1. Motor fails to start (no response at all)

• Causes:
  • Power supply issues: Power outage in the supply line, tripped air switch, loose or poor contact of terminal blocks (such as phase wire falling off, neutral wire disconnected).
  • Internal motor faults: Open circuit in the winding (e.g., enameled wire burned out), broken lead wire; bearing jamming (in severe cases, the rotor is locked and cannot rotate).
  • Control equipment faults: Burned contactor coil, faulty button switch (e.g., start button stuck), incorrect action or too small setting value of the thermal relay.
• Customer performance: After pressing the start button, the motor makes no sound, no vibration, and the ammeter shows no reading.

2. Abnormal noise when starting the motor

• Causes:
  • Mechanical friction: Worn bearings (damaged balls/races, making "rustling" or "clunking" sounds), lack of oil in bearings (dry friction noise); friction between the rotor and stator core (rubbing, mostly due to excessive bearing clearance or bent rotor shaft).
  • Assembly issues: Loose motor foot bolts (vibration noise during operation), eccentric installation of couplings or pulleys (noise caused by rotational imbalance).
  • Electrical noise: Short circuit in the winding (excessive local current, making a dull "buzzing" sound), unbalanced three-phase voltage (abnormal sound before phase loss operation).
• Customer performance: There is a harsh, dull, or irregular noise at the moment of startup, accompanied by increased motor vibration.

3. Motor runs at low speed and has insufficient power after startup

• Causes:
  • Abnormal power supply: Unbalanced three-phase voltage (low voltage in one phase), phase loss operation (only two phases are powered, the motor is in a "semi-started" state, unable to reach normal speed and heats up severely); insufficient capacity or failure of the capacitor in single-phase motors (insufficient starting torque).
  • Overload: The load exceeds the motor's rated torque during startup (e.g., equipment jamming, overly tight conveyor belt), causing the motor to be "stuck".
  • Motor faults: Short circuit in the winding (partial coils burned out, reducing the effective number of turns and output power), broken rotor bars (broken rotor bars in asynchronous motors, resulting in insufficient electromagnetic torque).
• Customer performance: The motor rotates slowly, cannot drive the load, the body heats up quickly, and the ammeter reading far exceeds the rated value.

4. Motor trips when starting (air switch/leakage protector acts)

• Causes:
  • Short circuit fault: Insulation breakdown of the motor winding (short circuit between phase wires, or between phase wire and motor shell), causing an instantaneous large current to trigger the air switch to trip; wrong wiring (e.g., direct short circuit between phase wire and neutral wire).
  • Overload protection: Too long starting time (overload causes the starting current to continuously exceed the rated value), and the thermal relay or air switch overload protection acts.
  • Leakage problem: Damp windings (decreased insulation resistance), poor grounding of the motor shell, resulting in leakage current exceeding the leakage protector threshold (common in humid environments).
• Customer performance: The air switch trips instantly when starting, sometimes accompanied by sparks or a burning smell.

5. Difficulty in starting single-phase motors (buzzing but not rotating)

• Causes:
  • Faulty starting capacitor: Capacitance attenuation, internal open circuit, or short circuit (single-phase motors rely on the starting capacitor to generate a rotating magnetic field; the motor cannot start if the capacitor fails).
  • Centrifugal switch issues: Adhesion or disconnection of the centrifugal switch contacts inside the motor (failure to switch to the running winding after startup, causing overheating of the starting winding).
  • Too low power supply voltage: Insufficient starting torque cannot be provided.
• Customer performance: The motor makes a "buzzing" sound, but the rotor does not rotate or rotates extremely slowly. If the power is not cut off in time, the winding is easily burned.

6. Motor overheats quickly after startup

• Causes:
  • Too long starting time: Frequent starting or overload causes the starting current (usually 5-7 times the rated current) to act continuously, resulting in accumulated heat in the winding.
  • Phase loss operation: After phase loss in three-phase motors, the winding current increases sharply, and the temperature rises rapidly in a short time.
  • Poor motor heat dissipation: Damaged fan, excessive dust accumulation on heat sinks, preventing heat from dissipating in time during startup.
• Customer performance: A few minutes after startup, the motor shell becomes scalding hot, and even a burning smell of insulating paint can be detected.

Suggestions for customers:

• Before the first startup, check whether the wiring is correct, whether the fasteners are loose, and test whether the power supply voltage is normal.
• If the motor has no response, first check the power supply and control switches; if there is abnormal noise, cut off the power immediately to avoid expanding the fault.
• For difficulty in starting single-phase motors, prioritize checking the starting capacitor; for overheating of three-phase motors, focus on checking for phase loss or overload.