Cable Glands for Hazardous Areas

Why Cable Glands Matter

A cable gland is the weakest link in an Ex enclosure. It must:

• Maintain the protection method (flameproof integrity, increased safety creepage/clearance, dust-tight seal)
• Provide cable strain relief
• Seal against ingress (dust, water)
• Provide earthing continuity for armored cables
• Withstand mechanical and environmental stress

Using a standard industrial cable gland in a classified area is a common and dangerous mistake (see installation & inspection for common errors). Only certified Ex cable glands maintain the safety integrity of the installation.

Types of Ex Cable Glands

1. Flameproof Cable Glands (Ex d)

For use with flameproof (explosion proof) enclosures. These glands must prevent flame propagation through the cable entry.

Design Features

• Stopping mechanism — Compound-filled chamber or compression seal that blocks gas passage along the cable cores
• Threaded entry — Creates flameproof path through the gland body threads
• Minimum thread engagement — Typically 5 full threads minimum (varies by standard and gas group)
• Cable clamping — Seals around cable sheath to prevent gas entry

Variants

• Compound-filled (stopping box) — Cable enters gland, cores are sealed in epoxy or mastic compound. Permanent installation; difficult to remove.
• Elastomer seal (compression) — Rubber or polymer seal compressed around cores. Allows cable removal/replacement but requires correct cable diameter.

2. Increased Safety Cable Glands (Ex e)

For increased safety enclosures. Simpler than Ex d because no flame containment is required — the focus is on preventing ignition sources.

Design Features

• Secure cable clamping — Prevents conductor pullout under mechanical stress
• Seal against ingress — IP54 minimum (often IP66/67)
• Armor clamping and earthing — For SWA/STA cables, provides earth continuity
• No flameproof thread required — Standard metric or NPT threads acceptable

3. Intrinsically Safe Barrier Cable Glands

Special glands used where intrinsically safe circuits pass through a barrier (enclosure wall separating safe and hazardous areas). Also called "double-sealed" or "feed-through" glands.

Purpose

• Maintain segregation between IS and non-IS circuits
• Prevent gas migration from the hazardous to safe area
• Provide two independent seals (one on each side of the barrier)

4. Dust-Tight Cable Glands (Ex t)

For dust-ignition-protected equipment (Zone 20/21/22). Must achieve IP6X (dust-tight).

Features

• Elastomer or gel seal around cable sheath
• No stopping chamber required (dust doesn't propagate like gas)
• Compress seal tightly to achieve IP6X rating

5. EMC Cable Glands

For applications requiring electromagnetic compatibility shielding in addition to Ex protection. Common in instrumentation and control systems.

Features

• 360° shield termination
• Maintains shield continuity through the enclosure wall
• Often combined with Ex e certification

Thread Standards

Ex cable glands come with various thread types. Matching the gland thread to the enclosure entry is critical.

Critical: Never force-fit a gland. If the thread doesn't engage smoothly, it's the wrong type or size. Forced threads compromise flameproof integrity.

Cable Diameter Range

Every cable gland has a specified cable outer diameter (OD) range. Using a cable outside this range compromises the seal.

Typical Ranges

• M20: 6–12 mm cable OD
• M25: 13–18 mm cable OD
• M32: 18–25 mm cable OD
• M40: 26–34 mm cable OD
• M50: 34–44 mm cable OD
• M63: 44–56 mm cable OD

Ranges vary by manufacturer. Always check the gland datasheet and measure the cable before ordering.

Adapter bushings and reducers are available to accommodate smaller cables in larger glands, but they must also be Ex-certified for the same protection method.

Installation Procedure

Flameproof Gland (Ex d) Installation

1. Verify certification — Gland certificate matches enclosure gas group and zone rating
2. Check thread type and size — Must match enclosure entry exactly
3. Measure cable OD — Confirm it falls within gland's rated range
4. Prepare cable — Strip outer sheath to required length (per gland instructions)
5. Thread engagement — Minimum 5 full threads into enclosure (check certificate for specific requirement)
6. Seal cores (if stopping chamber type) — Pour or pack compound per manufacturer instructions; allow curing time
7. Tighten outer nut — Apply specified torque (typically 30–50 Nm for M20–M32)
8. Check flameproof joint — No gaps, paint, or damage on enclosure entry threads
9. Apply locknut or lockwire (if specified)
10. Document — Record gland type, certificate number, and cable details

Increased Safety Gland (Ex e) Installation

1. Verify certification — Gland is Ex e rated
2. Install gland — Thread into enclosure (no minimum engagement specified for Ex e, but good practice is 4+ threads)
3. Insert cable — Ensure armor (if present) is clamped securely and earthed
4. Tighten sealing elements — Compress rubber seal around cable sheath
5. Strain relief — Ensure cable is adequately supported within 300 mm of gland
6. Check IP rating — Seal must achieve at least IP54 (typically IP66)

Barrier Gland (IS circuits) Installation

1. Install gland body — Secure to both sides of barrier wall
2. Route cable through — Feed intrinsically safe cable through gland
3. Seal both ends — Compress seals on hazardous and safe sides independently
4. Label IS circuit — Blue identification per IEC 60079-14
5. Segregation check — Ensure IS cable is separated from non-IS cables (50 mm minimum, or separate conduit)

Torque Specifications

Under-tightening causes leaks and loss of flameproof integrity. Over-tightening can damage threads or crack enclosures.

