Type of protection “p” pressurization

EMMUA 214 States: Page 25

3.9.1 Definition

Protection is provided by covering the parts that may cause ignition to a critical depth in a fine powder such as quartz. This quenches any arc before the combustion products can ignite a surrounding gas. An additional form of external protection is required to limit the maximum current that may be safely used.

3.9.2 Standards and selection

i) Current standards

LEC 60079-5 (EN 60079-5) Explosive atmospheres Equipment protection by powder filling.

ii) Superseded standards

EN 50017 Powder filling

BS 5501 Part 4 Powder filling iii) EPL/category and zones of use

Powder filled equipment may be used in areas requiring EPL ‘Gb’ and I Gc’, or Category 2 and 3. Prior to 2007, such equipment was permitted to be used in Zones 1 or 2.

The Electrical apparatus is filled with powdered material so as to prevent any arc occurring in the apparatus from igniting the surrounding atmosphere.

Ex q (powder filling) is suitable for use in all European Zone 1 and Zone 2 applications. This method of protection can be used in gas groups IIA, IIB and IIC.

The method code “q” stands for quartz. The powder mediums chosen are sand, glass beads, or silica beads. Construction requirements are usually a metal box to IP54 ingress protection. Filling should be carried in a manner such that spaces, voids, are not present. It is usually shaken to remove voids when filling. The filling material is to be applied dry.