Inter-turn short-circuit (ITSC) fault is one of the most typical fault in different types of magnetically coupled circuits such as transformers and rotating or linear electrical machines. This paper presents a general study to approach the ITSC understanding and modeling as long as the circuit can be represented in state-space (SS) equations. The ITSC in any magnetically coupled windings can be accurately modelled by means of step-down autotransformer circuit in the faulty winding. Moreover, considerations about the leakage inductances estimation are studied and generalized. A case of study of ITSC is proposed: three-phase squirrel-cage induction machine. SS representation of the system is presented and simulated in MatLab environment by means of ODE and Simulink. Also, equivalent circuits derived from the SS representation are shown. For verification purposes Finite Element Analysis (FEA) and experimental test are conducted. A comparison between the proposed theoretical models, simulations and experimental results is performed.