NEMA Enclosure Types and Uses

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Electrical enclosure boxes are a necessity in any type of industrial construction. The National Electrical Manufacturers Association (NEMA) establishes the standards which these boxes must live up to. This varies, of course, in accordance with the particular environmental conditions at hand. NEMA enclosures contain live electrical wiring. Their primary function, therefore, is to prevent unintended contact with that wiring. Secondary functions include protecting the sensitive electrical elements inside from various contaminants such as corrosive agents, oil, water, dust.


NEMA enclosure types are numbered for quick reference. This numbering system is not necessarily an indication of the degree of protection the enclosures provide. Neither do the numbers refer to size. They refer primarily to the relative permeability various contaminants might have to the box. Rated for use in outside conditions some boxes are more impermeable to the elements than are those restricted to inside use. Neither the size of the numbers nor their order necessarily reflect that differentiation. NEMA box number 5, for example, is not rated for outside use yet numbers 3,4, and 6 are. Within those broad classifications of outside verses inside uses there are sometimes rather dramatic distinctions.

Perhaps one of the most confusing of the distinctions between NEMA enclosures are the subcategories. The Enclosure numbers are often followed by lettered subcategories. This is the case for Enclosures 6 and 6P, for example, which are designed to be temporarily submersible. Even that quality, however, varies between the boxes and the environmental elements at hand. Both are temporarily submersible in both water and oil but the length of time they can be submerged is dependent on factors like pressure (a factor of depth in most cases). Enclosures 4 and 4X, for example, are labeled water tight but their intended use is in conditions where they might endure occasional splashing, in locations such as dairies, ship docks and wastewater treatment plants. They are not intended to be submerged.

Intended exclusively for indoor use, Box 1 contrasts significantly with Box 6. While Box 6 may be found in such inhospitable locations as manholes, quarries and mines, Box 1 will more likely be found indoors. Rated as being able to withstand light splashing with water, Box 1’s primary function is to protect against dust. Even then, Box 1 is not completely dust tight. However, if the splashing were with a more corrosive agent like gasoline or coolant, Enclosure 13 would be the more appropriate choice.

In conclusion, NEMA enclosures are extremely varied in terms of the protection they provide. The numbering system helps understand this variance but it is not an easily memorized or self-explanatory system. If you need help choosing the NEMA enclosure that is best suited to your needs, feel free to contact us. We manufacture these enclosures so an expert is always at hand to answer all your questions about this rather complex subject.

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