(a) The commission may, after providing reasonable notice and opportunity to be heard, ascertain and set the fair value of the whole or any part of the property of a public utility, insofar as it is material to the exercise of the jurisdiction of the commission. The commission may make revaluations from time to time and ascertain the fair value of all new construction, extensions, and additions to the property of a public utility. If a public utility furnishes more than one classification of utility service the utility shall allocate the investment and expenses associated with the property used and useful in furnishing service among the utility services and it may not solely consider the utility's total investment and expenses in fixing rates for a particular service.

(b) In determining the value for rate-making purposes of public utility property used and useful in rendering service to the public, the commission shall be guided by acquisition cost or, if lower, the original cost of the property to the person first devoting it to public service, less accrued depreciation, plus materials and supplies and a reasonable allowance for cash working capital when required.

(c) For rate-making purposes, indebtedness, debt service, and payments by a regulated public utility to a person having an ownership interest of more than 70 percent in the utility shall be considered to be ownership equity, profits, or dividends except to the extent that there is a clear and convincing showing that

(1) the indebtedness was incurred, or the payments made, for goods or services that were reasonably necessary for the operation of the utility; and

(2) the goods or services were provided at a cost that was competitive with the price at which they could have been obtained from a person having no ownership interest.