When you look at the label of a piece of Ex equipment, you encounter a short but information-dense code string, such as "II 2G Ex db IIC T4 Gb." This code is a technical identity that defines where, and under what conditions, the equipment can be safely used. In this article we explain each piece of this code one by one.
The General Structure of the Ex Mark
A standard Ex equipment label contains, in order, the following elements: the CE mark, the notified body identification number if required, the special Ex mark (the explosion-protection symbol inside a hexagon), the equipment group and category, the Ex protection symbol and protection type, the gas or dust group, the temperature class, the equipment protection level (EPL), and, if applicable, the certificate number indicating special conditions of use. The table below breaks down the "II 2G Ex db IIC T4 Gb" example piece by piece.
| Code Part | Meaning |
|---|---|
| II | Equipment group: Group II, for use in surface industries (non-mining) |
| 2G | Category 2, gas environment (G); suitable for use in Zone 1 and Zone 2 |
| Ex | Special symbol showing the equipment is certified as Ex (explosion-protected) |
| d | Protection type: flameproof enclosure - IEC 60079-1 |
| IIC | Gas group: the broadest-scope group (also covers the most easily ignited gases, such as hydrogen and acetylene) |
| T4 | Temperature class: equipment surface does not exceed 135°C |
| Gb | Equipment Protection Level (EPL): "high" protection level for a gas environment |
You can find a detailed technical breakdown of this example, together with a real certificate number, in our article What Does Ex db IIC T4 Gb Mean?.
Equipment Group and Category
Group I is for mining equipment, and Group II is for surface industry equipment. The category number (1, 2 or 3) determines which zone the equipment can be used in; the letter "G" is for a gas/vapor environment, and "D" is for a dust environment. You can examine the category-zone match in detail in our articles What Are Zones 0, 1 and 2? and What Are Zones 20, 21 and 22?.
Common Protection Types
- Ex d (Flameproof Enclosure): Prevents an explosion that may occur inside the enclosure from spreading to the outside environment, through the enclosure's pressure-resistant structure.
- Ex e (Increased Safety): Contains additional structural measures that prevent sparks or overheating in normal operation; commonly used in terminal boxes and motor windings.
- Ex ia / Ex ib (Intrinsic Safety): Provides protection by limiting the energy in the circuit to a level insufficient for ignition; common in measurement and control circuits.
- Ex tb / Ex tc (Dust-Protected Enclosure): Based on limiting dust ingress into the enclosure and controlling surface temperature.
Gas Groups and Temperature Classes
| Gas Group | Example Substances |
|---|---|
| IIA | Propane, gasoline vapor (least critical group) |
| IIB | Ethylene and similar medium-level gases |
| IIC | Hydrogen, acetylene (most critical, broadest-scope group) |
| Temperature Class | Maximum Surface Temperature |
|---|---|
| T1 | 450°C |
| T2 | 300°C |
| T3 | 200°C |
| T4 | 135°C |
| T5 | 100°C |
| T6 | 85°C |
Equipment meeting the IIC group is also suitable for IIA and IIB gases; similarly, equipment meeting the T6 class covers all temperature classes from T1 to T6. In other words, for both parameters, the "smaller/more demanding" value automatically covers the "larger/less demanding" one.
Frequently Asked Questions
Is the Ex mark sufficient on its own?
No, the Ex mark always appears together with the CE mark, alongside the other information that must be present on the equipment's label (manufacturer, model, serial number, certificate number).
Are equipment group and category the same thing?
No. The equipment group (I or II) indicates the environment of use, while the category (1, 2, 3 or M1, M2) shows the level of protection within that group.
Why is the EPL separately stated on the label, isn't the category enough?
EPL is a complementary designation that expresses the protection level in a way compatible with the international IEC system; it is especially useful when comparing with IECEx-certified products.
What should I do if I see the letter 'X' on the label?
The letter 'X' at the end of the certificate number means there are specific conditions of use for the equipment's safe operation; these conditions are always stated in the user manual and must be followed.
Conclusion
Ex marking carries critical information, within a short code, about where and under what conditions the equipment can be safely used. Being able to correctly read this code is vital both in equipment selection and in field audits.
For more information, see our ATEX consultancy service.
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