The short answer
- NEMA 250 is the standard a manufacturer uses to self-declare a type, such as "NEMA 4X". NEMA writes it but does not test, certify or label anything.
- UL 50E / CSA C22.2 No. 94.2 is one harmonized standard that UL and CSA use to list enclosures to the same type numbers, with their mark and ongoing factory inspections.
- In the US, the NEC accepts equipment that is "approved", meaning acceptable to the authority having jurisdiction. A listing is the usual evidence, not the only route. In Canada, approval normally means certification.
- Buy a listed enclosure when your specification, your customer, your panel shop's listing program or your inspector requires one. Ask before you order.
Three documents, one set of type numbers
| Document | Published by | Used for | Notes |
|---|---|---|---|
| ANSI/NEMA 250 (now ANSI/NEMA EN 10250) | NEMA | Self-declaration of a type by the manufacturer; a certification body may also use it | Covers the non-hazardous-location types plus Types 7 and 9 for hazardous locations; includes the NEMA-to-IP conversion annex and field modification rules |
| UL 50E / CSA C22.2 No. 94.2 | UL and CSA Group, as one standard with two covers | Evaluating and listing enclosures by UL and CSA as certification bodies | Environmental requirements; no hazardous-location types and no IP cross-reference |
| UL 50 | UL | Listing | Non-environmental construction requirements (Type 1), including sheet metal thickness |
The type numbers mean the same environment in all of them: a Type 4X is a hosedown, corrosion-resistant enclosure whether it was self-declared to NEMA 250 or listed to UL 50E. The tests are the subject of the other ratings guides: NEMA enclosure types, NEMA 4 vs 4X vs IP66 and NEMA 3R vs NEMA 4. This guide is about who confirms them.
Self-declared: what "NEMA 4X" on a datasheet means
NEMA's own FAQ is direct about its role. NEMA is a standards development organization, "not a testing laboratory or a Certification Body", so it "neither tests products nor certifies for listing". A manufacturer "can choose to self-certify that the product meets the enclosure requirements of NEMA 250 or to seek independent, third-party certification", and NEMA says the choice depends on the market: "a CB listing or mark may be required by a customer or by the Authority Having Jurisdiction".
Anyone may describe complying self-declared products as "NEMA 4", "NEMA 3R" and so on, but the NEMA logo may not be used with that declaration, and NEMA issues no labels for self-certification. A self-declared rating is the manufacturer's statement that the design meets the standard. Its value rests on the design, the testing behind it and the consistency of production, none of which a third party checks.
Listed: what a third party adds
US federal workplace rules define the terms precisely. Equipment is "listed" if it appears in a list published by a nationally recognized laboratory "that makes periodic inspection of the production of such equipment" and that states it meets nationally recognized standards. "Labeled" means it carries that laboratory's mark, again backed by periodic inspection of production.
That periodic inspection is the key difference. A one-time test report, however good, is not a listing. A third-party test report to NEMA 250-2020 for a Type 4/12 product says so in its own footer: the report "does not entitle to carry any safety mark on this or similar products". UL and CSA, by contrast, test in their laboratories and send inspectors to the factory to check that production keeps to the evaluated materials and methods.
What the NEC and OSHA ask for
Paraphrasing the National Electrical Code; check the edition your authority having jurisdiction (AHJ) enforces:
- 110.2 Approval. Conductors and equipment are acceptable only if approved. Article 100 defines approved as "acceptable to the authority having jurisdiction". As one IAEI article puts it, a listing "is not an approval, but it sure goes a long way in facilitating the approval process".
- 90.7. The factory-installed internal wiring or the construction of listed equipment need not be inspected at installation, except to detect alterations or damage. Unlisted equipment gives the inspector more to evaluate.
- 110.3(B). Listed or labeled equipment is installed and used according to the instructions in its listing or labeling; OSHA's workplace rule says the same.
