Flameproof enclosure (Ex d): A comprehensive guideline

The Ex d type of protection, also referred to as flameproof enclosure, is one of the most frequently used methods to safely operate electrical equipment in hazardous areas. This technology is characterised by the fact that an explosion occurring inside the enclosure has no effect on the explosive atmosphere outside the enclosure.

1. The enclosure is constructed so that it will not be destroyed by the potential explosion pressure inside the enclosure.

2. What's more, all of the joint dimensions on the enclosure are designed so that the source of ignition created by a potential explosion is not transferred from the inside of the enclosure to the outside.

3. And lastly, the surface temperature of the enclosure has to be limited to prevent ignition of the explosive atmosphere surrounding the enclosure.

With this type of protection, equipment that generates a spark during normal operation due to its function can be installed in an Ex d enclosure and can therefore be used safely in hazardous areas. This makes this type of protection a popular solution for any industrial components which have not yet been approved for hazardous areas or which require a higher level of protection (Zone 1 instead of Zone 2).

1. Robust enclosures

The enclosures of Ex d equipment are made of materials such as steel, cast iron or die-cast aluminium which have high mechanical strength. These materials prevent the internal pressure which can be generated by an explosion from damaging the enclosure.

2. Joints as a safety feature

• Flameproof joints: The joint between the parts of the enclosure (e.g. at threads or covers) is precisely calculated. It allows explosion gases to escape but cools them to such an extent that they cannot cause ignition outside the enclosure.
• Joint length and width: The dimensions of the joint depend on the gas group and the type of equipment. Flammable gases (like hydrogen) require longer and narrower joints, for example.

1. Versatility: Suitable for a wide variety of applications, in particular for equipment which generates sparks or high temperatures, such as switchgear, motors or control systems.

2. High level of safety: Effective protection against ignition in hazardous areas.

3. Approval for various different gases: Ex d equipment can be certified for various different gas groups (e.g. IIA, IIB, IIC).

1. Size and weight: The robust enclosures often entail a high weight and a large design, which makes them more difficult to use in confined spaces or in mobile applications.

2. Maintenance requirements: Each time the enclosure is opened, the flameproof joint must be carefully inspected to ensure that it is working properly.

3. Costs: These enclosures are expensive to manufacture and certify.

Regular inspections are essential to ensure the safety of Ex d equipment. The following measures are important:

1. Checking the enclosure for damage: Mechanical damage can reduce the pressure resistance.
2. Cleaning and inspecting the flameproof joints: Dirt or corrosion can prevent the joints from working properly. If screws are loose or missing, this can also mean that the joint is no longer flameproof.
3. Ensuring that screw connections are correct: Screw connections require approval to be installed in an Ex d enclosure. They also need to meet the requirements for flameproof joints and be designed to withstand the potential explosion pressure. It is also essential that the entry and clamping range are the correct size.

The Ex d type of protection offers a reliable and proven solution for using electrical equipment in hazardous areas. With its ability to control internal explosions and protect the environment, flameproof enclosure remains one of the most important degrees of protection in the industry. Although it entails certain limitations such as size and maintenance requirements, these are outweighed by the advantages it brings in terms of safety and versatility.