With industrial computers it is important to understand in what conditions the machines can be used in and what elements they offer protection against.
However, unlike the European system designated under the IEC the NEMA rating uses a single digit code to signify the protection the enclosure will offer. The code not only signifies how much protection is offered against foreign bodies (such as dust and dirt) and liquids but also designates whether the enclosure can operate outdoors or indoors (or indeed both).
It should be noted however that the numerical size of the number does not signify the greater resistance to penetration from foreign bodies and water unlike the European IP rating in which the higher the number the greater the protection.
To understand the NEMA system it is best to take a look at a few examples. NEMA 4 is perhaps the most widely used NEMA code. NEMA 4 enclosures can be found in all sorts of industrial settings this is because the NEMA 4 code suggests the enclosure: “is constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, and hose-directed water; and that will be undamaged by the external formation of ice on the enclosure.”
Now if you contrast the NEMA 4 enclosure with NEMA 5 that offers: “computer enclosure constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against settling airborne dust, lint and fibres; and to provide a degree of protection against dripping and light splashing of liquids.” It can be seen that NEMA 4 offers better protection against water and can be used outdoor which is why NEMA 4 enclosure are more often found in industrial applications.