A Detailed Electric Motor Preventive Maintenance Checklist

Electric motors rarely fail without warning. Strange noises, rising temperatures, and minor vibrations, the signs could be many. What’s often missing is a structured way to catch those signs in time, which a preventive maintenance checklist offers.

Below, you’ll find a detailed checklist built specifically for electric motor maintenance. It’s practical, to the point, and designed to help you stay ahead of failures and not react to them. You can use it for the maintenance of any type of electric motor including starter motor, induction motors, servo motors, stepper motors, and universal motors.

What is an Electric Motor Preventive Maintenance Checklist?

An electric motor preventive maintenance checklist is a document that lists all maintenance and inspection tasks required to keep a motor fully functional. It covers mechanical checks, electrical tests, lubrication points, and cleaning steps, and helps technicians follow a consistent routine of maintenance.

What are the Benefits of an Electric Motor Preventive Maintenance Checklist?

As a structured tool, a maintenance checklist, guides technicians through critical inspection tasks and proves beneficial in many ways, and listed below are the notable benefits of electric motor maintenance checklist:

• Detects Phase Imbalance and Voltage Irregularities

  By checking voltage levels and phase balance regularly, you can spot electrical issues before they lead to serious problems like overheating or winding failures.

• Prevents Bearing Seizure

  Following a checklist helps you keep track of lubrication intervals, so you’re not running motors with dry or contaminated bearings that could seize without warning.

• Identifies Shaft Misalignment and Vibration Issues

  When vibration and alignment are part of routine checks, it’s easier to catch early signs of mechanical stress that could wear out the motor or connected machines.

• Helps Schedule Load Balancing

  Monitoring current draw through a checklist lets you notice overload patterns in time, before they overheat the motor and damage internal windings.

• Tracks Thermal Condition to Breakdown

  Including temperature checks in your routine helps you catch hotspots early, so insulation doesn’t degrade and lead to sudden short circuits or failures.

• Reduces Maintenance Guesswork

  Across different shifts, when everyone uses the same checklist, there’s less chance of missing the faults, no matter who’s on shift or which site it is, and consequently, you avoid costly breakdowns.

Electric Motor Preventive Maintenance Checklist

Following are the 9 checklist items that every checklist for the preventive maintenance of electric motors must include. Get into these checklist items for thorough inspection and timely repair of your electric motors:

1. Power Supply System

• Terminal Box & Power Cables
• Inspect for loose, corroded, or overheated terminals.
• Tighten all cable connections with torque wrench to specified torque.
• Check for signs of insulation damage, fraying, or discoloration.
• Confirm cable gland sealing is intact to prevent dust/moisture ingress.
• Verify phase identification tags are present and legible.

• Voltage Supply
• Measure and record voltage at all three phases using a multimeter.
• Verify that voltage is within ±10% of the rated motor voltage.
• Check for phase imbalance (should be less than 2%).

• Grounding System
• Inspect ground cable for continuity and proper lug connections.
• Use an insulation tester to confirm grounding resistance is within safe limit (typically < 1 ohm).
• Verify the grounding terminal is clean and free of paint/rust.
  

• Power Quality (Advanced – for sensitive motors)
• Perform harmonic analysis using power quality analyzer.
• Record Total Harmonic Distortion (THD) — should typically be <5%.
• Monitor for voltage spikes, dips, and transients over a period (if recurring failures occur).

2. Motor Windings

• Insulation Resistance Testing
• Disconnect motor from power supply and discharge windings before testing.
• Use a 500V or 1000V megohmmeter (as per motor voltage class) to test insulation resistance between each winding and ground.
• Record readings; acceptable value should be ≥1 MΩ per kV + 1 MΩ (minimum rule of thumb).
• Test insulation resistance between phase windings (phase-to-phase).
• Compare results with previous records to detect insulation degradation trends.
  

• Polarization Index (PI) Test
• Conduct PI test by taking insulation resistance at 1 minute and again at 10 minutes.
• Calculate PI = IR at 10 min / IR at 1 min; acceptable value is >2.
• Investigate if PI < 2 (may indicate moisture or contamination in windings).
  

• Dielectric Absorption Ratio (DAR)
• Perform DAR if PI is not practical due to time or equipment constraints.
• Calculate DAR = IR at 60 seconds / IR at 30 seconds; acceptable if >1.25.
• Document readings in maintenance logbook.
  

• Visual Inspection of Windings (for accessible windings)
• Remove motor end covers (if possible) and inspect stator windings for:
• Signs of overheating (darkened varnish, burnt smell).
• Dirt, moisture, oil, or chemical contamination.
• Loose or damaged winding ties or bracing.
• Clean dry windings using dry compressed air (at safe pressure ≤ 30 psi) to remove dust.
  

