The ability to detect turn-to-turn short-circuit faults (turn-faults) is an important aspect of ensuring reliable machine operation. Turn-faults create a low impedance short-circuit path within the winding, resulting in large fault currents, creating winding hotspots and an increased rate of insulation degradation. This causes the fault to propagate within the winding, increasing fault severity, until reaching a point of catastrophic failure. Early detection of a turn-fault allows mitigation strategies to be put in place, reducing the amount of damage caused to the machine. As a turn-fault develops from insulation failure, the residual series resistance of the insulation in the short-circuit path reduces; this work considers the impact of a range of short-circuit path resistance values on the ability for a PWM harmonic based turn-fault detection algorithm to operate correctly, determining how far the fault resistance must fall (or conversely, how far the fault-current must rise) in order to be detectable by the algorithm. It is concluded that the algorithm is capable of successfully operating with a fault path resistance around two orders of magnitude (100mΩ) larger than the short circuit path without any additional resistance (1.4mΩ).