On U.S. electric wiring charts, a white or gray electrical wire indicates a neutral power conductor wire, a green wire or green wire with a yellow stripe is a protective ground wire, and a red wire is a second hot wire in single-phase live wires. The U.S. National Electrical Code only mandates the color of the neutral wire and the earth wire, though in practice, electricians and electrical contractors follow the abovementioned local conventions.
In the United States, any color, except the two colors mandated by the NEC, are allowed for use as power conductors. Most contractors and electricians, however, adopted a common electrical power wiring code. Black wires are commonly used for power in circuits, while red wires indicate a secondary hot wire connected to the second leg of an electrical system in a 220-volt circuit. In smoke-detector circuits, for example, a red wire serves as an interconnection or communication between alarms, while the black and white wires respectively accept the 120 volts AC and serve as neutral wire.
Most wires with green insulation and non-insulated wire indicate a grounding conductor. It is connected directly to the earth and is designed to protect consumers or an appliance from shock in case a hot wire accidentally makes contact with any conductive part of the appliance's frame.
The blue and yellow wires carry power, but not for powering outlets for plug-in devices. The blue-and-yellow wire is typically used for running power between three-way switch boxes and lights through a ceiling box.