Ex d vs Ex e Cable Gland — Key Differences, Standards & Selection Guide

When specifying cable glands for hazardous area installations, the choice between Ex d (flameproof) and Ex e (increased safety) types is one of the most consequential decisions an electrical engineer will make. Both protection concepts appear across oil & gas, chemical, mining, and pharmaceutical facilities, yet their underlying principles, construction requirements, and installation rules are fundamentally different. This guide explains exactly what separates an Ex d cable gland from an Ex e cable gland, when each applies, and how to select the right type for your specific application.

Understanding Ex d and Ex e Protection Concepts

Hazardous area protection methods are governed by the IEC 60079 series of standards. Each protection concept is assigned a two-letter code and addresses a specific ignition risk in a different way. Ex d and Ex e represent two of the most widely used approaches in industrial electrical installations worldwide.

What Is Ex d (Flameproof)?

Ex d, defined under IEC 60079-1, is a protection concept built on containment. An Ex d enclosure is designed to withstand an internal explosion of a flammable gas mixture and to prevent the propagation of that explosion to the surrounding atmosphere. The enclosure does not prevent ignition inside, it contains and quenches the explosion, cooling escaping gases through precisely machined flame paths so they exit below the ignition temperature of the surrounding atmosphere.

A cable gland used with an Ex d enclosure must therefore maintain the integrity of this containment. It must not allow gas to migrate through the cable and enter the enclosure from outside, and it must itself be capable of resisting internal explosion pressure. This is why Ex d cable glands are robust, metal-bodied devices with certified thread engagement depths, and typically require a compound-filled barrier to seal around individual conductors.

What Is Ex e (Increased Safety)?

Ex e, defined under IEC 60079-7, takes a fundamentally different approach. Rather than containing an explosion, increased safety equipment is designed to prevent ignition in the first place. Ex e enclosures and terminals are constructed to a higher standard than general industrial equipment, with enhanced creepage and clearance distances, higher ingress protection ratings, and tight control over surface temperatures, so that arcs, sparks, and excessive heat simply do not occur in normal or specified abnormal operating conditions.

An Ex e cable gland must therefore deliver a certified level of ingress protection (typically IP54 or higher), maintain a reliable mechanical seal against the cable, and meet the dimensional and material requirements set out in IEC 60079-7. It does not need to withstand explosion pressure, but it must not introduce any path for moisture, dust, or contaminants that could compromise the enclosure’s safety rating.

How Each Cable Gland Type Works

Ex d Cable Gland, Sealing Mechanism

An Ex d cable gland works in two distinct zones simultaneously. At the enclosure entry, it provides a certified threaded connection with a defined flame path length that resists and quenches any internal explosion pressure before gases can escape to the outer atmosphere. Inside the cable entry chamber, a compound, typically a two-part epoxy resin or putty, is injected around the individual conductors to fill every interstitial void within the cable. This compound barrier prevents flammable gas from migrating along the cable’s interstices from the outside hazardous atmosphere into the protected enclosure interior.

The combination of a pressure-resistant enclosure connection and a gas-impermeable internal seal makes the Ex d cable gland the only type suitable for use with flameproof enclosures in the most demanding gas groups and zones.

Ex e Cable Gland, Sealing Mechanism

An Ex e cable gland achieves its protection through mechanical compression alone. A clamping or compression element tightens against the outer sheath of the cable to form a seal that meets the required IP rating. A second clamping element grips the cable to provide strain relief and prevent the cable being pulled through the gland under load.

There is no compound filling and no internal conductor-level seal. The assumption built into IEC 60079-7 is that an increased safety enclosure will not experience internal ignition, so preventing gas migration into the enclosure is less critical than maintaining a robust, durable external seal that keeps the enclosure’s ingress protection intact throughout its service life.

