Ex n type of protection for Zone 2
The Ex n type of protection include under its umbrella a set of
different and simplified protection methods such as containment,
segregation and prevention which are used according to the equipment to
be protected. Each of these protection methods guarantees the protection
against an explosive atmosphere only during normal operation and do not
take into consideration possible failure. For all these reasons, the Ex
n type of protection is suitable only for zone 2. Zone 2 is defined as a
place in which an explosive atmosphere consisting of a mixture with air
of flammable substances in the form of gas, vapor or mist is not likely
to occur in normal operation, if it does occur, will persist for a
short period only. So in zone 2 the probability of an explosive
atmosphere is extremely low.
For this reason, products for zone 2 are cheaper than Ex d zone 1 products. This characteristic, combined with the fact that zone 2 is the most widespread hazardous area within an industrial plant, has allowed over the years to register a constantly growing trend for the products suitable for this area. In the last years, revenues for zone 2 products have grown of 7% in relation to products for zones 0/20 and 1/21 and the worldwide sales for these products settle at around 60% compared to products for zones 0 / 20 and 1/21.
Within the Ex n protection, the equipment is divided into “non-sparking” and “sparkling” equipment, which produces arcs, sparks or high surface temperatures during normal operation.
Based on this, we distinguish 5 types of protection:
• Ex-nA: non-sparking electrical equipment
• Ex-nC: Sparkling electrical equipment
• Ex nR: restricted-breathing enclosures
• Ex-nL: energy-limiting equipment
• Ex-nP: simplified pressurization equipment
Ex-nA – mode of protection for non-sparking equipment, which, in normal
operation, do not produce arcs, sparks, or overheating and therefore
the risk of explosion is minimal. This type of protection can be applied
to asynchronous motors, junction boxes, terminal boards, sockets and
plugs and lighting fixtures.
2. Ex-nC – mode of protection for sparkling electrical equipment. In this mode of protection, there are different techniques aimed to prevent the contact between flammable substances and sparkling parts. The available techniques are:
• Enclosed-break device: special devices aimed to avoid the spread of the explosion, are installed inside the equipment. As the Ex d type of protection, this method allows the possibility of an explosion inside the equipment but tries to contain the damage.
• Hermetically sealed device: deals with the device as a unit and give details of the construction which based upon the principle of isolation by hermetically sealing the device, permanently, from the external atmosphere by soldering, brazing welding or fusion.
• Sealed-device: deals with the device as a whole which, due to its special construction cannot be opened during normal service and is sealed effectively against the ingress of the external surrounding atmosphere
• non-incendive component: deals with the components, having electrical contacts, making & breaking type, which does not cause ignition of the surrounding atmosphere
3. Ex-nR -electrical devices with restricted-breathing enclosure. The protection is guaranteed by the limitation of power dissipation and then the temperature delta between the device and the surrounding environment, so that the created depression once it is de-energized delays the ingress of explosive atmosphere for a limited time prescribed by the standard. The equipment must be equipped with a special connection that allows to check the breathing properties.
4. Ex-nL – mode of protection applicable to those devices within which an explosion is not possible due to the low level of energy emitted by the equipment itself.
5. Ex-nP: mode of protection that creates an overpressure inside the equipment where there are the sparkling components so that the external potentially explosive atmosphere has a lower pressure and therefore cannot enter the equipment.