In this paper, we studied on the detection of series arcing which is a main cause of electrical fires in low-voltage indoor wiring system. To distinguish series arcing state from normal one, we proposed a detection method based on that the magnitude of arc voltage included in AC voltage varies at random during series arcing. We designed and fabricated a high-pass filter with the low cut-off frequency of 3 kHz to attenuate AC voltage by -80 dB or below, and to pass arc voltage without distortion. Also, a phase shift algorithm which eliminates the periodic component of arc voltage was used for nonlinear loads like incandescent lamps controlled by a dimmer.