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Meaning of explosion-proof level
Feb 29, 2020
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The classification of explosion-proof levels, what each sign represents, what is the difference ...



Definition of explosion-proof mark

Explosion-proof mark refers to the mark used to describe the explosion-proof level, temperature group, explosion-proof type and applicable area of explosion-proof electrical equipment.

Explosion mark requirements

Explosion-proof electrical equipment must have a clear permanent convex mark "Ex" in the obvious place. Small equipment can be welded on the casing with a sign plate or marked with a concave mark.

The nameplate of the equipment casing must be clearly marked and firmly fixed. The nameplate should have the following contents: an obvious “Ex” mark on the upper right; an explosion-proof mark indicating the type, category, level, temperature group of the explosion-proof in order; Numbers and other special conditions that need to be marked, as well as the date of manufacture or product serial number.



Explosion-proof mark detailed introduction

Explosion-proof electrical equipment is in accordance with the requirements of the GB 3836 standard.The explosion-proof markings of explosion-proof electrical equipment include:

Explosion-proof type + equipment category + (gas group) + temperature group

 1.Explosion-proof type

According to the explosion-proof measures adopted, explosion-proof electrical equipment can be classified into flameproof, increased safety, intrinsically safe, positive pressure, oil-immersed, sand-filled, potted, n-type, special, and dust-proof Wait. Their identification is shown in Table 1.

Table 1 Basic types of explosion protection


2. Device category

Electrical equipment for explosive gas environments is divided into:

Class I: electrical equipment for underground coal mines;

Class II: Electrical equipment for explosive gas environments other than coal mines.

Class II explosion-proof “d” and intrinsically safe “i” electrical equipment are classified into IIA, IIB, and IIC.

Electrical equipment for combustible dust environment is divided into:

A-type dust-tight equipment; B-type dust-tight equipment;

A type dustproof equipment; B type dustproof equipment.

3 .Gas group

The explosive transmission capacity of an explosive gas mixture indicates the level of its explosion danger. The greater the explosive transmission capacity of an explosive mixture, the higher its danger. The explosive transmission capacity of an explosive mixture can be expressed by the maximum test safety clearance. At the same time, the ease with which explosive gases, liquid vapors, and mists can be ignited also indicates the level of explosion danger, which is represented by the minimum ignition current ratio. Class II explosion-proof electrical equipment or intrinsically safe electrical equipment is further divided into IIA, IIB, and IIC according to the maximum test safety clearance or minimum ignition current ratio applicable to explosive gas mixtures.

As shown in table 2.

Table 2 Relationship between the group of explosive gas mixtures and the maximum test safety clearance or minimum ignition current ratio


4 .Temperature group

The ignition temperature of an explosive gas mixture is the temperature limit at which it can be ignited.

Electrical equipment is divided into T1 ~ T6 groups according to their highest surface temperature, so that the highest surface temperature of the corresponding electrical equipment of T1 ~ T6 group cannot exceed the allowable value of the corresponding temperature group. The relationship between temperature group, equipment surface temperature and ignition temperature of flammable gas or vapor is shown in Table 3.

Table 3 Relationship between temperature group, equipment surface temperature and ignition temperature of flammable gas or vapor


5 .Requirements for setting signs

(1) Marks should be placed in obvious places on the main body of electrical equipment;

(2) The marking must take into account that it is still legible and durable under possible chemical corrosion. For example, the logo Ex, explosion-proof type, category, and temperature group can be marked on the shell with a convex or concave pattern,The material of the signboard should be chemically resistant materials such as bronze, brass or stainless steel.

6. Examples of internationally used explosion-proof electrical equipment marks

Table 4


* NEC is the American Electrical Code. In 1996, Chapter 505 was added to the American Electrical Code, which aims to harmonize with the hazardous area classification method of the I EC standard system that is widely used internationally. NEC 500 indicated as suitable for North American hazardous location classification system

Examples (Q & A)

1. What are the parts of China's explosion-proof signs? Explain their meaning separately?

Explosion-proof mark generally consists of the following 6 parts:

① Explosion-proof mark EX—indicates that the equipment is explosion-proof electrical equipment;

② Explosion-proof structure form—Indicate what measures the equipment adopts for explosion-proof, such as d is flameproof type, p is positive pressure type; i is intrinsically safe type;

③ Explosion-proof equipment categories-divided into two categories, I is the electrical equipment used in coal mines, and II is the electrical equipment used in factories;

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

⑤Temperature group—It is divided into six groups T1 ~ T6, indicating the allowable high surface temperature of the device.

⑥ Equipment protection level: Ga, Gb, Gc.

2. The explosion-proof mark of an instrument is EXdIIBT4 Gb, please explain its meaning.

Answer EX-General mark of explosion-proof;

d——structure form, flameproof type;

II——Category, for factory use;

B——Explosion-proof level, B level

T4——temperature group, T4 group, the highest surface temperature is ≤135 ℃.

Gb-equipment protection level Gb.

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