ATEX Panels: The Ex d and Ex e Protection Concepts
ATEX panel: A panel for an explosive atmosphere is equipment certified with a protection concept suited to its zone. The Ex d flameproof concept allows an explosion to occur inside the enclosure while preventing flame transmission to the outside, whereas the Ex e increased safety concept aims to prevent arcs and excessive temperature arising at all; the two can also be combined in one assembly.
Contents
Making a panel suitable for an explosive atmosphere is not about a thicker enclosure; it is about following to the letter the rules of a design certified for a defined zone, gas group and temperature class. In this field an enclosure drilled on site, or an unsuitable cable gland, voids the whole certificate. This article covers zone classification, the Ex d and Ex e protection concepts, temperature class and gas group, and the practical constraints that appear in panel design.
Zone classification and equipment categories
Explosive atmospheres are divided into zones according to how long a hazardous atmosphere is present. For gases and vapours, zone 0 means continuously, zone 1 occasionally in normal operation and zone 2 only under fault conditions; the corresponding classes for dusts are zones 20, 21 and 22. Each zone corresponds to a permitted equipment category and equipment protection level, and for zone 1 category 2 with protection level Gb is the typical requirement. When planning panel location, the best approach wherever possible is to place the panel outside the hazardous area and leave only the necessary actuators and sensors in the field, which markedly reduces both cost and maintenance complexity.
What is the difference between Ex d and Ex e?
The Ex d flameproof concept is based on enclosing components that inevitably produce arcs inside a very robust housing. The housing withstands an internal explosion and, through defined flame paths, allows hot gases to cool as they escape so that the external atmosphere is not ignited. The Ex e increased safety concept takes the opposite approach: additional measures are taken so that arcs, sparks and excessive surface temperature do not arise in normal operation, with enlarged insulation distances, terminals secured against loosening and low temperature rise forming the basis of the concept. A combined solution is common in practice: switching devices sit in an Ex d compartment while the terminal and distribution section occupies an Ex e enclosure.
Temperature class, gas group and reading the label
The maximum surface temperature the equipment can reach must stay below the ignition temperature of the surrounding gas with a safe margin, and this relation is expressed through temperature classes running from T1 to T6, where T6 represents the lowest surface temperature. Gas groups are divided into IIA, IIB and IIC according to ignition energy and flame transmission properties, with IIC containing hydrogen and acetylene as the most demanding group. An Ex label carries this information in sequence, and reading it correctly shows directly which zone the equipment may be used in. The ambient temperature range is also stated on the label, and use outside that range falls outside the scope of the certificate.
Practical constraints in panel design
| Label field | Example value | Meaning |
|---|---|---|
| Equipment group | II | Surface industries other than mining |
| Category and atmosphere | 2 G | Suitable for zone 1, gas atmosphere |
| Protection concept | db eb | Flameproof enclosure combined with increased safety |
| Gas group | IIC | The most demanding group, including hydrogen and acetylene |
| Temperature class | T4 | Maximum surface temperature limited to 135 degrees Celsius |
| Equipment protection level | Gb | The high protection level required for zone 1 |
In Ex e enclosures the number and arrangement of terminals is not free; enlarged insulation distances, the current permitted per terminal and the temperature rise limit inside the enclosure jointly determine it. An Ex e panel is therefore noticeably larger than a standard panel performing the same function. Cable entries are made only with certified Ex glands, unused holes are closed with certified plugs, and no new opening may be made in the enclosure on site. In Ex d compartments the class, number and torque of the cover bolts are part of the certificate, and one missing bolt destroys the flameproof property. Thermal management is also constrained: since fans and louvres are usually not possible, the internal heat load has to be reduced by design.
Certification, installation and site intervention
Equipment for explosive atmospheres is certified with the involvement of a notified body for the relevant category, and the manufacturer supplies a declaration of conformity together with instructions for use. During installation the earthing, sealing, gland type and torque values in those instructions are applied without exception. The fundamental rule on site intervention is that no change outside the design may be made to a certified enclosure; an extra pushbutton, a new cable entry or a different terminal is possible only with manufacturer approval and an update of the certification scope. Periodic inspection is carried out by competent personnel using a defined checklist, and the records are retained.
Key takeaways: ATEX panel
- Ex d contains the explosion, Ex e prevents it — the two concepts work on different logic and can be combined.
- Zone, category and protection level must match — zone 1 typically requires category 2 and level Gb.
- Temperature class follows the gas ignition temperature — it is declared on the label together with the gas group.
- A certified enclosure is never modified on site — a new hole, different gland or added device voids the certificate.
- Standard source — IEC publication catalogue: iec.ch.
Frequently asked questions
Is it possible to keep the panel outside the hazardous area?
Wherever possible it is the best solution. Placing the control and distribution board in the safe area and leaving only certified actuators, sensors and field boxes in the hazardous zone reduces cost and maintenance complexity. It also simplifies gas testing and permit procedures during maintenance.
Why is an Ex e panel larger than a standard panel?
Because the increased safety concept imposes larger insulation distances, a lower current per terminal and a tighter temperature rise limit. The same number of circuits needs more terminal volume and wider internal spacing. This must be reflected in space planning at an early design stage.
Can I convert a standard panel into a certified Ex panel?
No. Ex compliance requires the enclosure, terminals, glands and internal components to be part of a design certified as a whole. Certifying an existing panel afterwards is not practically feasible; the correct route is to select an Ex solution certified for the application.
Related articles
- IP Protection Rating Explained: How to Read an IP Code
- Enclosure Material and Powder Coating: How to Choose Correctly
- Earthing System Types: TN-S, TN-C-S, TT and IT
- All technical articles
Devpan provides engineering support in projects with explosive atmospheres for the selection of Ex solutions matched to the zone classification, interface design and safe-area boards. Contact us to review the requirements of your project. Related Devpan solution: electrical panel design services.
