Issuance of Revenue Bonds and Other Revenue Securities by Municipalities.

Revenue bonds and other revenue securities at any time issued by a municipality for the purpose of extending, enlarging or improving any water, sewer, gas or electric system then owned by such municipality shall not be deemed to constitute bonds or indebtedness of such municipality within the meaning of sections 222 and 225 of this Constitution if by their terms such bonds or other securities are not made a charge on the general credit or tax revenues of the issuing municipality and are made payable solely out of revenues derived from the operation of any one or more of such systems.