• Surge Comparison Test
• Perform using a surge tester to detect turn-to-turn short circuits.
• Compare waveform across three phases; major deviation indicates incipient winding failure.
• Conduct only under supervision of qualified technicians due to high voltage.
  

• Winding Resistance Measurement
• Use a digital micro-ohmmeter to measure DC resistance of each phase.
• Verify phase resistance balance — all phases should be within ±2% of each other.
• Check connections and re-test if any reading is unusually high or low.

3. Bearings

• Bearing Type Identification and Schedule Planning
• Identify bearing type (sealed, shielded, or re-greasable).
• Refer to the manufacturer’s lubrication schedule and recommended grease type.
• Record operating hours to determine lubrication or replacement intervals.
• Mark lubrication schedule visibly on the motor for maintenance crew.
  

• Lubrication of Bearings
• Clean grease fittings before applying new grease.
• Use a calibrated grease gun to avoid over-lubrication.
• Apply recommended quantity of correct grease (check datasheet; typically in grams).
• For motors with drain plugs: open drain plug during greasing to flush out old grease.
• Run the motor briefly after greasing to distribute grease evenly.
  

• Noise and Vibration Check
• Use an ultrasonic leak detector or stethoscope to listen for abnormal bearing sounds (grinding, clicking).
• Record bearing vibration levels using a vibration analyzer.
• Compare readings to ISO 10816 vibration severity chart.
• Identify frequency signatures of outer race, inner race, cage, and ball defects.
  

• Temperature Monitoring
• Measure bearing housing temperature with infrared thermometer during running condition.
• Ideal range: typically <80°C; investigate anything above 90°C.
• Monitor for rapid temperature increases, which may indicate imminent failure or lubrication issue.
  

• Visual and Physical Inspection (during shutdowns)
• Inspect bearing housings for grease leaks, cracked seals, or damage.
• Check shaft axial and radial play by hand — excessive movement suggests worn bearings.
• Spin shaft by hand to detect roughness or binding.
  

• Bearing Replacement (when required)
• Use pullers or induction heaters — avoid hammering or forced removal.
• Clean shaft and housing before installing new bearing.
• Apply proper mounting technique (cold or hot fit, depending on type).
• Confirm bearing seated fully and securely.
• Record replacement in motor maintenance history.

4. Rotor and Shaft Assembly

• Shaft Runout and Straightness
• Use a dial indicator to measure total indicated runout (TIR) of the shaft at the drive and non-drive ends.
• Acceptable runout is typically <0.05 mm; higher values may indicate a bent shaft.
• Mark and monitor for any increase over time, which could signal progressive damage.
  

• Rotor Condition
• During overhauls or disassembly, inspect rotor laminations for:
• Cracks, looseness, scoring, or signs of overheating.
• Broken rotor bars (for squirrel cage motors).
• Tap bars lightly with a mallet and listen for hollow sound to identify cracks.
• Check for unbalanced dirt or dust accumulation on rotor surfaces.
  

• Shaft Surface Condition
• Inspect shaft for signs of wear, pitting, or corrosion — especially at bearing and coupling contact points.
• Use a micrometer to measure shaft diameter and compare with original specs.
• Verify keyways for wear or deformation.
  

• Rotor Bar and End Ring Testing
• Conduct a current signature analysis (CSA) or rotor influence check (RIC) to detect broken rotor bars.
• Look for sideband frequency components in the spectrum indicative of rotor faults.
• Document test results and trends if equipment is monitored routinely.
  

• Shaft Key and Coupling Fit
• Inspect key for shearing, looseness, or damage.
• Ensure the key fits snugly in the shaft and hub keyway without excessive play.
• Check coupling bore for signs of fretting or misalignment.
  

• Rotor Balance (Dynamic)
• If vibration persists after other components are ruled out, perform dynamic balancing of the rotor.
• Balance in two planes using a rotor balancing machine.
• Record amount and location of balancing weights added or removed.

5. Coupling and Drive Mechanism

• Coupling Alignment
• Perform alignment using feeler gauges (for flexible couplings) or dial indicators / laser alignment tools (for rigid couplings).
• Measure and correct:
• Parallel (radial) misalignment
• Angular (axial) misalignment
• Recheck alignment after motor warm-up if thermal growth is significant.
• Document alignment values before and after adjustment.
  

• Coupling Wear and Condition
• Inspect flexible elements (rubber inserts, spider, or grid) for cracks, hardening, or deformation.
• Check for excessive backlash or play between coupling halves.
• Verify that set screws, locking rings, or bolts are tight and properly torqued.
• Clean any buildup of grease, oil, or debris on coupling surfaces.
  

