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The Five Most Common Faults That Will Happen in AC and DC Motors

If an electrical motor is thought to have a problem, there are five common areas where the fault may lie. The initial problem (and most common issue with malfunctioning motors) may be with the power circuit or quality of the power supply. Breakages can also happen when there are faults with insulation or an air gap, along with possible defects with the motor’s stator or rotor.

Here, we review some common problems with AC and DC motors and their possible causes.

The Motor Is Not Mounted Correctly

Inadequate mounting of the motor can lead to defects when it is not correctly levelled as part of the installation process. If the housing is not properly bolted to the rest of the assembly or the surroundings, uneven stresses may arise. This is sometimes called ‘soft foot’ and leads to irregular operation, distortion of the bearings and physical failure over time. To correct this, stainless steel shims may be used under high feet or parts of the base to level them.

The Motor is Clogged With Dust

In physically dirty environments, the accumulation of dust inside a motor can lead to short-circuiting. In dusty conditions, it is important to keep the surrounding area clean and to employ DIP (dust ingress protection) measures. For preference, motors with IP dust ratings of 5 (limited ingress – no harmful deposit) or 6 (totally protected against dust) are the most reliable in these type of operating conditions.

Water is Inside the Motor

Water ingress is a similar hazard – if liquids get into the terminal box or stator coils, short-circuiting will occur and the motor will burn out. In damp, humid or wet areas, sufficient protection measures need to be deployed.

The Motor is Overheating

Overheating can occur if the motor is too small for the task, not fit for purpose or if changes to the load occur. High ambient temperatures are also a cause of overheating. Protection circuitry against over-temperature operation is recommended so that if the motor overheats it shuts down. Booster fans can help, along with variable speed drives.

The Motor Has Been Stored Incorrectly

Storage for extended periods in one position means that internal bearings can etch into the metal of the shaft. Therefore, it is advisable to rotate the shaft a quarter of a turn (ninety degrees) every month. Similar problems can occur with bearings etching marks into the motor shaft when there is vibration, so storage on cushioned mats is recommended.

Finally, to minimise failures, regular preventative maintenance inspections and tasks should be carried out. Power supply circuitry should include overload protection to remove transient voltage spikes.

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