Intense vibration is one of the most common causes of undesirable performance in AC or DC motors. For instance, intense motor vibration typically can cause indentations on bearing raceways, causing bearing failure. It can also loosen motor windings and fracture the motor insulation. Or it can loosen the motor from its mounting, or damage workpieces or other equipment.

Intense motor vibrations usually indicate a problem with the motor's components or configuration. Therefore, engineers must understand several factors that cause intense motor vibration and ways to troubleshoot these problems.

Vibration is the periodic motion (or mechanical oscillations) of an object about an equilibrium point. For example, if a vibrating motor could be watched in slow motion, one would notice movements in different directions. This movement can be described using a sinusoidal waveform. Frequency describes the number of oscillations in a given time, measured in Hertz (Hz) or cycles per second. Amplitude measures the maximum distance a vibrating body moves on either side of its stationary position. It is measured in meters. Acceleration measures how quickly a vibrating body's speed changes with time, and it is measured in meters-per-second squared (m/s2).

Causes of vibration in electric motors

Internal defects are among the most common causes of vibrations in electric motors. However, more often than not, the vibrations (or vibration amplitude) resulting from these defects are too low to be detected or not considered important enough for repair measures to be done. Moreover, these defects grow slowly and significantly affect the motor’s performance only during the later stages of its operating life.

Therefore, engineers are often more concerned about other causes of motor vibration like misaligned shaft mounting and disturbances from other connected machinery.

No. 1: Misaligned shaft mounting

Vibrations can arise when the machine’s shafts are out of line. For instance, consider a motor and a pump assembly used in a facility. In such a scenario, if this motor and pump axes are not parallel or the motor is set at an angle to the pump, it will introduce an additional driving force, causing lateral and torsional vibrations.

Misaligned shafts are often caused by poor assembly processes after maintenance activities, thermal expansion, and component shifting. However, they can be corrected using alignment equipment like laser alignment tools or dial indicators.

No. 2: Disturbances from other connected machinery and components

If the vibration problem persists after using these alignment tools, then the problem might be caused by the driven source. In such a scenario, engineers might want to isolate the motor from the driven source using vibration-absorbing components like elastomeric couplings to reduce vibration.

Components like bearings, drive belts, and gears might be the cause of vibration. For instance, when a roller bearing’s race becomes pitted, the movement of the rollers along these pitted regions will cause vibration (and noise). Likewise, a worn gear tooth or drive belt will produce vibration. Engineers might want to check (and replace) these components.

No. 3: Imbalances

Imbalances often occur in electric motors due to variations in the current in the stator or rotor. These variations are usually caused by failure of motor components like rotor windings, weak stator support, or shorted stator laminations. All of these cause a weighted spot (or unbalanced weight) in the motor, which moves around as the shaft rotates about its axis. As a result, the components experience a centrifugal force, which causes vibration.

Electric motor centrifugual force equation. Electric motor centrifugual force equation.


m = mass of the imbalance

w = angular velocity of the imbalance

r = distance of the imbalance from the center of rotation

Engineers can correct imbalances using vibration analysis tools. These tools detect imbalances, and then engineers can proceed to balance the electrical motor statically or dynamically. Static balancing is usually done when engineers notice a single heavy spot in the rotor, even when the rotor is stationary. In contrast, dynamic balancing is usually performed when the rotor has an infinite number of imbalances distributed along its axis of rotation.


It is essential to reduce the vibration of electric motors to achieve optimal performance and service life. Most motors can handle negligible amounts vibration, or can be designed for higher shock and virbation, such as those on a EV. But most stationary industrial uses will see better equipment value from a well-design installation and regular maintenance and inspection.

If the information above did not resolve some of motor vibration concerns, consider reaching out to a leading supplier of AC motors or DC motors to understand more, or review key mo motor vibration standards.