The model number of an explosion-proof distribution box encodes its protection type, applicable hazardous zones, gas or dust group, temperature class, and equipment protection level.

Key Components of the Model Number

1. Equipment Group
   • I: For mining environments (methane gas)
   • II: For other explosive atmospheres outside mines, such as industrial gas or dust areas
2. Category / Zone
   • 1 / Zone 0: Very high risk, continuous or long-term explosive atmosphere
   • 2 / Zone 1: High risk, occasional explosive atmosphere
   • 3 / Zone 2: Normal risk, rare or brief exposure
3. Atmosphere Type
   • G: Gas, vapor, or mist
   • D: Combustible dust
   • Some devices may have dual markings like G/D for mixed hazards
4. Protection Method
   • Ex d: Flameproof enclosure, containing internal explosions
   • Ex e: Increased safety, preventing sparks or overheating
   • Ex i: Intrinsically safe, limiting energy to prevent ignition
   • Ex t: Dust protection, preventing ignition of combustible dust
5. Gas/Dust Group
   • IIA, IIB, IIC: Specifies the type of gas the box can safely handle, with IIC being suitable for the most volatile gases like hydrogen
6. Temperature Class
   • T1–T6: Maximum surface temperature of the enclosure; lower numbers indicate higher allowable temperatures before ignition risk
7. Equipment Protection Level (EPL)
   • Gb / Gc: Gas protection levels
   • Db / Dc: Dust protection levels
   • Indicates the degree of protection and suitability for specific zones

Example

A model number like II 2G Ex db IIB T4 Gb can be interpreted as:

• II: Industrial explosive atmosphere
• 2G: Category 2, suitable for Zone 1 gas areas
• Ex db: Flameproof enclosure
• IIB: Gas group, suitable for ethylene and similar gases
• T4: Maximum surface temperature 135°C
• Gb: Equipment protection level for gas, suitable for Zone 1

Additional Notes

• Some manufacturers, like HRMD92 series, include extra identifiers for enclosure material (stainless steel, aluminum), hinge type, and optional features like meters, breakers, or PLCs .
• Customization may be reflected in the model number or suffixes, indicating special configurations or additional safety features.
• Always cross-reference the model number with the certification label to ensure compliance with ATEX, IECEx, or local standards . By understanding each segment of the model number, you can determine the suitability of the distribution box for specific hazardous environments, its protection method, and operational limits.