No such grant shall be exclusive, nor shall it be made for a longer period than 20 years from its effective date. No grant shall be renewed earlier than two years prior to its expiration unless the City Council shall by a vote of at least twoÚthirds (2/3rds) of its members first declare by ordinance its intention of considering a renewal thereof. All grants of the rights 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.