What Ex eb means
Ex eb is an ATEX and IECEx protection concept defined in IEC 60079-7. The designation stands for:
- Ex, explosion protection
- e, increased safety (Erhöhte Sicherheit in German, the language of the original standard)
- b, Equipment Protection Level b, suitable for Zone 1
The principle of increased safety is straightforward: design the equipment so that sparks and excessive temperatures simply cannot occur. This is achieved by applying more stringent construction requirements than standard IEC electrical standards, larger creepage distances, better terminal retention, higher ingress protection, and tighter temperature control.
Unlike Ex d (flameproof), Ex eb equipment is not designed to contain an internal explosion. There must be no ignition-capable source inside an Ex eb enclosure. If the equipment inside could spark, for example a contactor or motor winding, then Ex eb alone is not sufficient and combined protection (Ex db/eb) or a different method must be used.
Technical requirements
The key requirements that differentiate Ex eb from standard electrical equipment are defined in IEC 60079-7:
| Requirement | Ex eb specification | Reason |
|---|---|---|
| Creepage distances | Greater than IEC 60664 for equivalent voltage/pollution degree | Prevent tracking between conductors under contamination |
| Clearance distances | Greater than standard; gas-group dependent | Prevent arcing across air gaps |
| Terminal locking | Must resist accidental loosening; tightening torque specified on certificate | Loose connections arc and spark |
| Ingress protection | Minimum IP54 for Group II equipment | Prevent entry of dust and water that could cause tracking |
| Maximum voltage | 11 kV maximum for Group II | Higher voltages require additional precautions |
| Exposed conductors | Not permitted within the Ex eb enclosure | Exposed live conductors can arc to adjacent parts |
| Surface temperature | Must not exceed the T class at maximum load | Hot surfaces ignite flammable atmospheres |
All of these requirements apply to the equipment as installed, not just as supplied. The installation contractor is responsible for ensuring that torque requirements are met and that cable entries maintain the IP rating.
IP rating requirement
The minimum IP54 requirement for Ex eb Group II equipment is often misunderstood. IP54 means:
- 5, dust-protected (limited ingress; no harmful deposit)
- 4, protected against water splashing from any direction
In practice, while most manufacturers offer a lower rating, indEx Enclosures rates all its enclosures to a IP 66 rating, significantly above the minimum. This is partly because the enclosures serve outdoor and industrial environments where higher IP protection is needed regardless, and partly because higher IP ratings provide greater margin against creepage failure over the operating lifetime.
For outdoor installations, IP66 (dust-tight; protection against powerful jets) is standard. The IP rating must be maintained by using appropriately rated cable glands that are correctly installed and torqued.
Terminals and connections
Terminals are the most critical component in an Ex eb enclosure. The certification requires:
- Terminals must be individually certified to Ex eb (not just suitable by construction)
- The maximum tightening torque must be marked on the terminal or the enclosure certificate
- Terminals must include a feature to prevent accidental loosening, a captive screw, locking washer, or spring-loaded clamp
- The minimum and maximum conductor cross-sections must be specified
- Creepage between adjacent terminals must meet the standard for the relevant voltage and pollution degree
Polyamide (nylon) terminals are common in Ex eb enclosures because of their good tracking resistance. PE (polyethylene) terminals are used where chemical resistance is required. The terminal material and spacing are verified during type examination, you cannot substitute a different terminal type without re-evaluation.
Wire ferrules (bootlace ferrules) are strongly recommended and often required. Bare stranded conductors in screw terminals can produce loose strands that reduce creepage distances or cause arcing.
Zone suitability
| Zone | Ex eb suitable? | Notes |
|---|---|---|
| Zone 0 | No | Zone 0 requires EPL Ga; Ex eb is EPL Gb |
| Zone 1 | Yes | Primary application; EPL Gb covers Zone 1 and 2 |
| Zone 2 | Yes | Ex eb is more than sufficient; Ex ec may suffice |
| Zone 20 | No | Dust Zone 20 requires EPL Da |
| Zone 21 | With Ex tb | Ex tb (dust) combined with Ex eb for dust applications |
| Zone 22 | With Ex tc | Ex tc (dust) combined with Ex ec for Zone 22 |
For dust hazardous areas, the 't' protection concept applies (IEC 60079-31) rather than 'e'. A terminal box used in a Zone 21 dust area would be marked Ex tb (not Ex eb), even if the construction is similar. The IP requirement for dust zones is typically IP6X (dust-tight).
Typical applications
Ex eb is the standard protection method for a wide range of Zone 1 electrical equipment:
- Terminal boxes and junction boxes, the most common application; field cable connections in Zone 1 process plant
- Control station enclosures, pushbutton and pilot light assemblies (using Ex eb certified buttons that cannot spark)
- Distribution boards, where no switching occurs inside; isolating switches that do switch may require additional protection
- Marshalling panels, multi-way field cable terminations in Zone 1 substations
- Instrument junction boxes, where the instruments themselves use intrinsic safety, but the junction box housing the terminals is Ex eb
- Lighting fittings, fluorescent and LED luminaires certified Ex eb where the lamp and ballast cannot spark