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.
energize | January 2022 | 41