Explosion-proof distribution boxes are marked with codes indicating their suitability for hazardous gas or dust environments, including equipment group, category, zone, temperature class, and Equipment Protection Level (EPL).

ATEX and IECEx Markings

Explosion-proof equipment in Europe is typically marked according to ATEX and IECEx standards. A typical marking might read: II 2G Ex d IIC T6 Gb. This can be decoded as follows:

• Equipment Group (II): Indicates industrial equipment for non-mining explosive atmospheres .
• Category (2): Defines the level of protection; Category 1 is very high, 2 is high, and 3 is increased protection .
• Atmosphere Type (G or D): 'G' for gas, vapor, or mist; 'D' for dust .
• Type of Protection (Ex d): 'd' indicates flameproof enclosure; other types include 'e' (increased safety), 'i' (intrinsic safety), 'p' (pressurized), and 't' (protection by enclosure for dust), .
• Explosion Group (IIC): Specifies the gas group; IIA (propane), IIB (ethylene), IIC (acetylene, hydrogen), .
• Temperature Class (T6): Maximum surface temperature of the equipment; T1 = 450°C, T6 = 85°C .
• Equipment Protection Level (Gb): Indicates the safety level for gas; Ga = very high, Gb = high, Gc = increased . For dust atmospheres, markings may include Ex tb IIIC T80°C Db, where 'tb' indicates protection by enclosure for dust, IIIC is the dust group (metal dust), T80°C is the maximum surface temperature, and Db is the EPL for dust .

Zone Classification

ATEX and IECEx use a zone-based system:

• Gas Zones:
  • Zone 0: Continuous or long-term presence of explosive gas (EPL Ga)
  • Zone 1: Likely presence during normal operation (EPL Gb)
  • Zone 2: Unlikely, short-term presence (EPL Gc)
• Dust Zones:
  • Zone 20: Continuous dust (EPL Da)
  • Zone 21: Likely dust (EPL Db)
  • Zone 22: Unlikely dust (EPL Dc) These zones help determine the required protection level and type of enclosure for the distribution box .

NEC and North American Markings

In the United States, explosion-proof equipment follows the NEC/CEC system:

• Class I: Flammable gases or vapors
  • Groups A (acetylene), B (hydrogen), C (ethylene), D (propane/methane)
• Class II: Combustible dust
  • Groups E (metal), F (carbon), G (grain/flour)
• Division 1: Hazard present under normal conditions
• Division 2: Hazard present only under abnormal conditions
• T-Code: Maximum surface temperature (T1–T6) to prevent ignition . A typical NEC marking: Class I, Division 1, Groups C & D, T4, meaning suitable for ethylene or propane/methane vapors, present under normal operations, with a maximum surface temperature of 135°C.

Additional Marking Information

• Ambient Temperature Range: Marked as Ta or Tamb; if abnormal, an 'X' is added to indicate special conditions .
• Ingress Protection (IP) or NEMA Type: Indicates protection against solids and liquids, e.g., IP66 or NEMA 4X .
• Manufacturer and Certification: Includes CE marking, serial number, and notified body for ATEX/IECEx compliance . Understanding these markings ensures that the distribution box is correctly selected for the hazardous environment, preventing ignition of flammable gases or dust and ensuring compliance with international safety standards.