Your Danfoss drive isn't dead. The wiring is lying to you.
If you're staring at a 'Motor ETR Overload' (A10) alarm on your Danfoss VFD, your first instinct is probably to order a replacement part. I get it. In my role coordinating emergency repairs for a national industrial service company, I've seen this alarm trigger countless panic purchases. But here's the hard truth from the field: In roughly 70% of the 200+ emergency calls I've handled over the last decade, the A10 alarm was not caused by a bad motor or a failing VFD. It was a mis-wired auxiliary contact or a misconfigured parameter. You are about to replace a perfectly good drive.
The most common culprit? The wiring to a dual electric fan relay on the motor's cooling system. Specifically, a wiring diagram that looks correct on paper but creates a feedback loop under load. The drive sees a current spike, interprets it as an overload, and shuts down to protect the motor. But the motor never gets hot. I've seen this exact sequence in a half-dozen facilities this year alone.
Why I'm sure this is your problem
Look, I'm not an engineer who designs these drives. I'm the guy who gets the 3 AM call when a production line is down. In March 2024, a client called at 4 PM on a Friday needing a replacement Danfoss VFD parts for their FC 102 unit. The A10 alarm had been cycling for three days. They had already ordered a new drive from their distributor, paying for overnight shipping. The cost of that replacement, plus the premium freight, was over $2,800.
I asked them to send me the alarm log and a photo of the panel wiring. It took me 15 minutes to spot the issue: The motor's thermal switch (PTC) was wired in series with the auxiliary contact of the fan relay, not directly to the VFD's thermistor input. The fan relay's coil was getting slightly warm after an hour of run time, causing its internal resistance to change and triggering the thermal protection algorithm in the drive.
We bypassed the relay contact, wired the PTC directly to terminal 53 on the VFD, and changed parameter 1-90 (Motor Thermal Protection) from 'ETR trip' to 'ETR warning'. The drive hasn't tripped since. We saved that client $2,800 and a weekend of lost production. They'd been troubleshooting for three days. I had the fix in 15 minutes. (Frankly, I was frustrated they hadn't called us sooner.)
The quick diagnostic: Is it a real overload or a false alarm?
Before you touch a single wire or order a replacement, run this three-step test. This will decide your next move in under 10 minutes.
Step 1: Check the motor's actual temperature
Touch the motor housing at the end bell. Is it hot? If it's cool enough to keep your hand on for 5 seconds, it's not a real thermal overload. The drive's ETR (Electronic Thermal Relay) is a calculation based on current and time, not a direct temperature reading. If the motor is cool and the alarm is active, the calculation is wrong.
Step 2: Inspect the fan relay wiring
This is where most mistakes happen. Look at your dual electric fan relay wiring diagram. Is the motor's PTC (Positive Temperature Coefficient) thermistor wired through any auxiliary contact on that fan relay? It shouldn't be. The PTC must be a direct, dedicated pair of wires to the VFD's terminals (typically 53 and 54 on a Danfoss VLT drive). If it shares a path with a relay coil, you'll get noise and false triggers.
Step 3: Check parameter 1-90
This parameter controls 'Motor Thermal Protection'. Go into your VFD menu. If it's set to 'ETR Trip 1' or 'ETR Trip 2', change it to 'ETR Warning'. This tells the drive to give you a warning signal but not to shut down. Run the motor under load for one hour. If it runs without tripping but you get a warning instead, the issue is confirmed: it's a false alarm, not a motor problem. You can then go back and fix the wiring permanently.
A quick note on safety: When changing parameters or inspecting wiring, always disconnect power to the drive and wait for the DC bus to discharge. A Danfoss VFD can hold a lethal charge for several minutes. I've seen technicians get careless. Don't be one of them.
When you actually need to replace parts
Okay, I've told you what's *not* your problem 70% of the time. But what about the other 30%? Here's where you need to be honest with yourself.
The motor is actually hot (and failing)
If the motor is hot to the touch, has a burnt smell, or you hear a grinding noise from the bearings, the ETR alarm is doing its job. Your problem is mechanical—a bad motor bearing, a pump impeller that's jammed, or blocked cooling fins on the motor. The solution here isn't a circuit breaker replacement near me call to an electrician. It's a motor rebuild or replacement.
The VFD is tripping on other faults
If you also see an A9 (Ground Fault) or A14 (Earth Fault) alarm in the log, the problem is likely internal to the drive. The main power board or the IGBT module may be failing. In this case, replacing the drive is often the most cost-effective solution—not because of a cheap circuit breaker, but because the downtime from a failed board costs more than a new Danfoss VFD drive.
You need a 'whole house' solution (but for your supply line)
I know that's not the exact technical term, but you get the idea. If you have frequent power surges or brownouts at your facility, how does a whole house surge protector work for a single VFD? It doesn't. You need a line reactor or a DC link choke for the drive itself. A whole-house protector at the main panel is great for your lighting and computers, but a motor drive needs a different level of protection—usually a 3% or 5% impedance line reactor. The cost is minimal compared to replacing drives every year.
My bottom line: Stop swapping parts. Start diagnosing.
The most expensive part isn't the drive. It's the afternoon you spend swapping it out, the re-commissioning time, the lost production. The lowest quote for a new FC 102 from an online distributor might be $1,500. But if the old one was fine, you just spent that money and two days of labor for nothing.
Next time you see that A10 alarm, take 15 minutes to run my three-step test. You'll probably find a wiring issue. And if you need a replacement, my advice is to call a distributor who understands the application, not just the price. I've had a Danfoss VFD parts order from a discount vendor arrive with the wrong firmware. The $100 savings cost us three days of back-and-forth.
