VSD runs but motor doesn't reach set speed
The drive shows it's running and outputting, but the motor turns slowly, sluggishly, or never reaches the commanded speed.
Safety first
A motor not reaching speed may be overloaded and overheating. Watch current and temperature. Keep clear of the driven equipment.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
Current limit holding speed back
Most likelyThe drive is in current limit because the load is too high, so it can't accelerate to setpoint.
- 2
Speed reference lower than expected
#2The reference (pot, analogue, network) is set lower than intended, so the drive runs slow by command.
- 3
Max-frequency / speed limit set low
#3A parameter capping maximum frequency/speed prevents reaching the desired speed.
- 4
Mechanical overload / drag
#4A binding load or partial jam holds the motor back.
- 5
Wrong motor data / control mode
Least likelyIncorrect motor parameters or an un-tuned mode gives poor torque, especially at low speed.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
Check the drive's live speed reference and whether it's in current limit.
Reference at the desired speed and not in current limit.
Reference fine, not limiting — check max-speed parameter and load.
Low reference → correct it. In current limit → the load is too high; investigate.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Motor won't reach speed
→ step 2 - 2decision
Is the reference correct and the drive NOT in current limit?
Yes→ step 3No→ step 4 - 3decision
Is the max-speed/frequency limit high enough?
Yes→ step 5No→ step 6 - 4result
Low reference → correct it; in current limit → load too high, investigate.
- 5decision
Is current within rating with good torque and correct motor data?
Yes→ step 7No→ step 8 - 6result
Raise the max limit to suit (within safe limits).
- 7result
Re-check reference and limits.
- 8result
Overload or wrong motor data — address load / re-tune.
Common mistakes apprentices make
- Not noticing the drive is in current limit because of an overload.
- Overlooking a low max-frequency parameter.
- Assuming a drive fault when the reference is simply set low.
- Skipping motor data/tuning when low-speed torque is poor.
When to stop & escalate
A genuine mechanical overload goes to the mechanical team. Persistent low-speed torque problems after correct setup may need the drive's tuning support.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
Related faults
VSD trips on overcurrent / overload
The drive trips with an overcurrent or overload code — on start, on acceleration, or under running load. It may restart and trip again on the same point in the cycle.
Motor overload keeps tripping
The thermal/electronic overload trips repeatedly, either on start or after the motor has run for a while. Resetting only buys you a short run before it trips again.
VSD/drive ignores the direction command
A drive runs but only one way — the reverse (or forward) command is ignored, even though the drive is running and the motor turns.