None of the three announces itself. All three are visible to structured inspection long before they cause a trip.
Most drive failures that look sudden were building for months. Three of the most common contributors share a property: they are quiet. They do not trip anything while they develop — but they are all observable, if someone looks.
Loose connections
Vibration and thermal cycling gradually relax bolted and screwed connections. A slightly loose power terminal has slightly higher resistance; higher resistance means local heating; heating accelerates the loosening. By the time discoloration is visible, the connection has been cooking for a while. Thermal inspection finds these as hot spots; torque checks during planned shutdowns prevent them.
Heat
Temperature is the master variable of power-electronics life. Blocked filters, tired fans, dirty heatsinks, sun-heated cabinets, or simply a hotter production season all push component temperatures up. The consequences arrive later — capacitor aging, semiconductor stress — which is why temperature problems deserve attention even when nothing has tripped yet.
Harmonics and supply quality
Drives both produce and suffer from distortion in the electrical environment. Supply-side events — notching, transients, unbalanced phases, brown-outs — stress rectifiers and DC-bus components. Grounding and cable-routing problems can couple noise into control circuits, producing faults that appear random. When a drive trips "for no reason", the reason is often upstream of the drive.
The common defense
All three enemies respond to the same discipline: periodic structured inspection — visual, thermal and electrical — during planned windows, with findings recorded so trends are visible from one visit to the next.
This article is general guidance. Diagnosis of a specific installation requires qualified personnel and measurement on site.