Ex d, Ex e, Ex i, Ex n… Protection Concepts Explained (2025)
TL;DR
Every ATEX / IECEx marking starts with an “Ex” plus a letter: d, e, i, p, n…. Those letters tell you how the equipment prevents ignition. Flameproof Ex d contains an explosion, Ex i removes energy, Ex e blocks arcs, Ex n relies on normal operation. Pick the right concept and you slash cost, weight and maintenance—pick the wrong one and you risk an audit shutdown.
1. Why protection concepts exist
Zone classification only says “how often” an explosive atmosphere exists; protection concepts say “what engineering method keeps the spark away.” Each concept is codified in the IEC 60079 series and mapped to an Equipment Protection Level (EPL) and Zone:| Concept | Standard | Principle | EPL | Typical Zones |
|---|---|---|---|---|
| Ex d (Flameproof) | IEC 60079-1 | Contain & cool internal explosion | Ga/Gb (Da/Db) | 0, 1, 2 / 20, 21, 22* |
| Ex e (Increased safety) | IEC 60079-7 | No arcs, tight clearances | Gb (Db) | 1, 2 / 21, 22 |
| Ex i (Intrinsic safety) | IEC 60079-11 | Limit energy below ignition | Ga/Gb/Gc | 0, 1, 2 |
| Ex p (Pressurisation) | IEC 60079-2 | Keep enclosure air-purged | Gb/Gc | 1, 2 / 21, 22 |
| Ex n (Non-sparking / reduced energy) | IEC 60079-15 | No ignition under normal operation | Gc | 2 / 22 |
| Ex m (Encapsulation) Ex q (Powder fill) Ex o (Oil immersion) | -18 / -5 / -6 | Isolation by resin, quartz, oil | Gb/Gc | 1, 2 |
*Ex d dust versions (Ex tb) exist but are rare.
2. Deep dive into the “big four” concepts
2.1 Ex d – Flameproof enclosure
- 5–30 mm thick cast or forged housing.
- Flamepath gaps < 0.15 mm cool flames below ignition temp.
- Pros: survives internal faults; usable in Zone 0.
- Cons: heavy, expensive, requires Ex certified cable glands.
2.2 Ex e – Increased safety
- No make/break contacts; reinforced insulation; T≤ surface class.
- Common for Zone 1 motors (“Ex eb”) and junction boxes.
- Cheaper and lighter than Ex d but forbidden in Zone 0.
2.3 Ex i – Intrinsic safety
- Energy limited to ≤ 1.2 W (IIC gas) via Zener/galvanic barriers.
- Allows live maintenance without gas clearing.
- Perfect for sensors, IIoT, PLC I/O, NFC tags.
- Tip: Use blue IS glands to avoid mix-ups.
2.4 Ex p – Pressurised / Purged Enclosure
- Positive pressure keeps hazardous gas/dust out (≥ 0.3 kPa over ambient).
- Purge cycle (5–10 enclosure volumes) before power-up, monitored by pressure switch.
- Ideal for large control panels, VFDs, analyzers, HMIs that would be huge in Ex d.
- Pros: standard industrial hardware inside; lighter and cooler than flameproof.
- Cons: Needs reliable instrument air / inert gas supply and “loss-of-pressure” alarm interlock.
2.5 Ex n – Non-sparking / restricted breathing
- Minimal arcing under design load; enclosure prevents dust ingress
- Only for Zone 2/22; cheapest concept.
- Watch out: one loose screw can void certification.
3. Cost & weight comparison (industrial LED 100 W)
| Protection | Weight (kg) | List price (€) | Zone |
|---|---|---|---|
| Ex d | 18.2 | 1 950 | 1 / 2 |
| Ex e | 11.0 | 1 150 | 1 / 2 |
| Ex n | 8.4 | 720 | 2 |
Vendor quotes from Q3-2024; shows why Zone 2 design pays.
4. How to choose the right concept
- Check Zone & Gas/Dust group.
- Define maintenance strategy. Live-working? Choose Ex i.
- Assess ambient conditions. Dust layers? Ex t or Ex d instead of Ex n.
- Compare T-class to process temperature.
- Factor weight & cable cost. Skids benefit from Ex e/Ex n.
5. Common mistakes and audit findings
- Mixing Ex e terminals inside an Ex d motor without temperature rise test.
- Installing Ex n luminaires in Zone 1—instant non-conformity.
- Painting flamepath surfaces—kills heat dissipation & certification.
