In order to comply with the installation codes of practice for hazardous areas, cable glands using elastomeric sealing rings should only be used on cables that are substantially round, compact with an extruded bedding and have non-hygroscopic fillers such as Figure 1. However, this cable construction is not always possible especially when it comes to multi-core cables. Figures 2 and 3 show cables that should not be used with glands with elastomeric sealing rings.
IEC 60079-14: Explosive atmospheres; Electrical Installation, Design, Selection and Erection Prescribes the selection of electrical equipment in hazardous areas. Knowledge of this Standard is imperative when selecting cables and cable glands for use in hazardous areas and merely referring to the product certification is not enough.
IEC 60079-14 Section 9.3.2. States that: Cables for fixed installations – 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; If cables do not pass one of these criterias and such cables link between a hazardous and non-hazardous area the result may be flammable gas, liquid or vapour migration through the interstices of unfilled cables to the inside of; for example, control room equipment. The situation is likely to be most acute with equipment installed in Zone 0 or Zone 1 locations (where the presence of a hazardous atmosphere has a greater likelihood and duration). If these conditions are likely to occur a barrier gland should be used.
IEC 60079-14 Section 10.6.2 – requires the use of Barrier Glands for Ex d installations. Conventional flame-proof Ex d cable glands with seals are designed primarily to retain the explosive pressure within an Ex d enclosure and prevent the passage of hot gasses through the cable entry to the surrounding atmosphere. The design of such cable glands relies on elastomeric seals sealing around the bedding of filled cable to perform this function. It has been established that if cables are not effectively filled, substantially round and are hygroscopic, hot gasses and pressure produced by an explosion within an Ex d enclosure can bypass the protective elastomeric seals of a conventional Ex d Gland. These hot gases can be forced down the interstices of unfilled cable resulting in the potential damage to the cable and/or non-Ex d equipment. The use of barrier glands effectively blocks these explosive gases from migrating down interstices of unfilled cable.
Ex p Pressurized Equipment may also necessitate the use of Barrier Glands. Where necessary, to prevent the drop in pressure, the ingress of combustible gas or vapour by diffusion, or to prevent leakage of protective gas, wiring systems shall be sealed. If cables are not compact and filled barrier glands should be used.
Ex nR IEC 60079-14 Section -10.8 states; “The sealing of restricted-breathing enclosures shall be such as to maintain the restricted breathing properties of the enclosure. Where the cable used is not part of the certificate and/or instruction manual and is not effectively filled, it may be necessary to use a cable gland or other method (e.g. epoxy joint, shrinking tube) which seals around the individual conductors of the cable to prevent leakage from the enclosure”.
GAS MIGRATION THROUGH CABLE ON SITE
EXPLOSIVE GASSES THROUGH UNFILLED CABLE
For a number of years, installers in hazardous areas have been relying on barrier glands with a two-part epoxy based putty as a way of effectively stopping explosive gasses and liquids from diffusing down unfilled cables. Whilst effective once properly installed, the problems with the two-part putty based compound have always been the time taken to mix and then insert and pack the putty between the cables voids and into the barrier gland chamber. The mixing process can take several minutes depending on the volume of putty required and has always been subjective as the putty is only properly mixed when the two parts are hand moulded into an “even colour”.
The insertion of the putty between the individual cores of the multi-core cable is not only time consuming but there could be additional risks in that the putty may not have been inserted and packed correctly which results in the potential of voids and gaps for gas or liquids to migrate through. In addition, once the putty has been inserted between the cable cores and the barrier chamber, the time taken for the putty to harden can be up to several hours. Because of these premixing and installation problems, barrier glands have always required special skills from the installers and particular attention from inspectors. Recently a two-part liquid pour resin system was reintroduced into the market which, whilst being effective in filling all the gaps and interstices in a cable, its two-part sachet mixing system does not adequately address the time taken and risks involved during the mixing process. The sachet mixing process is still very subjective and inaccurate especially in varying temperatures and can result in the resin setting either too quickly or not setting properly at all.
CCG’s VORTEx® Barrier Gland with an instant mixing, injecting resin has all but eliminated the hassles surrounding the preparing, mixing and applying of compounds/resins in Barrier Glands. The VORTEx® Injection Resin® system is instantly and 100% accurately mixed whilst being simultaneously injected into the barrier gland in one single action. This reduces the installation time and gives an increased confidence in the installation compared to the epoxy putty or sachet mix liquid pour resins. The Injection resin flows into all the cable voids and interstices, completely filling the cable end. This forms a 100% barrier to any migration of explosive gases or fluids down the inside of an unfilled hygroscopic cable. VORTEx® Injection Resin® barrier glands are tested and fully comply with the latest IECEx standards and installation codes of practice.