Explosion-Proof Distribution Boxes: Classification and Technical Specifications Based on GB3836 Standards

Explosion-proof distribution boxes are electrical enclosures designed and manufactured

according to specific standards. Their core function is to ensure that if an

explosion occurs inside the enclosure, it will not ignite the surrounding explosive

atmosphere. In industries such as coal mining, petroleum, and chemical processing, where explosive gas mixtures may be present, tailored explosion-proof measures are essential due to varying production conditions and hazardous

substances. China has established a comprehensive standard system, primarily

GB3836, to regulate the design, manufacturing, inspection, use, and maintenance

of explosion-proof distribution boxes.

The current national standard GB3836 systematically classifies explosion-proof distribution boxes into the following ten main types:

Flameproof Enclosure (Ex d): These boxes feature a robust enclosure

capable of withstanding the pressure from an internal explosion of a gas

mixture. Specific flamepath gaps (joints) prevent the internal explosion

flames and hot gases from escaping and igniting the external explosive

atmosphere.

Increased Safety (Ex e): This type applies to boxes where, under normal

operation, no arcs, sparks, or dangerously high temperatures occur. The

design emphasizes enhanced safety margins to prevent the generation of

ignition-capable arcs, sparks, or temperatures even under specified abnormal

conditions (e.g., overloads).

Intrinsic Safety (Ex i): All circuits within this type of box are intrinsically

safe. An intrinsically safe circuit is designed such that any electrical spark or

thermal effect produced under specified conditions (including normal

operation and specific fault conditions) is incapable of igniting the

designated explosive gas mixture. Subdivided into safety levels 'ia' and 'ib'.

Pressurized Enclosure (Ex p): These boxes have a pressurized enclosure.

Protective gas is supplied internally and maintained at a pressure higher

than the surrounding explosive atmosphere, preventing the ingress of

external explosive mixtures.

Oil-Immersion (Ex o): Equipment, or its spark-producing/overheating parts, is completely immersed in oil. This prevents

ignition of an explosive atmosphere existing above the oil level or outside

the enclosure. An example is an oil-immersed circuit breaker within a high-voltage flameproof assembly.

Powder Filling (Ex q): The enclosure is filled with a specified granular

material, such as quartz sand. If an arc occurs internally or the enclosure

surface overheats, the filling material absorbs heat and extinguishes the arc, preventing ignition of the external atmosphere.

Non-Sparking (Ex n): Equipment in this category is designed so that, during

normal operation, it will not ignite the surrounding explosive atmosphere.

Furthermore, its construction ensures that it does not produce arcs, sparks,

or hot surfaces capable of causing ignition under foreseeable fault

conditions specified for the type.

Encapsulation (Ex m): Electrical components or the entire apparatus that

could produce ignition hazards (sparks, excessive heat) are completely

encapsulated (potted) within a compound (e.g., epoxy resin). This isolates

them from the explosive atmosphere, preventing ignition.

Hermetic Sealing (Ex h): The enclosure is made permanently gas-tight, typically through fusion sealing (e.g., glass-to-metal, ceramic-to-metal), ensuring external explosive mixtures cannot enter and contact live

parts.

Special Protection (Ex s): This designation covers boxes employing

explosion-protection methods not covered by the previous nine types. These special

measures must be certified by a nationally recognized testing authority, and their specific protective principles must be clearly defined in the relevant

product standard.