A method for locating harmonic producing source in the low-voltage distribution network is presented. The method aims to employ natural load variability of the existing non-linear installations. By performing multi-point time-synchronized acquisition of the voltage and current waveforms and analysing spectral characteristics of the signals, harmonic impedance of the cable section associated with non-linear load is estimated. A certain rejection algorithm is applied in order to discard data sets with unreliable information. To validate the method, a field test was established in the low-voltage grid. The results demonstrate capability of the proposed technique to accurately estimate harmonic impedances and successfully identify location of harmonic current source in the grid.