(a) Investments may be made in the bonds of any corporation that at the time of the investment is incorporated under the laws of the United States or any state of the United States, or the District of Columbia, and transacting the business of supplying electrical energy or artificial gas or both for light, heat, power and other purposes; provided, that at least seventy-five percent (75%) of the gross operating revenues of any such corporation are derived from that business, and not more than fifteen percent (15%) of the gross operating revenues, are derived from any one (1) kind of business other than supplying electricity and gas; and provided further, that corporation is subject to regulation by the Tennessee public utility commission or a public utility commission, or other similar regulatory body duly established by the laws of the United States or the states in which such corporation operates, subject to the following conditions:

(1) The corporation has all franchises necessary to operate in territory in which at least seventy-five percent (75%) of its gross income is earned, which franchises shall either be indeterminate permits or agreements with or subject to the jurisdiction of the Tennessee public utility commission, or other duly constituted regulatory body, or extend at least five (5) years beyond the maturity of the bonds;

(2) The outstanding full paid capital stock of the corporation is equal to at least two thirds (⅔) of the total debt secured by mortgage lien on any part or all of its property; provided, that in case of a corporation having nonpar value shares, the amount of capital that such shares represent is the capital as shown by the books of the corporation;

(3) The corporation has been in existence for a period of not less than eight (8) fiscal years and at no time within the period of eight (8) fiscal years next preceding the date of the investment has the corporation failed to pay promptly and regularly the matured principal and interest of all its indebtedness direct, assumed or guaranteed, but the period of life of the corporation, together with the period of life of any predecessor corporation or corporations from which a major portion of its property was acquired by consolidation, merger or purchase shall be considered together in determining the required period;

(4) For a period of five (5) fiscal years next preceding the investment the net earnings of the corporation have averaged per year not less than twice the average annual interest charges on its total funded debt applicable to that period, and for the last fiscal year preceding the investment its net earnings have been not less than twice the interest charges for a full year on its total funded debt outstanding at the time of the investment, and for that period the gross operating revenues of any such corporation have averaged per year not less than one million dollars ($1,000,000), and the corporation has for each year either earned an amount available for dividends or paid in dividends an amount equal to four percent (4%) upon a sum equivalent to two thirds (⅔) of its funded debt;

(5) The bonds must be part of an issue of not less than one million dollars ($1,000,000) and must be mortgage bonds secured by a first or refunding mortgage secured by property owned and operated by the corporation issuing or assuming them, or must be underlying mortgage bonds secured by property owned and operated by the corporations issuing or assuming them. The bonds are to be refunded by a junior mortgage providing for their retirement; provided, that the bonds under the junior mortgage comply with the requirements of this section and that the underlying mortgage is either a closed mortgage or remains open solely for the issue of additional bonds which are to be pledged under the junior mortgage. The aggregate principal amount of bonds secured by the first or refunding mortgage plus the principal amount of all the underlying outstanding bonds shall not exceed sixty percent (60%) of the value of the physical property owned as shown by the books of the corporation and subject to the lien of the mortgage or mortgages securing the total mortgage debt; and provided further, that, if a refunding mortgage, it must provide for the retirement on or before the date of their maturity of all bonds secured by prior liens on the property; and

(6) Not more than twenty-five percent (25%) of the assets of any trust shall be loaned on or invested in bonds of electric and gas corporations, and not more than ten percent (10%) of the assets of any trust shall be invested in the bonds of any one such corporation, as authorized by this section.

(b) In determining the qualifications of any bond under this section where a corporation has acquired its property or any substantial part thereof within five (5) years immediately preceding the date of the investment by consolidation or merger, or by the purchase of all or a substantial portion of the property of any other corporation or corporations, the gross operating revenues, net earnings and interest charges of the several predecessor or constituent corporations shall be consolidated and adjusted so as to ascertain whether there has been compliance with the requirements of subdivision (a)(4).

(c)

(1) The gross operating revenues and expenses of a corporation, for the purposes of this section, shall be, respectively, the total amount earned from the operation of, and the total expense of maintaining and operating all property owned and operated by or leased and operated by the corporation, as determined by the system of accounts prescribed by the Tennessee public utility commission, public utility commission or other similar regulatory body having jurisdiction in the matter. The gross operating revenues and expenses, as defined in this subdivision (c)(1), of subsidiary companies may be included; provided, that all the mortgage bonds and a controlling interest in stock or stocks of the subsidiary companies are pledged as part security for the mortgage debt of the principal company; and

(2) The net earnings of any corporation, for the purpose of this section, shall be the balance obtained by deducting from its gross operating revenues, its operating and maintenance expenses, taxes other than federal and state income taxes, rentals and provision for renewals and retirements of the physical assets of the corporation, and by adding to the balance its income from securities and miscellaneous sources, but not, however, to exceed fifteen percent (15%) of the balance;