Abstract: Methods and apparatuses for monitoring a power circuit are disclosed. Electric conditions in the power circuit are sampled by a sensor device attached to the power circuit. The sampling can be based on a first sampling window and a second sampling window, the second sampling window being shorter than the first sampling window. Results of the sampling are analysed to determine at least one device drawing current from the circuit and to determine for the at least one device a harmonic vector based on the first sampling window and a transient vector based on the second sampling window. A signature vector for the at least one device is determined based on the harmonic vector and the transient vector.