Unambiguous detection of stator inter-turn faults for induction machines at their incipient stage, i.e., few turns' fault, has recently received great attention. Traditionally, inter- turn faults are detected using negative sequence current and impedance. However, their effectiveness under supply unbalance conditions is questionable. Recently line current third harmonic (+3f) has also been used in an attempt to achieve this goal. But, issues such as inherent structural asymmetry and voltage unbalance also influence the +3f. In this paper, positive and negative sequence third harmonics (plusmn3f) of line current under different operating conditions have been explored by combining space and time harmonics. The suggested fault signature was obtained by removing residual components from tested quantities. Simulation and experimental results using one second of data indicate proposed plusmn3f signatures are capable of very effectively detecting even single turn fault and distinguish it from voltage unbalance and structural asymmetry.