NEC 503, Class 3

Location
Anchorage
Occupation
Engineer
I have a building that I am designing a building with a 24 foot ceiling and have a room that falls under the classification 3 division 1. Elsewhere in the code, there is limits as to height above the floor that can be declassified. I am not finding anything of that nature in for the Class 3 area. Is there height limitations? Could you refer me to something that I can refer to for the heights?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
In general the NEC does not tell you what areas are classified, other than in the occupancy specific Articles 511, through 516.
You need someone to provide the classification documentation that is required by 500.4, as there are no article specific occupancies for Class III installations.
 

paulengr

Senior Member
I have a building that I am designing a building with a 24 foot ceiling and have a room that falls under the classification 3 division 1. Elsewhere in the code, there is limits as to height above the floor that can be declassified. I am not finding anything of that nature in for the Class 3 area. Is there height limitations? Could you refer me to something that I can refer to for the heights?

Other NFPA Codes give guidance on ratings, heights, etc. NEC is only concerned with installations in those areas, not how they are determined.

You don’t set the areas but it is helpful to know when someone makes a mistake. Go to nfpa.org and look at the list. For instance I had a comical engineer screw up and use the generic chemical plant standard applied to coal handling and ended up missing the part that says all pulverized burner piping is not a hazardous location.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Since the process involved was not disclosed in the OP, it's impossible for this forum to give much guidance on the classified envelope. The points and recommendations made by the don_resqcapt19 above are worth reviewing. That said, a close review of Section 500.5(D) and Article 503 will indicate that the NEC puts the greatest emphasis on housekeeping and suitable equipment selection in those locations. Hence the difference between Division 1 and Division 2 installations is virtually nonexistent in Class III. For all practical purposes, Class III has never been considered significant enough for its own classification standard such as NFPA 497 or 499. Article 506 does tip its hat by essentially including fibers and flyings as a subgroup of dusts for Zone classified locations.
 
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