A practical inspection checklist to keep industrial motors running: what to check, how often, and the measurements that matter most.

Visual and Environmental Inspection: Begin every inspection with strict lockout/tagout and a quick job hazard assessment. Scan the motor exterior for corrosion, paint blisters, cracks, and oil or dust buildup that signal heat or contamination issues. Verify enclosure integrity by checking end bells, conduit entries, cable glands, and gaskets for tightness and proper sealing to prevent ingress of moisture or abrasive particles. Confirm the grounding path is clean and secure, and ensure strain reliefs protect cables from vibration. Look for missing nameplate data, broken fan shrouds, blocked ventilation paths, and clogged drain plugs that trap condensation. Inspect mounting hardware for looseness and signs of fretting at the foot interface. Make sure the shaft guard is intact and that rotation arrows and phase tags are visible. Note nearby sources of heat, chemicals, or airborne debris that can shorten motor life. Document conditions with photos and clean the exterior using nonconductive brushes and controlled air, avoiding aggressive blasting that can drive contaminants inward.

Lubrication and Bearings: Bearings are the heart of reliability, so focus on correct lubrication and seal health. Verify the specified grease type and NLGI grade, and never mix incompatible chemistries. Follow the manufacturer's re-grease volume and interval, and purge old grease where provisions exist to avoid overgreasing that elevates temperature and churns the lubricant. Inspect bearing caps, purge ports, and end covers for leakage, dust trails, and cracked seals. For oil-lubricated designs, check oil level, color, viscosity grade, and odor; milky or dark oil indicates water or oxidation. Examine desiccant breathers and replace saturated elements to control humidity. Use a sonic or stethoscope probe to listen for roughness, chatter, or tonal changes that suggest spalling. Assess axial and radial play against acceptable limits. On variable-frequency drives, mitigate bearing currents by using insulated bearings on the non-drive end and a shaft grounding brush on the drive end. Trend temperature at both housings to catch lubrication breakdown early.

Electrical Integrity of Windings and Connections: Healthy windings begin with tight, clean connections. De-energized, inspect terminal lugs, bus bars, and jumpers for discoloration, looseness, and insulation damage. Verify proper phase identification and torque to specification using a calibrated tool. Test insulation resistance with a megohmmeter, applying temperature correction and trending results over time; a declining curve is a warning. Use polarization index or dielectric absorption testing to gauge moisture and contamination within the insulation system. Measure phase-to-phase winding resistance to detect imbalances that hint at turn damage or poor joints. Check internal lead dress and tie cords for abrasion and ensure anti-tracking varnish remains intact. Validate embedded RTDs or thermostats for continuity and proper setpoints, and confirm protection relays see the sensors. For medium-voltage assets, consider offline tests such as partial discharge or surge comparison only when planned and risk-assessed. Ensure terminal boxes are clean, dry, and sealed, with clearances maintained to avoid creepage and tracking under high humidity.

Vibration, Balance, and Alignment: Elevated vibration accelerates bearing wear and fatigue. Survey overall velocity and acceleration in three axes at both bearings and the motor foot. Look for signatures of unbalance (1× running speed), misalignment (1× and 2× with axial emphasis), and looseness (broadband). Inspect couplings for cracked hubs, worn elastomer inserts, misfit keys, or bent grids; verify guard clearance. For belt drives, check tension, sheave wear, and angular alignment to prevent side loading. Correct soft foot by measuring foot gaps and shimming until stable; looseness at the base can masquerade as alignment issues. Balance the rotor if vibration persists after alignment and structural checks. Consider resonance by performing a bump test on the base and comparing natural frequencies with operating speed. Trend data and set alarm thresholds appropriate for frame size and criticality. Proper shaft alignment reduces energy consumption, temperature, and seal wear, translating to longer intervals between interventions.

Thermal Management and Cooling Systems: Heat is a primary driver of insulation aging, so manage temperature aggressively. Use infrared thermography or contact sensors to scan bearings, end bells, stator housing, and the terminal box for abnormal hot spots. Confirm cooling air pathways are open; on TEFC designs, clean fins and verify fan blades are intact and rotating in the correct direction. For open motors, keep screens and filters clean to maintain airflow without ingesting debris. Where air-to-air or air-to-water heat exchangers are used, check differential pressure, coolant flow, and signs of fouling or leakage. Evaluate ambient conditions, altitude, and load profiles that raise internal temperature. Motors on VFDs may run hotter at low speeds; consider auxiliary fans or minimum-speed rules to sustain airflow. Monitor bearing temperature trends to validate lubrication health. Ensure thermal sensors and overload elements are set to the nameplate current and insulation class, and investigate any recurring thermal trips rather than simply resetting.

Power Quality, Controls, and Protection: Poor power quality undermines motor life and torque. Measure voltage imbalance, keeping it minimal to avoid disproportionate current heating in one phase. Assess total harmonic distortion and switching rise times on VFD applications; install dV/dt or sine-wave filters when cable runs are long, and use properly rated shielded cable with correct grounding at one end to control common-mode currents. Review starter components: contactors should have clean poles and crisp engagement, with overload relays set to full-load amps and coordinated with upstream protection. Confirm correct phase rotation and that undervoltage, ground fault, and phase loss protections are functional. Inspect control terminals for tightness and insulation integrity, and verify interlocks and permissives operate as designed. Check the motor's grounding and bonding network to minimize shaft voltage and noise coupling into instrumentation. Trend current versus load to catch dragging loads, misalignment, or winding deterioration before failures cascade.

Documentation, Scheduling, and Condition-Based Strategy: Sustained reliability hinges on disciplined documentation and risk-based planning. Build a CMMS route with standardized checklists covering cleanliness, bearings, electrical tests, vibration, temperatures, and protective device settings. Establish baselines at commissioning so trends highlight deviation early; capture photos, measurements, and corrective actions with timestamps and asset IDs. Rank motor criticality and tailor intervals accordingly, intensifying inspections for harsh environments or intermittent duty. Integrate condition-based tools such as vibration monitoring, motor current signature analysis, thermography, and lubricant analysis to shift from time-based to evidence-driven maintenance. Stock essential spares like bearings, seals, fans, and couplings, and record torque values, fits, and alignment targets. Use root cause analysis after anomalies and close feedback loops with operations to address process drivers. Emphasize safety with clear lockout/tagout procedures and training, and avoid intrusive tests unless the risk is justified. The outcome is predictable performance, fewer surprises, and lower lifetime cost.