I. Zoning
How are zones determined? According to industry standards, zoning is defined as follows: Gas zones—classified based on the frequency and duration of explosive gas presence (Zone 0: continuous or long-term frequent presence; Zone 1: periodic or occasional presence during normal operation; Zone 2: short-term presence during abnormal conditions), in accordance with GB 50058-2014 “Code for Design of Electrical Installations in Explosive Atmospheres.”
Dust zones—dust release sources are classified by release frequency into continuous, primary, and secondary grades, corresponding to Zone 20 (continuous dust cloud presence), Zone 21 (periodic or occasional release during normal operation), and Zone 22 (short-term presence during abnormal conditions). Release sources—points such as vessel rupture/leakage sites, loading/unloading points, and poorly ventilated dead zones must be marked. Coverage—any electrical equipment (lighting, power, control, communication) located within an explosive hazard zone must comply with explosion-proof requirements; the use of standard, non-explosion-proof electrical equipment is strictly prohibited. Zoning is the first step in explosion-proof customization; if the zones are defined incorrectly, everything else is futile.
II.
Explosion-Proof Types
How to select the explosion-proof type.
Based on industry explosion-proof standards, the protection types are selected as follows: Flameproof (d)—the enclosure is designed to prevent internal explosions from propagating to the surrounding environment (utilizing precision machining for pressure resistance and gap dimensions, and cooling escaping gases below the ignition temperature); suitable for Zones 0, 1, and 2 (motors, transformers, control devices). Increased Safety (e)—equipment that does not produce arcs or sparks during normal operation but incorporates additional measures to enhance safety (preventing dangerous temperatures, arcs, or sparks); suitable for Zones 1 and 2 (junction boxes, motors, luminaires). Intrinsically Safe (i)—explosion protection achieved by limiting ignition energy so that neither arcs nor sparks—under normal or fault conditions—can ignite the surrounding atmosphere (using safety barriers with current-limiting resistors to restrict output current); suitable for instruments, sensors, and I/O devices. Others—Pressurized (p), Encapsulation (m), Oil-immersed (o), Powder-filled (q), Non-sparking (n) (Zone 22 may utilize Non-sparking type ‘n’ or Dust Ignition-proof type ‘tD’); Combined—Flameproof plus Intrinsically Safe—protection types are matched to the specific equipment and zone: Flameproof/Increased Safety for motors and lights; Intrinsically Safe for sensors and instruments;
Flameproof plus Encapsulation for control cabinets.
III. Ratings and Groups
Determining ratings, groups, and temperature classes.
According to industry standards for explosion-proof equipment selection, classifications are determined as follows: Gas categories—explosive gas environments are divided into three levels: IIA, IIB, and IIC (IIC is the most difficult to ignite and has the strictest requirements; hydrogen and acetylene fall under IIC); Dust categories—explosive dust environments are divided into three levels: IIIA, IIIB, and IIIC (IIIC, involving conductive dust, is the most hazardous); Temperature classes—six levels ranging from T1 to T6 (T1 ≤ 450°C, T2 ≤ 300°C, T3 ≤ 200°C, T4 ≤ 135°C, T5 ≤ 100°C, T6 ≤ 85°C), where the equipment surface temperature must remain below the ignition temperature of combustible materials present on-site; Equipment Protection Levels (EPL)—Ga, Gb, and Gc correspond to specific zones (Ga for Zone 0, Gb for Zone 1, Gc for Zone 2); Selection example—for Zone 2, Category IIA, ignition temperature 480°C, ambient temperature -25 to 40°C, and armored cable wiring, one could select equipment with EPL Ga/Gb/Gc, Category IIA/IIB/IIC, and an armored cable entry device that meets the temperature requirements—correct selection requires matching all three parameters: level, category, and temperature class. Purchasing IIC equipment for a IIA location is a waste of money, whereas purchasing IIA equipment for an IIC location is life-threatening.
IV.
Motors and Electrical Equipment
How to handle motors and electrical equipment.
