When any electrical utility is engaged in both interstate business and intrastate business in this State and at any time transmits electricity either into or from this State (a) by the use, either wholly or in part, of any transmission line or other facilities also used in intrastate service in this State, (b) if such electricity is generated by the use, either wholly or in part, of any facilities also used in intrastate service in this State or (c) if such electricity is a part of any supply of electricity acquired by purchase, exchange or any means other than actual generation and any part of such supply of electricity is also at any time used in intrastate service in this State, the Commission may require such electrical utility to maintain at or near the State line, within this State, a meter or meters of a type or types to be approved by the Commission before installation which shall accurately and separately measure and register such electricity coming into and going out of this State. Any such electrical utility shall make such records and reports of the meter readings as the Commission may require, all to the end that the Commission in the performance of its duties in relation to intrastate operations and rates in this State may at all times be able to determine with reasonable accuracy the results of the intrastate operations in this State of such electrical utility apart from its interstate operation or its operations in any other state or states and to segregate with reasonable precision the property devoted to interstate service or to the services of any other state or states.