I review VFD documentation, warranty claims, and field reports for a living—roughly 300 items a month as a quality compliance manager at an electrical equipment distributor. Over four years of that, one pattern keeps coming back: a customer calls in a panic because their Danfoss VFD is 'throwing alarms,' and when we pull the actual alarm list, it turns out the drive is behaving exactly as designed. The problem isn't the drive. The problem is that nobody read the right line of the alarm list.
Here's the thing: a Danfoss VFD alarm list is not an obituary for the drive. It's a triage system. It tells you whether the drive can keep running, whether it has stopped, or whether it's refusing to restart until someone investigates. Those three conditions cost very different amounts of money. In this article, I'm going to compare them directly, then compare the three ways you can read the alarm list (the panel, PC software, or the manual), and finally compare how the alarm lists across the FC 102, FC 202, and FC 302 series lineup. The goal isn't to memorize codes—it's to know which one is worth money in your pocket and which one is going to cost you.
Warnings vs. Trips vs. Lockouts: The Core Comparison
On a Danfoss VFD, alarm events come in three classes. They're displayed with different prefixes and behaviors, and they require different responses.
Warnings (W Codes): The Drive Is Still Running
A warning means conditions are drifting outside normal range, but the drive continues to operate. For example, a motor overtemperature warning often appears when the motor is running hotter than it should, but hasn't hit the trip threshold yet. The drive is telling you: something is going in the wrong direction, and you have time to act. That time is cheap. Cleaning a cooling fan, checking a sensor, or tightening a connection costs far less than replacing a motor.
Trips (A Codes): The Drive Has Stopped
A trip is an 'A' code, like A.1 Overcurrent, A.2 Overvoltage, A.4 Undervoltage, A.5 Overtemperature, or A.9 Motor Phase Loss. The drive has come to a stop and will not continue until the fault is cleared. Most trips can be reset from the local control panel. But here's where I see people lose money: a reset is not a diagnosis. If you clear the same trip three times without checking the cause, you're not fixing anything—you're just rolling dice with your process. The reset function is part of the drive's protection scheme. When we verify drives against IEC 61800-5-1, reset and restart behavior is part of the safety evaluation, and the drive is expected to stay down until the condition is acknowledged.
Lockouts: No Restart Until Someone Understands
Lockouts are the strictest class. The drive has invoked a protection that requires a deliberate manual reset—sometimes on the panel, sometimes by cycling power. Lockouts are intentionally inconvenient. That inconvenience is a design choice: it forces a human being to look at the fault before the machine moves again. A lockout is rare on modern Danfoss drives, but when it appears, it deserves your full attention.
So here's the side-by-side: a warning says 'watch me.' A trip says 'fix me.' A lockout says 'understand me.' The cost curve follows the same shape. Ignore a warning and you get a trip. Reset a trip without diagnosis and you get a repeat trip, a burned motor, or a damaged pump. The cheapest moment to act is always the first one—and the alarm list is what gives you that moment.
Reading the Alarm List: Panel vs. PC Software vs. Manual
The same alarm list can be read three ways, and this comparison surprises more than a few maintenance teams. I've watched a technician stand in front of a drive, scrolling through menus, while the production line waits behind him. There's a faster way.
Local Control Panel (LCP): Always There, Best for One or Two Drives
Every Danfoss VLT FC series drive ships with a local control panel. You can scroll to the alarm log and see the recent events, with time stamps, without any extra tools. For a single drive, or a quick visual check, this is the right tool. It's free, it's always on the door, and it doesn't require a laptop or a cable.
PC Software (VLT Motion Control Tool MCT 10): The Lower TCO for Multiple Drives
What most people don't realize is that MCT 10 is free. Connect it through the drive's USB port (standard on FC 100/300 series drives) or a fieldbus connection, and you can pull the full alarm log, view trend data, and compare what's changed over time. That trend data is where the real diagnosis happens. A panel will tell you 'A.5 Overtemperature' right now. A trend graph will tell you that the cooling fan started degrading last Tuesday. That's the difference between replacing a fan and replacing a drive.
We didn't used to have a formal process for downloading alarm logs during preventive maintenance visits. It cost us when a customer reported a 'sudden' A.5 trip—the trend data showed the drive's cooling had been deteriorating for weeks. The warning had been there, but nobody had pulled the log on the previous visit. Now it's step one on our checklist.