Regarding industry explosion-proof technology, the approach for motors and electrical equipment is as follows: Explosion-proof motors—utilize sealed, clamped, and secured assemblies; ensure the casing limits surface temperatures to below the smoldering temperature of the dust layer (typically less than two-thirds of the dust cloud ignition temperature); and employ dust-proof sealing, measures to prevent surface accumulation, and pressure-relief designs for dust explosion protection. Protection ratings—motor casings containing exposed live parts must have a rating of at least IP54 (IP20 for other cases); for motors under 1000V, the terminal box may only connect to the motor interior if the motor itself is rated IP44 or higher, while the terminal box’s external protection must be at least IP54. Explosion-proof lighting—designed to prevent the equipment from becoming an ignition source and to ensure low temperature rise. Explosion-proof terminal boxes—feature a sealed structural design. Dust-specific risks—dust presents a unique risk of secondary explosions (where the initial blast kicks up accumulated dust, triggering a much larger explosion), a hazard that standard gas-explosion-proof motors cannot handle; cable entries require specialized dust-proof sealing rings. Grounding—explosion-proof electrical equipment must be reliably grounded to prevent static electricity accumulation, with grounding resistance meeting required standards. Electrical components are the heart of the explosion-proof production line; the four key elements—dust-proof sealing, accumulation prevention, pressure relief, and grounding—are all indispensable.
V.
Electrical Cabinet Wiring
Implementation of electrical control cabinets and wiring.
In accordance with industry explosion-proof standards, the wiring for electrical control cabinets is handled as follows: Six key factors for custom explosion-proof cabinets—mounting method (floor-standing, wall-mounted, or recessed), cable entry/exit direction (top, bottom, left, or right), number of doors and opening direction, specific dimensions (depth, width, height), explosion-proof marking (Ex db, Ex eb, Ex px, Ex ia, etc.), explosion-proof group (IIA, IIB, IIC), temperature class (T1 to T6), and ingress protection rating (IP54, IP65, IP66); Cable wiring—use of cables and conductors meeting explosion-proof requirements, neat and secure routing, and well-sealed cable entry devices to prevent the ingress of explosive gases or dust; Design specifications—GB 3836.15-2024 “Explosive atmospheres – Part 15: Electrical installations design, selection and erection” (covering equipment selection, prevention of ignition sparks, electrical protection, power disconnection and electrical isolation, cable and wiring systems, cable entry systems and sealing elements, rotating electrical machines, luminaires, electric heating, and specific requirements for protection types d, e, i, and p); Fundamental standards—GB/T 3836.1-2021 “Explosive atmospheres – Part 1: Equipment – General requirements” (general requirements for construction, testing, and marking)—electrical control cabinets and wiring act as the “blood vessels” of an explosion-proof production line; sealing, entry, and plugging components must all be airtight and secure.
Conclusion
How should explosion-proof customization for non-standard production lines be approached?
The conclusion is to address explosion-proofing through five steps: hazardous area classification, protection type, equipment group/level, motor specifications, and electrical cabinet design.
Zones—Gas: Zones 0, 1, and 2 (based on frequency and duration of presence); Dust: Zones 20, 21, and 22 (continuous, primary, and secondary release sources); all electrical equipment in hazardous areas must be explosion-proof (GB 50058-2014). Protection Types—Flameproof ‘d’ (enclosure withstands internal explosion without propagation; for motors, transformers, and control units in Zones 0/1/2); Increased Safety ‘e’ (additional measures to ensure no sparks during normal operation; for junction boxes, motors, and lights in Zones 1/2); Intrinsically Safe ‘i’ (energy limited below ignition threshold; for instruments, sensors, and I/O); others include Pressurized ‘p’, Encapsulated ‘m’, Oil-immersed ‘o’, Powder-filled ‘q’, and Non-sparking ‘n’ (with ‘n’ for Zone 22 and ‘tD’ for dust ignition protection); Levels—Gas: IIA/IIB/IIC; Dust: IIIA/IIIB/IIIC (IIIC conductive dust is most hazardous); Temperature Classes—T1 to T6 (T6 ≤ 85°C), must be below the ignition temperature of combustible materials on-site; EPL—Ga/Gb/Gc corresponding to the zones. Motors—Sealed and tightened; surface temperature below dust layer smoldering temperature (and < 2/3 of dust cloud ignition temperature); dust-tight sealing, dust accumulation prevention, and pressure relief; protection rating IP54 (for exposed live parts); sealed junction boxes; secondary explosion prevention; reliable grounding. Electrical Cabinets—Mounting method, cable entry/exit, and cabinet door dimensions; explosion-proof markings (e.g., Ex db/eb/px/ia); levels IIA/IIB/IIC; temperature classes T1 to T6; protection ratings IP54/65/66;
cables compliant with explosion-proof requirements and sealed entries (GB 3836.15-2024, GB/T 3836.1-2021).
Industry rule of thumb for custom explosion-proof equipment: Zone determines type, level determines price, and temperature determines safety—these three factors must align for the equipment to pass acceptance inspection.
