Pratley has been manufacturing flameproof junction boxes since the 1960s. Over the years, it has refined the design of these, making Pratley’s cast iron flameproof junction boxes well-known in the mining and petrochemical industries.
With the recent IECEx approval of these junction boxes, Pratley has proven its commitment to world-class product development and innovation. One of these innovations is to offer the increased-safety (Ex e) Kwikblok terminals as a termination option inside the junction box, essentially doubling the level of protection.
“By combining our flameproof junction box with our Kwikblok terminals, we can prevent arcing or sparking across the connections themselves,” explains Pratley Electrical R&D; manager, Sven Breedt. “In addition, electrical current limitations prevent those terminals from exceeding their service temperatures, together with limiting creepage and clearance or tracking distance. This means that the terminals are spaced such that there can be no arcs or sparks across the connections, adding a second dimension to the safety.”
Constant hazardous environments
Flameproof junction boxes are specifically designed to house equipment that arcs or sparks, meaning that any termination type can be fitted into these enclosures. However, with the inclusion of increased-safety terminals inside a flameproof enclosure, the terminations rating is pushed up to Zone 0 (two independent levels of protection via EPL Gb, per SANS/IEC 60079-14/26), meaning it can now be installed in an environment where there is a constant hazardous environment.
Here a typical application would be on the inside of a fuel storage tank with a dip sensor or a pump power supply unit, where the internal environment of the tank poses a constant hazard in terms of both oxygen and flammable vapour or gas, which can be ignited.
“While this is a useful combination, it is not that common in industry, which is why we advocate the use of our junction boxes together with our own Ex e Kwikblok terminals as an extra level of protection,” adds Breedt.
Another key differentiator of Pratley flameproof cast iron junction boxes is their IP68 rating, the standard being a minimum IP54 rating. The increased rating means that Pratley’s junction boxes are completely dust-protected and watertight with up to 2 m of water head.
“Should you not need a Zone 0 rating, we recommend our non-sparking end connectors, as these have a locknut to secure the connection so that they cannot vibrate loose,” highlights Breedt. “Here, a sleeve is also fitted on the outside as a means of insulation. The important part to remember, if you are advising anyone on such an installation, is that this termination is now suitable for Zone 0 applications, with minimal additional consideration.”
Gases and dust
There is a separate zoning system for gases and dust. Zoning itself is based on a risk assessment approach, meaning that Zone 0 is where there is a specific hazard, in relation to an explosive gas atmosphere, under all circumstances and normal operating conditions. This means it is either submerged in, or near to, a source of explosive gas such that the concentration is explosive for the entire duration of the equipment’s use.
Zone 1 is where the hazard is present only some of the time, such that in most normal operating conditions there is minimal risk of a hazardous vapour being present around the enclosure. Zone 2 is where it is unlikely that there is a hazardous atmosphere or where there is an insufficient concentration that can be ignited under normal operating conditions.
In terms of dust, Zone 20 is where there is an explosive dust atmosphere, such as dust packed onto or around the enclosure, or suspended in the surrounding air, for the entire duration of that enclosure’s use. Zone 21 references only a part-time hazard around the enclosure, while Zone 22 refers to abnormal operating conditions only.
The Pratley junction boxes are manufactured from fine-grained cast iron for increased strength, robustness and impact resistance. This is critical, as they are intended to withstand extremely high explosion pressures, unlike Ex e enclosures that are intended to prevent an explosion inside the enclosure altogether.
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