There seems to be a lot of interest in the current carrying ability of
printed circuit conductors and the data used in creating the nomographs in
IPC-D275.  Here is a start on the subject...

The original data on current carrying capability comes from an ANSI wire
specification.  The exact number escapes me, but I'll keep looking.  Also,
Giovanni Leonida did a very nice job covering the subject in his book titled
The Handbook of Printed Circuit Design, Manufacture, Components and Assembly
which I will try to summarize.

The resistance of a wire or printed circuit conductor is dependent on the
cross-sectional area of the conductor, the length of the conductor, the
specific resistivity of the metal, the temperature and the frequency of the
signal.  For this explanation, we will use copper in all of the examples and
assume a rectangular shape (rather than a round wire).

The factors are;

        p = Resistivity of Copper
        L = Length of conductor
        H = Thickness of conductor
        W = Width of conductor
        T = Temperature
        f = Frequency

Because of the ASSCI format, exponents will be expressed as;

        2.5 x 10 e-6    2.5 times ten to the minus sixth power
        2.5 x 10 e+6    2.5 times ten to the plus sixth power

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