Low-voltage three-phase induction motors are the backbone of industrial operations. But like any hardworking machine, they need regular maintenance to stay reliable. In this blog, we’ll walk through a human-friendly, step-by-step checklist for performing a complete 6-month periodic maintenance inspection.
This guide is ideal for electricians, maintenance engineers, and plant technicians looking to maximize motor performance and lifespan.
Step 1: Pre-Maintenance Safety Measures
1.1 Isolate Power
Before doing anything, isolate power at the substation drawer to ensure zero electrical energy is available during the maintenance process.
1.2 Lockout/Tagout (LOTO)
Apply the lockout/tagout procedure. Each technician should receive a personal lock to secure the power source.
1.3 Local Isolation
Also isolate the local start/stop station to double-confirm that the motor cannot start accidentally.
1.4 Verify Zero Energy
Use a voltage tester to confirm no live voltage exists. Always wear appropriate personal protective equipment (PPE).
Step 2: Visual Inspection
Inspect the motor for any obvious signs of damage or wear:
- Housing and terminal box
- Cooling fins and fan cover
- Cable gland
- Signs of overheating, corrosion, oil leaks, or dust build-up
Step 3: Electrical Testing
3.1 Winding Continuity / Resistance Test
Use a digital multimeter or ohmmeter to test:
- UV, VW, and UW winding pairs
- Ensure resistance values are within ±10%
- Record values and compare with fingerprint/reference values
3.2 Insulation Resistance Test
Use a 500V or 1,000V insulation tester (megger):
- Test between U, V, or W to Earth (if terminals are connected)
- If disconnected, test between UV, VW, UW
- Acceptable resistance is over 1 MΩ
- Record results for trending and comparison
Step 4: Earthing Test
Use a clamp-type earth resistance tester to check ground connection:
- Confirm resistance is within standard (usually <5Ω or <2Ω)
- Record measured values for future reference
Step 5: Protection and Control Circuit Check
5.1 Retightening
Inspect and retighten any loose control or power connections in the substation drawer.
5.2 Test Protection Devices
- Test overload relays and contactors
- Confirm trip settings match the motor’s full-load current
- Simulate fault if safe to ensure proper trip function
5.3 Verify Logic and Interlocks
Double-check the control logic and any interlock conditions are functioning correctly.
Step 6: Reconnection and Test Run
- Remove all LOTO tags and locks only after verifying all systems are secure
- Reconnect terminals and control wiring properly
- Restore power and perform a test run
- Observe for any abnormal sounds, vibration, or temperature rise
Step 7: Lubrication
- Follow manufacturer’s lubrication schedule (typically every 4,000 working hours)
- Use correct grease type as recommended
- Wipe off excess grease and seal the grease nipple after application
Step 8: Predictive Maintenance: Thermal Imaging
Use a thermal camera to scan while the motor is running:
- Inspect winding temperature
- Scan terminal connections
- Check bearing heat levels
- Document anomalies for future analysis
You can download the complete 6-month motor checklist from here
Conclusion
Performing this 6-month maintenance checklist not only prevents breakdowns but also ensures optimal efficiency and safety. Regular testing, inspections, and lubrication are essential habits for any facility using low-voltage three-phase motors.
Stay safe, stay efficient, and let knowledge enlighten your world.