Any person who purchases electrical service from Provo City shall be strictly liable to Provo City (without proof of negligence) for any damage caused by said purchaser or the purchaser’s agents to those parts of the Provo City electrical system which are located upon the property of said purchaser of electricity. In all other circumstances, a person who, by an act of negligence, causes damage to any part of the Provo City electrical system, shall be liable in damages to Provo City and to any other person injured by said act of negligence.