• Coupling Guard
• Confirm that the guard is securely mounted and not interfering with rotating parts.
• Check for missing bolts, deformations, or corrosion on the guard.
• Ensure the guard provides full coverage as per safety regulations (e.g., OSHA).
  

• Belt Drive Systems
• Inspect belts for cracking, glazing, fraying, or uneven wear.
• Check belt tension using a tension gauge or deflection method — adjust if needed.
• Verify pulleys are aligned; use a straightedge or laser alignment tool.
• Clean pulley grooves to prevent slippage.
• Replace belts as a complete set if one shows signs of failure.
  

• Gearbox Coupling
• Check oil level and condition in the gearbox (if externally visible).
• Listen for unusual noise or knocking sounds during operation.
• Check gearbox mounting bolts and alignment with the motor shaft.
• Inspect input/output shafts for wear or leakage at seals.

6. Cooling and Ventilation System

• Cooling Fan Condition
• Inspect fan blades for cracks, distortion, or buildup of dust/debris.
• Spin the fan manually to check for smooth rotation and absence of rubbing or imbalance.
• Confirm that the fan is securely fastened to the shaft and not slipping.
• Replace damaged or missing fan blades immediately.

• Fan Cover / Shroud
• Verify the fan cover is securely in place and not bent or rubbing the fan.
• Clean accumulated dust or foreign matter that may restrict airflow.
• Check for corrosion, broken welds, or missing fasteners.
  

• Airflow Path and Ventilation
• Inspect intake and exhaust vents for obstructions (dirt, paper, plastic, rodents, etc.).
• Use compressed air (low pressure) to blow out dust from internal airflow paths — ensure the motor is powered down first.
• Confirm no exhaust air recirculation in confined spaces — especially in enclosed installations.

• External Filters and Louvers
• Clean or replace external air filters as per the maintenance schedule.
• Inspect louvers or mesh for clogging or deformation.
• Secure any loose filter frames or access panels.
  

• Enclosed Cooling Systems (TEFC, CACA, CACW, etc.)
• For TEFC motors: verify internal cooling passages are clean.
• For CACA (air-to-air heat exchangers): inspect and clean heat exchanger fins.
• For CACW (air-to-water systems): check coolant flow, pressure, and heat exchanger cleanliness.
• Inspect seals and connections on closed-loop systems for leaks or corrosion.
  

• Temperature Monitoring Devices (if equipped)
• Inspect RTDs, thermistors, or thermocouples embedded in windings or bearings.
• Test temperature sensors for correct readings using a multimeter or PLC input.
• Check wiring and terminations for looseness, corrosion, or insulation damage.

7. Motor Housing and Mounting

• Motor Frame and Exterior Housing
• Inspect for cracks, corrosion, dents, or warping on the motor body.
• Check paint or protective coating for peeling, rust patches, or signs of chemical attack.
• Clean the exterior using a dry cloth or approved solvent (as per safety guidelines).
• Look for oil, grease, or dust accumulation that may affect cooling or safety.
  

• Mounting Base and Foundation
• Inspect the motor base for cracks, warping, or corrosion.
• Check for gaps or improper contact between baseplate and foundation.
• Ensure anti-vibration pads or shims (if used) are in place and in good condition.
• Verify leveling using a spirit level — re-shim or adjust base if tilt or instability is observed.
  

• Foundation Bolts and Fasteners
• Inspect all mounting bolts, nuts, and washers for looseness or wear.
• Torque bolts to manufacturer-recommended specifications.
• Look for signs of bolt elongation or rusted threads.
• Replace missing or damaged bolts and mark tightened bolts with torque paint.
  

• Structural Support for Vertical Motors
• Check vertical mounting brackets or plates for deformation or fatigue.
• Verify that thrust loads are adequately supported, especially in vertical pump motors.
• Confirm that vertical motor enclosures are properly supported to prevent sag or tilt.
  

• Grounding Bonding on Motor Housing
• Inspect frame grounding strap or bonding wire for proper connection.
• Ensure continuity between motor frame and grounding system.
• Check the grounding lug for corrosion or looseness.

8. Control Circuitry and Connections

• Control Panel Visual Inspection
• Check for signs of overheating, discoloration, or burnt components.
• Inspect for dust, moisture, insect intrusion, or corrosion inside the panel.
• Ensure panel door gaskets are intact and the panel is sealed properly.
• Confirm panel layout matches the latest wiring diagram.
  

• Terminal Connections and Wiring
• Tighten all control wiring terminals using a torque screwdriver to rated torque.
• Inspect wires for signs of insulation damage, brittleness, or color fading.
• Confirm wire labeling is clear and matches schematic.
• Look for signs of arcing, carbon tracking, or loose strands near terminals.
  

