USF Schneider Electric — Motor not reaching rated speed — insufficient torque
At a glance
- Severity
- DEGRADED
- Domain
- MOTORI
- Reference standard
- IEC 60034-12
- Product / context
- Underspeed Fault
What it means
The motor starts but does not reach rated speed. It operates with high slip, overheating, and abnormal noise. The developed torque is insufficient for the required load.
Probable causes
- Supply voltage too low (excessive voltage drop on the cable).
- Broken rotor bar in a squirrel-cage motor.
- Mechanical load exceeding the motor rated torque.
- Incorrect connection (delta instead of star for 400V supply, or vice versa).
Where to start
Measure the voltage on all three phases at the motor terminals under load. Is the voltage at least 95% of the nameplate rated voltage?
Full guided diagnosis in the app
The diagnostic tree for this fault has 7 guided steps with measurements, checks and resolutions. You'll find it in ElectraIQ, one of the four IndexOS apps: free, works offline.
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