Electrical equipment used in dust explosion hazardous areas should be selected as dust explosion-proof electrical equipment in accordance with the current national standard GB 12476.2-2010 "Electrical Equipment for Combustible Dust Environments Part 2: Selection and Installation". Explosion proof electrical equipment used in dust explosive environments has a similar structure to explosion-proof electrical equipment used in explosive mixed gas environments, and is difficult to distinguish from its appearance. However, it is strictly prohibited to use it interchangeably (except for electrical equipment that has obtained dual explosion-proof certification for gas and dust). The explosion-proof mark on its nameplate should be used to identify whether the explosion-proof electrical equipment is suitable for dust explosive environments.

Dust explosion-proof mark
Generally speaking, common electrical equipment used in combustible dust environments should use explosion-proof markings in accordance with Article 29 of GB 12476.1-2013 "Electrical Equipment for Combustible Dust Environments Part 1: General Requirements".

The commonly used explosion-proof types and their corresponding explosion-proof signs are as follows:

1Positive pressure protection type "pD"

The principle of positive pressure protection explosion-proof electrical equipment in the explosion-proof certificate is to maintain the overvoltage inside the enclosure above the environment to prevent the formation of explosive dust environment inside the enclosure. The explosion-proof mark should at least include the Ex symbol; Explosion proof type code pD; The area where the equipment can be used; Shell protection level (IP code); Composition of the highest surface temperature value (℃). For example:

2Shell protection type "tD"

The principle of the explosion-proof electrical equipment with shell protection in the explosion-proof certificate is to prevent the ignition of combustible dust by setting a dust tight shell that can prevent all visible dust particles from entering or a shell that does not completely prevent dust from entering but takes measures to ensure that the amount of dust entering is not sufficient to affect the safe operation of the equipment. The explosion-proof mark should at least consist of the Ex symbol, explosion-proof type code tD, equipment usable area (with prefix A or B), enclosure protection level (IP code), and maximum surface temperature value (° C), for example:

Two different types of shell protection "tD" are specified: Type A and Type B. These two types have the same level of protection.

Both Type A and Type B are interchangeable, and the use of either type does not confuse the requirements for equipment selection/installation. They only use different methods, with the main difference being:

3Intrinsically safe "iaD" and "ibD"

The explosion-proof types of intrinsic safety explosion-proof electrical equipment are divided into iaD and ibD, which restrict any electrical sparks or thermal effects generated by the connecting wires inside the equipment and exposed to explosive environments, so that the energy generated is lower than that of electrical equipment that can cause ignition. The explosion-proof mark should be marked with the Ex symbol; Explosion proof type code iaD or ibD; The area where the equipment can be used; Composition of the highest surface temperature value (℃). For example: Ex iaD 20 T120 ℃

4Pouring and sealing protection type "mD"

Sealed protection type is an electrical equipment that encapsulates sparks or heating components that may ignite explosive environments into a composite material, preventing them from igniting dust layers or dust clouds under operating or installation conditions. The explosion-proof mark should be marked with the Ex symbol; Explosion proof type code mD; The area where the equipment can be used; Composition of the highest surface temperature value (℃). For example: Ex mD 20 T120 ℃

Some explosion-proof electrical equipment can be used in both dust explosion hazardous environments and explosive gas mixture environments. The explosion-proof mark indicated on its nameplate should have both the explosion-proof mark applicable to combustible dust environments and two explosion-proof certificate marks applicable to explosive gas mixture environments.
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