If you’ve ever walked through an oil and gas processing plant, a chemical manufacturing facility, or a grain handling warehouse, you’ve likely spotted a variable frequency drive (VFD) tucked beside a motor, quietly adjusting speed and cutting energy use. For decades, VFDs have been the workhorses of industrial efficiency, helping facilities reduce electricity bills by 20-50% compared to fixed-speed motor operation. But one question I get asked constantly—especially from maintenance managers and plant safety officers—is this: Can a VFD actually be used in a hazardous environment? VFD
As a VFD supplier who’s worked with these environments for more than 12 years, I’ve seen both the risks of using standard VFDs where they don’t belong, and the game-changing value of properly rated VFDs built for hazardous locations. Let’s break this down, no confusing jargon, just real-world experience and facts that will actually help you make the right call for your facility.
First, let’s define what a “hazardous environment” actually is, because not every workplace that’s “dusty” or “smelly” qualifies. The National Electrical Code (NEC), which we follow closely here in North America, classifies hazardous locations (or “classified areas”) based on three key factors: the type of material present, how likely that material is to be in the air in dangerous amounts, and how easily it ignites.
There are three classes, right? Class I is for flammable gases or vapors—think propane stations, paint booths, or areas near natural gas pipelines. Class II is for combustible dust, like flour mills, woodworking shops, or grain silos. Class III is for ignitable fibers or flyings, which would be things like cotton mills or textile plants. Each class is then split into divisions or zones (depending on if you follow NEC or the International Electrotechnical Commission (IEC) standards, which are used globally) that describe how often the hazardous material is present.
Now, why would a regular VFD be a problem here? Standard VFDs operate by switching DC power on and off rapidly to create AC power at different frequencies, which is how they adjust motor speed. That rapid switching produces two big things: heat, and electrical arcs. Arcs might sound small, but even a tiny spark can ignite a flammable gas, dust, or fiber if the concentration is right. Standard VFDs aren’t sealed to keep those sparks inside, and they run hotter than many industrial devices, which is a recipe for disaster in a classified area.
I remember a call I got back in 2018 from a grain plant in Iowa that tried to save money by using a cheap, off-the-shelf VFD on their main conveyor motor in a Class II, Division 1 area—meaning combustible grain dust is almost always present in the air. They skipped the extra cost for a hazardous location-rated VFD, thinking it was just a conveyor, nothing that could actually explode. A week later, the VFD overheated, the plastic casing warped, and an internal arc sparked a dust cloud that damaged a section of their processing line. No one was hurt, but the downtime cost them over $400,000 in lost production, plus repairs. That’s when I really realized how much misinformation is out there about VFDs in hazardous environments.
So the good news is: yes, VFDs absolutely can be used in hazardous environments, but only if they’re built and rated specifically for that location. This isn’t a “one-size-fits-all” upgrade. A VFD rated for Class I, Division 1 isn’t the same as one for Class II, Zone 2. It has to match your exact classification, and it has to be installed correctly.
Let’s talk about what makes a VFD “hazardous location rated.” First, the enclosure. Standard VFDs use vented or open frames to keep them cool, but in a hazardous area, those vents are a no-go. Hazardous rated VFDs have completely sealed enclosures that prevent flammable materials from getting inside, where they could come into contact with arcs or hot components. They’re also pressure-tested to make sure they don’t crack under the heat or vibration of industrial use.
Next, internal components. Every part of the VFD—capacitors, transistors, circuit boards—has to be rated to not ignite the surrounding area. Manufacturers like us test every VFD to make sure that even if there’s an internal fault, the arc or heat won’t escape the enclosure. We also use what’s called “intrinsic safety” for some lower-power VFDs, which limits the amount of electrical energy in the device so that it can’t produce a spark hot enough to ignite flammable materials. For higher-power VFDs, we use “explosion proof” enclosures that are built to contain an internal explosion and prevent it from reaching the outside.
Then there’s the rating standard. This is critical, because not all certifications are the same. In North America, you look for NEC ratings: Class I, Division 1 or 2, Class II, Division 1 or 2. Globally, IECEx ratings are the standard, with zones like Zone 0, 1, or 2 for gases and dust. Zone 0 is the most dangerous, where flammable gas is present 24/7, and Zone 2 is the least, where gas is only present occasionally during maintenance. If you’re operating a plant in Europe, Asia, or any other part of the world outside North America, IECEx is non-negotiable—our VFDs are certified to both NEC and IECEx, so we can support facilities anywhere.
