How Electrical Wiring Is Classified

If you plan on doing some electrical wiring, the size of the wire to use is going to become an issue. Here is a quick guide on how the wire is classified.

The American Wire Gauge (AWG), also known as the “Brown and Sharpe” wire gauge system is a standard used in the United States and other countries to denote the diameter of nonferrous electrically conducting wire. There are 40 different wire sizes in the AWG system.

As the number of the gauge size increases, the diameter of the wire decreases. This tends to cause confusion when the system is not understood. The reason for the backwards method of denoting the size is that it is based on the number of times the wire must be drawn through drawing dies to produce the smaller size. Thus a 22 gauge wire needs to be drawn through the die more times than a 0 gauge wire. Steel wire uses a completely different measuring system and should not be confused with electrically conducting wire gauges using AWG.

The larger size gauges are denoting by the use of zeros. 0000 wire is normally denoted as 4/0 wire. 4/0 wire has a diameter of 0.58 inches. The smallest size is 40 gauge which has a diameter of 0.0032 inches. It takes six size increases to double the diameter of the wire. Although the ratio is not exact, it is close. The 40 gauge diameter of 0.0032 inches increases to 0.0063 inches in 36 gauge wire.

Each AWG gauge size can be rated for a maximum number of amps of load that it can safely carry. This is called the ampicity of the wire. It is depended on several variable factors such as the type of insulation, ambient conditions where the wire is being used, and the length of the wire run. Proper wire sizing is of utmost importance. An overload of the wire’s ampicity would cause the generation of heat. Although copper or aluminum wire would take a large amount of heat before melting, the wire insulation would melt much quicker. This would increase the possibility of arching and a subsequent wire hazard.

In other parts of the world, the metric system is used and the AWG gauge system is not used. The metric wire measuring system uses the cross sectional area expressed in square millimeters. The cross sectional area is used rather than diameter because it is a better reflection of the load carrying capacity of the wire. The metric system and the AWG system do not match up exactly. This difference is more pronounced in certain size ranges and leads to problems when the wiring is a mix of AWG and metric sized wires.