Abstract: Three electricians were installing a new 480-volt, 400-ampere circuit breaker in a distribution switchboard at a frozen food manufacturing plant. They were performing the work as part of a major plant expansion. The switchboard was a General Electric AV, 3000-ampere, 480-Y/277-volt unit. The employees were working during a normal production shift, and the switchboard was energized at the time. One of the electricians was standing inside the switchboard frame holding the circuit breaker, and the other two were believed to be connecting the circuit breaker wiring to the switchboard. An electrical fault occurred, and the ensuing electric arc burned all three employees. The employee holding the circuit breaker died of his injuries. The other two employees were hospitalized.