I also want to clear up a common myth: some people think that if they just install a VFD in a clean box, it’s safe for a hazardous area. That’s not enough. We’ve seen cases where a plant put a standard VFD in a generic stainless steel enclosure, but the enclosure wasn’t pressure-tested or certified for explosion containment. Last year, a chemical plant in Texas did that, and when the VFD’s internal fault created an arc, the enclosure cracked, and the gas outside ignited. That’s why certification isn’t just a marketing label—it’s a legal and safety requirement. Facilities that use unrated equipment in classified areas can face fines from OSHA (in the U.S.) or other regulatory bodies, and if there’s an incident, insurance won’t cover the damages.
Now, let’s talk about the real benefits of using a properly rated VFD in a hazardous environment, because it’s not just about safety—it’s about money. I mentioned earlier that standard VFDs cut energy use by 20-50%, but in a hazardous environment, where energy costs can be higher (you’re running high-power motors for conveyor systems, pumps, mixers, etc.), that savings is even bigger. A friend of mine who runs a chemical plant in Louisiana switched their fixed-speed pumps to hazardous location-rated VFDs two years ago. They used to run the pumps at full speed 24/7, even when the demand was low. Now, with VFDs, they adjust speed based on process needs, and their annual energy bill for that section of the plant dropped by 38%. That’s tens of thousands of dollars back in their pocket every year.
Another benefit: equipment longevity. Hazardous environments are tough—high heat, dust, moisture, vibration. VFDs adjust motor speed and reduce start-up current, which means less wear and tear on motors. We’ve had customers in grain silos tell us their motors now last 5-7 years instead of 2-3, because the VFD eliminates the stress of full-speed starts and stops. That’s less downtime, fewer replacements, and more safety—no one wants to be changing a motor in a grain silo during a scheduled maintenance outage.
But here’s the thing: you can’t just buy any hazardous location-rated VFD and install it yourself. Installation is almost as important as the VFD itself. For example, the wiring has to be rated for the same hazardous class, the grounding has to be done to exact specifications to prevent static electricity arcs, and the VFD has to be configured correctly for the motor it’s powering. We work with a lot of electrical contractors who say they’ll take on hazardous area installations, but many of them don’t have the specialized training for VFDs. That’s why we offer on-site support for our customers—our technicians are certified to install and commission hazardous location VFDs, so we make sure every step is done right.
I also recommend doing a full audit of your facility’s classified areas before choosing a VFD. A lot of plants think their entire facility is hazardous, but often only specific zones—like near a storage tank, or a conveyor that transfers flammable materials—are classified. If you put a Class I, Division 1 VFD in a Zone 2 area, you’re wasting money on over-rated equipment, and if you put a Zone 2 VFD in a Division 1 area, you’re taking a huge safety risk. We’ve saved customers thousands of dollars by auditing their areas and suggesting the exact VFD rating they need, no more, no less.
Let me circle back to that Iowa grain plant I mentioned earlier. After their incident, they reached out to us. We audited their facility, found that their conveyor zone was Class II, Division 1, and installed hazardous location-rated VFDs on all their main conveyors. A year later, they told us they’ve had zero issues, their energy bill is down 42%, and they’ve had no safety concerns. That’s the outcome we want for every customer.
If you’re reading this and you’re in a facility that operates in a hazardous environment, don’t make the same mistake that Iowa grain plant or the Texas chemical plant made. Don’t assume all VFDs are the same, and don’t skip the certification to save a few bucks. The safety of your team and the future of your operation depend on it.
If you have questions about whether a VFD is right for your classified area, or if you need help finding the right rated VFD for your motors, reach out to our team to discuss your specific needs. We’ll walk you through the classification process, the right certifications for your region, and the installation requirements to keep your facility safe and efficient.
Low Voltage Distribution Cabinet References
National Electrical Code (NEC) Article 500: Hazardous (Classified) Locations
International Electrotechnical Commission (IEC) Standard 60079: Explosive Atmospheres
Occupational Safety and Health Administration (OSHA) 29 CFR 1910.307: Electrical Equipment in Hazardous Locations
Industrial VFD Hazardous Area Applications: Safety and Performance Guidelines, IEEE Industry Applications Society, 2021
Nanjing Aubo Electric Co., Ltd.
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