Upon receipt of a proper application, the utility shall install an underground extension with sufficient capacity and suitable materials which, in its judgment, will assure that the applicant, or customer, will receive safe, adequate, and reasonable electric service to meet his requirements. The design and construction of the underground extension shall conform to accepted good engineering practice in the electric industry to provide an installation at reasonable cost, consistent with the objectives of §A of this regulation. If the applicant demands an installation more costly than that normally furnished by the utility to meet the objectives of §B of this regulation, then the applicant shall pay the cost of his additional requirements.