English Name: Explosion proof grade

Temperature Group: T1-T6

Explosion Proof Grade: Ex(ia)ⅡC T4

Explosion proof equipment definition: Electrical equipment that will not ignite an explosive atmosphere in its surroundings under specified conditions.

Class I: Coal mine down electrical equipment;

Class II: All other explosive gas environment electrical equipment except coal mines and underground areas.

Class II can be divided into Class II A, II B, and II C classes. Equipment marked with Class II B can be used under the conditions of Class II A equipment. Class II C can be used under the conditions of Class II A and II B.

Class III: Explosive dust environment electrical equipment except coal mines.

Class IIIA: Flammable flying fluff; Class IIIB: non-conductive dust; Class IIIC: Conductive dust.

Highest surface temperature: The highest temperature that any part of the electrical equipment may reach when it works under the most unfavorable operating conditions within a specified range. The highest surface temperature should be lower than the combustible temperature.

For example, if the ignition temperature of explosive gases in an explosion-proof sensor environment is 100 ℃, then the maximum surface temperature of any component of the sensor should be lower than 100 ℃ under the worst working conditions.

Electrical equipment for explosive atmospheres is classified into temperature groups T1-T6 according to its highest surface temperature.

Source of ignition: There is a large amount of electrical instruments used in the production process, various friction electric sparks, mechanical wear sparks, static sparks, and high temperatures are inevitable, especially when the instruments and electrical equipment are faulty.

Subjectively, many industrial sites satisfy the conditions for explosions. When the mixture concentration of explosive substances and oxygen is within the explosive limit range, if there is an explosion source, an explosion will occur. Therefore, taking preventive measures against explosions is very necessary.

Flammable substances: Many production sites produce certain combustible substances. In coal mines, about two-thirds of the sites have explosive substances; in the chemical industry, about 80% of the workshop areas have explosive substances.

Oxygen: Oxygen is everywhere in the air.

(1) Explosive substances (flammable air flammable dust): substances that can react with oxygen (air), including gases, liquids, and solids. (Gas: hydrogen, acetylene, methane, etc.; Liquid: alcohol, gasoline; Solid: dust, fiber dust, etc.)

(2) Air or oxygen

(3) Source of ignition: Includes open flames, electrical sparks, mechanical sparks, static sparks, high temperatures, chemical reactions, and light energy, etc.

The meaning of hazardous area classification is to measure the actual possibility of danger in an area, and accordingly, specify the explosion-proof types that are applicable.

1. Hazardous area classification by the International Electrotechnical Commission/European Committee for Electrotechnical Standardization

Zone 0: Explosive gases always or for a long time exist; Areas with a continuous danger level greater than 1000 hours per year;

Zone 1: Flammable gases may occur or exist during the normal operation of instruments; Discontinuous danger level of 10~1000 hours per year;

Zone 2: Generally, there is no flammable gas, and even if it occurs occasionally, its existence time is very short; Areas with a danger level of 0.1~10 hours per year in case of an accident;

China divides the effective areas in the same way.

This is the highest surface temperature of electrical equipment related to gas ignition temperature (assuming an environmental temperature of 40℃), and the ignition energy is unrelated to the ignition temperature. All combustible gases and their groups are listed in part one of the standard BS5345.

IEC explosion proof grade standard format:Ex(ia)ⅡC T4

Corresponding Standards of Various Explosion Proof Types

Explosion Proof Type Selection Table for Electrical Equipment in Gas Explosive Atmospheres

Gas Groups

Explosive Gas Hazardous Levels

According to the minimum spark energy that can ignite explosive gases, China and most countries and regions use the International Electrotechnical Commission (IEC) standard to divide explosive gases into four hazardous levels.

Explosive Substance Classification

Applicability of Explosion Proof Methods to Hazardous Locations

Protection Code

As an instrument used in explosive hazardous areas, the protection level of its casing should also be specified and assigned a certain code, namely an IP rating number.

The shell protection level specified in IEC144 is represented by a code corresponding to its resistance to external object impact and puncture, as well as its waterproof ability. For example, the measurement circuit board of intrinsically safe instruments should not be removed from its housing, otherwise it will violate the minimum requirements of IP40. The protection level consists of two digits, preceded by the word IP.

Explosion Characteristics

Power Supply Limitations

The power supply restrictions are mainly reflected in the following three aspects:

1. Isolate the power electronics from electronic components.
2. Take measures to prevent external interference electromagnetic fields from coupling to electronic components through relays or current output terminals.
3. Limit the working power supply and voltage of the sensing circuit.

Intrinsic Safety Type can be divided into two categories: ia and ib. Ib intrinsic safety circuits must ensure that the circuit elements do not ignite or explode under normal operating conditions and when there is a single fault in the system. Ia intrinsic safety circuits require that the circuit elements do not ignite or explode under normal operating conditions and when there are two faults.