Always use a calibrated torque wrench. Visual "tightness" is not sufficient. Document torque values during installation and re-verify during inspections.

IP Ratings for Cable Glands

The Ingress Protection rating indicates resistance to dust and water. Higher IP ratings are required for harsher environments.

Match the IP rating to the environment. Offshore and coastal areas typically require IP66 minimum. Indoor dry areas may accept IP54.

Common Installation Mistakes

1. Using Non-Certified Glands

Standard industrial glands (even with IP66) do not have Ex certification. They lack stopping mechanisms, proper thread engagement specifications, and gas group ratings. Using them voids the enclosure certification.

2. Incorrect Cable Diameter

Installing a 10 mm cable in a gland rated for 13–18 mm leaves gaps in the seal. The gland cannot compress properly, allowing gas ingress or flame propagation.

3. Insufficient Thread Engagement

Flameproof glands require minimum thread engagement (typically 5 full threads). Shallow engagement shortens the flameproof path and may allow flame escape.

4. Damaged Threads

Cross-threading, forced installation, or corrosion damage threads. Damaged threads do not provide flameproof integrity. Never force a gland — if it doesn't thread smoothly, stop and check sizing/type.

5. Paint on Threads

Paint inside flameproof threads creates gaps and prevents metal-to-metal contact. Threads must be clean and bare metal. If painting enclosures, mask all entries or clean threads after painting.

6. Incorrect Torque

Finger-tight is not sufficient. Use a torque wrench and document the value. Over-torque can crack aluminum enclosures or strip threads.

7. No Strain Relief

Cables must be supported within 300 mm of the gland. Unsupported cables cause stress on connections inside the enclosure and may pull cores out of terminals.

8. Missing Blanking Plugs

Unused cable entries must be sealed with certified Ex blanking plugs (same protection method as the enclosure). An open entry is an ignition path and an ingress point for dust/water.

Inspection Requirements

Per IEC 60079-17, cable gland inspection includes:

Visual Inspection (Every 12 Months for Zone 1)

• ☐ Gland is present and complete (no missing parts)
• ☐ No visible damage (cracks, corrosion, deformation)
• ☐ Cable entry seal intact
• ☐ Gland identification/marking legible

Close Inspection (Every 36 Months for Zone 1)

• ☐ Gland certificate matches enclosure and zone
• ☐ Thread engagement verified (visual check for depth)
• ☐ Cable diameter within gland's rated range
• ☐ No paint, dirt, or contamination on flameproof threads
• ☐ Locknut or lockwire present (if specified)
• ☐ Strain relief within 300 mm

Detailed Inspection (Every 72 Months for Zone 1, or After Modification)

• ☐ Disassemble and inspect stopping chamber (if accessible without destroying compound)
• ☐ Check thread condition (no damage, cross-threading, wear)
• ☐ Verify torque (may require re-torquing)
• ☐ Test IP rating (rare, but may be specified for critical applications)

Major Manufacturers

Leading suppliers of certified Ex cable glands:

• CMP Products — Wide range of Ex d, Ex e, Ex t glands; global availability
• Hawke International — Specialist in harsh environment cable glands; subsea and offshore focus
• Weidmüller — German manufacturer; comprehensive ATEX/IECEx range
• Bartec — Full explosion protection portfolio including glands
• R. Stahl — High-quality Ex d and Ex e glands
• Pepperl+Fuchs — Intrinsic safety specialists; barrier glands
• Jacob — Large metric and NPT Ex gland selection
• Eaton Crouse-Hinds — North American focus; ATEX and NEC-certified glands

Standards Reference

• IEC 60079-0 — General requirements (cable entry sealing requirements)
• IEC 60079-1 — Flameproof enclosures (Ex d cable gland stopping requirements)
• IEC 60079-7 — Increased safety (Ex e cable entry requirements)
• IEC 60079-14 — Installation (cable gland selection and installation guidance)
• IEC 60079-31 — Dust ignition protection by enclosure (Ex t cable gland sealing)
• EN 50018 — Flameproof enclosures (older standard, still referenced)
• EN 50019 — Increased safety (older standard)

Related Topics

• Protection Methods — Ex d, Ex e, Ex i, and others explained
• Installation & Inspection — IEC 60079-14 and 60079-17 requirements
• Explosion Proof vs Intrinsically Safe — Choosing the right protection method
• CompEx Certification — Training covers cable gland installation