Purge & Pressurize Enclosure Requirements

[megloff11x]

One of the ways around Class I Division 2 is to use a purged and pressurized enclosure. NFPA 496 doesn't specify any enclosure requirements save that it not be damageable under normal operating conditions.

However, several vendors of such enclosure systems for purchase indicate that they use NEMA 4 or NEMA 12 enclosures, and that nothing less is an acceptable starting point.

Going back to NFPA 496, venting to the hazardous area is allowed if no combustible particles make it out. It says nothing about NEMA ratings of the enclosure.

Can you build your own such purged and pressurized enclosure as long as it meets NFPA 496, or does code require that your starting point be a NEMA rated box, and if so, where does it say this?

 

[rbalex]

Re: Purge & Pressurize Enclosure Requirements

Your basic understanding is correct - neither NFPA 496 nor the NEC specifies a particular "minimum" NEMA enclosure and only requires specific performance standards.

That being said, as a quick summary, an installation must still be one that is already suitable in "ordinary locations" for type "X" or "Z" protection, or Division 2 locations for type "Y." That "suitability" may require various "listed" forms of enclosures; e.g., you may still require an UL 508 industrial control cabinet.

 

[petersonra]

Re: Purge & Pressurize Enclosure Requirements

Originally posted by megloff11x:
One of the ways around Class I Division 2 is to use a purged and pressurized enclosure.

I don't like the phrasing you use. You are not looking for a "way around Class I, Divison 2", but rather a way reducing the added risk that goes with having electrical equipment in such an area.

Pressurization is one perfectly good technique for reducing that risk.

 

[charlie]

Re: Purge & Pressurize Enclosure Requirements

I am closing this thread. It is a duplicate of one in the NEC forum.