NEMA enclosures are used in industrial applications to house and protect variable frequency drives and other electrical equipment. Each enclosure has its own rating to designate the type of application for which that particular enclosure was built for; NEMA 3R and NEMA 4X were built for and are most commonly used for outdoor installations. Having an understanding of each enclosure is important when choosing which one is best for your particular application.
NEMA 3R enclosures are generally used for applications such as rooftop air handling units, irrigation pumps, and water/waste-water pumps. They are made from carbon-steel and equipped with white-powder coated paint and fans for temperature regulation. The fans include filters to keep dust, dirt, and insects from entering the enclosure. NEMA 3R enclosures are versatile in the fact that a viewing window can be installed for internal component viewing, and they can be wall-mounted in environments with potential flooding issues. Installation is rather simple and costs are lower than the alternative, but the enclosures are not protected in corrosive environments.
The alternative, NEMA 4X enclosures, are more expensive due to the addition of an air conditioner in place of the fans. However, there are some significant advantages to using the more costly enclosure. NEMA 4X enclosures are stainless steel creating a corrosive-free enclosure, they are equipped with an air conditioner in lieu of fans for better temperature control, and they are the preferred alternative when NEMA 3R cannot be used. Like NEMA 3R enclosures, they can be wall-mounted and a viewing window can be installed, but installation of the enclosure is more complex. The biggest disadvantage of the NEMA 4X enclosure is its high cost; the larger the enclosure the higher the cost, and operation and maintenance can get pricey as well.
Overall, it is crucial to understand the differences between the enclosures to make an informed decision and save money in the long run. For more detailed information on the features of both NEMA enclosures, check out this article from HPAC Engineering Magazine.