VFD Enclosure Ratings Explained: IP vs. NEMA
Variable frequency drives, like all electrical equipment, should be kept cool, clean, and dry. We get calls every day from end users, contractors, and engineers who understand this concept but get lost in the jungle of enclosure ratings that exist.
Not only do you have multiple systems like NEMA, IP, and UL types, but you also have a rating system that is often based on conditions that are tough to draw a realistic parallel to. Some ratings give a gallon per minute (GPM) or nozzle size in their ratings, but how does that help someone just trying to figure out which is the best VFD enclosure?
Rather than go through every possible rating and testing method, we’re going to cover the VFD enclosure ratings you’re most likely to see on the VFDs you’re looking at. We’ll explain the basic differences between the rating systems and then break down the protection you’re looking for based on indoor, outdoor, and special environments. We’ll also include a VFD enclosure ratings quick reference chart for help at a glance.
What’s the difference between IP, NEMA, and UL?
For many specifications, the battle of IP vs. NEMA ratings for VFDs will always continue, so it’s good to know how to work with both. There are some geographic differences between the different rating systems – IP tends to be European, and NEMA/UL tend to be used in North America. Some have drawn a comparison between metric and imperial systems. Even with these generalizations, you’ll often see IP ratings used throughout North America, especially as overseas manufacturing and importing becomes more common.
IP stands for “Ingress Protection,” which is a standard issued by the IEC. It uses a linear system with two digits. The first digit tells you the protection level against solid objects like fingers, wires, and dust. The second digit tells you the protection level against liquid. The higher the number, the higher the protection.
NEMA is the National Electrical Manufacturers Association. Their system of enclosure ratings is not linear – NEMA 12 is more protective than NEMA 1, but less than NEMA 4. For this system you have to memorize how protective each designation is.
NEMA enclosure ratings are a self-certification from the manufacturer that they meet the required specifications. UL types are similar to NEMA, but they must be third-party certified by the Underwriters Laboratories, also known as UL. Because of this, we’ll only discuss IP and NEMA ratings for the rest of this article.
Is it easy to convert between IP and NEMA ratings?
If a VFD gives an IP rating but a job specifies a NEMA rating, is it easy to convert between the two systems? For general use, it’s easy to make a general comparison, but the more details you dig into the more complex it becomes.
For example, IP gives water flow ratings in mm, liters per minute, and kPa, where NEMA measures in inches, gallons per minute, and psi. Although you can convert between them, it’s tough to determine how much the variation matters.
Does it matter if one measures at 10 liters per minute where one measures at 2.5 gallons per minute? Although close, these aren’t exactly the same.
We’ll draw some general comparisons throughout the rest of this article, but if the fine details matter for your situation, you’ll need to get the actual test requirements and speak to the manufacturer to verify if it works in your situation.
What’s the best VFD enclosure for indoor use?
When you’re talking about indoor enclosures, the general assumption is that there’s a fairly clean environment that VFDs are being installed in. If the VFD will be sprayed or has a heavy amount of airborne contamination, then you should be looking at an outdoor enclosure.
There are three main conditions that you’ll want to account for on indoor applications: no protection, finger safe, and dust-tight.
No protection
No protection is something we often advise against. This means that not only is the drive not protected from conditions, but there’s no protection against members of your team accidentally touching live electrical connections.
In the IP system, this is known as IP00. There’s not a NEMA rating for this condition but look for terminology like “open chassis” or “open frame.”
There are certain cases where this is appropriate. You may buy a VFD chassis that has no protection because you’re planning to integrate it into a panel or MCC before use.
We often get requests for this level of protection for drives being installed in an electrical room with restricted access. Although this is better than being installed somewhere with open access, we still don’t recommend this practice. Accidents happen everywhere, and it’s better to be protected from accidental contact by making the drives at least finger safe.
Finger safe
Finger safe is one of the rare terms that means what you would expect. The electrical components of the drive are protected from accidental contact that could pose a risk. This is commonly an IP20 or IP21 rating, comparable to a NEMA 1 rating.
It’s possible to achieve this rating with just the VFD chassis. If there’s some sort of protection guarding the electrical connections, such as the standard enclosure or a conduit adapter.
