The neutral point ungrounded system is widely used in China because of its power supply reliability. When an intermittent arc grounding fault occurs, active grounding the fault phase bus can extinguish the arc and suppress the overvoltage. Use of the bus active grounding device adds an extra grounding process with fault characteristics, which can provide data support for subsequent fault line selection. As far as the zero-mode network of the system is concerned, the magnitude and direction of the zero-mode current flowing on each line depends on the location of the fault and changes in the equivalent voltage source. Because of the input of the bus active grounding device, the fault originally located on the line is transferred into the bus, so the electrical characteristics of the two transient processes before and after can be comprehensively used. The zero-mode current of each line is extracted to calculate the line energy, and the energy difference between two transient processes is compared with the threshold value to realize fault line selection. This method uses the current signals of the respective feeders, and it does not require data comparison between feeders. The accuracy and robustness of the proposed method are verified by simulations.