Trouble

Probable cause

1. Upon starting motor fail to gain speed and hums

1. Failure or inadmissible drop of supply voltage
2. Confused starting and finishing leads of stator winding
3. Motor runs overloaded
4. Truble in driven mechanism

2. Running motor stops

1. Supply voltage failure
2. Defects in switchgear and in supply mains
3. Wedging in motor driven mechanism
4. Protective gear has operated

3. Motor shaft rotates but     normal spee  is not gained

1. Phase failure during acceleration
2. Supply voltage drop
3. Excessive overload

4. Motor runs hot

1. Overcurrent
2. Too high or too low supply voltage
3. Too high ambient temperature
4. Abnormal cooling conditions (clogged coolling ducts)
5. Abnormal operation of driven mechanism

5. Stator winding runs hot, motor    hums heavily  and fails to    gain speed

1. Turn - to - turn fault in stator winding
2. Winding of one phase is  grounded at two points
3. Two phases shorted out
4. Phase failure

6. Bearing run hot and produce     knocking noise

1. Misalignment of motor and driven mechanism shafts
2. Damaged bearing

7. Motor vibrates    heavily when  running

1. Insufficiently rigid foundation
2. Coarse stitching of belt
3. Misalignment of motor and driven mechanism shafts
4. Transmission element or  coupling out of balance

8. Too low     insulation    resistance of stator winding

1. Dirty or damp winding