Preventative Maintenance

Preventive maintenance programs are the key to the reliable, long-life operation of electric motors.
Whilst AC Induction Motors are particularly reliable in service, almost all electrical equipment requires periodic planned inspection and maintenance. Planned preventative maintenance ensures electrical motors, and starters are kept in good working condition at all times. This is critical for businesses that rely on electric motors. A scheduled routine of motor inspection should be carried out throughout the motor’s life. The periodic motor inspection helps prevent serious damage to motors by locating potential problems early.

Periodic Preventative Maintenance Inspections

Planned electric motor maintenance programs are designed to help prevent breakdowns, rather than having to repair motors after a breakdown. In industrial operations, unscheduled stoppage of production or long repair shutdowns is expensive, and in marine shipping environments, a potential safety issue. Periodic inspections of motors are therefore necessary to ensure the best operational reliability.

Preventive maintenance programs require detailed checks to be effective. All motors onsite (factory, ship, etc) should be given their own individual identification (ID) number and have a record log. The record log is usually computerised these days. The motor records kept should identify the motor, brand, inspection dates, and descriptions of any repairs previously carried out. By record keeping, the cause of any previous breakdowns can help indicate the cause of any future problems that might occur.

All preventative maintenance programs should refer to the equipment manufacturer’s technical documentation prior to performing equipment checks.

There are simple routine maintenance checks that can be applied to three-phase induction motors, which help ensure a long service life to a motor. 

The Simple checks that can be carried out, include a review of the service history, noise, and vibration inspections. Previous noise issues could for example be due to motor single phasing. The previous vibration may have been due to worn bearings, which allow the Stator to turn. Other checks include visual inspections (damage and burning), windings tests (insulation resistance & continuity), brush and commutator maintenance (dc motors, not AC Induction Motors), and bearings and lubrication.

Inspection frequency and the degree of inspection detail may vary depending on such factors as the critical nature of the motor, its function, and the motor’s operating environment. An inspection schedule, therefore, must be flexible and adapted to the needs of each industrial or marine environment.

Induction Motor Preventative Maintenance

The main failure points of AC Induction Motors are either the Stator coil or the bearings which allow the Rotor to rotate.


Stator coils are wound coils of copper wire, that surround the Rotor of an Induction Motor.

In Single Phase Induction Motors there is a single length of copper wire, that is wound as the Stator.

In three-phase Induction Motors, there are three separate lengths of copper wire, that are wound together, to form the Stator.

Therefore in a Single Phase Induction Motor, the Stator can go faulty if breakage occurs somewhere along the length of the single would copper wire.

In a three-phase induction motor, however, there are other reasons that a motor may fail, and also preventative maintenance checks we can make.

The three separate coils of wire contained within the stator of a three-phase induction motor, need a high insulation resistance between them.

Dust or moisture can reduce the insulation resistance between the three separate coils of wire.

If the insulation drops too much (below 1-2 Mega Ohms), then the motor may stop working.

Periodic checking of the insulation resistance can help identify issues before they prevent the motor from running.


The bearings by the fact that they are a moving part, and therefore subject to friction, are more likely to fail.

Periodic preventative maintenance, or automatic (using IOT Sensors) Vibration testing can be used as an early indicator of bearing wear.

(c) Craig Miles 2019-2021.

+44 (01522) 740818

Published by Craig Miles

Craig Miles

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