1. Direct Answer: Gland Specification and Zone 1 Requirements

For a Type 3S 11kV feeder cable with 82–88 mm outer diameter (typically a 3x95mm² to 3x240mm² conductor), the appropriate Ex d cable gland must be sized to accommodate the cable’s full outer diameter while maintaining the flange-threaded sealing design required by ATEX EN 60079-1 for Zone 1 explosive atmospheres. A typical selection for a 3x95mm² Type 3S cable would be an M100 or M105 flange-threaded gland rated for ATEX II 2G Ex d IIB T4, with a compressive sealing ring (typically 2 mm thick polyurethane or equivalent elastomer) that creates a pressure-tight barrier against explosive gas ingress, and a separate earthing screw or braided conductor that bonds the cable’s steel wire armor directly to the enclosure’s earth continuity. This is not simply a matter of finding any cable gland that fits the cable diameter—it is a critical safety component that must be certified, specified, and installed with precision.

对于外径 82–88 mm 的 Type 3S 11kV 馈电电缆（通常是 3×95mm² 至 3×240mm² 导体），适当的 Ex d 格兰头必须能容纳电缆的完整外径，同时保持 ATEX EN 60079-1 要求的用于 Zone 1 爆炸性大气的法兰螺纹密封设计。3×95mm² Type 3S 电缆的典型选择是一个 M100 或 M105 法兰螺纹格兰头，额定值为 ATEX II 2G Ex d IIB T4，配有压缩密封圈（通常为 2 mm 厚聚氨酯或等效弹性体），形成防爆气体入侵的压力紧密屏障，以及单独的接地螺钉或编织导体，将电缆钢丝铠装直接连接到外壳的接地连续性。

The selection of an Ex d gland for a Type 3S cable in Zone 1 is not a casual specification choice. Zone 1 is an ATEX hazard classification that means explosive gas is likely to occur in normal operations, and the electrical enclosure where the cable terminates must be designed to contain any potential explosion that might originate inside it. The “Ex d” designation means the enclosure is designed as a flange-joint explosive container—if an internal explosion occurs, the gland and the connecting flange must together withstand the pressure, cool the escaping gases below the ignition temperature, and prevent flame from propagating outward into the surrounding atmosphere where methane might be present. This is extraordinary engineering responsibility placed on a small component.

2. Understanding Ex d: What Makes a Gland Explosionproof

To understand why Ex d gland selection is so critical, we must first understand what makes any electrical component “explosionproof” in the context of mining regulations. The concept is not that the component will never allow an explosion to occur inside it—that is unrealistic for electrical equipment that carries high voltage and amperage. Rather, the concept is that if an explosion does occur inside the equipment, the design must prevent that internal explosion from being communicated outward to ignite explosive gas in the surrounding atmosphere.

Consider an electrical switchgear enclosure located in a Zone 1 hazardous area of an underground mine. If a high-voltage arc occurs inside the enclosure (due to component failure or fault condition), the arc is an ignition source at extremely high temperature. In a non-explosionproof enclosure, this arc and the resulting hot gases would escape directly into the mine atmosphere through any opening or gap, potentially igniting methane and coal dust surrounding the equipment. The result would be a catastrophic mine explosion.

In an explosionproof Ex d enclosure, the design prevents direct escape of the internal explosion. The enclosure is built as a rigid container with all electrical connections sealed through specially designed glands. If an internal arc occurs, the hot gases and pressure are contained momentarily within the enclosure. The design of the flange joint where the gland attaches is engineered so that the gases passing through the narrow gap between the flange and the gland body are cooled below the ignition temperature of methane (approximately 595°C), and the velocity of the escaping gases is reduced so that they cannot support a flame. The net result is that while an internal explosion can occur, the external atmosphere is protected from ignition.

The Ex d gland itself is the mechanical component that implements this philosophy at the point where the cable enters the enclosure. The gland must provide a pressure-tight seal (so that explosive gases do not leak in around the cable), a flange surface that creates the geometric gap for cooling, and an earthing path so that the cable’s armor and the equipment frame are at the same electrical potential (preventing potential arcing). All of these functions must be provided while accommodating the cable’s physical size and allowing safe installation by field personnel.

