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Motor Preventive Maintenance: 10-Point Daily Inspection Checklist

Release Date ：2026-10-10

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Most motor failures are not sudden - around 90% give early warning signs that simply go unnoticed. A five-minute daily inspection can often stop an emergency shutdown before it starts. This article condenses motor preventive maintenance into a 10-point checklist that any electrician can follow.

SHANGDIAN motor daily inspection with infrared thermometer

1. The 10-Point Daily Inspection Checklist

#	Item	How to check	Normal / warning
1	Frame temperature	Infrared thermometer	Typically below 80 C for Class B; investigate if higher
2	Noise and vibration	Listening rod on bearing housing, hand on frame	No rhythmic clicking, no abnormal amplitude
3	Bearing temperature	Thermometer on end shields	Within 40 K of ambient; check lubrication if higher
4	Current	Clamp meter on all three phases	Balanced, not above rated current
5	Voltage	Multimeter phase-to-phase	Unbalance under 5%, not below 90% of rated
6	Insulation resistance	Megger periodically	At least 1 MOhm for LV motors (1 MOhm per kV rule of thumb)
7	Base bolts	Visual + spot torque check	No looseness, no corrosion
8	Fan and air path	Visual check of inlet	No blockage, fan undamaged
9	Terminals	Inspect junction box with power off	No discoloration, looseness or oil contamination
10	Environment	Visual around the motor	No water, dust build-up or blocked cooling

2. How Often Should You Inspect?

Daily (5 minutes): temperature, noise, current and appearance.
Periodic (every 3-6 months): insulation resistance, bolt tightening, bearing lubrication, air-path cleaning.
Annual overhaul: bearing inspection, winding DC resistance, coupling alignment check.

3. Two Details Most People Get Wrong

1. More grease is not better. Over-greasing heats the bearing; fill the bearing housing to roughly one-third to one-half of its volume. For grease grade and regreasing intervals see our bearing grease selection guide.

2. Discharge before testing insulation. After a megger test, always discharge the winding to ground before touching it - capacitive charge can be dangerous. For the full checklist after a long shutdown, see our pre-start checklist for idle motors.

4. Keep a Per-Motor Inspection Card

Record the date, frame/bearing temperatures, three-phase currents, insulation resistance and any anomalies for each motor. Trend data matters more than single readings - a rise from 65 C to 75 C over weeks is more worrying than a sudden 80 C reading. Trend analysis is what lets you predict failure instead of reacting to it.

5. When to Stop and Repair

Frame temperature above the warning value and still rising;
Rhythmic bearing noise or abnormal electromagnetic hum;
Insulation resistance clearly below 1 MOhm;
Vibration rising together with current fluctuation.

Never run a motor "until failure" in these cases - arrange a shutdown before a small fault becomes a major rewind. When replacement is needed, SHANGDIAN (Shanghai Electric Motor Factory) supplies YE3/YE4/YE5 low-voltage motors and YBX explosion-proof motors; contact our engineers for maintenance guidance or spare-part support.