Electric Network Frequency(ENF) is a recently developed technique for the authentication of audio signals. ENF gets embedded in audio signals due to electromagnetic interferences from power lines and hence can be used as a measure to find the geographical location and time of recording. Given an audio signal, this paper presents a technique of finding the power grid the audio belongs to. Towards this, we first extract the ENF sinusoid using a very narrow bandwidth filter centered around the nominal frequency. The filter is designed using a frequency response masking approach. The ENF is estimated from the ENF sinusoid using Short time Fourier Transform technique. In order to classify a given audio, we first estimate ENF from the ENF sinusoids obtained from audio and power signals. Further, we use a matched filter in order to decide the corresponding power grid of the audio.