Abstract: A mobile electrical transformer assembly is mounted on a trailer and includes a three phase transformer. The electrical switching for the transformer includes a circuit interrupter having three vertical towers at transversely spaced positions. Each tower and its associated lightning arrester is mounted on two arms of one of three vertical posts in a row. In respect of the outer posts, both of the arms are pivotal about the vertical axis of the post to move the tower and the arrester outwardly to increase the spacing. The arm of each tower includes a bracket at the bottom mounted for pivotal movement about a horizontal axis for movement of the tower from a vertical operating position to an inclined transport position. The arm of each arrester is movable so that the arresters are moved in the transport position to a location out of alignment with the respective tower.