Barrier Gland vs Non-Barrier Gland — When Do You Need Each?
Choosing between a barrier gland and a non-barrier gland for SWA cable entries into Ex d equipment is one of the most commonly tested topics in CompEx Ex01, Ex02, Ex03, and Ex04. The decision depends on three factors: the type of cable entry (threaded or clearance), the internal volume of the enclosure, and the protection type.
What is a Barrier Gland?
A barrier gland (also called an Ex d barrier gland) seals the spaces between the armour wires of SWA cable with a compound or mechanical barrier. Without this seal, armour wire spaces create a path through which gases or flames could travel into or out of an Ex d enclosure — bypassing the flamepath protection. A barrier gland eliminates this path.
What is a Non-Barrier Gland?
A non-barrier gland grips and seals the cable outer sheath and armour but does not fill the spaces between the armour wires. For Ex d equipment, this is only acceptable when the threaded entry itself provides the flamepath — and only when the enclosure volume is small enough that the explosion pressure is insufficient to force gases through the armour spaces.
The Decision Rules
| Entry Type | Volume | Gland Required |
|---|---|---|
| Threaded entry | ≤2 litres (≤2000cm³) | Non-barrier acceptable for SWA |
| Threaded entry | >2 litres (>2000cm³) | Barrier gland required for SWA |
| Clearance entry | Any volume | Barrier gland always required for SWA |
A clearance entry (smooth bore hole) provides no flamepath at all — gases can flow freely through the gap between the cable and the hole. Without a barrier gland sealing the armour wire spaces, there is a direct unobstructed path between the inside and outside of the enclosure. This is why clearance entries always require a barrier gland, regardless of enclosure volume.
Ex e Equipment
The barrier/non-barrier rule applies to Ex d enclosures only. Ex e increased safety equipment always uses non-barrier glands — the increased safety principle does not rely on containment, so the armour wire space is not a concern. However, Ex e glands require correct accessories (IP washers, locknuts) to maintain the IP rating of the enclosure.
Checking in the Field
When inspecting or selecting cable glands, always check the enclosure volume (from the Ex certificate or equipment label) and the entry type. If you're unsure whether an entry is threaded or clearance — a threaded entry has visible thread within the entry hole; a clearance entry is a smooth bore.
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