What is an Ex d Enclosure?

iWAP107 on table with internals

An Ex d enclosure is designed to contain an explosion and stop any flames, sparks, and hot gases from escaping into the surrounding atmosphere should an internal explosion occur. In addition, an Ex d enclosure protects the fitted equipment against external moisture, dirt, dust, or water.

The enclosure may house equipment such as, contactors, relays, power supplies, transformers, radio devices and other electrical equipment with potentially hot surfaces.

Sometimes referred to as ‘flameproof’ or “explosion-proof”, an Ex d enclosure includes 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

Flame paths are gaps within the enclosure that, if an internal explosion occurs, ensure that by the time the flame has reached the end of the flame path it has been starved of oxygen or cooled down to such an extent that nothing but air propagates from the explosion. The flame never escapes the enclosure and so cannot ignite an ambient gas.

Ex d enclosures can be considered explosion-proof or flameproof. Some flameproof boxes have flame paths that operate surface to surface, like a flange touching a joint, whereas others like a typical IIC gas group enclosure have a lid that screws into the body of the enclosure. In these enclosures, the flame path is in the thread, forcing the flame to move in and out of the thread before it can reach the outside atmosphere. In this design, the thread quenches the flame.

iWAP107

The flameproof protection concept works on the premise that it is not attempting to prevent gas or oxygen from penetrating everywhere in an environment. It instead looks to contain a resulting explosion from gas and oxygen that penetrates the enclosure.

This means that standard pieces of electronics, including wireless technology, can be placed within an Ex d enclosure in a hazardous area without the need for further costly certifications provided the manufacturer of the wireless hardware meets the conditions of the enclosure solution.

Clauses/Considerations

While Ex d it is a go-to standard for placing equipment in hazardous areas, it isn’t an intrinsically safe solution, and there are still considerations to make about the general equipment housed within it and the standards they need to comply with. For example, ensuring the dissipated power is within the allowed limits to achieve the required T-Class

When looking to purchase 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 in EN / IEC 60079-1 for the “flameproof” (pressure-tight encapsulation) type of ignition protection.

One such aspect to factor in when considering your equipment is the volume taken up by the equipment within the enclosure itself. The enclosure needs to have a certain amount of free cross-sectional area. The less free volume inside the enclosure, the more amplified the explosion could become inside the available free space (due to pressure piling) and therefore the pressure of that explosion will increase.

iWAP107: Ex d enclosure

Application Examples

Its commonplace to find Ex d enclosures in zone 2 areas where other more specialised setups would be considered too time-consuming or expensive to develop and certify specially.

For equipment that cannot be certified as increased safety, intrinsically safe or to any other protection concepts, such as motor starters with large contactors that could cause a spark, an Ex d enclosure is a standard solution for housing such a piece of equipment that, were it to cause an explosion, would contain that explosion within the enclosure.

Ex d Enclosures – A Cost-Effective Solution

Because of the nature of the certifications Ex d enclosures hold, it is one of the go-to standards of protection concepts for hazardous areas, allowing for installations of effectively any equipment needed.

Many of the vendors and manufacturers that supply these enclosures provide almost universal or very flexible certificates against the 60079-1 flameproof standard. The flexibility and lack of requirement for further certification for the equipment being housed can make it cost-effective

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