equipment protected by “m” type enclosures

Division of explosion-proof areas in explosive gas environments
In explosion-proof certification, hazardous areas are divided into explosive gas environments and combustible dust environments based on the different states of substances present in the location. According to the duration of presence of hazardous substances in the location, these areas with different states are further divided into three zones based on the length of time the dangerous substances are present.
That is: for explosive gas environments, Zones 0, 1, and 2.
Zones 0: Locations where explosive gas atmospheres are continuously present or exist for long periods, typically above 1000 hours/year.
Zone 1 - Areas where explosive gas environments may occur during normal operation, generally 10-1000 occurrences/year
Zone 2 - Under normal operation, explosive gas atmospheres are not likely to occur or, if they do, are only present for short periods and infrequently, typically less than 10 hours per year.
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