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IEC 60079-7

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IEC 60079-7

Equipment Protection by Increased Safety 'e'

IEC 60079-7 specifies 'increased safety' (Ex e) protection — applied to equipment that does not produce arcs, sparks or hot surfaces in normal operation. Used primarily for terminals, junction boxes, motors without slip rings, and lighting fixtures.

Organisme
IEC
Family
Hazardous Areas
Première publication
1976
Dernière révision
2017 (Edition 6)
Prochaine révision
Active maintenance
Statut
current
Accès
Paid (IEC webstore — ~200 CHF)

Structure du document

IEC 60079-7:2017

Equipment protection by increased safety 'e'

Specifies enhanced construction requirements for non-sparking equipment : insulation distances, temperature limits, IP rating, mechanical strength. Less expensive than flameproof but more limited (no normal-operation arcs allowed).

Concepts clés

Increased safety principle
Engineer the equipment so that it does NOT produce ignition sources during normal operation (no arcs, no sparks, no hot surfaces > T-class). Then add safety margin in clearances, creepage distances, materials, mechanical strength.
Ex eb vs ec
Ex eb = standard increased safety, suitable for Zone 1 (EPL Gb). Ex ec = relaxed requirements for Zone 2 only (EPL Gc), introduced in 2015 to replace the deprecated 'nA' protection method.
Limiting temperature rise
Critical for Ex e motors : the motor must not exceed its T-class even when stalled or under fault conditions. Manufacturers specify a t_E time : maximum time a stalled motor can remain energized before exceeding limits. Tripped before t_E by thermal overload protection.
Where you find Ex e
Terminal boxes (most common — junction boxes on Ex d motors etc.), squirrel-cage motors WITHOUT brushes/slip rings, lighting fixtures (LEDs, fluorescent), some space heaters, transformers.

Notes & guidance

Where Ex e fits in the Ex protection toolkit

Ex e occupies the middle ground between IS (low power, Zone 0) and flameproof (any power, Zone 1+). Specifically :

  • Higher power than IS : can handle motor terminals, lighting circuits
  • Lower cost than Ex d : no need for explosion containment construction
  • Limited to non-arcing equipment : ruled out for relays, contactors, switches with normal-operation arcing

In practice, the most common Ex e application is the terminal compartment of an industrial motor. The motor body itself is Ex d (the rotor brushes / commutator could spark, must be contained), but the connection terminals don’t arc in normal operation — they get Ex e (lighter, easier to access for maintenance). The marking becomes Ex de (compound : ‘d’ for motor body, ‘e’ for terminal box).

Junction boxes are another major application — distributing power to multiple Ex devices, with no internal arcing under normal operation.

Ex e motor protection

The catch with Ex e motors : the stall current must not heat the windings beyond the T-class. Manufacturers specify :

  • tE time : time at stall before T-class exceeded (typically 5-40 seconds)
  • IA/IN : starting-current-to-rated-current ratio

The thermal overload relay protecting the motor must trip in less than tE even under worst-case stall. This is documented and verified at commissioning.

Ex ec — the new Zone 2 option

The 2017 edition reorganized Zone 2 protection methods. The old “Ex nA” (non-sparking) classification was merged into “Ex ec”, the relaxed Ex e variant for Zone 2 only.

Effect : Ex e equipment for Zone 2 became slightly easier to certify (less rigorous environmental testing) while keeping the basic non-arcing principle. New designs use Ex ec for Zone 2. Legacy nA designations are still seen on older equipment.

Industries concernées

  • Oil & Gas (terminal boxes everywhere)
  • Petrochemical (junction boxes, lighting)
  • Chemical industry
  • Marine and offshore

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