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Thread: NEMA 4 Enclosure in Class II, Div. 2, Grp. F & G Hazardous Area?

  1. #1
    Join Date
    Feb 2012
    Waterloo, Ontario, Canada

    NEMA 4 Enclosure in Class II, Div. 2, Grp. F & G Hazardous Area?

    Is it acceptable to install a NEMA 4 enclosure and push-buttons, indicators in a Class II, Div. 2, Grp. F&G hazardous area? There will be a VFD inside the control panel along with other non-rated components. The control panel will be installed in the USA.

    I am getting conflicting advice on this.

    On one hand, my local panel builder is telling me that I need to purge the panel with an enclosure purge system.

    On the other hand, I have a NFPA book entitled "Electrical Installations in Hazardous Locations, 3rd edition, written by Peter J. Schram (NFPA's Chief Electrical Engineer) and Mark W. Eraley (Assistant Chief Electrical Engineer, staff liason to the National Electrical Code) (ISBN0-87765-356-9) that reads...

    "4-3.2.2 Dusttight Equipment

    For most equipment in Class II, Division 2 locations, the National Electrical Code indicates that dusttight equipment can be used.

    Dusttight equipment is defined in the National Electrical Code as "so constructed that dust will not enter the enclosing case under specified test conditions." A fine priont note is added referencing ANSI/NEMA 250, paragraph 250.5.05. This reference indicates that either of two different test methods can be used: A dust-blast method or an atomized water method.

    NEMA and UL designations for dusttight equipment are Types 3, 3S, 4, 4X, 6, 6P, 12, 12K and 13. NEMA Type 9 enclosures (dust ignitionproof) are also accepted."

    Reading the above, it would appear that a NEMA4 enclsoure and operators, lights, etc. would be acceptable for a Class II, Division 2, Group F&G hazardous area.

    What is accepted in the USA?

  2. #2
    Join Date
    Apr 2004
    Mission Viejo, CA
    Assuming the installation is in the US, dusttight is acceptable; however, while the NEMA 4 enclosure probably has multiple "Type" certifications, "NEMA 4" alone isn't recognized as dusttight. The NFPA book is in error. Although both authors are very sharp, the book is out of date and was never "official." "Suitable" NEMA dustight enclosures are 3, 3S, 3SX, 3X, 5, 12, 12K, and 13. See NEC Table 110.20 or 110.28, depending on the edition. NEMA 9 (dust-ignitionproof) would also be acceptable, but unnecessary.
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
    Join Date
    Dec 2003
    If you check with the Manufacturer of the enclosure, they will also confirm that their panels is not rated for class 2 situations.

    we use purge / pressurization. See NFPA 70 - 500.7d and NFPA 496 - standard for purged / pressurized enclosures.


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