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NEMA 250

2018 Edition, 2018

Complete Document

Enclosures for Electrical Equipment (1000 Volts Maximum)



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Referenced Items:

IEC 60529
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Product Details:


Description / Abstract:

This Standard covers enclosures for electrical equipment rated not more than 1000 Volts and intended to be installed and used as follows:

a. enclosures for indoor locations, Types 1, 2, 5, 12, 12K, and 13; and

b. enclosures for indoor or outdoor locations, Types 3, 3X, 3R, 3RX, 3S, 3SX, 4, 4X, 6, and 6P; and

c. enclosures for hazardous (classified) locations Types 7 and 9

This Standard covers the requirements to provide protection to the enclosed equipment against specific environmental conditions. The requirements of this Standard mandate that enclosures and equipment shall be installed and used in accordance with manufacturer’s instructions and 110.3(B) of the National Electrical Code®, ANSI/NFPA 70.

This Standard covers the requirements for enclosures that are installed and ready for use in nonhazardous (unclassified) locations.

This Standard additionally covers the requirements for dust-tight enclosures that are installed and ready for use where permitted by National Electrical Code® (NEC) in Class II, Division 2; Class III, Division 1; Class III, Division 2; and Zone 22 hazardous (classified) locations as defined by the NEC, ANSI/NFPA 70, or by Nonincendive Electrical Equipment for use in Class I and II, Division 2, and Class III, Divisions 1 and 2 Hazardous (Classified) Locations, ANSI/ISA 12.12.01. Where dust-tight enclosures are integral to or incorporate separable electrical connections (e.g., plug and receptacle, plug and connector body, inlet and connector body) for use in Class II, Division 2; Class III, Division 1; Class III, Division 2; and Zone 22 hazardous (classified) locations, the combination shall be designed to ensure that current cannot be ruptured at the separable electrical connections while energized parts are exposed.

This Standard also references requirements for Class I; Division 1 explosion-proof enclosures marked Type 7 and Class II, Division 1 dust-ignition-proof enclosures marked Type 9. The reference requirements are in accordance with ANSI/UL 1203 with the associated area classifications and installation requirements in accordance with ANSI/NFPA 70/NEC.

This Standard supplements requirements for enclosures that are contained in the individual product Standards.

This Standard does not cover the requirements for protection of the enclosed equipment against conditions such as condensation, gas vapor ignition, thermal damage, icing, corrosion, or contamination, which may occur within the enclosure or which may enter via conduit or unsealed openings.

This Standard does not cover protection of personnel from contact with enclosed electrical equipment where the enclosures or equipment are incompletely installed or where enclosed electrical equipment has been rendered accessible for servicing, maintenance, testing, troubleshooting, internal measurements, or calibration or by damage.

A product that contains features, characteristics, components, materials, or systems new or different from those in use when the Standard was developed, and that involves a risk of fire, electric shock, or injury to persons shall be evaluated using the appropriate additional component and end-product requirements as determined necessary to maintain the level of safety for the user of the product as originally anticipated by the intent of this Standard.
ANSI/NEMA MW 1000, 2014