• Control Relays and Contactors
• Inspect contactors for pitting, welding, or wear on contact points.
• Test coil operation by manually activating control signal (if safe).
• Measure coil resistance using a multimeter and compare with OEM specs.
• Replace worn-out auxiliary contacts or contact kits if switching is unreliable.
  

• Control Power Supply
• Measure control voltage (e.g., 24V DC or 110V AC) under load using a multimeter.
• Verify transformer or SMPS output matches expected range.
• Check fuses or circuit breakers protecting control power — replace blown fuses with correct rating.
  

• Timers, Sensors, and Interlocks
• Test timer relays for proper delay, on/off timings, and repeatability.
• Confirm interlock operation (mechanical or electrical) in both manual and auto modes.
• Test start/stop pushbuttons, selector switches, and emergency stop for continuity and response.
  

• Wiring Ducts and Routing
• Check for overcrowded wiring ducts — ensure cables are neatly routed and not under stress.
• Secure any loose wires using cable ties or clips.
• Inspect for sharp bends or rubbing against sharp panel edges — apply grommets or protection where needed.
  

• Programmable Logic Controllers (if used)
• Confirm input/output (I/O) status matches real-world devices.
• Backup PLC program to external storage or server.
• Clean dust from PLC modules using dry air.
• Check battery status (if applicable) and replace as recommended.
  

9. Protection Devices

• Overload Relays
• Visually inspect for mechanical damage or overheating signs.
• Confirm settings match motor Full Load Amps (FLA) as per nameplate.
• Manually trip and reset the relay (if applicable) to verify mechanical operation.
• Test relay operation under simulated overload using a test set or resistor bank.
• Record tripping time and compare with the manufacturer’s trip curve.
  

• Fuses and Circuit Breakers
• Check fuse ratings and types (time-delay, fast-acting) — verify they match circuit design.
• Inspect for discoloration, melted links, or loose fuse holders.
• Use a continuity tester to confirm the fuse is intact.
• Test circuit breakers for mechanical operation (ON/OFF/Trip).
• Measure breaker trip settings (thermal, magnetic, electronic) against motor rating.
• Exercise MCCB/MCB manually to prevent mechanical seizing.
  

• Ground Fault and Earth Leakage Protection
• Inspect current transformer (CT) wiring and connections.
• Test ground fault relay or ELCB/RCD using the built-in test button.
• Use an external test kit to inject leakage current and verify tripping at rated sensitivity (e.g., 30mA, 100mA, 300mA).
• Document trip time and leakage current value.
  

• Short-Circuit Protection Devices
• Verify short-circuit protection (HRC fuses, MCCBs) coordination with upstream/downstream devices.
• Confirm device interrupting capacity is suitable for system fault level.
• Look for arc flash damage or burned terminals indicating past fault events.
  

• Thermal Protection (Embedded Sensors)
• Inspect motor thermistors (PTC/NTC) and RTDs for correct installation and wiring.
• Use a multimeter to measure sensor resistance and compare with standard charts.
• Simulate over-temperature condition (if safe) and confirm that thermal protection triggers alarm or motor trip.
• Check integration of temperature sensors with controller or protection relay.
  

• Surge and Transient Protection
• Inspect surge suppressors (MOVs, TVS diodes) for signs of failure or discoloration.
• Confirm correct installation across supply terminals.
• Use a tester (if available) to verify clamping voltage or response.
• Replace devices nearing end-of-life or those showing signs of repeated stress.

What are the Tips to Follow for Electric Motor Maintenance?

Following are useful electric motor maintenance tips that will keep your electric motor running smoothly over a long period of time:

• Wipe dust and debris

  Clear all ventilation paths and surfaces to support efficient cooling, reduce overheating risks, and prevent contaminants from reaching internal components.

• Investigate unusual noise or vibration

  Look into abnormal sounds or movements to detect misalignment, loosened parts, or bearing wear before they develop into major operational failures.

• Tighten all electrical connections

  Secure each terminal and joint properly to prevent voltage drops, overheating, or electrical faults during operation.

• Apply only the recommended amount of lubricant

  Follow manufacturer instructions precisely to maintain smooth bearing motion and prevent damage from excess or insufficient lubrication.

• Keep checking motor temperature

  Identify overheating issues early by scanning the motor surface during operation and comparing readings to acceptable temperature ranges.

• Align the motor properly

  Position the motor and driven component precisely to reduce mechanical stress, extend part life, and support smooth power transmission.

To Wrap Up

An electric motor maintenance checklist is only as useful as the discipline behind it and you need to stick to it to ensure sustainable output from your motors. Once the core checks are defined and scheduled, the rest is about execution and then there will be no alarms, no surprises, just motors doing what they’re meant to do.