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Low Voltage Qualification Practice Test

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In the proper de-energize sequence for a unit substation, which component is opened after the ACBs are opened and locked out?
Correct Answer:
Open LBF (main)
Explanation:
The main idea is to ensure complete isolation of the unit substation before any work is done. After the ACBs are opened and locked out, the next essential step is to open the main load-break switch (LBF). This provides a final, authoritative disconnect from the source, ensuring there is no energized path into the substation so maintenance can be performed safely. Grounding the primary or secondary sides is generally done after full isolation and once it’s confirmed safe, and creating a job plan is part of the planning process rather than the immediate de-energizing action.

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