The evolution of Pratley’s Flameproof Cast Iron Junction Box

The evolution of Pratley’s Flameproof Cast Iron Junction Box
Pratley’s Flameproof Cast Iron Junction Box

Pratley has been manufacturing flameproof junction boxes since the 1960s. Over the years, it has refined the design of these enclosures, 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 Pratley’s unique increased-safety (Ex e) Kwikblok® terminals as a termination option inside the flameproof 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 Research & Development 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.

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, that can be ignited.

“While this is a useful combination, it is not that common in the 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 Sven. 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. Here a sleeve is also fitted on the outside as a means of insulation,” highlights Sven. “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,” notes Sven.

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. That means it is either submerged in or nearby 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 which are intended to prevent an explosion inside the enclosure altogether. Flameproof enclosures can contain the explosive pressures and hot gases and allow the latter to exit the enclosure via a precision-machined flame path.

Pratley Ex d Flameproof Cast Iron Junction Boxes are available in the following sizes and configurations:

  • Size 1 – Rated Ex d for Group I mining (coal dust and methane gas) as well as Group IIC gases (hydrogen, acetylene and carbon disulphide) as well as Group III for dust (combustible flyings, combustible dust and conductive dust). A gasket on the flange prevents dust ingress.
  • Size 2 – These are quite a lot larger in size and are rated for Ex d I/ IIB + H2, meaning coal dust, methane and hydrogen.
  • Size 4 – The largest of the three enclosures is for Ex d I/IIB, which is coal dust, methane and ethylene.

In terms of the entry points on the enclosures, Size 1 has an M20 entry suitable for Size 0 and Size 1 cable glands. These are precision-machined, threaded entries that can accept flameproof entry devices such as cable glands, adaptors, reducers and blanking plugs (all available in Pratley’s extensive range of IECEx Ex d rated products). Size 4 has an M40 entry while Size 2 has an M25 entry. To accommodate any unused entries, these junction boxes are available in a 1-by-2 way configuration (a Size 1 with two open entries), a size 1-by-3 way T-type configuration, or a size 1-by-4 way configuration.

If you have a four-way enclosure and only want to use two of the entries, then Pratley flameproof blanking plugs can be fitted. These blanking plugs are flameproof-certified and will therefore uphold the integrity of the flameproof enclosure, both in terms of its flameproof properties and water and dust ingress properties (IP rating).

Main features of the Pratley Ex d Flameproof Cast Iron Junction Boxes:

  • A robust, fine-grained, iron casting with precision machined entries.
  • Suitable for both fiey mines and surface application.
  • Complete with 4 x zinc-plated Grade 12.9 steel fasteners.
  • Fitted standard with both internal and external earthing facilities.
  • Epoxy powder coated in orange.
  • Can be fitted with either Pratley non-sparking end connectors or Pratley Kwikblok® terminals
  • Flameproof blanking plugs are available.
  • Fully certified to SANS and IECEx Standards for flameproof installations in Group I, IIB, IIB+H2, IIC and IIIC environments.

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Combining Pratley flameproof junction boxes with Kwikblok terminals prevents arcing or sparking
Combining Pratley flameproof junction boxes with Kwikblok terminals prevents arcing or sparking