- 110.28 Enclosure types. Enclosures for the equipment the section names, rated 1000 V nominal or less and intended for the locations in Table 110.28, are marked with an enclosure type number from that table. The code adds that IP ratings are not a substitute for enclosure type ratings.
Workplaces. In US workplaces, OSHA 29 CFR 1910.303(a) requires electrical equipment to be approved, and 1910.399 defines what is acceptable:
- Accepted, certified, listed, labeled or otherwise determined to be safe by a nationally recognized testing laboratory (NRTL).
- For a kind of equipment that no NRTL lists or labels, inspected or tested by another federal agency or by a state, municipal or local authority enforcing the NEC.
- For custom-made equipment designed, fabricated for and intended for a particular customer, determined to be safe for its intended use by its manufacturer on the basis of test data which the employer keeps and makes available for inspection.
The third route is narrow and puts the record-keeping on the employer, but it exists. It is the employer's determination, made on the manufacturer's test data; NEMA4 Enclosure makes no statement about OSHA acceptability. Talk to your safety and compliance people before relying on it.
Industrial control panels and UL 508A
NEC 409.2 defines an industrial control panel as an assembly of two or more power circuit components, control circuit components, or both, and UL 508A is the standard for listing one. UL's guidance for inspectors explains what its marks cover:
- A listed enclosed industrial control panel covers the enclosure, every component inside it and every component mounted on its walls at the panel shop.
- A listed industrial control panel enclosure has only been checked against the construction requirements of UL 508A. Once field components are added, UL advises the AHJ to treat the assembly as unlisted equipment, and the AHJ can require a third-party field evaluation to UL 508A.
- A listed open industrial control panel has no complete enclosure; the enclosure is supplied as part of the installation, and the AHJ checks, among other things, its mechanical strength and durability and its wire-bending space.
NEC 409.110 also requires an enclosure type number on the panel. If your panel will carry a UL 508A label, ask the panel shop which enclosures its listing program accepts before you buy the box. The sizing guide covers the layout side.
Field evaluation for one-off equipment
When equipment is not listed, a field evaluation is the usual alternative. IAEI describes it as a service by qualified testing laboratories, "evaluating the product in the field on a one-time basis for that particular site". Two NFPA documents govern it: NFPA 790, the competency standard for third-party field evaluation bodies, and NFPA 791, the recommended practice for evaluating unlabeled electrical equipment. Equipment that passes is labeled by the field evaluation body. Field evaluations cost time and money, so plan them before the equipment arrives on site.
Canada: approval means certification
The Canadian Electrical Code, Rule 2-024, requires electrical equipment to be approved, and the CE Code defines approved as certified by a certification body accredited by the Standards Council of Canada. Provincial and territorial legislation sets the details and, in most jurisdictions, bars the sale of electrical equipment without an approval mark. The enclosure requirements are the same UL 50E / CSA C22.2 No. 94.2 document. For a Canadian installation, ask the inspection authority before you order an uncertified enclosure.
When you need a listed enclosure
Buy a listed enclosure if any of these is true:
- The specification, drawing or purchase order says "listed", "labeled", "UL" or "CSA".
- The finished panel must carry a UL 508A or CSA label and the shop's program requires a listed enclosure.
- The installation is in Canada, or your AHJ has told you it expects listed equipment.
- Your customer or your corporate standard requires third-party marks.
- The location is hazardous (classified). Those enclosures must be listed for the class and division or zone by a third party. NEMA4 Enclosure does not offer hazardous-location enclosures.
Where none of these applies, a manufacturer-rated enclosure is a legitimate choice, and the person who approves the installation still decides. Show the inspector the rating, the drawings and the intended use early.
What "not UL listed" means when you buy from us
NEMA4 Enclosure wall-mount enclosures in 304 and 316L stainless are manufacturer-rated NEMA 4X-type / IP66 - not UL listed. HMI enclosures have an IP65-type front seal with the display installed, also manufacturer rated. In practice that means:
- The enclosure carries no UL or CSA mark, and no third party inspects our production.