You can also achieve this by placing an unprotected chassis into a NEMA 1 enclosure. Our recommendation is to always to enclose a VFD. Although this may not technically increase the protection level in all situations, it increases arc flash protection to have a steel box between your team and any potential hazards.
Dust-tight
Dust-tight enclosures will include gasketing around openings and filters on all air intakes and outlets. This leads you to a NEMA 12 rating, which is similar to an IP52.
If it’s just some gasketing and filtration, why doesn’t everyone do NEMA 12 instead of NEMA 1? Aside from the extra cost for those parts, the main reason to look at NEMA 1 is airflow. When you restrict the airflow in and out of a panel, you don’t dissipate heat as quickly. This means you may need to increase the size of the enclosure, the VFD chassis, or the fans and cooling system, adding more cost and space.
Thinking outside the rating
Rather than get stuck on whether something technically meets a standard for a dust-tight enclosure, you can often work with a trusted VFD advisor to be creative about how to protect your VFD. The MDI FF1 line, or fan forced line, is a good example of this.
Although this is rated as NEMA 1, there are several features that can help this be equivalent to a NEMA 12. The air intake of these drives is filtered, but the output is not. By sizing the fans appropriately, you can keep a positive pressure inside the panel, keeping air flowing through the outlets and preventing dust from coming back in. It’s a great option for many standard indoor environments but may not be up to the dustiest of conditions.
This series also often mounts the heat sink of the VFD on the outside of the VFD, called “flange mounting.” This means that heat dissipation is happening outside of the panel and doesn’t need to be handled within the enclosure. Combining factors like flange mounting and fan forced positive pressure, you can gain more protection without increasing heat dissipation needs by moving to NEMA 12.
What VFD enclosure is best for outdoor use?
Although dust is a concern for outdoor environments, the biggest concern is typically water, with the biggest differentiator being whether it’s protecting against rain or watertight.
Rain protection
When you’re looking at an outdoor environment, protecting from rain is one of the key factors. A NEMA 3R, similar to an IP24, protects from downward falling water. This is typically rated based on the degree from vertical that the water is falling.
This means intakes and outlets may not be filtered for dust protection, but they will be covered by a shroud or go through multiple 90° turns to keep water from entering. Doors will also be gasketed to prevent water from leaking through.
Watertight
Watertight enclosures are not submersible but are protected against sprays of water from all directions. This is good for situations where nearby equipment often sprays water or is sprayed down to be cleaned. This is a NEMA 4 or IP66 rating.
Similar to a dust-tight enclosure, when you enclose a VFD to be watertight it becomes more difficult to dissipate heat. You also usually lose the option to flange mount the VFDs. Because of this, watertight enclosures often have to be oversized or have some sort of air conditioning to dissipate heat. This increases heat and space, which is why many will stick with a dust-tight or rain-protected enclosure unless absolutely necessary.
Unusual environments
There are many other combinations of NEMA and IP ratings, but only a few are common enough to call out when it relates to VFDs. Let’s look at corrosive environments and combined ratings.
Corrosion protection
Protection against corrosive materials is not factored into the IP ratings. NEMA factors this in with an “X” rating, most commonly the NEMA 4X. This means that it has the same protection as a NEMA 4 watertight enclosure but is made from a corrosion-resistant material such as stainless steel.
Combined ratings
Occasionally you’ll see a rating like NEMA 3R/12 or NEMA 4/12. Combined ratings mean that it fulfills the requirements of both ratings. For example, a NEMA 3R/12 fulfills the rain protection requirements of a NEMA 3R but also has filtered air intakes/outlets to fulfill the requirements of a NEMA 12. This particular rating would be similar to an IP54.
But which enclosure rating does my system need?
There are plenty of factors we didn’t talk about. What if your facility has explosive gases or conductive filaments in the air? What if it needs to be submerged? There are plenty of fringe cases that are worth talking to your trusted VFD advisor about.
For most of the cases you’ll encounter, you’ll use one of the ratings we discussed. These ratings are summarized in the VFD Enclosure Quick Reference Table graphic for an at-a-glance answer.
Getting this right is vital to the life of your VFD and the safety of your team. VFDs need to be enclosed from all the potential hazards but not over-engineered to get the right balance of protection and cost. Talk to a VFD specialist today who can help you choose the right enclosure for your environment.