Overview
Wire is the path that lets electric current travel from one part of a circuit to another. It may look simpler than a resistor, capacitor, or transistor, but selecting and installing wire correctly involves conductor material, size, insulation, temperature, environment, current, voltage, mechanical protection, terminations, and—in building wiring—the electrical code.
What a wire has to do
- Carry the required current without overheating.
- Keep voltage drop within acceptable limits.
- Withstand the applied voltage.
- Survive the ambient temperature and environment.
- Resist abrasion, moisture, oil, sunlight, chemicals, or flexing when required.
- Fit the terminals, connectors, raceways, and equipment for which it is listed.
- Remain mechanically protected throughout its installation.
Conductor materials
Copper is the most familiar conductor in electronics and branch-circuit wiring because it combines good conductivity, ductility, reliable terminations, and wide availability. Aluminum and copper-clad aluminum are also important, especially in larger feeders and services, because they reduce weight and material cost. They require terminals and installation methods suitable for the particular conductor material.
Solid and stranded wire
| Construction | Advantages | Typical uses |
|---|---|---|
| Solid | Simple, compact, holds shape, easy to terminate in many fixed applications. | Building cable conductors, breadboards, jumpers, fixed internal wiring. |
| Stranded | More flexible and resistant to repeated bending than an equivalent solid conductor. | Machine wiring, cords, vehicles, control panels, equipment leads. |
| Fine-stranded | Very flexible. | Portable cords, welding cable, battery cable, robotics, moving machinery. |
American Wire Gauge
In the American Wire Gauge system, a smaller gauge number means a larger conductor. Thus 12 AWG is larger than 14 AWG, and 4 AWG is much larger than 10 AWG. Above the numbered AWG range, large conductors are often specified in kcmil, thousands of circular mils.
Wire size affects resistance, voltage drop, heating, mechanical strength, and the terminals and raceways that can accept it. It does not by itself tell you how many amperes may legally or safely be carried in every installation.
The National Electrical Code
The NEC is especially important here because conductor ampacity is not simply a physics calculation. Code rules take into account conductor insulation, temperature ratings, terminals, the number of current-carrying conductors together, ambient temperature, wiring method, location, overcurrent protection, and special equipment rules.
Continue through these pages
The Basics page introduces gauge, resistance, heating, voltage drop, identification, splicing, and terminations. Conductors & Insulation covers copper, aluminum, stranding, and common insulation markings. NEC & Building Wiring is aimed especially at electricians and apprentices. Additional pages cover cable and wiring methods, flexible cords, signal and low-voltage wire, history, and advanced engineering.