- The rating describes the design: the enclosure as delivered, door closed and latched, with every opening closed by a fitting of at least the same rating.
- Approval of the installation remains with your AHJ, your panel shop or your specification. Check with them before you order.
- Every product page has reference CAD and a PDF drawing, and custom work starts with a drawing for your approval, so you have something concrete to show.
If your project needs a listed enclosure, buy one. That is the honest answer, and it saves everyone a failed inspection.
Our ratings. All NEMA4 Enclosure ratings are manufacturer ratings. Custom enclosures are offered as NEMA types 1, 3R, 4, 4X, 6P, 12 or 13, manufacturer-rated for the specified design; hazardous-location types 7, 8, 9 and 10 are never offered. NEMA does not test, certify or endorse enclosures.
Frequently asked questions
What is the difference between NEMA 250 and UL 50E?
NEMA 250 is used by manufacturers to self-declare an enclosure type. UL 50E, published with CSA as C22.2 No. 94.2, is used by UL and CSA to evaluate and list enclosures to the same type numbers. NEMA 250 also covers hazardous-location Types 7 and 9 and the IP conversion table; UL 50E covers neither.
Does NEMA certify enclosures?
No. NEMA writes the standard but neither tests products nor certifies them. A manufacturer either self-declares the type or has the enclosure listed by a certification body such as UL or CSA.
Does the NEC require a listed enclosure?
The NEC requires equipment to be approved, which means acceptable to the authority having jurisdiction. Listing is the usual evidence but not the only one; the AHJ decides, so ask before you order.
Can a manufacturer-rated enclosure be used in a UL 508A panel?
Ask your panel shop before you buy. The listing covers the whole enclosed panel, and the shop's program decides which enclosures it may use. UL advises inspectors to treat a listed enclosure fitted with components it was not listed with as unlisted equipment.
What is a field evaluation?
A one-time evaluation of unlisted equipment at a particular site by a qualified third-party field evaluation body, following NFPA 790 and NFPA 791. Equipment that passes receives that body's field evaluation label.
Sources
- NEMA, "NEMA FAQs: Enclosures" (Q5 self-certification and CB listing, Q7-Q8 labels and trademark, Q18 NEMA 250 vs UL 50E / CSA C22.2 No. 94.2, Q19 NEC 110.28)
- nVent HOFFMAN, Spec-00486, Standards organization summary (UL 50 Type 1 vs UL 50E; UL/CSA lab testing and factory inspections; sheet metal gauge in UL 50)
- OSHA 29 CFR 1910.399, definitions (acceptable, approved, listed, labeled, certified; custom-made equipment)
- OSHA 29 CFR 1910.303 (a) approval and (b)(2) installation per listing instructions
- IAEI Magazine, "The Inspector's Approval" (approved, AHJ, 90.7, field evaluation)
- EC&M, "Understanding General Requirements of the NEC, Part 16" (2026): NEC 110.28 and Table 110.28
- UL, "Understanding Industrial Control Panels" (2017): enclosed, open and enclosure-only listings; field evaluation to UL 508A; NEC 409.110 markings
- UL, Industrial Control Panel FAQs (what the listing mark covers)
- TÜV Rheinland test report CN25IYGM 001 to NEMA 250-2020 (a test report does not entitle a safety mark)
- IAEI Magazine, "Field Evaluations and the Development History for NFPA 790 and NFPA 791" (2014)
- NFPA 791, Recommended Practice and Procedures for Unlabeled Electrical Equipment Evaluation (standard page)
- UL / ULC, "Acceptance of Electrical Equipment in Canadian Provincial and Territorial Jurisdictions" (CEC Rule 2-024, SCC accreditation)
- ANSI webstore, UL 50E, Enclosures for Electrical Equipment, Environmental Considerations