This paper deals with the consequences of some manufacturing imprecision related to the use of a fractional-slot concentrated winding (FSCW) in recent permanent-magnet synchronous machine (PMSM) designs. Although these topologies improve the efficiency of motors, they also lead to consider complex models, including undesirable harmonics, which can be strongly different from classical models expressed in a rotating frame. This may affect the control and the monitoring techniques used to detect some commonly reported faults such as turn short-circuit faults in the windings. Thus, adaptations are needed to improve classical fault detection methods. This paper considers an undesirable additional air gap, due to an imperfect manufacturing process, between the stator back iron and the teeth of a modular PMSM having an FSCW. A finite-element method and permeance network modeling are used to study the behavior of the machine. Good agreement is obtained between the two methods, validating the significant effects of such manufacturing faults on the behavior of the machine. Experimental tests confirm the occurrence of additional air gaps and their consequences on some classical interturn fault detection methods. Improvements are also proposed in order to consider relevant indicators even in the presence of inherent manufacturing faults.