§ 6-k. Electric utility depreciation reserve funds. The governing board of any municipal corporation operating an electric public utility service shall establish solely by appropriations from the revenues of such service, a depreciation reserve fund, the assets of which shall be used solely for, and for no other purpose than, the improvement, extension, or replacement of such service, or the payment of indebtedness incurred in relation to the construction, improvement, extension or replacement of such service, except as otherwise provided in section 123.00 of the local finance law and section eight of this article. Such governing board shall require that out of the revenues of such service there shall be deposited in the reserve fund, annually, quarterly, or monthly in its discretion, the amounts entered in the depreciation reserve account of such service as the depreciation accruals for any such period. A depreciation reserve account is an account in which the original cost of the service is being distributed to expenses in substantially equal annual, quarterly or monthly amounts during the expected service life of the component parts of the service, by direction of the public service commission. The moneys in the fund shall be deposited and secured in the manner provided by section ten of this article. The governing board, or the chief fiscal officer of such municipal corporation if the governing board shall delegate such duty to him, may invest the moneys of such fund in the manner provided in section eleven of this article. Any interest earned or capital gains realized on the moneys so deposited or invested shall accrue to and become part of the fund. The separate identity of the fund shall be maintained whether its assets consist of cash or investments or both.