arpadveress 
This interpretation sheet has been prepared by IEC technical committee 31: Equipment for explosive atmospheres. Source: IEC.
Question 1:
The requirements given in 5.3.2 of IEC 60079-31:2013 (Edition 2) permit threaded entries for dust protected enclosures to be:
• Tapered threads with not less than 3 threads,
• Parallel threads with not less than five threads, with a tolerance class of 6H or better according to ISO 965-1,
• Parallel threads with less than five threads with a tolerance class of 6H or better according to ISO 965-1 and are provided with an additional seal or gasket.
Does the description of threads include other thread forms such as ISO 228-1 threads (these threads are commonly referred to as BSPP or Type G threads and BSPT or Type R threads)?
Answer 1:
No, only metric and NPT threaded entries are permitted for enclosures having equipment dust ignition protection by enclosure.
NOTE It has been determined that some sizes of Type G and NPT threads will engage but will result in a mismatched thread engagement. The intention of the restriction to only metric and NPT regarding threaded entries for dust ignition protection by enclosure is to minimize the risk of mismatch of thread forms in enclosure entries.
Question 2:
Where a thread adapter is fitted and assessed as a factory-assembled part of the dust protected enclosure, what are the permitted thread forms?
Answer 2:
A thread adapter may use thread forms other than metric and NPT, whether as an Ex Equipment thread adapter or as a thread adapter fitted and assessed as a factory-assembled part of the dust protected enclosure.
Question 3:
Can a blanking element be installed in a thread adapter which is fitted and assessed as a factory-assembled part of the dust protected enclosure?
Answer 3:
Yes, a blanking element can be installed in a thread adapter which is fitted and assessed as a factory-assembled part of the dust protected enclosure.
Question 4:
What is the required marking when a thread adapter is fitted and assessed as a factory assembled part of the dust protected enclosure?
Answer 4:
Clause 16.2 of IEC 60079-0 (Editions 6 and 7) requires identification of the specific thread type and size of threaded entries. In the case where the thread adapter is fitted and assessed as a factory-assembled part of the dust protected enclosure, the requirement for identification applies to the thread form of the adapter for the field wiring connection.
It has been withdrawn by now.
Keep up good work!
Arpad
veress@exprofessional.com
