Supervised multi-class classification models that identify not just that a deviation is occurring but which specific failure mode is developing -- because arriving at an asset with the wrong parts and tools because the fault was misidentified wastes the maintenance intervention and risks unnecessary downtime. Failure modes addressed by equipment class: for induction motors and rotating equipment, the classifier distinguishes bearing defects (inner race, outer race, ball defect -- each producing characteristic BPFI/BPFO/BSF frequency peaks in the vibration spectrum), rotor imbalance (1x vibration peak at running speed), shaft misalignment (1x and 2x peaks with axial vibration component), stator winding insulation degradation (partial discharge signatures in high-frequency current measurements), and fan blade damage (frequency peaks at 1x per blade count). For hydraulic systems, the classifier distinguishes pump cavitation (high-frequency acoustic emissions, irregular pressure pulses), internal leakage (flow/pressure relationship deviation), and contamination (particle count sensor trend). For electrical switchgear and transformers, the classifier addresses hot spots (thermography or distributed temperature sensors), partial discharge, and insulation breakdown. Feature engineering for classification: frequency domain features extracted from vibration spectra (peak amplitude at fault frequencies, frequency band energy ratios, sideband spacing), time domain statistical features (RMS, kurtosis, crest factor), and envelope analysis features -- the signal processing steps that convert raw sensor readings into the features that discriminate between failure modes. Model training approach when class imbalance is severe (many healthy examples, few examples of each failure mode): SMOTE oversampling for minor fault classes combined with class-weighted loss functions; physics-informed synthetic data generation for failure modes where historical examples are absent entirely. Classification output provides the failure mode probability vector, not just the predicted class, so the maintenance engineer sees "bearing outer race defect: 78% probability, imbalance: 15%, other: 7%" and can make an informed decision about what to inspect first.