Enclosure Ratings: UL Type vs. NEMA – What’s the Difference?

Sensitive electrical and electronic equipment often operates in environments where dust, dirt, chemicals, gas, moisture, and other fluids are present. These conditions can negatively impact the performance and longevity of electrical equipment. To combat this, electrical enclosures are used to protect the equipment. Given the wide range of potential contaminants, different enclosures are designed to offer varying levels of protection.



For variable frequency drives (VFDs), the most commonly used enclosure ratings are NEMA 1, 12, 3R, 4, and 4X. Each rating provides a specific degree of protection. But how is this level of protection defined, and who ensures that enclosures meet these standards?



In North America, the National Electrical Manufacturers Association (NEMA) and Underwriters Laboratories (UL) are the two primary agencies that set these standards. They define the design, contaminant protection, and testing procedures for enclosures to ensure compliance with their respective ratings.



The key difference between NEMA and UL rated enclosures lies in the testing and compliance process:

  • NEMA Rated Enclosures: These are self-certified by the manufacturer. NEMA ratings do not require third-party testing or verification by an accredited organization. For instance, a manufacturer can self-certify an enclosure as NEMA 12 by applying a gasket to protect against dust, dirt, and splashing water.
  • UL Rated Enclosures: These must undergo rigorous testing and a compliance process conducted by a UL accredited test facility. To achieve a UL Type 12 certification, an enclosure must withstand pressurized water spray and exposure to blown concrete dust for a specified duration.


Butcher Power Products recommends using our UL type rated enclosures for VFDs due to the extensive testing and additional peace of mind they provide. Ensuring that VFDs remain clean and dry is crucial for their long lifespan, and UL type rated enclosures are a reliable choice to meet these needs.