The City shall not sell, exchange, lease, or in any way lien or dispose of the property, easements, or other equipment, privilege, or asset belonging to and appertaining to any utility which it may acquire, unless and except the proposition for such purposes shall first have been submitted, at an election held for that purpose in the manner provided in this charter, to the electors of the City and approved by them by a three-fifths (3/5) majority vote of the electors voting thereon. All contracts, negotiations, licenses, grants, leases or other forms of transfer in violation of this provision shall be void and of no effect as against the City. The provisions of this section shall not, however, apply to the sale or exchange of any articles of equipment of any city-owned utility as are worn out or useless, or which could, with advantage to the service, be replaced by new and improved machinery or equipment.