An electrician was tasked with and briefed on laying out a power cable to feed a skid in support of a plant outage. After laying out the cable, the electrician noticed that one of two 480v disconnect switches near his work area was open. The open switch was locked open and tagged with a worker tag. The electrician assumed that the open switch was feeding a turbine deck power supply and therefore should have been in the closed position. The electrician then unlocked and closed the disconnect resulting in energization of an un-terminated cable and caused a phase to phase short circuit. No one was injured.
The two disconnect switches were not clearly labeled with their purpose.
Additionally, the configuration of the two switches and feeds was recently changed. The electrician was not aware of the changes.
What Can We Learn?
The Procedure for control of temporary power required validation of all connections prior to closing a switch.
Self Check – the T in S.T.A.R. makes us Think about our expected outcomes. Using STAR may have helped the electrician perform the proper validation prior to closing the switch.
Based on his previous knowledge, the electrician felt he was performing the right action. Overconfidence led him to take an action without being given instructions.
The recent changes to the positioning of the disconnect switches and their feed created an error likely situation. (Physical Environment)
Ask the Right Questions