The complete guide to wiring
Opening up an outlet or light switch box, you might be confronted with a bewildering array of wires of different colors. Black, white, bare copper, and other colors closely intermingle, yet each one has a specific purpose. Knowing the purpose of each wire will keep you safe and your house's
electrical system in top working order.
Electrical Cable and Wire Color Markings Non-metallic (or NM) 120-volt and 240-volt electrical cable come in two main parts: the outer plastic sheathing (or jacket) and the inner, color-coded wires. The sheathing binds the inner wires together, and its outer markings indicate the number of wires and size of wire (gauge) within the sheathing. The color of the sheathing indicates recommended usages. For example, white sheathing means that the inner wires are 14-gauge and yellow sheathing indicates that they are 12-gauge. But looking deeper, the color of the wires inside of the sheathing reveals that different colored wires serve different purposes. The National Electrical Code (NEC) says that white or gray must be used for neutral conductors and that bare copper or green wires must be used as ground wires. Beyond that are general, industry-accepted rules about wire color that indicate their purpose.