explosion-proof lamps:Requirements for additional enclosures inside Ex equipment with protection level “ta”

If the equipment with protection level “ta” contains components that generate arcs and sparks, additional enclosures should be provided for these components within the main enclosure. The additional enclosures should meet the requirements of enclosures with protection level “tc”, except for the following exceptions and modifications:

— The heat resistance, cold resistance and UV resistance tests as stipulated in Clause 6.1.1.1 of IEC 60079-31 Edition 2.0 “Explosive atmospheres – Part 31: Equipment dust ignition protection by enclosure ‘t'” are not applicable;

— The COT of non-metallic materials should be at least equal to the lower limit of the specified ambient temperature and at least 20 K higher than the maximum operating temperature;

— The additional enclosure is not considered as an external surface, so the UV resistance and anti-static requirements are not applicable.

— The requirements for threaded introduction, hinges and threaded fasteners are not applicable;

— The internal additional enclosure shall be subjected to impact tests in accordance with Clause 6.1.1.2 of IEC 60079-31, but no heat and cold resistance pre-treatment is required;

— Pressure tests are not applicable;

— The protection grade shall comply with IP6X.

Reference Materials: IEC 60079-31 Edition 2.0 Explosive Atmospheres – Part 31: Equipment Protection by Enclosure “t” for Dust Ignition [S]