Electrical Apparatus for Use in Zone 21 and Zone 22 Hazardous (Classified) Locations − Protection by Enclosures “tD”
|Publication Date:||1 January 2006|
This standard is applicable to electrical apparatus protected by enclosures and surface temperature limitation for use in explosive dust atmospheres classified as zone 21 or zone 22 hazardous locations in accordance with Article 506 of the NEC®. It specifies requirements for design, construction and testing of electrical apparatus.
This standard supplements the general requirements in ANSI/ISA-61241-0.
The ignition protection is based on the limitation of the maximum surface temperature of the enclosure and on other surfaces which could be in contact with dust and on the restriction of dust ingress into the enclosure.
The application of electrical apparatus in atmospheres which may contain explosive gas as well as combustible dust, whether simultaneously or separately, requires additional protective measures.
Where the apparatus has to meet other environmental conditions, for example, protection against ingress of water and resistance to corrosion, additional methods of protection may be necessary. The method used should not adversely affect the integrity of the enclosure.
This standard does not apply to dusts of explosives which do not require atmospheric oxygen for combustion, or to pyrophoric substances.
This standard is not applicable to electrical apparatus intended for use in underground parts of mines as well as those parts of surface installations of such mines endangered by firedamp and/or combustible dust.
This standard does not take account of any risk due to an emission of flammable or toxic gas from the dust.