The Reset Is a Diagnostic Clue, Not a Fix
If your Kaeser compressor just threw a motor overcurrent fault, here's the short answer: don't reset it until you've figured out why it tripped. The reset button clears the alarm. It does not clear the cause. And every time you clear that alarm without fixing the underlying problem, you're gambling with the machine.
I gambled in 2017 on a Kaeser SM10 at a food processing plant. I reset the overcurrent fault four times in six days. The fourth time, the motor windings shorted permanently. The rewind quote: $1,780. The root cause—which the kaeser air compressor parts diagram would've shown me in ten minutes—was a clogged intake filter worth $46. That math still stings.
Why I'm Qualified to Say This
I've been servicing Kaeser rotary screw compressors since 2016—SM10s, CSD series, and the Omega blower line. I came up through an independent service shop, which meant no factory tech was coming to rescue me. You learned the machine, or you made expensive calls. I made enough of those.
To be specific: I've personally made (and documented) 23 significant service mistakes over my career, totaling roughly $7,200 in wasted budget. That's not a humblebrag. It's context. I now maintain our team's troubleshooting checklist, and this article is basically that checklist with a painfully earned story attached.
Here's exactly what happened in 2017.
The plant manager was pacing when I arrived. Their SM10 had been tripping on motor overcurrent for two days, and a production line was down. In my first year on the job, I made the classic rookie mistake: I treated the trip like a household circuit breaker. I looked at the Sigma Control display—MOTOR OVERCURRENT—and hit reset. The compressor started, pressure built, and I left like a hero.
Four hours later, the phone rang. Same fault. I went back, hit reset again. This time it ran three hours. I did it once more the next morning. Every reset took seconds and felt productive. Every one of them was wrong.
On the fourth trip, the motor wouldn't start at all. When I measured phase-to-phase resistance, I found a short between the windings. The motor was cooked. The motor shop quoted $1,780 for a rewind, plus a week of downtime. While we waited, I pulled the intake filter. You could barely see light through it. The airend had been suffocating for days, the motor was straining harder, and I had kept clearing the alarm instead of tracing the cause.
Root cause: a $46 filter. My fix: four resets, three return visits, one destroyed motor, and a customer who had every right not to trust me.
What Actually Causes Overcurrent on a Kaeser Compressor?
To troubleshoot this properly, you need to understand what's in the current path. This is where the kaeser air compressor parts diagram becomes your best tool. On an SM10—and most Kaeser rotary screw compressors—the relevant path looks like this:
Mains power → disconnect → contactor → overload relay → motor → airend
The airend is the compression element. Anything that makes the airend harder to turn increases motor current. The main culprits:
- Restricted intake air. A clogged air filter, blocked inlet duct, or stuck intake valve creates a vacuum the motor has to fight against. This is the one that got me.
- High discharge pressure. A failing minimum pressure valve or a pressure setpoint cranked too high forces the airend to compress against more resistance than it's designed for.
- Mechanical wear. Worn airend bearings, damaged rotors, or motor bearing degradation usually show up as rising current before they get loud enough to notice.
- Electrical faults. Loose connections, worn contactor contacts, or voltage imbalance across phases. (Honestly, this one still catches me off guard more than I'd like to admit.)
Here's the counter-intuitive part that tripped me up in 2017: I saw "overcurrent" and assumed electrical. The parts diagram would have reminded me that the motor is directly coupled to the airend. Make the airend harder to turn, and the motor current climbs—even if the electrical supply is perfect. The clogged filter wasn't just an airflow problem. It was putting a physical strain on the entire drive train.
How to Reset It the Right Way (20 Minutes vs. 10 Seconds)
The reset procedure on a Kaeser Sigma Control system is simple enough: press STOP, wait for the controller to cycle, then press RESET. But the right order of operations requires some work before you touch that button.
Step 1: Record the fault code. Don't clear anything yet. Write down the exact message the Sigma Control display shows.
Step 2: Inspect the intake system. Open the filter housing and look at the element. If it's anywhere near the end of its service interval, replace it regardless of how it looks. This is the $46 check that would have saved me $1,780.
Step 3: Check the discharge side. Note the system pressure and look for separator element restriction. An excessive pressure differential across the separator also loads the airend.
Step 4: Verify the electrical side. Lock out the unit, verify it's de-energized, and inspect the contactor contacts and connection tightness. If this step involves anything beyond "look inside an energized panel," stop and call someone qualified. NFPA 70E electrical safety rules exist for good reasons.
Step 5: Reset and monitor. Clear the fault, start the machine, and watch the current draw on the Sigma Control display through at least one full load/unload cycle.
This checklist takes about 20 minutes. The reset alone takes 10 seconds. The distance between those two numbers is where expensive lessons live.
Getting the Right Kaeser Parts Diagram
You need the diagram for your specific model, not a generic one. On the SM10, the data plate is on the right side near the motor end cap. The serial number there is what you'll need to pull the correct drawing from Kaeser's service documentation portal.
If you don't have access to that portal, the operator's manual—ships with the machine and available through Kaeser's website—includes the essential exploded views for the major systems: intake, separation, cooling, and electrical. For an SM10, the intake group diagram is the one to study first.
Here's the key: don't just look at individual parts. Trace how they connect. On the intake group diagram, you can follow the air path from the filter housing through the intake valve and into the airend. Knowing that path is what makes a clogged filter an obvious suspect—which is exactly the connection I failed to make in 2017, even though I had opened that same diagram a dozen times.
When You Shouldn't DIY the Reset
Here's where I have to be honest about the boundaries of my advice. If the compressor has tripped more than twice in a single day, stop resetting it. You have a genuine problem, and every reset while that problem persists stresses the motor and the contactor further.
If the motor is hot to the touch, let it cool completely before troubleshooting. Motor insulation degrades with every overheated cycle. A hot motor isn't just a symptom—it's a timer ticking toward failure.
If you smell anything burning, skip the reset entirely. That isn't a nuisance trip; that's damage in progress.
This approach worked for us, but our situation was a mid-size service shop with trained technicians and full documentation access. If you're a facility manager who doesn't do electrical work, your mileage may vary. A service call costs a few hundred dollars. A motor rewind costs $1,780. The math isn't complicated.
One more thing I'll admit freely: I've never fully understood why some Kaeser overcurrent faults read intermittent before they become permanent. My best guess is that mechanical load varies with ambient temperature—a machine that barely trips on a cool morning can be the same machine that fails on a hot afternoon. If someone has a better theory, I'd genuinely like to hear it.
But this I know for certain: the reset button is a diagnostic tool, not a repair. Use it that way, or pay like I did.