3. Why Type 3S Cables Demand Special Gland Attention

Type 3S cables present particular challenges for gland termination compared to smaller or more flexible cables. The reasons are physical and practical, and understanding them helps explain why generic cable glands are insufficient.

First, Type 3S cables are extremely heavy and stiff due to their solid steel wire armor (SWA). A Type 3S 3x95mm² cable weighs approximately 7,800 kg per kilometer. When a 15-meter length of this cable is suspended vertically (as is typical in shaft installations), the total weight exceeds 117 kilograms. The cable’s rigidity means it cannot easily be flexed or maneuvered at the point of entry. If the gland is designed with tight tolerances or difficult installation geometry, the field technician may struggle to insert the cable to the required depth, potentially leaving the cable’s outer jacket unstripped or the armor incompletely engaged in the gland’s compression mechanism.

Second, the SWA armor itself must be terminated in the gland with precision. The armor serves two functions: mechanical protection (which continues right up to the enclosure entrance) and electrical continuity (the armor must conduct fault currents from the cable to the enclosure ground). The gland must grip the individual steel wire strands of the armor (not crush them) and establish a reliable mechanical and electrical connection. Most conventional cable glands achieve this through a compression collet or ring that squeezes around the armor as the gland nut is tightened. For Type 3S cables with large-diameter armor wires (typically 3.15–3.3 mm diameter), this compression must be carefully controlled to ensure the wires are not deformed, which could reduce their tensile strength.

Third, the outer jacket of a Type 3S cable (typically PVC) is quite stiff and resistant to the deformation that occurs when the cable is inserted into a gland. Inferior glands may not fully compress and seat the cable, leaving small air gaps that could allow explosive gas to creep in along the cable surface. The gland design must account for this—the stripping depth, the compression geometry, and the sealing material all must work together to overcome the stiffness of the jacket.

4. The Physics of Cable Gland Design: Flange-Threaded Architecture

To appreciate why certain glands are suitable for Ex d Zone 1 applications and others are not, it helps to understand the engineering of the flange-threaded gland design. This is not arcane theory—it directly impacts which glands you can safely specify.

An Ex d flange-threaded gland consists of several components working in concert. The gland body is a metal (typically brass or ductile iron) sleeve that threads onto a corresponding stud or holes in the enclosure flange. The cable enters the gland from one end. Inside the gland, a compression collet (a split ring that grips the cable) is seated in a tapered bore. As the gland nut is tightened, the tapered bore compresses the collet, which in turn grips the cable’s outer diameter. This creates a mechanical seal around the cable.

The critical safety feature is the flange itself—a flat, machined surface on the gland that interfaces with a corresponding flange on the enclosure. When the gland is fully seated on the enclosure flange, these two surfaces are in tight contact, typically with a gasket material (such as a 2 mm polyurethane ring) between them. This gasket deforms slightly under compression, creating a pressure-tight seal. The gap between the gland flange and the enclosure flange is typically only 0.1–0.2 mm—far too narrow for a flame to propagate through.

The design also includes an earthing mechanism. A dedicated earthing screw or braided conductor connects the cable’s armor or inner conductors to the gland body, which in turn is bonded to the enclosure frame. This ensures electrical continuity, so that any voltage differential between the cable and the equipment is immediately equalized, preventing potential arcing.

The ATEX EN 60079-1 standard specifies the geometry of this flange interface in detail—the width of the flange, the surface finish, the allowable flatness deviation, and the pressure-tightness requirements. A gland that does not meet these specifications is not Ex d certified, regardless of how similar it might appear visually.

5. SWA Armor Earthing: The Critical Safety Function

In Type 3S cables, the steel wire armor serves not just as mechanical protection but as a critical safety conductor. When a phase conductor in the cable is damaged (crushed, abraded, or punctured), the armor must immediately conduct the resulting fault current to ground. If the armor is not properly grounded at the equipment entry point, this fault current has no path to ground, and the fault may escalate to an arc condition—exactly the scenario the armor is designed to prevent.

The gland’s earthing function is therefore non-optional. The gland must provide a dedicated electrical path from the cable’s armor to the enclosure’s earth/ground system. In most Ex d gland designs, this is achieved through an earthing screw that is installed through the gland body into a threaded hole in the compression collet or a dedicated earthing ring. The technician removes a small protective cap, inserts a wire or braided conductor under the earthing screw head, and tightens the screw. This creates a mechanical and electrical connection that conducts fault current directly from the armor to the enclosure frame.

