What must be done prior to changing the tap settings on a distribution transformer?

• A. Install smaller fuses
• B. De-energize the transformer
• C. Ensure that the secondary circuit is open
• D. Reduce the secondary load to 0

Answer: (B)

Before changing tap settings on a distribution transformer, you must de-energize the transformer. Turning off the voltage removes all energy from the windings, preventing dangerous arcing, electric shock, and equipment damage that can occur when taps are moved while live. After shutting down, follow proper lockout/tagout procedures and verify zero energy with the appropriate test equipment before making the tap changes. Once the taps are set, re-energize and verify voltages to ensure proper operation.

Other options don’t provide the necessary safety of removing all voltage from the system; simply opening the secondary or reducing load does not eliminate the potential on the primary windings.