Wire Gauge and Current Limits Including Skin Depth and Strength 


March 20, 2014  
AWG Wire Sizes (see table below)AWG: In the American Wire Gauge (AWG), diameters can be calculated by applying the formula D(AWG)=.005·92^{((36AWG)/39)} inch. For the 00, 000, 0000 etc. gauges you use 1, 2, 3, which makes more sense mathematically than "double nought." This means that in American wire gage every 6 gauge decrease gives a doubling of the wire diameter, and every 3 gauge decrease doubles the wire cross sectional area. Similar to dB in signal and power levels. An approximate but accurate enough form of this formula contributed by Mario Rodriguez is D = .460 * (57/64)^{(awg +3)} or D = .460 * (0.890625)^{(awg +3)}. Metric Wire Gauges (see table below)Metric Gauge: In the Metric Gauge scale, the gauge is 10 times the diameter in millimeters, so a 50 gauge metric wire would be 5 mm in diameter. Note that in AWG the diameter goes up as the gauge goes down, but for metric gauges it is the opposite. Probably because of this confusion, most of the time metric sized wire is specified in millimeters rather than metric gauges.Load Carrying Capacities (see table below)The following chart is a guideline of ampacity or copper wire current carrying capacity following the Handbook of Electronic Tables and Formulas for American Wire Gauge. As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the voltage drop, insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility. NOTE: For installations that need to conform to the National Electrical Code, you must use their guidelines. Contact your local electrician to find out what is legal!Maximum Frequency for 100% Skin DepthThis data is useful for high frequency AC engineering. When high frequency AC is conducted by a wire there is a tendency for the current to flow along the outside of the wire. This increases the effective resistance. The frequency listed in the table shows the frequency at which the calculated skin depth is equal to the radius of the wire, and is an indication that above this frequency you should start considering the skin effect when calculating the wire's resistance.Breaking Force for Cu WireThis estimate is based on nickfree soft annealed wire having a tensile strength of 37000 pounds per square inch.
This chart of American Wire Gauge (AWG) wire sizes and rated ampacities is data intended for the pleasure of our readers only. Typographical errors, etc. are probable, since the typist is not a professional (our CEO). Please point out errors. The data listed are incomplete and should be used as a guideline only. Please contact manufacturers for the latest data. We hope that this information is helpful. Now go out and design something that needs a charger, power supply, or battery pack! 

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