Q&A: Types and standards of explosion-proof electrical equipment

Question 1 : Explosion-proof electrical equipment is divided into several categories?

A: There are two major categories: Category I : Coal mine underground electrical equipment; Category II : Factory electrical equipment.

Question 2 : What is the classification of Class II explosion-proof electrical equipment? What is the sign?

Answer: According to the national standard GB 3836-83 , Class II explosion-proof electrical equipment is divided into three levels, the signs are A , B , and C , respectively . The grading standards are shown in the table below.

Class II explosion-proof electrical equipment classification standards

Note: MESG— Maximum test clearance for flammable gas mixtures, in mm .

MICR— The ratio of the minimum ignition current to the minimum ignition current of methane for combustible gas mixtures.

II A , II B , II C are also the detonation ratings of flammable gas mixtures.

Question 3 : Explain the following terms:

Maximum test safety clearance MESG ;

Minimum ignition current MIC ;

The minimum ignition current is greater than MICR .

A: The maximum test safety clearance ( MESG ) - refers to a mixture of a test gas and air in a shell filled with a certain concentration under the specified test conditions, after ignition, through the 25mm long joint surface can not ignite the shell The maximum clearance between shell joints of explosive gas mixtures.

Minimum igniting current ( MIC ) —The minimum current that can ignite flammable gas mixtures when ignited for 3,000 ignition tests with a 24V , 95mH inductive spark of a specified test apparatus . This current is reduced by 5% and cannot be ignited.

Minimum ignition current ratio ( MICR ) - The ratio of the minimum ignition current of a mixture of various flammable gases (or vapors) to air to the minimum ignition current of a mixture of methane and air.

Question 4 : Is the class II explosion-proof electrical equipment divided into several temperature groups? What is the sign?

Answer: According to the national standard GB3836-83 , Class II explosion-proof electrical equipment is divided into 6 groups based on its maximum surface temperature , marked as T1~T6 . The grouping criteria are as follows:

T1-T6 corresponds to the ignition temperature group of the explosive gas mixture

Question 5 : How to use explosion-proof instruments?

A: Generally, it can be selected based on the following two points.

1 According to the instrument installation, the use of hazardous areas to use the instrument to select the type of explosion-proof:

0 Area - only choose ia, S-type (refer designed for Type 0 S region);

Zone I - may be of any type other than n ;

Zone 2 - all explosion-proof types are optional;

2 According to the possible flammable gas, vapor transmission level and ignition temperature group, select the instrument explosion-proof rating and the maximum allowable surface temperature group. See Table 8-3 . This table is based on GB3836-1983 .
Table 8-3 Examples of Combustible Gases, Steam Explosion Levels, and Pilot Temperature Groups  

Explanation:

a , flammable gas, vapor transmission level is also the explosion-proof level of electrical equipment, the two are the same, are divided into IIA , IIB , IIC three.

b . The ignition temperature group of flammable gas and vapor corresponds to the maximum surface temperature group of electrical equipment. For example, in group T4 , the ignition temperature is 200 °C ≥ T > 135 °C .

Question 5 : What are the parts of the explosion-proof mark in China? Explain their meaning?

Answer: Explosion-proof marks generally consist of the following five parts:

â‘  EX- proof mark indicates that the device is explosion-proof electrical equipment;

2 Explosion-proof structural form - indicates what kind of measures the equipment uses for explosion protection, such as d is flameproof type, p is positive pressure type; i is the safety type;

3 explosion-proof equipment categories - divided into two categories, I for the mine underground electricity equipment, II for the factory electrical equipment;

4 explosion-proof level - divided into A , B , C three levels, indicating the strength of its explosion-proof ability;

5 temperature group - divided into six groups T1 ~ T6 , indicating the maximum allowable surface temperature of the device.

Question 6 : The explosion-proof mark of a meter is EXdIIBT4 . Please explain its meaning.

Answer: EX - Explosion-proof mark;

d - structural form, flameproof type;

II - category, factory use;

B-- proof level, Class B

T4 - temperature group, T4 group, maximum surface temperature ≤ 135 °C .

