NEMA Rating? Seismic Rating? What Does it All Mean?

BY: Shane Weaver

The difference in usage for NEMA rated and seismic rated enclosures

So you need to set up a server room or electrical enclosure. But you don't want just any enclosure. Your enclosure needs to be resistant to dust, or dirt, or salt, or water…or maybe all of the above. And what if you're in an area that's prone to earthquakes? How do you know your rack can stand up to environmental hazards?

You've probably heard of NEMA ratings and seismic ratings, but maybe you're not completely clear on what those are, or how they work together. Let's see if we can't clear the air a little bit and help you understand how to rate your rack.



First, let's talk NEMA. Despite what your child might tell you, NEMA is not a wayward clownfish trying to find its way back home, but is actually the National Electrical Manufacturers Association. NEMA is an organization founded in 1926 that currently has about 450 members companies, all of them manufacturers of electrical or medical imaging equipment.

Contrary to what many people may think, NEMA isn't actually a testing or rating agency like, say, UL, ETL or any of the other National Recognized Testing Laboratories (NRTL). NEMA instead publishes standards and guides for equipment, and its member manufacturers produce equipment, like enclosures, that meet those standards. Member manufacturers can self-verify their products, or they can choose to have them certified by a valid third party testing agency, such as an NRTL.

NEMA certification is voluntary, so not all products from a given manufacturer may meet NEMA standards. However, there is often a need in particular applications to have equipment that is certified to handle certain environmental challenges, and in such cases a NEMA rated product may be necessary. Steel and cement mills, mines, quarries, subway tunnels, shipyard docks, construction sites…these are all places that might benefit from an environmentally rated NEMA enclosure.

The NEMA rated enclosures offered by

NEMA Enclosure Ratings & What They Mean

NEMA rated enclosures are given a numerical rating of 1-13. It is not progressive, meaning higher numbered ratings don't necessary possess all the benefits of the numbers below it. Rather, each number is designated to be resistant to a certain array of environmental hazards. There are variations within some of the ratings denoted by letter (S, R, X, etc.) that indicate a specific level of additional resistance, or lack thereof.

Here's a brief list of NEMA enclosure ratings and what they mean:

  1. Dust, light, and splash resistant; however, not completely dust-tight or waterproof. Prevents contact with live parts. Typically used in general purpose settings in “normal” conditions
  2. Drip tight. For areas where heavy condensation may be an issue. Similar to NEMA-1 but with added drip shielding
  3. Weather resistant. For outdoor use. Protects components from dirt, windblown dust, rain, snow, sleet, and ice
    • 3R - lacks windblown dust protection
    • 3S - can operate while covered in ice
    • 3X (RX, SX) - additional corrosion protection (commonly used near salt water)
  4. Watertight. For use in areas near large bodies of water or large quantities of liquid
    • 4X - offers addition corrosion protection
  5. Dustproof. Features gaskets to ensure dust cannot penetrate
  6. Able to be submerged (temporarily) in water or oil
    • 6P - able to be submerged for prolonged periods on occasion (not intended to be permanently submerged)
  7. Certified for use in hazardous indoor areas designated in NFPA standards as Class I, Group A (Acetylene), Group B (Hydrogen), Group C (Propane and Ethylene) and Group D (Benzene, Butane, Methane, Propane)
  8. Certified for the same areas as NEMA 7, but also outdoor use
  9. Certified for use in hazardous indoor/outdoor areas designated in NFPA standards as Class II, Group E (Metal Dust), Group F (Carbon and Charcoal), Group G (Flour, Starch, Wood, Plastic)
  10. Meets requirements of the Mine Safety & Health Administration (MSHA)
  11. Protects against corrosive liquids and gases (general purpose use)
  12. Protects against some dust, dirt, lint, fibers and liquids (dripping and light splashing). Intended for indoor general purpose usage. Construction does not include knockouts.
    • 12K - Same protection as NEMA 12, but knockouts are permitted
  13. Similar protection to NEMA 12, but also provides some protection against splashing, spraying and dripping of oil and other (non-corrosive) coolants


To get a more in depth idea of what exactly is and isn't covered in each NEMA rating, check out NEMA's list of enclosure types:
Here are a few of the NEMA rated enclosures offered by


A map of the seismic zones of the United States

Seismic Enclosures

People sometimes conflate NEMA ratings and seismic ratings, but they're not actually the same. As discussed, NEMA ratings apply to (a) protecting people from possibly harmful components within an enclosure, and (b) protecting the components from various environmental hazards. Seismic rated enclosures, as the name implies, are meant to be used in areas with heavy vibration. This includes areas prone to earthquakes, but also extends to any area that might experience a whole lot of shakin' goin' on: areas near railroad tracks, power plants, airports, and tornado prone areas can all benefit from seismic enclosures. There's also a national security aspect: an area that could potentially serve as a target for an attack would want to ensure that sensitive equipment is protected.

While anyone can use a seismic enclosure if they desire the added vibration resistance, whether or not it's required for a particular area, it boils down to an area being considered essential or non-essential. There are certain areas that need to remain functional in the event of an earthquake to serve the population in an emergency situation (think hospitals, data centers, fire stations, government agencies) and areas where it's less important (businesses, schools, homes, etc.). If you're working with an “essential” operation, or one that guarantees 100% server uptime but is located in a particularly sensitive area, a seismic enclosure is one you may want to strongly consider. There are other options – you could outsource your data to a Cloud service that guarantees 100% uptime, for example. However, in such cases your data may be less secure than if it were housed on-site. So you'll need to weigh your options and determine what is best for you.

Different types of seismic racks and enclosures

Seismic Requirements

When selecting a seismic enclosure, there are certain features to keep in mind:

  • Heavy duty doors – rather than a single latch point (typically of non-seismic enclosures), an earthquake ready unit needs a minimum of three extra latches, plus high quality hinges that can endure the flexing and twisting of a seismic event.
  • Full welding – this provides an especially rigid structure. Welded equipment mounts can further reinforce a frame's strength.
  • Mounting hardware – locking nuts and washers can help add extra strength to shelves, drawers and other rack-mounted components.

As with NEMA ratings, there are standards for seismic enclosures. But while NEMA ratings are determined by what substances and situations they provide protection against, seismic ratings are determined based on the areas most prone to earthquakes. There are 4 zones, with Zone 1 being the least threatened by seismic activity, and Zone 4 being the most threatened (ie. areas near an active fault line). Telcordia Technologies determines these zones and issues the standards that seismic enclosures must meet.

The Telcordia GR-63 CORE Seismic Standard is the rating you're looking for. To receive this rating, an enclosure needs to have been put through a simulated seismic event without frame damage or dislodging of components. Beware of so-called "seismic-certified" enclosures that are said to meet International or Uniform Building Code (IBC & UBC) standards. Typically these ratings are the result of calculations based on the cabinet's individual components, and not the stringent tests that Telcordia standards require.

So when you have a need for an electronic enclosure in a sensitive area that's susceptible to hazardous conditions, be they salt water, earthquake, chemicals, dust, dirt or what-have-you, hopefully you have a better understanding of what type of enclosure rating you should be looking for to make sure it's up to the task of protecting the components within.

If you need any help, we're always available to assist you in finding the right solution. Give us a call and we'll be sure you get the right enclosure for your application. So, when in doubt, remember that we're here to answer any questions you might have. If you have specific questions about NEMA ratings or protective enclosures, you can email us at


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