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In this paper, the detection and isolation of open-switch faults in induction motor (IM) drives are addressed from a model-based perspective. Residuals are synthesized by using nonlinear observers followed from a directional characterization. First, it is observed that the IM model can be written in a recurrent decoupled structure by taking the stator currents and mechanical velocity as outputs. In this way, residuals can be insensitive to load torque and operating conditions, and simultaneous faults can be addressed. A pulsewidth modulation three-phase inverter is studied as power actuator for the IM. Hence, in order to isolate faults related to the six switching devices, a directional residual evaluation in the -frame is employed. Hence, three residuals are constructed to isolate the faulty switches. The ideas presented in this paper are validated experimentally in a test bench of 1-hp IM under single and simultaneous faults.