Short-circuiting in element conductors in the AC power cord is one of the main causes of fire accidents originating from electric equipment. It is not easy to detect this type of short-circuit fault with a conventional circuit breaker, because the duration of a short circuit is rather short, and the magnitude of the short-circuit current is smaller than the threshold for operation. In this paper, voltage and current waveforms are analyzed in detail when element conductors for a 100-V AC power cord are artificially short-circuited. The authors focus on a feature that characterizes the short-circuit phenomenon, namely, the distortion of the voltage waveform from the sinusoidal shape between arc generation and the extinction of the conductor elements. Two possible diagnosis methods are discussed for short-circuit detection: one is based on the duration of specified voltage range, and the other is based on the area formed between the measured and reference voltage waveforms.