Motor Problem | Cause | Remedy |
Motor fails to start | Blown fuses | Replace fuse with proper type and rating |
Overload Trips | Check and reset overload in starter |
Improper power supply | Check to see that power supplied agrees with nameplate specifications and load factor |
Improper line connections | Check connections with wiring diagram supplied with motor |
Open circuit in winding or control switch | This is normally indicated by a humming sound when switch is closed. Check for loose wiring connections. Confirm that all control contacts are closing. |
Mechanical failure | Check to see that motor and drive turns freely. Check bearings and lubrication |
Short circuited stator | Indicated by blown fuses. Motor must be rewound |
Poor stator coil connections | Remove end belts. Locate poor connections with test lamp. |
Rotor defective | Check for broken bars or end rings |
Motor may be overloaded | Reduce motor load |
Motor stalls | One phase may be open | Check supply lines for open phase |
Wrong application | Change type or size. Consult motor manufacturer |
Overload | Reduce load |
Low voltage | Check that nameplate voltage is maintained. Check connection. |
Open circuit | Fuses blown. Check overload relay, stator and push buttons |
Motor runs and then dies down | Power failure | Check for loose connections to line, to fuses and to control |
Motor does not come up to speed | Motor is applied for the wrong application | Consult manufacturer for right application of motor |
Voltage too low at motor terminals because of line drop | Use higher voltage on transformer terminals or reduce load. Check connections. Check conductors for proper size. |
Starting load too high | Check load motor is supposed to carry at start. |
Broken rotor bars or loose rotor | Look for cracks near the rings. A new rotor may be required as repairs are usually temporary not permanent |
Open primary circuit | Locate fault with testing device and repair. |
Motor takes too long to accelerate and/or draws high current (Amps) | Excessive load | Reduce load |
Low voltage during start up | Check for high resistance. Adequate wire size. |
Defective squirrel cage rotor | Replace with new rotor |
Applied voltage too low | Improve voltage at terminals of transformer by tap changing. |
Wrong rotation | Wrong sequence of phases | Reverse connections at motor or at switchboard. |
Motor overheats while running under load | Overload | Reduce load |
Frame or bracket vents may be clogged with dirt and prevent proper ventilation of motor. | Open vent holes and check for a continuous stream of air from the motor. |
Motor may have one phase open | Check to make sure that all leads are well connected. |
Grounded coil | Locate and repair |
Unbalanced terminal voltage | Check for faulty leads, connections and transformers. |
Motor vibrates | Motor misaligned | Realign |
Weak support | Strengthen base |
Coupling out of balance | Balance coupling |
Driven equipment unbalanced | Re-balance driven equipment |
Defective bearings | Replace bearing |
Bearings not in line | Line bearings up properly |
Balancing weights shifted | Re-balance motor |
Poly-phase motor running single phase | Check for open circuit |
Excessive end play | Adjust bearing |
Unbalanced line current on poly-phase motors during normal operation | Unequal terminal volts | Check leads and connections |
Single phase operation | Check for open contacts |
Unbalanced voltage | Correct unbalanced power supply |
Noisy Operation | Airgap not uniform | Check and correct bracket fits or bearing. |
Rotor unbalance | Rebalance |
Hot bearings general | Bent or sprung shaft | Straighten or replace shaft |
Excessive belt pull | Decrease belt tension |
Pulley too far away | Move pulley closer to motor bearing |
Pulley diameter too small | Use larger pulleys |
Misalignment | Correct by realignment of drive |
Hot bearings ball | Insufficient grease | Maintain proper quantity of grease in bearing |
Deterioration of grease or lubricant contaminated | Remove old grease, wash bearings thoroughly in kerosene and replace with new grease. |
Excessive lubricant | Reduce quantity of grease, bearing should not be more than 1/2 filled |
Overloaded bearing | Check alignment, side and end thrust. |
Broken ball or rough races | Replace bearing, first clean housing thoroughly |
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