Glands; To Barrier Or Not To Barrier
For this article, we are considering the barrier gland requirements for typical cable and gland installation methods in to Ex d enclosures, junction boxes, instruments etc, and when traversing zones or from a hazardous zone to a safe zone. Conduit and MIMS etc are not considered for this article.
When is a barrier gland required by the Standards?
Well, the answer to that largely depends on where you are and what iteration of IEC 60079-14:2013 you are working with.
Let’s take a look at the different requirements between the three most common iterations we work with regularly – IEC, AS/NZS and BS EN.
Clause 10.6.2 States;
The cable entry system shall comply with one of the following:
a) Cable glands sealed with setting compound (barrier cable glands) in compliance with IEC 60079-1 and certified as equipment;
b) Cables and glands meeting all of the following:
– cable glands comply with IEC 60079-1 and are certified as equipment
– cables used comply with 9.3.2(a)
– the connected cable is at least 3 m in length;
Cables used for fixed installations in hazardous areas shall be appropriate for the ambient conditions in service. Cables shall be:
a) Sheathed with thermoplastic, thermosetting, or elastomeric material. They shall be circular and compact. Any bedding or sheath shall be extruded. Fillers, if any, shall be non-hygroscopic;
Where there is a likelihood that gas or vapour migration may occur through the interstices between individual cores of a cable, and the cable leads to a non-hazardous area or between different zones, then the construction and application of the cable shall be taken into account. Appropriate control measures to mitigate this condition shall be considered (see Annex E).
Where there is a likelihood that propagation of flames may occur through the interstices between individual cores of a cable, this shall also be considered.
The AS/NZS iteration of the Standard has an extensive chapter of deviations in Appendix ZZ. Both clauses 9.3.2 and 10.6.2 have been rewritten.
Essentially, when there is any doubt as to the compactness of the cable, to prevent flame propagation apply 10.6.2 (a), which is a barrier gland. Many companies make claims regarding the compactness of their cables. In our experience, very few of these manufacturers have performed sanctioned testing demonstrating compliance with the requirements.
Unless specifically accepted in writing by the plant or asset owner, we recommend the use of barrier glands for Ex d equipment, when traversing zones and from a hazardous to non-hazardous zone.
This requirement is seen to be more onerous than IEC 60079-14.
BS EN 60079-14:2014
The BS EN iteration of the Standard also contains a National Annex with country specific requirements.
In this instance, the BS EN Standard utilizes the flow chart from the previous IEC 60079-14:2007 revision. This is seen by some as less onerous than the current IEC 60079-14:2013 revision.
No matter where you are or for what market the equipment is destined, be sure to confirm which Standards you are required to comply with. There may even be Project Engineering Specifications that are more onerous than the National Standards.
A good rule of thumb is if you’re unsure, apply a barrier gland.
References: IEC 60079-14, AS/NZS 60079.14 & BS EN 60079-14