Abstract: Two electricians were replacing a circuit breaker in a motor control center. They removed the unit and replaced the circuit breaker. They then put the unit back in the motor control center. The load side of the circuit breaker was not energized, but the line side was. One of the electricians began connecting the load side lugs to the circuit breaker. The second electrician was watching. A third electrician entered the area and watched as the first electrician (employee #1) tightened the load side lugs. When he tightened the lugs, he caused an electrical fault. The resulting electric arc burned all three employees. The two electricians who were replacing the circuit breaker were hospitalized for their injuries.