Analysis Automation Motor Testing Motors & Drives Reliability & Maintenance Center

Check Before Activating Motors

EP Editorial Staff | March 1, 2021

A little preventive maintenance on motors that have been in storage or returned from a repair shop will go a long way toward preventing expensive damage.

It’s bold to assume that motors that have been in storage for a length of time or that have been repaired or replaced can be put into service without some kind of inspection.

It only requires a short amount of time, and relatively minimal effort, to go through a checklist before powering up a newly installed motor. Here are some things to consider if a motor has been removed from long-term storage and/or received from a repair shop.

Before installing a motor that has been in storage for more than a few weeks:

• Thoroughly inspect and clean the motor to restore it to “as shipped” condition.

• If the motor has been subjected to vibration, disassemble it and check for bearing damage, e.g., false brinelling and fluting.

• Grease-lubricated motor bearing cavities should have been filled with grease for storage. To protect the windings from contamination, remove the drain plugs before adding the lubricant specified on the lubrication plate. Then purge old or excess grease from the bearing cavity by running the motor at no load for 10 to 20 min. and replace the drain plugs. If any moisture is present in the purged grease, the bearings are probably rust damaged and should be replaced.

• If the motor has been stored for several years, the grease has likely dried out or separated and the drainpipe is probably plugged. Disassemble the motor, clean out the old grease, and repack the bearings.

• To prevent winding contamination, drain oil-lubricated motors before moving them.

• Test the winding’s insulation resistance (IR) and dielectric absorption ratio (DAR) and record the results. If the IR and DAR test results are satisfactory, perform a no-load test operation.

Before putting a repaired or replacement motor into service, briefly start it to check its operation.

• If the motor vibrates or emits unusual noises or odors, immediately de-energize it and look for the cause.

• Magnetic or electrical problems that exhibit as vibration or noise will instantly improve when the power is off.

• No improvement may indicate an anomaly such as rotor or driven-load unbalance or misalignment.

• If the motor operates normally, allow it to reach full speed before shutting off the power.

• Always lock out and tag out the motor before connecting the driven load.

• Once the motor and driven load operate properly, record the full-load voltage and current for all three phases on the motor data sheet for this installation. If possible, also record the input power with load.

• If the motor is so equipped, monitor the bearing and winding temperatures until they reach a steady state. Document these values as well as the ambient temperature and humidity.

• For critical applications, record the initial vibration signature of the complete machine as a baseline. EP

These tips are adapted from the EASA, St. Louis ( publication, Getting the Most from Your Electric Motors. Download the full e-booklet at



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