NEMA 250 - Enclosures for Electrical Equipment
Enclosures for Electrical Equipment (1000 Volts Maximum)
How NEMA Types map to environments
Key facts
- Full title
- ANSI/NEMA 250, Enclosures for Electrical Equipment (1000 Volts Maximum)
- Published by
- NEMA (National Electrical Manufacturers Association)
- Current edition
- ANSI/NEMA 250-2020, approved 8 December 2020; supersedes the 2018 edition
- Scope
- Enclosures for electrical equipment rated up to 1000 V
- Defines
- Enclosure Type ratings plus construction, test, rating and marking requirements
- Testing
- NEMA does not test or certify; the manufacturer self-declares. Independent listing uses UL 50 / UL 50E (with CSA C22.2 No. 94.2)
- IP cross-reference
- Annex A maps each NEMA Type to a minimum IP code - one way only
What NEMA 250 covers
ANSI/NEMA 250 is the North American standard for enclosures used with electrical equipment rated up to 1000 V. It defines the familiar Type ratings, from general-purpose indoor Type 1 to corrosion-resistant Type 4X, and specifies the construction, testing, rating and marking each Type must meet.
One point trips up almost every first-time buyer: NEMA is a standards-development organisation, so it publishes the criteria but does not test or certify enclosures. A manufacturer self-declares that a product meets a given Type. Independent verification, which most jurisdictions expect on the installed product, is a separate step done by a recognised testing lab.
How the Type ratings work
Each Type describes how an enclosure is built to protect people from the hazardous parts inside and to protect the equipment against a defined set of conditions: falling dirt, dust, rain, splashing or hose-directed water, submersion, ice, oil and corrosion. The exact tests differ by Type.
The numbers are not a ranking. A higher number does not include the lower-numbered tests, and indoor and outdoor Types are interleaved - Types 3, 4 and 6 are outdoor, but Type 5 is indoor. An X in the Type (3X, 3RX, 3SX, 4X, 6P) marks a corrosion-resistant variant, verified by an extended salt-spray test. The right choice is the Type that matches the real environment, not the largest number.
NEMA 250, UL 50 / UL 50E and CSA 94.2
NEMA 250 defines the Type ratings; UL 50 and UL 50E cover the same enclosures but with third-party testing. UL 50 addresses construction, while UL 50E covers the environmental performance. ANSI/UL 50E and CSA C22.2 No. 94.2 are a single binational standard published under two covers for the US and Canada.
The test philosophies differ from the IP code in a telling way: a UL or CSA water-tight test fails if even a single drop enters, whereas IEC 60529 permits a defined, harmless amount of ingress. Hazardous-location (Type 7 and 9) requirements and the NEMA-to-IP cross-reference live only in ANSI/NEMA 250, not in UL 50E.
Why a NEMA Type does not convert back to an IP code
NEMA 250 includes a cross-reference (Annex A) that maps each NEMA Type to a minimum IP code. That mapping runs one way only: a NEMA Type can be stated as at least a certain IP code, but an IP code cannot be converted back into a NEMA Type.
The reason is scope. To earn a Type, an enclosure may have to pass corrosion (salt-spray), external-icing, gasket-aging, dust and oil tests that the IP code never checks. Two enclosures with the same IP rating can differ in all of those respects, so an IP code alone does not carry enough information to assign a NEMA Type.
NEMA 250 enclosure Types at a glance
| Type | Location | Key protection |
|---|---|---|
| 1 | Indoor | Incidental contact and falling dirt (general purpose) |
| 2 | Indoor | Adds dripping and light splashing of liquids |
| 3 | Outdoor | Rain, snow, sleet and windblown dust; undamaged by external ice |
| 3R | Outdoor | Rain, snow and sleet; external ice (may be ventilated) |
| 3S | Outdoor | Type 3 plus external mechanisms operable while ice-laden |
| 4 | Indoor / Outdoor | Windblown dust, rain, splashing and hose-directed water; external ice |
| 4X | Indoor / Outdoor | Type 4 plus corrosion resistance |
| 5 | Indoor | Settling airborne dust and dripping liquids |
| 6 | Indoor / Outdoor | Hose-directed water and occasional temporary submersion; external ice |
| 6P | Indoor / Outdoor | Occasional prolonged submersion at limited depth; corrosion resistant |
| 12 / 12K | Indoor | Dust, falling dirt and dripping non-corrosive liquids (12K has knockouts) |
| 13 | Indoor | Dust, spraying water, oil and non-corrosive coolant |
Tools that use this standard
Related standards
| Standard | Relationship | What it means |
|---|---|---|
| IEC 60529 (IP code) | Cross-referenced with | NEMA 250 Annex A maps each NEMA Type to a minimum IP code one way only; an IP code cannot be converted back to a NEMA Type because NEMA also tests corrosion, ice and oil. |
| UL 50 / UL 50E and CSA C22.2 No. 94.2 | Harmonized with | The same enclosure Types evaluated with third-party testing: UL 50 covers construction, UL 50E the environmental performance, published binationally with CSA. |
| NFPA 70 (NEC), Article 110.28 | Referenced by | The US National Electrical Code specifies which enclosure Type is required for a given location. |
Frequently asked questions
What is NEMA 250?
What is the difference between NEMA 250 and UL 50E?
Is a higher NEMA type number better?
What is the difference between NEMA 4 and 4X?
Can I convert a NEMA type to an IP rating?
Does a NEMA rating mean the enclosure is UL listed?
Does NEMA 250 cover hazardous locations?
Source: NEMA. An overview for design reference - verify against the current edition before relying on it for compliance.