Except by agreement of the suppliers involved, no supplier shall offer electric service to additional ultimate users outside its service area or construct or acquire a new electric line or extend an existing line into the service area of another supplier for the purpose of furnishing service to ultimate users therein without first applying to the board and receiving approval thereof, after due notice and hearing under rules and regulations of the board. Such approval shall be granted only if the board finds that the customer or customers proposed to be served cannot or will not be furnished adequate electric service by the supplier in whose service area the customer is located, or that the provision thereof by such supplier would involve wasteful and unwarranted duplication of facilities. This section shall not apply to agreements referred to in subsection (2) of section 70-1002.