Before work may safely commence on a high voltage system, what must first be done after disconnection and isolation?

Correct Answer: Option D — The circuit must be tested and proved dead first with a live-line tester, then grounded.

Safety procedures under IEEE 45 require isolating high voltage circuits, proving them dead with an approved live-line tester, and immediately applying safety grounds. Testing before grounding ensures technicians verify absence of voltage prior to discharging any residual capacitance.