Question 7 : The explosion-proof mark of a polyester power junction box is EXedIICT4 . Please explain the meaning.

Answer: EX - Explosion-proof mark;

Ed - structural form, e : increased safety type, d : flameproof type;

II - category, factory use;

C - Explosion-proof level, Class C

T4 - temperature group, T4 group, maximum surface temperature ≤ 135 °C .

Question 8 : The explosion-proof mark of an imported gas chromatograph is EEXdps IIB+H2T4 . Please explain the meaning.

Answer: EEX - the European Community explosion-proof mark;

Dps - The instrument uses explosion-proof, positive pressure, special three explosion-proof measures;

II - factory electrical equipment;

B-- proof level, Class B

+ H2 - also applies to H2 sites ( B -level explosion-proof does not apply to H2 , the instrument can also be used in H2 sites due to a variety of explosion-proof measures );

T4 - The maximum surface temperature rise ≤ 135 °C .

Question 9 : The explosion-proof mark of a Japanese-made instrument is JISia3Ng4 . Please explain the meaning.

Answer: JIS - Japanese Industrial Standard Code;

Ia - intrinsically safe explosion-proof, ia grade;

3n - Explosion-proof grade 3n , preventing all 3 explosive gases, equivalent to China's IIC ;

G4 - temperature group, equivalent to China's T4 .

Description JISia3nG4 is an explosion-proof mark originally adopted in Japan, and now Japan has adopted the IEC standard. The above-mentioned explosion-proof mark is now designated as JISEXiaIICT4 .

Question 10: an imported instruments of proof mark Class1, Division1, GroupB, C, D, T 4A, please explain its meaning.

A: Class 1—1 , flammable gases or vapors;

Division 1—1 areas where there is or may be explosion or burning;

GroupB , C , D— applicable to the presence of hazardous gases in Groups B , C , and D ;

T4A— max surface temperature ≤120 °C .

The above explosion-proof marks correspond to EXIIA , IIB and IICT4 in China and can be used in hazardous areas in Zone 0 and Zone 1 . However, it should be noted that this table cannot be used for acetylene sites.

Question 11 : The explosion-proof signs of an imported instrument are as follows. Please explain the meaning.

UL/FM/CSA Class1 , GroupB , C , D , T5

Class3 , GroupE , F , T5

CENELEC EEXedIICT5

A: UL - American Insurance High Laboratory;

FM - American Factory Joint Research Association;

CSA - Canadian Standards Association;

CENELEC - European Electrotechnical Commission.

Description The instrument's explosion-proof performance has been UL , FM , CSA , CENELEC test approval.

Class1 , GroupB , C , D , T5— Applicable to NEC- specified Group B , C , D combustible gas, surface temperature ≤100 °C .

Class2, GroupE, F, T5 applies predetermined NEC E, F group dust, the surface temperature of ≤100 ℃.

EEXedIICT5— Conforms to EN standards ( EN is the EC standard code, its explosion-proof standard and IEC equivalent), explosion-proof instrument for factories, increased safety, explosion-proof, explosion-proof grade C , maximum surface temperature ≤100 °C .

Question 12 : Is there a limit to the transmission distance of the transmitter output signal?

A: The current capacity of the capacitive transmitter, the power supply is 24VDC , according to the maximum output of the instrument 22.5mA , the minimum operating voltage 10.5VDV count, the load resistance is 600Ω .

For explosion proof transmitters, as long as the sum of the device resistances of the wire array and the transmitter strip does not exceed 600 Ω , the transmission distance of the wire is not limited. However, for intrinsically safe transmitters, the length of the wire is specified. Because intrinsically safe is a system, it is not only an intrinsically safe instrument, but also includes associated equipment and external wiring. Associated equipment is generally a safety barrier, and it has a requirement for the length of the wire. Each barrier is marked with the maximum allowable inductance and the maximum allowable capacitance. If the distributed capacitance and inductance of the wire plus the unprotected capacitance and inductance of the transmitter exceeds the specified range, the instrumentation system is not intrinsically safe.