In the United States, what circuit does black wire insulation indicate in a three-wire 120 V AC cable?
Why In US residential AC wiring the color code for a three-wire 120 V cable is fixed: black (or red for a second hot) is the ungrounded "hot" conductor carrying the live 120 V, white is the grounded neutral that returns current, and green or bare copper is the equipment safety ground. So black insulation marks the conductor you must treat as energized.
Watch out Neutral is the tempting pick because it also carries current, but neutral is white; it is bonded to ground at the service panel and normally sits near zero volts. "Negative" does not apply at all, since 120 V house wiring is AC, not DC.
Black = Back-feed danger (hot), White = neutral, Green = ground. Only the black one bites.