use of gasket with explosion proof enclosure

[gareth0127]

we have an explosion proof enclosure which contains arcing devices and it seems somebody has decided to install a rubber gasket between the machined faces of the enclosure.

I can see reference to the use of o rings with explosion proof boxes but only when they are used in a recess as part of the original design.

If I am correct in my expectation that this violates the code, can anybody point me to the regulation that states you can not use homemade gaskets on flamepaths? Ive looked and can not see it

 

[Smart $]

I don't believe you will find it in the NEC. The hazardous location rating is designed into equipment by the manufacturer. Only modifications per the manufacturer's instructions are permitted while retaining the listing. As for manufacturing requirements to obtain the classified listing is concerned, you might look to UL and ANSI/NEMA for such answers.

 

[mike7330]

check with manufacture, but my understanding is 2 machined surfaces, no gaskets, as the hot gases escape they are cooled on the flat metal as they leave the box. You can not have any damage to the flat surfaces of the box/ fitting or it is shot. This was explained to us at a code class years ago.

 

[don_resqcapt19]

If the gasket was not part of the fitting design, it is not being used as tested by the manufacturer. About the only code rule that would tell you this would be one that I don't really like to use, but have to in some cases...110.3(B).
I would bet that the gasket was installed to keep water out. Explosion-proof fittings with just a NEMA 7 or 9 marking are not suitable for use in wet locations, for use wet locations, they need to have a NEMA 3, 4 or 6 marking in addition to the 7 or 9 marking.