# Re: [SI-LIST] : Question Re: Wire Gauge and resistivity

From: Doug McKean ([email protected])
Date: Mon Nov 13 2000 - 11:27:25 PST

Doug Brooks wrote:
>
> 1. Can someone point me to a URL that would have a spec sheet that would
> include the resistivity and temperature coefficient of resistivity for the
> type of copper used in PCB construction?
>
> 2. Can someone point me to a URL that explains how to make resistance
> calculations of wires at different temperatures using the temperature
> coefficient of resistivity. I know how to do it, but I can't find a
> reference that I can point to in an article to tell others how to do it.
>
> 3. What is the original derivation of the AWG (American Wire Gauge) system.
> There is obviously a logarithmic relationship between gauge and
> cross-sectional area: Wire Gauge ~ Log(1/Area) but why is that?

There's several ...

1. Diameter in mils (1/1000 inch): Diameter = 325 / 1.123^Gage
2. Gage = INTEGER((LOG(325) - LOG(Diameter)) / LOG(1.123))
3. D = 0.3252 * e^(-0.116*gauge)

But why? Might have something mathematically to do
with the relationship of area (a power function).
Don't know.

> How were the original gauge numbers defined?

I think in terms of circular mils,
starting with 50 AWG with diameter of 1 mil.

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