Abstract: In the operation and inspection of transmission cable, there had been cases of cross linking transposition failure defects, which were caused by the different arrangement modes of the coppers in the two cross linking protection grounding boxes of a cross linking unit. Such defects led to a significant increase in grounding loop current, affecting the power supply reliability of cable lines. The loop induced voltages were analyzed through the phasor method under ideal conditions, based on the schematic diagram of a unit with a cross linking transposition failure defect, to get the reason for the increase of the loop current. Further simulation was performed using the software of ATP-EMTP to visualize the impact that would be caused by the defect under the non-ideal condition. A cross linking transposition failure defect could be effectively avoided by changing the positions of a wiring column in cross linking protection grounding boxes or by adding an insulating block to the boxes.