American wire gauge



American wire gauge (AWG), also known as the Brown & Sharpe wire gauge, is a logarithmic stepped standardized wire gauge system used since 1857, predominantly in North America, for the diameters of round, solid, nonferrous, electrically conducting wire. Dimensions of the wires are given in ASTM standard B 258. The cross-sectional area of each gauge is an important factor for determining its current-carrying ampacity.
The AWG tables are for a single, solid and round conductor. The AWG of a stranded wire is determined by the cross-sectional area of the equivalent solid conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG.
AWG gauges are also used to describe stranded wire. The AWG gauge of a stranded wire represents the sum of the cross-sectional areas of the individual strands; the gaps between strands are not counted. When made with circular strands, these gaps occupy about 25% of the wire area, thus requiring the overall bundle diameter to be about 13% larger than a solid wire of equal gauge.
As indicated in the Formulas and Rules of Thumb sections above, differences in AWG translate directly into ratios of diameter or area. This property can be employed to easily find the AWG of a stranded bundle by measuring the diameter and count of its strands. (This only applies to bundles with circular strands of identical size.) To find the AWG of 7-strand wire with equal strands, subtract 8.4 from the AWG of a strand. Similarly, for 19-strand subtract 12.7, and for 37 subtract 15.6. See the Mathcad worksheet illustration of this straightforward application of the formula.
#12/2 is a nonmetallic sheathed bundle of three solid 12 AWG wires having a bare ground in the middle of two insulated conductors in a flat-shaped NM-B yellow-colored sheath. The color is a North American industry standard for cables made since 2003, and aids identification. It is always used for countertop appliance outlets in kitchens, and often for outlets in bathrooms (for high-wattage hair dryers) and other rooms.
14/3 and 12/3 cables are also available, used mainly between three-way (two-location) switches, and to have separate wall controls for ceiling fans and their attached light fixtures, or to have one half of a duplex outlet switched and the other always on.
277/480-volt cable is identical to 120/240, except that neutral is grey and hot is yellow (plus an optional orange, used as the red is). The higher voltage, used only in large non-residential buildings, allows more than twice as much electrical power (in watts) to be drawn through the same gauge of wire.
All new cables are marked as being with ground or w/gnd, since installation of ungrounded cables has been prohibited by electrical codes for decades. The ground wire is typically the same gauge as the others, despite not being intended to carry large amounts of current for more than a few seconds in the event of a short circuit.