The resistance of this earthing path must be very low—typically less than 0.1 ohms for a properly installed gland. This low resistance ensures that a phase-to-armor fault generates a large current (many thousands of amperes) that trips the mine’s protection relays in milliseconds, before the arc temperature can reach dangerous levels.

A common field error is to assume that if the gland body is in contact with the enclosure frame, earthing is automatically achieved. This is incorrect. The contact between the gland nut threads and the enclosure threaded holes may have high resistance, especially if thread corrosion or surface oxidation is present. The dedicated earthing screw bypasses these uncertain paths and provides a direct, low-resistance connection. Installation procedures must explicitly require the earthing screw to be installed and torqued to the manufacturer’s specification.

6. Zone 1 Compliance: ATEX Directives and Certification

Underground coal mines are classified by regulatory authorities into hazardous zones based on the likelihood that explosive gas will occur. Zone 0 is where explosive gas is continuously or frequently present (rare in mines). Zone 1 is where explosive gas is likely during normal operation. Zone 2 is where explosive gas is possible but unlikely. These zone classifications drive the requirements for electrical equipment.

In Zone 1, equipment must be either non-sparking (impossible for high-voltage switchgear) or explosionproof (Ex d). There is no intermediate option. The cable gland connecting a 11kV switchgear enclosure to the external feeder cable must be certified to the ATEX Equipment Directive 2014/34/EU, which specifies that equipment intended for use in explosive atmospheres must comply with the essential health and safety requirements.

For cable glands, the relevant technical standard is EN 60079-1, which defines the construction and testing requirements for Ex d enclosures and their components. A cable gland that claims to be “Ex d Zone 1” must have documentation (a Declaration of Conformity and an EC-type examination certificate from a Notified Body) proving compliance with this standard. Simply having the letters “Ex d” printed on the gland is insufficient—you must request and review the actual test reports and certificates.

The certification must also specify the voltage rating (e.g., 11 kV), the temperature class (e.g., T4 for mining, meaning the surface temperature will not exceed 135°C), and the gas group (e.g., IIB for methane). For underground coal mining, the typical specification is ATEX II 2G Ex d IIB T4, which means the gland is certified for Group IIB gases (methane) with a temperature limit of 135°C.

7. Specification Matching Table: Type 3S Cable Sizes and Gland Selection

To help engineers select appropriate glands for Type 3S cables in Zone 1 applications, the following table provides a cross-reference between cable sizes and recommended gland designations. The gland sizes are expressed in metric thread sizes (M80, M100, etc.), which correspond to the thread diameter on the gland body that screws into the enclosure.

The table should be used as a starting point for gland selection, not as a definitive specification. Because each cable manufacturer’s products may have slightly different outer diameters, and because each gland manufacturer may have different compression ring dimensions, it is essential to verify compatibility on a case-by-case basis. The correct procedure is to obtain the actual outer diameter of your Feichun Type 3S cable (from the cable specification sheet), consult the gland manufacturer’s selection chart for that specific outer diameter, and confirm that the gland has the appropriate ATEX certification.

8. Cable Stripping and Preparation: Getting the Armor Right

Before a Type 3S cable can be properly terminated in an Ex d gland, the cable must be carefully prepared. This preparation is not optional or casual—improper stripping compromises both the mechanical grip of the gland and the electrical continuity of the armor.

The standard procedure for preparing a Type 3S cable for Ex d gland termination involves several steps, each of which must be done correctly. First, the outer PVC sheath is removed to expose the SWA armor. The length of sheath removed depends on the gland design, but typically 50–80 mm of sheath is stripped away. The stripping must be done carefully with a knife or specialized cable stripping tool—the goal is to remove the sheath cleanly without damaging the individual steel wires of the armor underneath.

Once the armor is exposed, the installer typically performs an armor continuity check. Using a multimeter on the resistance setting, the technician measures the resistance between any two armor wires. For a properly constructed armor, the resistance should be very low (typically under 1 ohm). If the resistance is higher, it suggests that corrosion or physical damage to the armor wires has compromised their continuity. In such cases, the damage must be repaired or the cable rejected.

