On Mon, 15 Aug 2011 15:12:37 +0100, "N_Cook" put
finger to keyboard and composed:

All online and my tables stop at 50 SWG. I don't know if the standard copper
resistivity formula breaks down over/less than 50 SWG. Wire in question ,
measured optically to about 0.05 mm diameter as too fine to mike up. About
19.7 ohm per metre but what is that in AWG or SWG ?

Resistivity is calculated according to the following formula:

rho = R x A / L

where ...

rho = resistivity = 1.68e-8 ohms/metre for copper
R = resistance
A = cross-sectional area
L = length of material

http://en.wikipedia.org/wiki/Electri...d_conductivity

Therefore ...

A = rho / (R/L) = 1.68e-8 / 19.7

A = pi x r^2 = pi x (dia/2)^2

dia = 2 x sqrt(A / pi) = 2 x sqrt(1.68 x 10^-8 / 19.7 / pi)
= 0.03295 mm

http://www.google.com/search?&q=2+x+...-8+/+19.7+/+pi)


According to the tables, your wire size appears to be 49 SWG.

http://en.wikipedia.org/wiki/Standard_wire_gauge

- Franc Zabkar
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