Rule 2 of 40 · Chapter I — Before You Touch Anything
De-energize before you open anything
Why this rule exists
Working a circuit hot is the single biggest source of avoidable electrical injury. Every hot task adds shock and arc-flash risk that de-energizing removes entirely. NFPA 70E treats energized work as a last resort requiring justification, not a default. The physics is unforgiving: a 120-volt circuit through a sweaty hand can push enough current to stop a heart, and a bolted fault can vaporize copper into a plasma arc in milliseconds. De-energizing is not caution for its own sake; it removes the hazard at its source.
In practice
Plan the shutdown before you touch a tool. Identify every source feeding the equipment, including backfeeds and secondary supplies. Open disconnects, then verify dead at the point of work. Where a shutdown affects others, coordinate and warn them first. Note that off at the breaker is not proof, so confirm it with a tester. For anything beyond simple, verified de-energization, treat the job as energized work and apply the full set of controls, or hand it to a qualified person.
When it doesn't apply
Some tasks genuinely cannot be de-energized: utility service work, certain diagnostics that require live readings, life-safety systems. Those demand an energized-work justification, rated PPE, and training you either have or you do not. If the only reason to work it hot is convenience, that is not a reason. Shut it down.