Enclosures for hazardous areas: understanding the differences
When it comes to specifying enclosures for hazardous area electrical applications, engineers must ensure they fully understand IP protection ratings.
As a manufacturer of enclosures for harsh industrial and hazardous environments, Cooper Crouse-Hinds often deal with customers who don’t fully understand what they require in terms of the IP protection rating of an enclosure and whether what they are asking for meets the end users’ technical specification.
The function of an enclosure is to protect the internal components from excess heat, humidity, dirt, dust or water. The customer could be sourcing an enclosure for a hazardous gas environment such as an oil platform or petrochemicals plant, or for a dusty environment such as a flour mill or sugar production plant.
In either case, it is crucial that the customer fully appreciates the differences between the IP ratings along with the requirements for one that is fully certified for use in a hazardous gas or dust environment. Also, in terms of modifying an enclosure – either prior to or after installation – it is equally important that the installer and end user fully appreciates what they are allowed to do with that Exe or Exd enclosure so as not to adversely affect its protection rating or invalidate the certification.
With an Exd enclosure, the box cannot be modified once it has been manufactured and assembled otherwise the protection rating will be affected. For example, drilling new cable entries must only be carried out by the manufacturer or by an approved local assembler (distributor). Once an Exe enclosure leaves the factory, although this is in a certified state, end users may then modify that box prior to or after installation within certain guidelines.
Any alterations need to be communicated to the manufacturer or local assembler to ensure that the correct certification is given or maintained. These modifications normally involve adding some extra cable entries or terminals.
This is why Cooper Crouse-Hinds supplies a range of standard hazardous area Exe enclosures to its network of approved local assemblers, who are then able to carry out modifications to those enclosures to suit the application, without adversely affecting the certification or protection rating.
Enclosures for hazardous gas or dust environments are normally manufactured from stainless steel or GRP, but also painted steel for some indoor, sheltered applications. Many customers don’t fully appreciate that an Exd or Exe enclosure has been put through a series of arduous tests. These include thermal conditioning (to represent rapid ageing), which simulate 20-plus years of operation in the field. In addition, hazardous enclosures are also subjected to a series of mechanical impact tests, in places that are considered to be the weakest points of the enclosure. If the material is considered to have a reduction in resistance to impact at lower temperatures, the box is also impact tested at the lower end of the box’s operating temperature range.
These tests are important because once installed in a harsh hazardous area, it is often difficult to service an enclosure due to the hazardous area or it could get inadvertently knocked or bashed in a working environment, so the enclosure must remain intact in order to continue performing the intended function for protection.
In recent years, European and International standards for hazardous area enclosures have become even stricter in terms of impact and thermal tests. In the latest standards, all openings on the enclosure are tested (opened and closed) prior to their IP test. Many companies can offer industrial-grade enclosures with an IP66 rating, but for hazardous areas, customers need to be absolutely certain that the enclosures they source are fully certified boxes that have been tested in terms of temperature ratings and impact protection.
It is generally accepted in the oil and gas industry that hazardous area enclosures need to be manufactured from 316L stainless steel as a minimum. Most of our hazardous area enclosures are made from electro-chemical polished 316L high-grade stainless steel as standard, as this offers enhanced corrosion resistance over other finishes.
GRP enclosures also offer technical advantages. The material is often graphite-loaded in order to avoid a build up of electrostatic charge, which is important for hazardous area applications. Moulded, non-metallic enclosures also enable the manufacturer to construct very modular or flexible design features for the customer, including quick-fitting of components such as pushbuttons, switches, lamps, and so on. Non-metallic enclosures also enable the design of low-sided enclosures for easier, faster wiring. With stainless steel fabricated boxes, it is a little more difficult to offer these features, but fabricated steel enclosures are very flexible in the size ranges offered. Special sizes can be quickly included, and they can also be provided in much larger sizes if required.
Gary Johnson is Technical Manager at Cooper Crouse-Hinds UK
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