Ex p Pressurised Enclosures | Explosive Atmospheres & Explosion Proof Protection Concepts

Ex p Pressurised enclosures

This method of explosion protection is a process which ensures that the pressure inside an Ex p enclosure is sufficient to prevent the entrance of a flammable gas, vapour, dust, or fibre and prevent a possible ignition. Another process maintains a constant flow of air (or an inert gas) to dilute to take away any potentially explosive atmosphere.

Often used for large electric motors or large control cabinets containing switchgear or circuit boards.

The principle of this explosion protection method is to first pressurise the enclosure with air or an inert gas and then to purge any flammable or hazardous gas that may be present within by passing a large volume of air or an inert gas through the enclosure.

Then, when the purging is complete, an overpressure is maintained to prevent hazardous gases from re-entering the Ex p enclosure. It is then possible for the hazardous equipment to be safely energised.

Main features of ex p enclosures

The main features of the Ex p purging and protection concept include:

No external hot surfaces above the temperature class
The design of any enclosure joints must comply with a minimum of IP40 ingress protection
Any plastic components contributing to the integrity of the Ex p enclosure will undergo high temperature and humidity testing
Parts fitted within an enclosure can include sparking contacts, semi-conductor devices and batteries as well as rotating parts

Types of explosion protection to electrical equipment

Type of Explosion Protection	Pressurised enclosure Ex p – EN IEC60079-2(G) / -4(D)
Protection Principles	Protection principle prevents the potentially explosive atmosphere reaching the ignition source
Flammable Material	Gas/vapour (G) \| Dust (D)
Category 1 EPL a – Very High Level of Explosion Protection	–
Category 2 EPL b – High Level of Explosion Protection	Ex pxb, pyb Explosion Protection
Category 3 EPL c – Normal Level of Explosion Protection	Ex pzc Explosion Protection

Pressurized enclosures Ex px, Ex py

Principle
The ingress of the surrounding atmosphere into the enclosure of electrical equipment is prevented by maintaining an ignition shield gas (air, inert or a diff erent suitable gas) inside it at a pressure above atmospheric pressure. The overpressure is maintained with or without constant flushing of the protective gas.

Important Design Parameters

Strength of the enclosure; the surrounding, flushed enclosure must withstand 1.5 times the overpressure experienced during normal operation
Flush before commissioning the electrical equipment
Shut-down or alarm if the fl ushing gas fl ow or overpressure fails

Ex p Applications

Equipment where during normal operation sparks, electric arcs or hot surfaces are generated and complex industrial equipment (controls) which must be operated in a potentially explosive atmosphere protected by this type of protection
Large machines, slip ring or collector motors, switch cabinets and control cabinets and analytical apparatus

Pressurized enclosures Ex pz

Principle
Use of a protective gas preventing ignition inside an enclosure to prevent the formation of an explosive atmosphere inside the enclosure by maintaining a pressure greater than the that in the surrounding atmosphere.

Important Design Parameters

The important diff erence from the pressurized enclosure is the restriction to an enclosure where no internal sources are available and no flammable gases or vapours can be released
Strength of the enclosure
Flush before commissioning the electrical equipment
Shut-down or alarm if the flushing gas flow or overpressure fails

Explosion Protection Ex p Applications

Equipment where during normal operation sparks, electric arcs or hot surfaces are generated and complex industrial equipment (controls) which must be operated in a potentially explosive atmosphere protected by this type of protection
Analytical apparatus without internal sources

Explosive Atmospheres &

Explosion Protection Concepts

💡 Thorne & Derrick, Specialist Suppliers & Stockists of Electrical and Process Instrumentation Equipment for installation in hazardous area location can assist with your project requirements. Know your Ex Concepts:

For further technical information see | Hazardous Area Zones | Explosive Atmospheres | T Class Ratings

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Ex p Pressurised Enclosures Equipment

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