Construction & Materials

Ex d Cable Gland Construction

Ex d cable glands are precision-machined, heavy-duty components. Key construction features include:

• Body material: Nickel-plated brass for standard industrial environments; 316L stainless steel for offshore, marine, or chemically aggressive settings.
• Thread form: Metric (M-thread), NPT, PG, or G (BSP) with certified minimum engagement depths that must be respected during installation.
• Barrier chamber: An integral cavity within the gland body into which sealing compound is injected or packed, surrounding every individual conductor core.
• Compound system: Injectable two-part resin or hand-packed putty, both achieve gas-tight performance to IEC 60079-1 when correctly applied.
• Armour termination: Available for SWA (steel wire armoured), wire braid, and unarmoured cables with appropriate clamping cones for each construction.
• IP rating: IP66 as standard; IP68 where submersible or buried installation is required.

Ex e Cable Gland Construction

Ex e cable glands are designed around reliable, long-term mechanical sealing. Their key features include:

• Body material: Nickel-plated brass or stainless steel, selected based on environmental exposure.
• Sealing element: Elastomeric O-rings or compression seals that grip the outer cable sheath, no compound is used.
• Cable retention: A dedicated clamping jaw or cone provides axial strain relief independently of the sealing element.
• Thread form: Same range as Ex d, metric, NPT, PG, BSP, to suit the enclosure entry thread.
• IP rating: IP54 minimum per IEC 60079-7; most modern Ex e glands achieve IP66 or IP68.
• Temperature rating: The elastomeric sealing elements must be rated for the full operating temperature range of the installation.

Ex d vs Ex e Cable Gland, Direct Comparison

Zone Suitability & Gas Groups

Both Ex d and Ex e cable glands are used in Zone 1 and Zone 2 hazardous areas, but they are never interchangeable. The gland type must match the protection concept of the enclosure it is fitted to.

Zone 1 Installations

Zone 1 areas are those where a flammable gas atmosphere is likely to occur periodically during normal operation. Both Ex d and Ex e enclosures, and their respective cable glands, are suitable for Zone 1. The choice depends entirely on which protection concept the equipment manufacturer has designed and certified the enclosure to.

Zone 2 Installations

Zone 2 areas are locations where a flammable atmosphere is unlikely to occur in normal operation and, if it does occur, will persist only for a short period. Both Ex d and Ex e equipment are permitted in Zone 2. In practice, Ex e equipment is sometimes preferred in Zone 2 where the lower installation complexity of an Ex e gland is advantageous and the risk profile supports it.

Gas Group Considerations

Gas group classification, IIA (propane), IIB (ethylene), IIC (hydrogen, acetylene), determines how easily a gas can be ignited and how an explosion propagates. IIC is the most demanding group. Ex d cable glands certified to IIC must have flame path dimensions engineered to quench hydrogen and acetylene explosions, which requires tighter tolerances and longer paths than IIA or IIB equipment. Always verify that the gas group marked on the cable gland certificate matches or exceeds the gas group of the installation area.

Applicable Standards & Certifications

IEC 60079-1, Flameproof Enclosures (Ex d)

This standard defines the complete construction, testing, and marking requirements for flameproof equipment and the cable entry devices used with it. It specifies minimum thread engagement lengths, flame path tolerances, explosion pressure test requirements, and, critically, the requirement that cable entry devices must prevent gas migration through the cable. This is the technical basis for the compound-filled barrier in Ex d cable glands.

IEC 60079-7, Increased Safety (Ex e)

This standard covers increased safety equipment design and verification. For cable entry devices used with Ex e enclosures, it specifies minimum IP ratings, mechanical strength requirements for cable retention, maximum operating temperatures for sealing materials, and creepage and clearance requirements at the cable entry point.

IEC 60079-14, Electrical Installations

The installation standard that brings the equipment standards together. It governs how cable glands are selected and installed in practice, and it requires that the cable gland type matches the protection concept of the enclosure being served. The current edition includes the well-known 3-metre rule, which specifies that barrier-type cable glands are generally required for cable runs exceeding 3 metres entering Ex d equipment.

ATEX Directive 2014/34/EU

The European regulatory framework requiring CE marking and third-party notified body certification for all equipment intended for use in explosive atmospheres. Both Ex d and Ex e cable glands sold for European installations must carry ATEX certification with the appropriate equipment category marking.

