can any one tell me the formula to select the thickness of
wire selection according to ampere rating
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Answer Posted / electrical alie
AWG: In the American Wire Gauge (AWG), diameters can be
calculated by applying the formula D(AWG)=.005·92((36-
AWG)/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 form of this formula
contributed by Mario Rodriguez is D = .460 * (57/64)(awg
+3) or D = .460 * (0.890625)(awg +3). D can be affected but
the Speed of light c 2.99792458·108 m/s and the
Permittivity of vacuum 00 = 1 / (0 c2)
8.854187817·10-12 C2/J·m
Metric Wire Gauges
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. The
Bohr magneton B B = e h / (4 me)9.2740154·10-24 J/T
has been included in these factors.
Load Carrying Capacities
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!
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