High-voltage electrical substations are used to distribute power between residential, industrial, commercial, and agricultural regions. Previous earthquakes have shown that electrical substations are seismically vulnerable. Although equipment of these substations had been designed individually according to the electrical and seismic requirements, they have shown poor seismic performance resulting from interaction problems. In recent decades, some research has been done on the effects of interaction between substation equipment items, which are connected by flexible or rigid conductors. Although more than two items are usually connected to each other, only two items are assumed in most studies. In this paper, the effects of interaction between three interconnected items are investigated using incremental dynamic analyses. Two failure modes are considered, including failure of insulators and disconnection of conductors. The results are presented in terms of maximum sustainable ground motion acceleration and failure probability, and discussions are made to choose the best pair of interconnected items.