Ex d enclosures are designed to contain explosions and prevent any flames, sparks and hot gases from escaping to the surrounding atmosphere in the event of an internal explosion. In addition, Ex d enclosures protect the installed equipment from external moisture, dirt, dust or water.

Enclosures can house contactors, relays, power supplies, transformers, radio equipment and other electrical equipment that may have hot surfaces.

Ex d enclosures are sometimes referred to as "flameproof" or "explosionproof" and include what is known as a flame path. The flame path design can vary depending on the construction of the Ex d enclosure system.

Flame Path

The flame path is a gap within the enclosure that, in the event of an internal explosion, ensures that by the time the flame reaches the end of the flame path, it has been depleted of oxygen or cooled to such an extent that it will only propagate air after the explosion. The flame never escapes the enclosure and therefore cannot ignite the surrounding gases.

Ex d enclosures can be considered either explosionproof or flameproof enclosures. Some fireproof enclosures have a flame path that operates surface to surface, such as flanged contact joints, while others, such as a typical IIC gas group enclosure, have a cover that screws into the body of the enclosure. In these enclosures, the flame path is in the threads, forcing the flame to move in and out of the threads before it reaches the outside atmosphere. In this design, the threads extinguish the flame.

The flame protection concept works in that it does not attempt to prevent gases or oxygen from penetrating everywhere in the environment. Instead, it attempts to control the explosion caused by gases and oxygen that penetrate the enclosure.

This means that standard electronic equipment (including wireless technology) can be placed inside an Ex d enclosure in hazardous areas without the need for further expensive certification, as long as the wireless hardware manufacturer meets the conditions of the enclosure solution.

Clause/Considerations

While Ex d is the preferred standard for placing equipment in hazardous areas, it is not an intrinsically safe solution and consideration still needs to be given to the general equipment installed within it and the standards it needs to comply with. For example, ensuring that the dissipated power is within the permitted range to achieve the required T-level

When purchasing an Ex d enclosure, it is important to consider the relevant tests/inspections that should be carried out. These are documented in EN/IEC 60079-0 (general requirements) and EN/IEC 60079-1 for the "flameproof" (pressure-resistant enclosure) type of ignition protection.

When considering your device, one aspect to consider is the volume that the device takes up within the enclosure. The enclosure needs to have a certain free cross-sectional area. The less free volume within the enclosure, the more violent the explosion is likely to be within the available free space (due to pressure build-up), and therefore the pressure of the explosion will increase.

Application Examples

Ex d enclosures are common in Zone 2, where other more specialized setups are considered too time-consuming or expensive to specifically develop and certify.

For equipment that cannot be certified as enhanced safety, intrinsic safety, or any other protection concept, such as motor starters with large contactors that could cause sparks, Ex d enclosures are the standard solution for housing such equipment, and if the equipment causes an explosion, the explosion is contained within the enclosure.

Ex d enclosures – a cost-effective solution

Due to the nature of the certifications held by Ex d enclosures, it is one of the preferred standards for hazardous area protection concepts, allowing any equipment required to be effectively installed.

Many suppliers and manufacturers that supply these enclosures offer almost universal or very flexible certificates to the 60079-1 flameproof standard. The flexibility and the lack of need for further certification of the installed equipment can make it cost-effective