The IEC 60079-14 standard in the 2013 edition [1] has greatly expanded the field of application of cable glands with sealing ring for entry into Ex-db explosion-proof enclosures. In particular, their use has been made possible for lengths exceeding 3 meters provided that the cable used meets the requirements of paragraph 9.3.2 (a) of the same standard.

This paragraph defines suitable cables as: circular and compact cables in which any padding or sheaths must be extruded with a sheath of thermoplastic, thermosetting or elastomeric material. Furthermore, any fillers must be made of non-hygroscopic material.

This modification immediately sparked fierce controversy as it linked an important aspect of explosion-proof safety to the choice of the cable.

For plant engineering and regulatory reasons, the demand for fire-fighting properties and mechanical resistance leads to the use of armored cable in many installation sites.

To understand the possible criticality of using the cable gland with sealing ring, let us start by describing the constituent parts of an armored cable:

• The conductors with their insulation: they are the carriers of the electric current.
• Filler material: This is the material that acts as a filler between the conductors and the armour.
• Shield or armour: provides mechanical or electrical resistance properties (shielding from magnetic fields).
• Sheath: the outermost part that provides the cable with both electrical insulation and mechanical protection.

When a cable gland with sealing ring is used, during the tightening phase, pressure is exerted by the sealing ring on the sheath and the filling material. The latter deforms, reacting to the compression and allowing the cable gland to seal. If the material deforms too much under the compression force of the sealing ring, gaps could be created which would affect the explosion resistance. Here the type of sheath material and especially the filling material becomes fundamental for the overall seal of the cable gland and the cable assembly.

It is important to be able to provide installers with a solution to this problem.

Especially in the offshore or naval sector, cables of the BFOU and RFOU type which comply with the NEK TS 606 standard have become established for reasons of plant engineering regulations.

These armored cables [3] have an internal filler made of halogen-free, low-smoke, and flame-retardant thermoplastic material, which can cause the cold flow problem.

To use these and other cables having the same problem, it is now possible to use the new Cortem NEVCF series cable glands, available with ISO cylindrical threads and standard NPT conical threads.

With the 'Ex db eb tb' protection method, they can be used for entry into explosion-proof, increased safety and dust-protected enclosures following the dictates given by the IEC/EN 60079-14 standard. They guarantee an IP 66/68 protection degree via flat gasket, in cylindrical threads or via sealant in conical threads.

Reference standards and bibliography

[1] year 2014 for the European version EN 60079-14.

[2] “high” here indicates temperatures greater than the maximum temperature of the material's use range. Creep is a more general phenomenon than cold flow which also affects metals and non-polymeric materials.

[3] for example with copper wire braid type armor, braided armor made of tinned copper wire.