Next, a small length of the inner sheath beneath the armor is also stripped away (typically 20–30 mm) to expose the power conductors and individual screen layers. This exposes the cable’s internal structure to the gland’s compression mechanism. The specific stripping depths depend on the gland design and the cable manufacturer’s instructions—there is no universal standard, so the installer must always consult both the cable specification and the gland installation guide.

Finally, the cable is inserted into the gland body to the depth specified by the gland manufacturer. This insertion depth is critical—if the cable is inserted too shallowly, the compression ring does not adequately grip the armor; if inserted too deeply, the cable’s internal conductors may be damaged by the compression mechanism. Most modern glands include an insertion depth reference mark on the gland body to guide the installer.

9. Installation Procedure: Step-by-Step Best Practice

Installing an Ex d gland on a Type 3S cable is a procedure that demands care and attention to detail. Field installations that are rushed or that cut corners risk creating a non-explosionproof connection that could fail in a hazardous condition. The following procedure represents industry best practice, based on decades of mining safety experience.

Step 1: Verify Gland Certification Before beginning any installation, verify that the gland has current ATEX certification documentation on hand. Request from the site’s electrical supervisor a copy of the gland’s Declaration of Conformity and EC-type examination certificate. Verify that the certification covers the cable size you are terminating and that the Zone 1 designation is explicit. Do not proceed without this documentation.

Step 2: Prepare the Cable Cut the cable to the required length, accounting for the entrance point into the enclosure. Using a calibrated cable stripping tool, carefully remove the outer PVC sheath to the depth specified in the gland manufacturer’s installation guide (typically 50–80 mm). Inspect the exposed armor wires for corrosion, damage, or breaks. If any damage is evident, consult the cable supplier and the mine’s electrical engineer before proceeding.

Step 3: Test Armor Continuity Using a multimeter set to resistance mode, measure the resistance between two steel wire armor strands at the point where the armor has been exposed. The reading should be less than 1 ohm. If the reading is significantly higher (above 5 ohms), do not proceed—the armor continuity is compromised, and the cable cannot safely be terminated.

Step 4: Strip Internal Sheath Carefully strip away 20–30 mm of the inner PVC sheath beneath the armor, exposing the individual screened conductors. This allows the gland’s compression mechanism to grip both the outer armor and the inner conductor bundle, creating the dual-path compression seal essential for Zone 1 compliance.

Step 5: Insert Cable into Gland Insert the prepared cable end into the gland body to the depth mark specified by the gland manufacturer. This typically corresponds to the point where the cable’s outer jacket contacts the inside shoulder of the gland. Use gentle, steady pressure—do not force the cable, as this could damage internal insulation.

Step 6: Hand-Tighten Gland Nut Before using a wrench, hand-tighten the gland nut until it contacts the enclosure flange with light finger pressure. This ensures the cable is fully seated and the flange gasket is beginning to contact the enclosure flange. Do not overtighten at this stage.

Step 7: Torque to Specification Using a calibrated torque wrench, tighten the gland nut to the torque specification provided by the gland manufacturer. For M100–M130 glands, this typically ranges from 40–60 N·m. Apply the torque gradually, in increments, rather than in one large movement. Stop when the wrench reaches the specified torque.

Step 8: Install Earthing Conductor Locate the earthing screw on the gland body (typically a stainless steel screw rated M6 or M8). Remove the protective cap if present. Take a stranded copper wire (typically 10 mm² to 16 mm² cross-section) or a braided copper conductor, and loosen the earthing screw. Position the conductor wire under the screw head, then tighten the screw to the manufacturer’s specification (typically 10–15 N·m). This creates the critical electrical path from the cable armor to the enclosure frame.

Step 9: Final Electrical Testing Using a multimeter set to resistance mode, measure the DC resistance from the cable armor (at the point where the armor is gripped by the gland) to the enclosure frame. The resistance should be less than 0.1 ohms. If the resistance is higher, loosen the earthing screw, clean any corrosion from the contact surfaces, and retighten. Re-measure until the resistance requirement is met.

Step 10: Photographic Documentation Before moving to the next installation step, take high-resolution photographs of the installed gland showing the torque wrench reading, the earthing conductor connection, and any identification markings on the gland. These photographs serve as evidence of proper installation for regulatory compliance audits.

