The occurrence of unpredicted and sudden failures in power cables seriously threatened the nearby control cables. Two cases of unbalance in the three-phase current load originate from a high horsepower pump and a sudden power off in an MW pump, resulting in an error signal detected in the adjacent control cable. However, these two cases just occurred once during the plant operation; no more history records can be a reference. In this paper, a typical power cable and control cable structure was constructed, typical accidents in power cables were considered, and electromagnetic interference was considered. The results show that the unbalance of the three-phase load results in a fold increase in interference current. Compared with the two-phase unbalance, the one-phase would bring a higher current. In other words, power off in a sudden situation brought a higher current than three-phase unbalance, especially a faster drop in current load. Finally, more attention should be given to the power cable operation, including unbalance in the power cable and an urgent power off.