Manual or PDF: The Interpretation Layer
Neither the panel nor the software will teach you what each code means. That's what the operating guide is for—the FC 102 Operating Guide (MG94A), the FC 202 Operating Guide, the FC 302 Operating Guide, and so on. Each contains the full alarm list, causes, and corrective actions. Download the PDF before you need it. Nobody wants to be searching for a manual at 3 a.m. And if you're sending your supplier a photo of the alarm display, check the reflection—yes, I get those photos where the only thing visible is a flashlight glare. (Ugh.)
My comparison conclusion: for one or two drives, the panel is fine. For a plant with multiple drives—or drives on critical processes—MCT 10 has a clearly lower total cost of ownership. It's free, it documents the event, and it gives you evidence. And evidence is exactly what you need when the conversation turns to warranty.
FC 102 vs. FC 202 vs. FC 302: Same Alarm List or Not?
This is the question I get most from engineers standardizing a facility: 'We've got FC 102s on HVAC, FC 202s on water, and FC 302s on conveyors. Do I need to learn three different alarm lists?'
The good news: for the common codes, the alarm list is essentially the same across the three series (thankfully). A.1 is overcurrent, A.2 is overvoltage, A.4 is undervoltage, A.5 is overtemperature, A.9 is motor phase loss. Danfoss standardized the code set across the FC family specifically so a technician moving from a pump drive to a conveyor drive doesn't have to relearn the language. That standardization has a real TCO benefit: your team learns one alarm language, and one set of troubleshooting habits, across every drive on the plant floor.
But there's a nuance. The parameter groups behind those codes differ by series. On an FC 302, an overcurrent trip might point to aggressive torque changes on a high-inertia load. On an FC 102, the same code might point to a stuck impeller or a failing bearing in HVAC equipment. Same code, different conversation. The alarm list is a starting point, not a verdict.
And the saying 'all Danfoss VFD alarm lists are the same' comes from an older era. The VLT 6000 and 8000 series had shorter code lists and a different numbering scheme. If you're coming from a legacy drive, don't assume the code numbers mean the same thing in the FC series. Look it up in the manual for the exact series. The documentation is free. The misdiagnosis isn't.
What This Means for Your Total Cost of Ownership
I'm a believer in total cost thinking, not price tag thinking. The cheapest quote for a drive is not the cheapest decision if it comes with hidden failures; the cheapest fix is the one you do at the right time. And the Danfoss VFD alarm list is one of the most underused cost-saving tools in an industrial facility because it gives you early access to problems that, left alone, get expensive. A ten-dollar thermistor check, triggered by a warning, can prevent a motor burnout that costs thousands.
This isn't hypothetical. In our Q1 2024 quality audit, we reviewed the previous year's warranty claims, and 23% of the 'component failures' turned out to be application issues that had shown up in alarm logs weeks before the failure. The pattern wasn't the hardware. The pattern was the lack of anyone reading the alarm list. And if you're chasing repeated A.4 undervoltage alarms, don't just stare at the drive—check what's feeding it. In plants with a lot of nonlinear loads, IEEE 519-2014 harmonic limits are often where the investigation starts.
So when someone asks me, 'is a fuel pump covered under warranty?'—or, more often, 'is this VFD covered under warranty?'—my first question is always: what does the alarm log say? If the log shows repeated undervoltage because the supply is undersized, the warranty conversation is going to be short. The drive was protecting itself from something outside its specifications. If the log shows clean operation followed by a sudden internal fault, that's a different story. The alarm log is your proof. And you can't download it after the fact.
Here's my practical starting point, for anyone building a qualification plan:
- One drive, quick check: use the local control panel. Read the alarm log, note the code, look it up in the correct manual.
- Multiple drives or recurring trips: connect MCT 10 and pull the trend data. It's free, and it shows the history the panel can't.
- Any warranty or compliance discussion: save the alarm log export. It's your evidence.
And the same logic applies beyond VFDs. Whether you're commissioning a control panel, installing a manual transfer switch, or swapping out a motor, the documentation and the operating history matter as much as the initial price. I've rejected roughly 12% of the first deliveries that cross my desk—not because the equipment was visibly bad, but because the documentation didn't match the spec. The product and the paper need to line up.
Look, I'm not saying every alarm is a crisis. I'm saying the alarm list is a diagnostic instrument, and the people who treat it that way are the ones who catch problems while they're still cheap. A Danfoss VFD alarm list doesn't predict the future. It tells you what's already been happening. That information is only as valuable as the action you take on it.
The most expensive alarm code on a Danfoss VFD alarm list isn't the one with the scariest name. It's the one nobody read.
