Abstract: Some power line workers and a foreman reviewed a wiring diagram to determine a way to bypass a disconnect switch so that they could replace it. The employees decided on the work procedure and bypassed the switch to remove all sources of electric energy. After they had isolated the switch, one of the power line workers removed an elbow and created an electric arc. He sustained severe burns as a result of the arc and was hospitalized for his injuries. According to the diagram, one of the switches needed for isolation should already have been open. Relying solely on the diagram, none of the employees checked the switch that had been marked open. It was still closed, and the elbow was energized when the injured employee removed it.