A method, performed by a power sourcing apparatus is provided. The method includes (a) providing an electronic signal to a powered device (PD) over a wire through a circuit device, the circuit device permitting current to flow at pre-determined frequencies, the pre-determined frequencies forming a first set of frequency components, (b) sensing the electronic signal over the wire to detect frequency components present in the electronic signal, the detected frequency components forming a second set of frequency components, and (c) classifying the electronic signal into one of a plurality of classes according to a pattern of frequency components present in the first and second sets. Apparatus for use in conjunction with the method are also provided.