Terms like “waterproof,” “sealed,” “dust tight” and the like are used to describe electrical and electronic enclosures. Unfortunately, these terms are inherently ambiguous. Is the enclosure merely rain-proof or is it fully submersible? Is it sealed so that no air will transfer, or is it sealed against intrusion by objects?
To clarify this situation with a clear set of standards, The National Electrical Manufacturer’s Association www.nema.org developed NEMA ratings. The ratings make it easy to specify enclosures with the right level of protection, however they can also be confusing. For example, NEMA 4 offers more stringent protection than NEMA 12. Many times engineers specify the wrong level of protection, either overspending or risking equipment damage. This guide will help you select the just-right NEMA rating for your application, like Goldilocks: neither too much nor too little.
NEMA 1: For indoor use. Protects users against contact with hazardous components and protects the components from the ingress of solid objects, such as fingers and falling dirt.
NEMA 2: For indoor use. Same as NEMA 1 but adds protection against the ingress of dipping and light splashing water.
NEMA 3: For indoor or outdoor use. Same as NEMA 2 but adds stronger protection against the ingress of water and dust. It protects against windblown dust, rain, sleet, and snow and will be undamaged by ice forming on the enclosure.
NEMA 3R: Same as NEMA 3 but without the protection against windblown dust. The standard doesn’t say this, but typically the difference is that there is no gasketing on NEMA 3R enclosures.
NEMA 3S: Same as NEMA 3 but adds the provision that external mechanism remain operable when ice laden.
NEMA 3X, NEMA 3RX, NEMA 3SX: the X signifies the addition of corrosion protection.
NEMA 4: Same as NEMA 3 but adds protection against hose directed water.
NEMA 4X: Same as NEMA 4 but adds protection against corrosion.
NEMA 6: For indoor or outdoor use. Protects against the ingress of objects, fingers, and falling dirt, hose directed water and is undamaged by ice formation. What’s more, it protects against occasional temporary submersion to a limited depth.
NEMA 6P: Same as NEMA 6 but adds protection of prolonged submersion to a limited depth and adds corrosion protection.
NEMA 12: Protects against the ingress of objects, fingers, falling dirt, settling dust and drips. It is similar to NEMA 3 but it is for indoor use, so instead of protecting against windblown dust it protects against settling airborne dust, lint, fibers, and flyings. It won’t protect against rain, sleet, and snow, but it does protect against seeping oil and coolant as well as dripping and light splashing water. Despite the large number it is a basic level of protection. It may be helpful to think of it as NEMA 1.2 rather than NEMA 12.
NEMA 13: Same as NEMA 12 but adds protection against oil and coolant splashing and spraying.
This guide is for non-hazardous locations. NEMA 7, 8, 9 and 10 are the ones to look at for hazardous environments.