The two schools
Preventive maintenance (PM) is calendar-driven: every 12, 24, or 36 months you de-energize, clean, torque, and re-test according to a fixed checklist.
Predictive maintenance (PdM) is condition-driven: continuous or periodic monitoring (thermal scans, partial discharge, online dissipation factor) tells you when a specific asset needs intervention.
Most US industrial facilities run pure PM. That's leaving real value on the table.
Where PM falls short
- A breaker that fails in month 13 of a 24-month cycle won't be caught
- Bus joints loosen from thermal cycling, not from time elapsed
- Insulation degradation in MV cables is exponential — a yearly check misses the knee of the curve
Where PdM wins
A modest PdM program — quarterly thermography + annual partial-discharge scans on MV gear — typically catches 80%+ of incipient faults before they trip. The ROI on a single avoided unplanned outage usually pays for several years of monitoring.
Recommended hybrid approach
- Keep PM on a 24- or 36-month cycle for everything
- Add quarterly IR thermography on every LV switchboard
- Add online PD monitoring for any MV gear above 5kV that's mission-critical
- Trend the data — single readings tell you almost nothing; trends tell you everything
The cost of monitoring has dropped dramatically over the last five years. There's almost no remaining excuse to run pure PM on critical gear.
