No such grant shall be exclusive, nor shall it be made for a longer period than twenty (20) years. No such grant shall be renewed earlier than two (2) years prior to its expiration unless the city commission shall by vote of at least four (4) of its members first declare by ordinance its intention of considering a renewal thereof. All grants of the right to make extensions of any public utility shall be subject as far as practicable to the terms of the original grant and shall expire therewith.