Nema Cabinet Ratings: Protecting a VFD from environmental conditions

Nema cabinet ratings are designed to protect electrical components from environment-specific threatening conditions. Nema cabinet ratings are made for a range of different environmental conditions. There are as many Nema cabinet ratings available as there are environmental conditions where equipment is installed.

VFD manufacturers will usually offer variable frequency drive (VFD) products in several different Nema cabinet ratings to cover a broad range of customer needs. Its important to choose the right Nema cabinet ratings for your VFD because:A.) you dont want your VFD to fail because then your operation is down / production is disrupted; and, B.) VFD warranty is often voided due to choosing the incorrect Nema cabinet ratings of VFD.

While there are a variety of Nema cabinet ratings available, the Type 1, 12, 3R, 3RX, 4, and 4X are specifically used in the Food and Beverage industry and HVAC industry. Of those Nema cabinet ratings, the Type 1, 12, and 3R options are used in over 95% of VFD installations. Type 3RX, 4, and 4X enclosures are available for unusually harsh and dusty environments. Whenever practically possible, mount the VFD in a stable environment, such as a mechanical room. Otherwise, make sure the Nema ratings for your VFD are susceptible to the environmental conditions of installation site.

UL Type 1 VFDs

  • Indoor locations only
  • Minimal dirt/dust in the air
  • No exposure to water spray or drips
  • Most common HVAC VFD enclosure

UL Type 12 VFDs

  • Indoor locations only
  • Dirty/dusty environment
  • Possibility to be splashed with water

UL Type 3R VFDs

  • Outdoor location
  • Minimal salt/corrosives in the air
  • Maximum ambient temperature 122F

UL Type 4 VFDs1

  • Indoor or outdoor locations2
  • Requirement to wash-down the VFD
  • Combination of dusty environment with
  • heavy moisture (fog)
  • Properly sized units may operate >122F

UL Type 4X VFDs1

  • Indoor or outdoor locations2
  • Requirement to wash-down the VFD
  • Significant salt/corrosives in the air
  • Properly sized units may operate >122F

UL Type 3RX VFDs

  • Identical to Type 3R except with stainless steel box
  • A degree of salt/corrosives in the air
  • enclosure appearance is important

When buying a VFD, make sure the VFD Nema cabinet ratings are susceptible to withstand the environmental conditions of installation site. If youre unsure which Nema cabinet best fits your application, contact Precision Electric with your application specifications; Precision Electric will provide you with a VFD quote that will meet your enclosure specifications. Call Precision Electricat 574-256-1000 for VFD repair, VFD replacement, or complex VFD project quotes.


Credit refs: most of the information in this articlewas originally published by ABB: LV drives division.

Some information was obtained from the ABB download center.Precision Electric is a certified ABB LV Drives

distributor and ABB Certified Startup Center. Certified Startup improves ABB Factory Warranties on LV Drives.

Additional information can be found at