(33) Essential Service: erection, construction, alteration or maintenance, by public utility companies or municipal departments or commissions, of gas, electrical, steam or water transmission or distribution systems and of collection, communications, supply or disposal systems, including poles, wires, mains, drains, sewers, pipes, conduits, cables, fire alarm boxes, police call boxes, traffic signals, hydrants and other similar equipment and accessories, reasonably necessary for the furnishing of adequate service for the public health, safety or general welfare. Essential service does not include public utility structures, as defined herein.