IECEx Certification Scheme

The international equivalent of ATEX, recognised across the Asia-Pacific region, Middle East, Africa, and Latin America. Many cable gland manufacturers obtain dual ATEX and IECEx certification to enable global project deployment without country-by-country re-certification.

Industries & Applications

Where Ex d Cable Glands Are Specified

• Oil & gas upstream: Wellhead control panels, motor control centres on drilling rigs, FPSO vessel power distribution
• Downstream refining: Pump house junction boxes, reactor area control cabinets, distillation column instrumentation
• Chemical manufacturing: Chlorine, hydrogen, and ammonia handling areas, all IIC gas group environments
• Mining: Underground flameproof motor starters, switchgear in methane-classified headings
• Offshore platforms: Any Ex d rated luminaire, motor terminal box, or junction box on a gas-hazardous deck

Where Ex e Cable Glands Are Specified

• Process instrumentation: Increased safety terminal boxes for thermocouple, RTD, and transmitter connections in Zone 1 and Zone 2
• Control & marshalling: Ex e marshalling cabinets serving Zone 2 signal cables from safe areas
• Lighting installations: Increased safety luminaires in Zone 2 areas of petrochemical and pharmaceutical plants
• Pharmaceutical manufacturing: Ex e enclosures in Zone 2 classified solvent processing areas where equipment surface temperatures are tightly controlled
• Food, beverage & grain: Zone 22 dust atmospheres where Ex e equipment with IP65+ ratings is commonly employed

How to Select the Correct Type

Selecting between an Ex d and Ex e cable gland is not a matter of preference, it is dictated by the protection concept of the enclosure and the requirements of IEC 60079-14. The decision process follows these steps:

1. Identify the enclosure protection concept. Check the nameplate. If it reads Ex d, you need an Ex d cable gland. If it reads Ex e, you need an Ex e cable gland. There is no middle ground.
2. Confirm the gas group. The cable gland certificate must cover the gas group of the hazardous area (IIA, IIB, or IIC).
3. Check the temperature class. Both the enclosure and the cable gland must be rated to the T-class of the installation area (T1 through T6).
4. Specify the thread form and size. Match the gland entry thread to the enclosure’s tapped entry, metric, NPT, PG, or BSP in the correct size.
5. Confirm cable construction compatibility. Armoured cables require armour clamping glands; unarmoured cables require unarmoured versions. The gland cable diameter range must encompass the actual cable OD.
6. Verify IP rating requirements. Consider the installation environment, outdoor, wash-down, buried, or submersible applications each impose minimum IP requirements beyond the basic standard.
7. Apply IEC 60079-14 cable length rule (for Ex d). Cable runs over 3 metres entering Ex d equipment require barrier cable glands in the majority of cases. Confirm with the installation designer.

Installation Considerations

Installing an Ex d Cable Gland

Ex d cable gland installation is a skilled, multi-step process. The critical difference from a standard installation is the compound filling stage. Once the gland body is threaded into the enclosure to the correct torque, the individual conductors must be spread apart within the barrier chamber and the sealing compound injected or packed until all voids are completely filled. The compression nut is then tightened to distribute and pressurise the compound. The circuit must not be energised until the compound has fully cured to the manufacturer’s specified time, typically 24 hours at ambient temperature for most two-part epoxy systems.

Incorrect compound application is the leading cause of Ex d cable gland certification failures during inspection. Common errors include insufficient compound volume, air voids trapped between conductors, and premature energisation before cure is complete.

Installing an Ex e Cable Gland

Ex e cable gland installation is mechanically simpler but still requires care to achieve the certified IP rating. The outer sheath seal must be tightened to the manufacturer’s specified torque, under-tightening results in poor IP performance, while over-tightening can damage the elastomeric sealing element and compromise the seal over time. The cable retention clamp must be tightened independently to the specified torque to ensure strain relief without relying on the sealing element for mechanical grip.

Frequently Asked Questions

Metalmech is proudly approved by major organizations such as ADNOC, EIL, Petroleum Development Oman, and KPC (Kuwait Petroleum Corporation).