【Y2025】Selection rules for Ex d, E**, Ex e

Text not part of the attachment, for reference only: China uses a method equivalent to that of IEC for classifying explosive hazard areas. **Standard GB 50058-92 specifies that explosive gas hazardous areas are classified into three levels—Zone 0, Zone 1, and Zone 2—based on their degree of hazard, while explosive dust hazardous areas are divided into two levels: Zone 10 and Zone 11.

Text not part of the attachment, for reference: Internationally, the major industrial **entities have basically two different views regarding the classification of explosive-hazardous areas. A system represented by the IEC (International Electrotechnical Commission), which includes countries such as Germany, the United Kingdom, Italy, Japan, and Australia; it classifies gases into Zones 0, 1, and 2, and dusts into Zones 10 and 11. Its definition is essentially the same as that of IEC (refer to China’s definitions for various regions; China adopts IEC standards on an equivalent basis). Another classification is used in North America, such as in the United States and Canada; it is represented by the definitions in NEC (the National Electrical Code of the United States). Gases are classified into Zone 1 and Zone 2 (with no Zone 0), and dusts are also classified into Zone 1 and Zone 2.

Text not part of the attachment, for reference only: Explosion protection, also known as pressure-resistant explosion protection, involves enclosing the instrument components that could ignite explosive mixtures within a specially strong enclosure capable of withstanding the explosive pressure from such mixtures inside, and preventing the spread of explosion to the mixture outside the enclosure. In other words, an explosion may occur inside the housing of an explosion-proof instrument, but it will not spread outside the housing. Therefore, strict explosion-proof requirements apply to the joints between various components of such instruments – such as the number of thread turns on the instrument cover, the precision of the threads, the zero point setting, the gaps between the range adjustment screws and the instrument housing, as well as the gaps between the sensing elements and the conversion elements of the transmitter, and the wire connections. Apart from being relatively bulky, flameproof instruments are simple in other aspects and do not require associated equipment such as safety barriers. However, before opening the table cover, the power must be turned off first; otherwise, if sparks are generated, they will be exposed to the atmosphere, posing a danger.

Text not part of the attachment, for reference: Intrinsic safety instruments are also known as safe spark instruments. Its feature is that, whether under normal conditions or in fault conditions, the sparks generated by the circuits and systems, as well as the temperatures reached, will not ignite explosive mixtures. Its explosion protection is achieved through the following measures: ① The instrument circuit is constructed using new types of integrated circuit components, allowing it to operate at lower operating voltages and currents; ② Safety barriers are used to separate the circuits in hazardous areas from those in non-hazardous areas, thereby limiting the energy that can be transmitted from non-hazardous areas to hazardous ones; ③ The connection wires of the instrument should not create excessive distributed inductance and capacitance, in order to reduce the stored energy in the circuit. The explosion-proof performance of these safety instruments is not achieved through external measures such as ventilation, inflation, oil filling, or flame isolation; rather, it is accomplished by the circuit itself, making them intrinsically safe. It can be used in all hazardous locations and with all explosive gas and vapor mixtures, and it can be maintained and adjusted while powered on. However, it cannot be used alone; it must be combined with intrinsically safe associated devices (safety barriers) and external wiring to form an intrinsically safe circuit in order to achieve its explosion-proof function.

Text not part of the attachment, for reference only: Flameproof type D; suitable for use in Zone 1 and Zone 2 ignition sources; cannot be opened for maintenance while powered on； Increased safety type e, mainly used in Zone 2 for ignition sources; it can also be used in Zone 1 to some extent. Maintenance can be carried out with the device powered on, but wiring cannot be disconnected while the device is powered on ； Intrinsic safety type ia, suitable for Zone 0, Zone 1, and Zone 2 ignition sources; allows opening of the cover while energized, and allows disconnecting wires while energized ； Intrinsic safety type ib, suitable for Zone 1 and Zone 2 ignition sources; allows opening of the cover while powered on, and allows wiring disconnection while powered on ； Positive pressure explosion-proof type P, suitable for Zone 1 and Zone 2 ignition sources; the cover cannot be opened while powered on ； There are also oil-flushing types, spark-free types, and so on, which are used less frequently.

Text not part of the attachment, for reference: Explosion-proof electrical equipment must be used in explosion-proof areas; the explosion-proof markings must be clear, and there must be an explosion-proof certification number. Note: Multiple national standards include this mandatory requirement. Some electrical equipment imported from abroad is explosion-proof, but it lacks an explosion-proof certification number. It is recommended that domestic companies still comply with the relevant **standards** when selecting electrical equipment.

Text not part of the attachment, for reference only: Instruments and installation materials installed in explosive hazard areas should be equipped with nameplates and explosion-proof markings. Before installation, it is necessary to check whether their models and specifications meet the design requirements, and they must be free of any damage or cracks on the outside.

Text not part of the attachment, for reference only: In Zone 1 areas with explosion hazards, instrument wiring, cables, and wires must be installed within galvanized steel pipes. Cylindrical pipe threads shall be used for connections between the wire protection tubes, as well as between the protection tubes and the junction boxes and pull box.

Text not part of the attachment, for reference only: When protection pipes, cable trays, and cable ducts pass through the boundaries between different levels of explosive hazard areas, sealing measures should be taken (such as using explosion-proof flame arresters, sealing components for isolation, or filling with sealants) to prevent explosive gases from spreading from one hazardous area to another.