ATEX cable entries — why an Ex e gland does not simply fit onto an Ex d enclosure

The decoding ATEX marking guide covers how to read the Ex marking on the nameplate of explosion-protected equipment. This article addresses a specific, commonly encountered pitfall in the cable entry of that equipment: the difference between an Ex d and an Ex e cable gland, and when a separate barrier gland is mandatory.

Two protection concepts, two kinds of gland

Ex d (flameproof): the enclosure itself withstands an internal ignition and contains the resulting pressure wave and flame within the enclosure. An Ex d cable gland combines a flameproof connection to the enclosure with a gas-tight internal seal at conductor level (often using a compound or filling material).
Ex e (increased safety): protection relies on excluding sparks and excessive temperatures through constructional measures (extra creepage and clearance distances, tightening torques), not on containing an internal ignition. An Ex e cable gland seals only mechanically on the cable sheath — a clamping element that surrounds the sheath — without compound and without any seal between the individual cores.

Why this difference matters for multi-core cables

A multi-core cable has voids between the cores and the sheath (the core). If such a cable terminates at one end in an Ex d enclosure and a gas path can form via that core to another space (for example a non-hazardous area, or a second Ex zone), an internal ignition inside the Ex d enclosure could propagate outward via that core — precisely what the flameproof enclosure is meant to prevent. To prevent this, IEC 60079-14 requires that, depending on the cable length between two Ex d enclosures (and whether the far end also terminates in an Ex d enclosure), a barrier gland may be required: a gland that provides a separate, gas-tight seal around each individual core.

Note: a barrier gland is itself always certified as Ex d, but is also used in Ex e installations where there is a risk that gas could migrate via the cable core — the choice for a barrier gland therefore depends on the gas-migration risk via the cable, not solely on the protection concept of the enclosure it is mounted on.

What a standard Ex e gland does and does not do

For its own application (an Ex e enclosure, without a significant internal ignition source), an Ex e gland is entirely adequate: the mechanical seal on the sheath prevents ingress of dust/moisture (IP rating) and retains the cable in place. What the gland does not do is provide a gas-tight seal between the individual cores — and that is precisely why it cannot simply take over the role of a barrier gland on an Ex d enclosure, even though it may sometimes mechanically fit (the thread may match without the internal construction being equivalent).

Practical relevance

When selecting or replacing a cable gland on explosion-protected equipment, it must be checked not only whether the gland itself is correctly certified (Ex d, Ex e, or as a barrier gland), but also whether the combination of cable type, cable length between enclosures and the enclosure's protection concept makes a barrier gland mandatory — a gland that at first glance "fits" (correct thread, correct IP rating) can still have the wrong internal construction for the application.

Common mistakes

Fitting an Ex e gland onto an Ex d enclosure because the thread and cable diameter range match — the internal, gas-tight seal of an Ex d/barrier gland is then missing, risking propagation of an internal ignition beyond the enclosure.
Assuming a barrier gland is only needed with Ex d — a barrier gland can also be mandatory in Ex e installations when the cable core poses a gas-migration risk between two spaces/zones.
Not factoring in the cable length between two Ex d enclosures — precisely this length (and thus the volume of cable core that can serve as a gas path) determines whether a barrier gland is mandatory, not the protection concept alone.