December 3, 1991 Appeal from the Supreme Court, New York County (Leland DeGrasse, J.). On or about July 17, 1986, in the vicinity of 40 Maiden Lane, New York County, Mr. Greg Henderson, twenty years of age, an employee of Consolidated Edison, was using a pneumatic drill (jackhammer), to enlarge an excavation beneath the roadway, to expose a steam leak. Suddenly that drill struck a live 13,500 volt electric main feeder cable, and the resulting explosion allegedly caused serious injuries to various