Wrong settings on a supply transformer's taps, poorly distributed single-phase loads, overloading (saturating) supply transformers, excessive VFDs on low voltage busses, excessive non-harmonic frequencies on a VFD, missing line-inductors on VFD applications and missing or open power factor correction capacitors

Thermal overloading of the motor

Current related problems; imbalances, harmonics etc

Broken rotor bars, mechanical issues, transient overloading, mechanical imbalances along with bearing problems and load issues such as cavitation