NEMA Enclosure Requirements for Class II Division II Area

TM519

Member
Location
United States
We had an analysis of our equipment done at our plant (welding receptacles, MCC's, etc) and the report states for several pieces of equipment that the enclosures need to be replaced with NEMA 9 enclosures due them being in Class II Division II areas. I cannot find anything definitive that states that NEMA 9 enclosures are required for these areas. The areas are indeed Class II Div II areas, as there is a lot of coal dust present, but is there any specific reference to what the enclosure requirements are for these areas? It is very confusing with terms such as "dust-tight" being used, but not a clear definition of what exactly that means. I can see that NEMA 9 would be sufficient, but is it overkill? I don't want to make any unnecessary changes if it is not required. Very much appreciate the insight as always.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
The general requirements for boxes and fittings in Class II, Division 2 is in Section 502.10(B)(4). For specific equipment enclosures, the evaluator should cite specific NEC Sections rather than make a general statement. Dusttight and Dust-igntionproof [NEMA 9] are not synonymous; but, even in Division 1, dusttight is often sufficient. See Table 110.28, notes for enclosures that are dusttight.

EDIT ADD: BTW, both dusttight and dust-ignitionproof are defined in Article 100.
 

TM519

Member
Location
United States
The general requirements for boxes and fittings in Class II, Division 2 is in Section 502.10(B)(4). For specific equipment enclosures, the evaluator should cite specific NEC Sections rather than make a general statement. Dusttight and Dust-igntionproof [NEMA 9] are not synonymous; but, even in Division 1, dusttight is often sufficient. See Table 110.28, notes for enclosures that are dusttight.

EDIT ADD: BTW, both dusttight and dust-ignitionproof are defined in Article 100.
Thanks so much this led me in the right direction and I have a much better understanding now upon reading further. Much appreciated.
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
Professional Electrical Engineer
For additonal information and just general curiosity on Class II, google or get a copy of NFPA 499.
It says coal properties vary from site to site, especially its ignition properties.
Also lists it as a Group F.

NFPA 497 covers explosive gases, Class I, instead of dusts

Crouse Hinds also has a good read.
Google this: Crouse Hinds 2017 Digest, Article 500-516 (PDF form)
 
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