10. Testing and Certification: Verifying Explosionproof Integrity

Once an Ex d gland is installed, the mine’s electrical authority or a qualified third-party testing organization should conduct verification testing to confirm that the installation meets ATEX Zone 1 requirements. This testing is not optional in most regulatory jurisdictions—it is a mandatory part of the equipment acceptance process.

The testing typically includes visual inspection (verifying that the gland is installed with proper flange contact, that the earthing conductor is visible and properly connected, and that no gaps or damage are evident), insulation resistance testing (measuring the resistance between conductors and ground to ensure no breakdown or moisture ingress), and in some cases, pressure-decay testing (where the enclosure is sealed and a pressure gauge monitors any leakage through the gland interface). Detailed testing procedures are defined in EN 60079-1 and by the mine’s electrical safety authority.

11. Real-World Installation Scenario: Vertical Shaft Termination

To bring this technical discussion into a concrete context, consider a realistic installation scenario common in underground coal mines: terminating a Type 3S 11kV feeder cable where it enters the pit substation enclosure at the bottom of the main pit shaft.

The Scenario: A new 300-meter vertical pit shaft has been sunk, and a Type 3S 3x185mm² feeder cable is to be installed to supply power from the surface substation to the underground load center at shaft bottom. The cable will be suspended in the shaft (supported at regular intervals by cable hangers) and will enter the enclosure through an Ex d gland mounted on the enclosure door flange. The enclosure is a high-voltage switchgear unit designed for 11kV distribution in Zone 1.

Gland Selection: The Feichun Type 3S 3x185mm² cable has an outer diameter of approximately 77–82 mm. Consulting the gland manufacturer’s chart and the ATEX certification documentation, the mine’s electrical engineer selects an M125 flange-threaded gland rated ATEX II 2G Ex d IIB T4, with a compression ring designed for cable outer diameters of 75–85 mm. The gland is certified for 11kV voltage and includes an integral earthing screw for armor bonding.

Field Installation: The cable is cut to the correct length. At the enclosure entrance, the installer carefully strips 70 mm of outer PVC sheath, exposing the SWA armor. An armor continuity check (multimeter resistance test) confirms the armor is intact. The inner sheath beneath the armor is stripped back 25 mm. The cable is inserted into the M125 gland to the depth mark (approximately 60 mm insertion depth for this cable size). The gland nut is hand-tightened, then torqued to 55 N·m using a calibrated wrench. The earthing screw is installed with a 16 mm² stranded copper conductor bonded to the enclosure ground bus, torqued to 12 N·m. A final resistance measurement confirms the armor-to-frame resistance is 0.08 ohms, well below the 0.1 ohm limit.

Testing and Certification: The mine’s electrical testing team performs pressure-decay testing on the gland assembly, confirming that no leakage occurs when the enclosure interior is pressurized to 50 mbar. Insulation resistance testing shows over 10,000 megohms between conductors and ground, indicating no moisture or contamination. The installation is documented with photographs and certification reports. The feeder cable is energized at 11kV and placed in service.

12. Conclusion: Proper Gland Termination Ensures Safety

The selection and installation of an Ex d cable gland for a Type 3S 11kV feeder cable is far more than a mechanical fitting task. It is a critical safety function that, when done properly, ensures that even if an electrical fault occurs within the connected equipment, the resulting explosion is contained and does not propagate into the mine atmosphere where it could ignite methane and coal dust. Conversely, improper gland installation—using an uncertified gland, failing to properly ground the armor, or cutting corners on installation procedures—creates a direct pathway for explosive gas to breach the enclosure and cause a catastrophic mine explosion.

Feichun Type 3S cables are engineered to the highest standards of the AS/NZS 1972 mining cable specification, with robust armor and reliable individual screening. To ensure that this engineering excellence translates into safe field installations, the cable must be properly terminated using certified Ex d glands, installed with careful attention to torque specifications and earthing procedures, and tested by qualified personnel before energization.

When planning an installation involving Type 3S cables in Zone 1 hazardous areas, engage your mine’s electrical authority and Feichun’s technical support team early in the design process. Feichun can provide detailed technical documentation on cable specifications, recommend appropriate gland manufacturers and models, and support site personnel with installation guidance and certification documentation. The investment in proper engineering and careful installation prevents the catastrophic consequences of a gland failure in an explosive environment.