Abstract: An electrician working for an electrical contractor was relocating machines on a customer's shop floor. As part of the work, he was relocating disconnect boxes. The boxes enclosed three-phase, 480-volt fusible-switch bus-duct plugs and were located on an overhead bus. The electrician had opened the switches for all the disconnects to which he would be making connections. However, he had not locked out those switches. As the electrician was terminating conductors connecting new wiring from machine to a disconnect box, a grounding conductor he was holding touched an energized conductor in the back of the disconnect box, causing an electrical fault. The ensuing electric arc burned the employee's face. He was hospitalized for his injuries.