Page 43 - Energize January 2022
P. 43

VIEWS AND OPINION



        and the terminals themselves. (Such
        as evidenced in the photos of a similar
        failed Junction box that was installed in a
        Zone -1 area.)
           Flame proof junction boxes made
        out of cast iron are highly susceptible to
        corrosion especially if their flame paths
        are unprotected. By comparison, good
        quality Ex-d flameproof junction boxes
        would have their critical flame paths
        treated with a metallurgical process that
        resists corrosion. In addition, they would
        have IP seals made from hydrocarbon
        resistant polymers that seal on the
        outer rim of the flame path which give
        additional protection to the flame path
        from corrosion. They would also have
        captive high tensile stainless-steel   Figure 1: The environmental effects on a flameproof junction box and its Ex-e terminals.
        fasteners which would not get lost at the
        time of installation. Unlike zinc coated   cable to an area with a lower level of Ex protection, leading to an explosion. (Sceptics may
        steel fasteners, high tensile stainless-steel   think that this cannot happen, but the infamous Torrens Island Gas explosion shows that this
        fasteners would not weaken over time due   does happen even when only in Zone 1 in which an explosive mixture is only present for a
        to corrosion. This is critical as the fasteners   relatively short period compared to Zone 0 where it is always present) SANS/IEC 60079-14
        need to secure the lid against explosive   clauses 9.3.2 and 10.6.2 are clear on how to address this risk.
        pressure for the lifetime of the installation.   In summary, the installer or specifier of Ex equipment should not be taking dangerous,
        Such good quality junction boxes would   second-hand subjective advice from a manufacturer but should objectively read the
        also have been independently tested for   certificates and the installation standards and should certainly not believe that putting an
        resistance to environmental corrosion to   Ex-e terminal inside an Ex-d enclosure will give the level of protection needed for Zone 0
        ASTM B117-03 and ISO 6988 standards.    applications.
           Another important consideration
        overlooked by the author is the fact that   Dr Geoff Mood is the Technical Director for CCG Cable Terminations (Pty) Ltd. He holds a
        an installation in a Zone 0 environment   doctorate in mechanical engineering and sits as an independent expert on a number of IEC
        could suffer from the risk of an explosive   Standard committees, including the Maintenance Team for IEC 60079-14.
        gas mixture (which is always present
        or present for long periods) or liquid   Contact CCG Cable Terminations, Phone 011 394-2020, info@ccgcablegland.co.za,
        migrating through the interstices of a   www.ccgcablegland.co.za



























                                                               Figure 3: A good quality flameproof junction box which has been
        Figure 2: Corrosion of a critical flame path on a cast iron junction box   specially treated with a corrosion resistant metallurgical process after
        after testing to ASTM B117-03 and ISO 6988 standards.   testing to ASTM B117-03 and ISO 6988 standards.



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