The difference between 20, 21 and 22 zones and the level of dust explosion protection

Knowledge of dust explosion proof motor

According to the characteristics of the dust explosion-proof motor, it is divided into 20 zones, 21 zones and 22 zones, and the explosion-proof grades of these three zones. When selecting the dust explosion-proof motor, the user can determine the applicable motor according to the site characteristics corresponding to the explosion-proof grade.

Dust hazard level

Zone 20: places and inside containers where combustible dust occurs continuously or frequently during normal operation and the amount is sufficient to form a mixture of combustible dust and air or an uncontrolled and extremely thick dust layer may form.

Zone 21: a place where the amount of dust that may occur during normal operation is sufficient to form a mixture of combustible dust and air but is not included in zone 20.

Zone 22: a place where combustible dust clouds occur occasionally and only for a short period of time under abnormal conditions, or where combustible dust occasionally accumulates or may have a dust layer and produce an air mixture of combustible dust.

Customers may have doubts when choosing the explosion-proof grade of dust explosion-proof motor. The former explosion-proof grade is different from the current one.

Question 1: why is it now Extd B21 instead of DIP B21?

Answer: according to the latest national standard code of dust explosion-proof motor: Gb 12476.5-2013 "electrical equipment for combustible dust environment" part 5: enclosure protection type "tD" representative, dust explosion-proof motor grade: Ex tD A20 T130°C, Ex tD A21 T130°C, Ex tD A22 T130°C;Ex tD B20 T130°C, Ex tD B21 T130°C, Ex tD B22 T130°C are used in places with combustible dust and combustible catkins.

The new dust explosion-proof rating: Extd B21 replaced the old dust explosion-proof rating: DIP B21

Note: the latest explosion-proof dust motor is rated as: ExtD B21 T135℃ IP65

Question 2: which grade is higher in areas 20, 21 and 22?

Answer: at present 21 area is the highest dust explosion-proof grade of the dust explosion-proof motor, can replace 22 areas to use, because 20 areas do not let in electrical appliances.

Examples of dust explosion-proof grade:

Previous explosion-proof grade of dust: DIP A20 TA,T4 and 20 in the explosion-proof mark of dust indicate that combustible dust exists continuously in the place where the explosion-proof motor is running, and its quantity is enough to form a mixture of combustible dust and air, and the coefficient of ignition and detonation is particularly high.Such places usually do not allow the operation of electrical equipment, or the motor can be used in the 21 or 22 areas with less dust through the lead wire.That is to say: 20 area is continuous dust place, cannot have electric appliance.

Previous grade of dust explosion-proof motor: DIP A21 TA, the 21 in T4 dust explosion-proof mark indicates that combustible dust may appear in the place where the explosion-proof motor runs. The quantity is enough to form a mixture of combustible dust and air, but it is not included in zone 20.The coefficient of ignition detonation is higher.

At present, the latest explosion-proof grade of dust explosion-proof motor is: ExtD B21 T135℃ IP65

Question 3: what is the difference between Extd B21 and Extd A21?The distinction between B and A in dust explosion proof mark?

There are also previous dust explosion-proof grades: DIP B21 TA, dust explosion-proof mark and DIP A21 TA.Whether the same difference

Answer: the difference between B and A in the dust explosion-proof mark: B means that the explosion-proof bonding surface of the motor is the straight interface bonding surface, A means that the explosion-proof bonding surface of the motor is the plane bonding surface, the two can be used together, but in fact the explosion-proof structure of the straight interface is safer than the explosion-proof structure of the plane.

There should be no difference in the price of these two kinds of dust explosion-proof marks, but the methods used by the manufacturer in choosing flameproof structural formula are different. Both A21 and B21 have the use level requirements of explosion-proof motors in dust environment zone 21.