The prices charged for all electrical energy supplied and sold to supply authorities pursuant to section three of this Act and section three hundred and eleven of the Public Works Act 1928 shall be so calculated as to produce, in respect of the period for which the prices are charged, an amount of revenue which, together with all other revenues which it is estimated by the Minister will be paid into the Electric Supply Account in respect of that period, is twenty-five per cent more than the total amount which it is estimated by the Minister will be required to make full provision in respect of that period for all charges and expenses in connection with the management, operation, and maintenance of every scheme. Charges and expenses as aforesaid shall include amounts required to be appropriated for the purposes of the Depreciation Reserve under section eleven of this Act and payments for interest required to be made from the Electric Supply Account under subsection five of section fourteen of the New Zealand Loans Act 1953, but shall not include the amounts required to be set aside for the reduction of capital liability under subsection one of section nine of the Finance Act (No. 2) 1944.

In each financial year the surplus of all such revenues over all such charges and expenses as aforesaid shall be applied firstly, in the setting aside of the amount required to be set aside for the reduction of capital liability under subsection one of section nine of the Finance Act (No. 2) 1944 and secondly, in the transfer of the residue of the surplus to the credit of the Reserve Fund in accordance with section thirteen of this Act.”

Notwithstanding the provisions of section seven of this Act, that section shall not apply to any amount paid or payable as interest on money expended, after the commencement of this Act, in connection with any scheme or extension.”