In hazardous areas with explosive dust or gases, vapors, such as coal powder, flour, aluminum powder, hydrogen gas, etc., static electricity may cause fires or explosions, posing great danger. Therefore, in explosive hazardous areas, the use of insulation materials should be minimized as much as possible. When choosing electrical insulation materials, it is advisable to consider maintaining the minimum insulation resistance to prevent discharge when exposed non-metallic parts come into contact with live parts. For non-metallic insulation materials, the anti-static ability of the equipment can be evaluated by measuring the surface resistance of the equipment casing.

Surface resistance, measured in ohms (Ω), refers to the resistance between two electrodes in contact with a measuring surface.

⑵ At ≤ 100 G Ω and (30 ± 5)% relative humidity.

2. In Class III explosive dust environments, if the non-metallic shell surface area of electrical equipment does not exceed 500 square millimeters, the risk of static electricity may not be considered; If the limit is exceeded, surface resistance testing verification is required. The determination requirements are the same as the limit requirements for surface resistance testing in Class II gas environments mentioned above. For fixed installation equipment that cannot meet the surface resistance limit, it can be used toexplosion-proofAdd an "X" after the symbol, add the corresponding warning symbol on the device, and inform the user in the user manual.

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