NEMA enclosure ratings chart

NEMA enclosure types at a glance

NEMA defines the types in its standard NEMA 250, Enclosures for Electrical Equipment. Each type names the conditions the enclosure is built and tested to withstand, not a size. A higher number does not include the tests of a lower one. Types 3, 4 and 6 are rated for outdoor use, for example, while Type 5 is indoor only.

Summarized from the NEMA type definitions as published by Wikipedia (from NEMA EN P1 2021), Siemon and Newark. NEMA 250 is the governing text.

Protection matrix for indoor and outdoor types

Distributors publish the NEMA 250 comparison as a grid. These two tables follow the grid Newark publishes. A Yes means the type provides a degree of protection against that condition.

The X versions of Types 3, 3R and 3S (3X, 3RX, 3SX) add corrosive agents to the same column.

Indoor types compared

Indoors the choice is usually between Type 1 for a clean electrical room, Type 12 for a factory floor with dust and drips, and Type 4 or 4X where the area is washed down.

NEMA to IP, and why the charts disagree

An IP code from IEC 60529 rates only the ingress of solids (the first digit) and water (the second digit). NEMA types also involve tests that IP does not cover, such as corrosion, icing and gasket aging. So a NEMA type can be converted to an approximate IP code, but an IP code cannot be converted back to a NEMA type. An IP66 box is not automatically a NEMA 4X box.

Published conversion charts do not even agree with each other. The table below shows what three widely cited charts give for each type. Where they differ, treat the lower code as the safe reading and ask the enclosure maker for the tested rating.

The three charts agree on Types 1, 6, 6P and 13. They split on 3R, 4, 4X and 12. All three say the conversion works in one direction only.

3R vs 4 vs 4X for outdoor equipment

Type 3R is the usual outdoor rating for disconnects, meter equipment and many outdoor drives and chargers. It keeps out rain, sleet and snow and drains water, but it does not claim protection against windblown dust or hose directed water.

Type 4 adds windblown dust and hose directed water. Wikipedia, summarizing the NEMA definition, describes the hose test as at least 65 gallons a minute from a 1 inch nozzle at not less than 10 feet for 5 minutes. Choose it where equipment is washed down or sits in blowing dust.

Type 4X is Type 4 plus corrosion resistance, so it is the pick near salt water, at wastewater plants, in food plants and in chemical areas. 4X boxes are usually stainless steel or a polymer. A sealed 4X box also holds heat in, so drives and other heat producing gear inside may need a heat exchanger or air conditioner.

How to choose an enclosure type

Start from the worst condition the box will actually see, not from the voltage or the brand.

• Clean indoor electrical room, Type 1.
• Indoor factory floor with dust, lint and dripping liquids, Type 12.
• Indoor machine tool area with sprayed oil or coolant, Type 13.
• Outdoors in rain and snow, Type 3R.
• Outdoors with blowing dust or ice on the operating handle, Type 3 or 3S.
• Hose down, indoors or out, Type 4.
• Hose down plus salt air or chemicals, Type 4X.
• Occasional or prolonged submersion, such as a vault or manhole, Type 6 or 6P.
• Classified hazardous locations, Types 7, 8 or 9, as the area classification requires.

Enclosures around a transformer installation

Most of the gear around an outdoor pad mounted transformer, such as the service disconnect, the meter enclosure and the switchboard, is specified by NEMA type, and 3R is the common floor for outdoor gear. The pad mounted transformer cabinet is a different case. Above grade pad mounted enclosures over 600 V that the public can reach are covered by IEEE C57.12.28, now in its 2023 edition, which sets an integrity system meant to keep unauthorized people away from live parts and to give a long field life with little maintenance, including coating and corrosion tests. So specify the transformer by that standard and the gear around it by NEMA type.

When you send us a spec for a pad mount or the switchgear next to it, include the enclosure ratings you need and whether the site is coastal or a washdown area. That changes the tank material and the enclosure on what we quote.

What does NEMA 4X mean

NEMA 4X is a Type 4 enclosure with added corrosion resistance. It protects against rain, sleet, snow, windblown dust, splashing water and hose directed water, and it resists corrosion, which is why it is used in washdown, coastal and chemical areas.

What is the difference between NEMA 4 and 4X

Both handle windblown dust and hose directed water. The X adds corrosion resistance. In practice 4X enclosures are usually stainless steel or a polymer, while Type 4 enclosures are often painted steel.

What does NEMA 3R mean

NEMA 3R is an enclosure for indoor or outdoor use that protects against falling dirt, rain, sleet and snow and is undamaged by ice forming on it. Unlike Type 3, it does not claim protection against windblown dust.

What is the difference between NEMA 3R and NEMA 4

3R covers rain, sleet and snow. Type 4 adds windblown dust, splashing water and hose directed water. If the equipment will be hosed down or sits in blowing dust, 3R is not enough.

Is NEMA 12 suitable for outdoor use

No. NEMA 12 is an indoor type for circulating dust, falling dirt and dripping noncorrosive liquids. Outdoors, use Type 3R or better.

What IP rating is NEMA 4X

Two of the three charts we compared give IP66 for NEMA 4 and 4X, and Engineering ToolBox gives IP56. All of them say the match runs one way, so a NEMA 4X box meets the IP rating but an IP66 box is not automatically NEMA 4X.

Can I convert an IP rating to a NEMA type

Not reliably. NEMA types include corrosion, icing and gasket aging tests that the IP code does not, so an IP number alone does not show those tests were passed.