Electrical explosion protection knowledge

I. Hazardous Area Division  

The term "hazardous location" refers to a measure of the actual potential for danger in a given area, thereby specifying the applicable explosion-proof type. The International Electrotechnical Commission (IEC)/European Electrotechnical Commission (IEC) classifies explosion-proof zones as follows:

Zone 0: Areas where the risk level continuously exceeds 1000 hours per year;

Zone 1: Areas where danger exists intermittently for 10 to 1000 hours per year;

Zone 2: Areas where the risk of an accident exists for 0.1 to 10 hours per year;

The effective areas defined in China are the same as those described above.

II. Analysis of Explosion-proof Marks
① Gas group

Note: The Chinese standard GB3836 specifies that the minimum ignition energy for Class IIC is 19 microjoules and the minimum ignition energy for Class IIA is 200 microjoules.

The gas grouping and ignition temperature are related to the mixed concentration of flammable gas and air under certain ambient temperature and pressure.

② Temperature group (T group)

This is the highest surface temperature of electrical equipment related to the gas ignition temperature (assuming an ambient temperature of 40°C); ignition energy is independent of ignition temperature. All flammable gases and their groups are listed in Part 1 of standard BS5345.

③ Explosion-proof marking

The following uses the CENELEC hydrogen explosion-proof mark as an example: E Ex ia ⅡC T4

④ Glossary
Explosion-proof electrical equipment (d): refers to electrical equipment that encloses components capable of igniting an explosive mixture within a housing that can withstand the explosion pressure of the internal explosive mixture and prevent the propagation of the explosion to the surrounding explosive mixture.

Increased safety type electrical equipment (e): Electrical equipment that, under normal operating conditions, will not produce sparks or dangerous temperatures that could ignite an explosive mixture, and whose structure is designed to enhance its safety to prevent ignition under normal and specified overload conditions.

Intrinsically safe electrical equipment (i): Electrical equipment that, under normal operation or under standard test conditions, cannot ignite an explosive mixture by sparks or thermal effects.

Non-sparking electrical equipment (n): Electrical equipment that does not produce an electric arc or spark under normal operating conditions, nor does it produce a high-temperature surface or hot spot that could ignite the surrounding explosive mixture, and generally does not experience a fault that could cause ignition.

Special Explosion-Proof Type (S): When electrical equipment or components adopt explosion-proof types not included in GB3836-83, the competent department shall formulate provisional regulations. These regulations shall be submitted to the Ministry of Labor and Personnel for record-keeping and, after inspection by a designated appraisal unit, shall be handled as special electrical equipment of type "S".

III. Explosion-proof standards and selection
① Corresponding standards for various explosion-proof types

② Selection table of explosion-proof types for electrical equipment in hazardous gas explosion locations

IV. Enclosure Protection Rating ( IP ) Code
(BS EN60529; 1992)
The first characteristic number prevents foreign objects from entering the fixed conductor.

The second characteristic number prevents harmful effects from water ingress.

For example, IP 65 requires dustproof and water-spray protection for the enclosure.