Every piece of explosion-protected electrical equipment installed in a hazardous area carries an Ex marking on its nameplate. That marking tells the trained reader exactly what the equipment is certified for: what zone it can be installed in, what gas group it is suitable for, and what its maximum surface temperature is. It is the primary document for verifying that the right equipment is in the right place.
In practice, the marking is frequently not read or not understood. Equipment is installed because it was “suitable for Zone 1”, but the marking string contains far more specific information than zone suitability, and the details beyond the zone classification are the details that most commonly generate mismatches in field installations.
The full Ex marking: decoded segment by segment
A complete IECEx marking for a typical piece of equipment in a gas Zone 1 application might read: [Ex] II 2G Ex d IIB T4 Gb. Here is what each segment tells you:
| Segment | Meaning |
|---|---|
| [Ex] | IECEx conformity symbol. Confirms the equipment is certified under the IECEx scheme. |
| II | Equipment Group II covers surface industries (not mining). Group I = mines with methane risk. |
| 2G | Category 2, Gas. Category 1 = Zone 0/20; Category 2 = Zone 1/21; Category 3 = Zone 2/22. G = gas; D = dust. |
| Ex d | Protection concept: flameproof enclosure. The enclosure can contain an internal ignition without transmitting flame to the surrounding atmosphere. |
| IIB | Gas group: IIA (propane), IIB (ethylene), IIC (hydrogen/acetylene). IIB covers IIA; IIC covers all. |
| T4 | Temperature class with maximum surface temperature of 135°C. Must be ≤ the ignition temperature of the gas minus safety margin. |
| Gb | Equipment Protection Level: Ga = Zone 0; Gb = Zone 1; Gc = Zone 2. |
The three details that generate the most mismatches in practice
The marking on a piece of Ex equipment is not a generic “this is safe for hazardous areas” declaration. It is a specific technical statement. Matching the marking to the zone classification drawing and the hazardous material inventory is the work that converts a label into a verified installation.
Protection concept reference: the most common types
| Code | Protection concept | Principle | Typical application |
|---|---|---|---|
| Ex d | Flameproof enclosure | Enclosure withstands internal explosion and prevents flame transmission to external atmosphere. | Motors, junction boxes, control gear in Zone 1/2 |
| Ex e | Increased safety | Enhanced measures to prevent sparks, arcs, or excessive temperatures in normal operation by ensuring no arc-producing contacts inside. | Terminal boxes, luminaires, distribution boards in Zone 1/2 |
| Ex i | Intrinsic safety | Limits electrical energy in the circuit to levels below the minimum ignition energy of the gas, including under fault conditions. | Instruments, sensors, transmitters, field devices in Zone 0/1/2 |
| Ex p | Pressurised/purged enclosure | Internal enclosure maintained at positive pressure with clean air, preventing hazardous atmosphere from entering. | Analysers, large control panels, VFDs in Zone 1/2 |
| Ex n | Non-sparking (Zone 2 only) | Enclosure constructed so that in normal operation it cannot ignite a surrounding explosive atmosphere. | Standard motors adapted for Zone 2; lowest cost Ex option |
What changes invalidate a certification
Modifications that affect the protection concept or integrity of the Ex enclosure invalidate the certification. Common examples: enlarging cable gland holes beyond the certified size, substituting non-certified glands, modifying flamepath dimensions in an Ex d enclosure, changing cable type from what is specified in the certification documentation, and adding uncertified components inside a certified enclosure.
Not Sure If Your Ex Equipment Markings Match Your Zone Classification?
Torr Energy conducts Ex equipment audits and hazardous area inspection services, verifying marking-to-zone conformance across your installation and identifying certification gaps.
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