Zone 1 hazardous areas require ATEX or IECEx certified explosion-proof cable glands with high-integrity sealing, while Zone 2 areas accept slightly relaxed designs, but a gland rated for Zone 1 may always be installed in Zone 2, never the other way around [S3].
The defining metric is the gas group and temperature class printed on the gland marking: IIA, IIB, or IIC for gas atmospheres, and T1 through T6 for maximum surface temperature, both of which must align with the specific substances handled in the enclosure location [S3]. Standard EN 60079-14 governs the selection of cable entry systems as part of the overall explosion protection installation, while the cable itself is not required to carry ATEX certification, only the gland does [S5].
Zone Definitions and Probability of Explosive Atmosphere
Zone 1 covers areas where an explosive gas or vapour mixture is likely to occur during normal operation, demanding higher-integrity, certified explosion-proof glands with proven containment capability [S2]. Zone 2 covers areas where an explosive atmosphere occurs only rarely and for short durations, permitting less stringent but still ATEX or IECEx certified solutions [S2].
The probability model driving this split is straightforward: Zone 1 anticipates an explosive mixture as part of routine process conditions, Zone 2 anticipates it as an abnormal or short-lived event, and Zone 0 (not the focus here) anticipates it continuously [S6]. Cable glands must therefore be selected to match the worst-case zone classification of the enclosure entry point, not the average operating condition, and the selection cascades from the equipment's own ATEX category marking on the certificate [S3].
Protection Concepts: Ex d, Ex e, and Barrier Glands
Ex d (flameproof) glands contain any internal explosion and prevent flame propagation through the cable entry, making them the default for Zone 1 flameproof enclosures, while Ex e (increased safety) glands prevent sparks, arcs, and excessive surface temperatures and are commonly used in Zone 1 or Zone 2 with increased-safety enclosures [S3]. Barrier glands add a compound seal (often epoxy or setting compound) around the individual cores, preventing gas migration along the cable interstices, which is critical where the cable runs between zones of different classification [S9].
For armoured cables such as SWA (steel wire armoured) or STA, double-compression glands clamp the armour for mechanical retention and electrical continuity (the armour must be grounded to the gland body), then seal on the inner sheath, and this construction is the standard recommendation for Zone 1 armoured-cable entries [S2]. For unarmoured cables in Zone 2, a single-compression gland with an elastomeric seal on the outer sheath is typically sufficient, provided the entry thread matches the enclosure and the IP rating meets the environmental exposure [S2]. Engineers building process-engineered valve assemblies into Zone 1 service will find the same double-seal logic applied at the actuator conduit entry.
Material Selection by Environment
Nickel-plated brass is the common, cost-effective choice for general industrial indoor and outdoor Zone 2 installations where harsh chemicals are not a primary concern [S3]. Stainless steel 316L is the default for offshore, marine, and chemical processing exposure, where chlorides and a wide chemical spectrum would otherwise attack brass within a few service years [S3].
Polyamide (nylon) Ex e glands are widely used for increased-safety applications in Zones 1, 2, 21, and 22, offering corrosion-proof, lightweight performance where there is no risk of high-impact mechanical damage [S1]. Aluminium glands are lighter and conductive but are restricted in some zones because friction or impact on aluminium can produce incendive sparks, so a documented risk assessment is required before specifying them in hydrogen-rich (IIC) or dust atmospheres [S3]. For typical material-grade reference and corrosion thresholds across gland body alloys, the cable gland encyclopedia entry consolidates the brass / 316L / nylon comparison side by side.
Thread Standards, IP Ratings, and Sealing Performance
Thread type must match the enclosure entry: metric (M) is the European default under IEC 60079-14, NPT is the North American standard for hazardous locations, and PG (Panzer-Gewinde) still appears on legacy German equipment, with adapters required when mixing types [S2]. Cable diameter range must produce a tight seal: typical gland size charts cross-reference outer diameters of 6-12 mm, 12-20 mm, and 20-32 mm against the gland size code, and undersized or oversized seals are the single most common cause of failed inspection [S2].
IP66 and IP68 are the two ratings most often called out on hazardous-area glands: IP66 resists powerful water jets, while IP68 (with a defined depth and duration, typically 1 m for 30 minutes as a minimum baseline, longer for submersed applications) protects against continuous immersion [S2]. Installation torque on the gland body and the locknut is published by the manufacturer and must be applied with a calibrated tool, since under-torquing produces a gas path and over-torquing cracks the elastomeric seal or distorts the armour cone. For process skids where cable routing and segregation interact with gland selection, the tray fill ratio and bend radius rules under the same hazardous-area code still apply.
Decision Matrix: Zone 1 vs Zone 2 Gland Specification
Selection breaks down across four criteria: certification level, gland construction, material, and acceptable cable types. On certification, Zone 1 requires ATEX category 2 (or IECEx equivalent) Ex d or Ex e barrier glands, while Zone 2 accepts category 3 Ex e single-compression [S3][S6]. On construction, Zone 1 specifies double-compression for armoured cable and barrier (compound-filled) for any cable crossing into a higher-classified area, while Zone 2 allows single-compression for unarmoured or armoured cables where the entry is into a non-flameproof enclosure [S2][S9].
On material, Zone 1 with offshore or chemical exposure forces 316L stainless or nickel-plated brass with documented corrosion resistance, while Zone 2 indoors accepts brass, nylon, or aluminium subject to risk assessment [S3]. On cable type, Zone 1 armoured applications demand SWA/STA with double-seal clamping, while Zone 2 unarmoured applications work with single-seal elastomeric compression, provided the cable itself blocks longitudinal gas migration [S2][S5]. A practical rule pulled from IEC 60079-14: the cable gland must match or exceed the enclosure's own zone rating, and a Zone 2 gland on a Zone 1 enclosure is a certification failure that will be flagged at the hazardous-area inspection [S3]. Engineers cross-referencing gland packing and sealing for valve stems should note that the elastomer compound families (EPDM, nitrile, Viton) overlap with the seal materials used inside barrier and compression glands.
Installation, Inspection, and Common Failure Modes
Three failure modes dominate hazardous-area gland inspection: incorrect thread engagement (less than the specified number of engaged threads, typically 5 for metric and 5 for NPT), missing or wrong elastomeric seal (a Zone 2 seal substituted into a Zone 1 gland), and armour not properly clamped so the cable rotates or pulls under its own weight, breaking the earth bond [S2][S9].
Inspection cycles under IEC 60079-17 typically grade glands as part of the 'Ex d' or 'Ex e' equipment routine, with visual check at 12 months and detailed inspection including torque verification at 4 years for continuous-process plants [S9]. A documented torque wrench reading at installation, recorded against the gland serial number, is the strongest defence in an incident investigation, and is also the format most EU notified bodies expect in the Ex verification dossier [S3].
Watch for the next ATEX 2014/34/EU and IEC 60079-0 maintenance cycle revisions that may tighten the marking rules around gas-group suffixes and add explicit UV-resistance requirements for outdoor polyamide glands, and track the published list of harmonised standards in the Official Journal of the European Union, since a gland certified to a now-non-harmonised standard loses its presumption of conformity on the date of withdrawal. For engineering teams standardising on a single vendor family across Zone 1 and Zone 2 entries, the cable and wire reference covers the conductor-side specifications that the gland must terminate.