Interconnections of plant or system primarily for the purpose of rendering emergency or temporary electric service to another electric utility, in order to maintain adequate reserve capacity for all the electric utilities involved or to pool spare plant or system capacity, shall not in itself establish an electric utility as part of the operating area of another for purposes of sections 70-604 to 70-619. When a district which purchases electricity for resale actually segregates its distribution system to its customers such that only a portion of its total customers normally receive the electricity transmitted by a given wholesale supplier district, that wholesale supplier district may be required to include in its operating area only that portion of the customers of the supplied district who are so indirectly supplied by electricity from that wholesale supplier district.