Enclosures for Electrical Equipment, NEMA 250-2018

Electrical Enclosures Ratings Standard NEMA 250-2018

Electricity, while essential to the fabric of modern life and within feet of anyone indoors at any given time, can bring forth immense potential hazards. From the possibility of sparking fire to the ability of the human body to act as a conductor, electrical hazards can be all too abundant. Measures to mitigate electrical hazards, such as electrical enclosures to surround hazardous parts, help protect both personnel and equipment.

Electrical enclosures are often associated with a “NEMA rating.” These ratings derive from a standard developed by ANSI-accredited standards developing organization the National Electrical Manufacturers Association (NEMA). The current edition of this standard is NEMA 250-2018: Enclosures For Electrical Equipment (1000 Volts Maximum).

NEMA 250-2018 outlines specifications to provide protection to enclosed equipment against specific environmental conditions. Electrical equipment installed under the guidance of this standard is rated 1000 Volts or less and is intended to be used and installed in a manner specific to its Type.

According to NEMA 250-2018, Types 1, 2, 5, 12, 12K, and 13 are meant for enclosures for indoor locations; Types 3, 3X, 3R, 3RX, 3S, 3SX, 4, 4X, 6, and 6P are for enclosures for indoor or outdoor locations; and Types 7 and 9 are intended for enclosures for hazardous (classified) locations.

The specific rating Type for an enclosure denotes the type of protection that the enclosure offers, and, of course, this varies among types, with some means of protection being offered by multiple Types. For example, all Types addressed in NEMA 250-2018 provide a degree of protection against access to hazardous parts and the ingress of solid foreign objects, such as falling dirt. Some environmental conditions, however, are only covered by specific NEMA Enclosure Types—e.g., Type 6P provides a degree of protection against the ingress of water under occasional prolonged submersion, as well as protection against other conditions.

In addition to Type designations, under the guidance of NEMA 250-2018, certain ratings can be appended with the PW ancillary rating if enclosures are constructed for exterior cleaning with high-pressure power washers.

Overall, the NEMA 250-2018 standard addresses the construction, features, applications, marking, design tests, and field modifications for electrical enclosures.

Please note that NEMA 250-2018 does not cover protection of enclosed equipment against condensation, gas vapor ignition, thermal damage, icing, corrosion, or contamination. Furthermore, the specifications for enclosures detailed in this standard are intended to be installed and used in accordance with manufacturer instructions and section 110.3(B) of NFPA 70-2017: National Electrical Code.

NEMA 250-2018 revises and supersedes the previous edition of the same standard, NEMA 250-2014.

NEMA 250-2018: Enclosures For Electrical Equipment (1000 Volts Maximum) is available on the ANSI Webstore.

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