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Posted by Mark Jones on 08/27/05 19:33
WinField wrote:
> I opened up one of my old school books [Grob|Third Edition "Basic
> Electronics"]
> - and found table 9*3 (p.212) Properties of Conducting Materials,
> specific resistance(s) @20C, CMIL.Ohm/ft (that's circular mils)
>
> (lower is better, except maybe for Mark's Community College)
>
> Gold - 14
> Copper - 10.4
> Silver - 9.8
>
> Wipe the egg off your face, if/when you get a gripe on reality.
> Copper & Silver connects would have LESS of your precious contact
> resistance.
My old textbook has a slight variation from these numbers,
but they are still close. Gold isn't chosen because it has the
best conductivity, but rather because its reactivity is very low.
Silver can't be used in its pure form because it tarnishes so
easily when exposed to the air. Copper suffers from the same
problem, only it is much slower to develop tarnish on its
surface. Gold can be exposed to the air for thousands of
years and still shine like the day it was first mined.
That is why gold is used in critical applications, not because
it has the lowest resistance. You can design a circuit using
gold contacts and be certain that contact resistance will
remain consistent over the life of the product. I have seen
silver/tin alloys develop corrosion after just a few months of
severe use outside, while the same contacts remain shiny
as new when they are changed over to gold plating. When
you are going to be a few hundred miles out in the boonies,
you want to know that your equipment is going to work
when everything is connected. Gold contacts reduce the
rate at which problems occur. This is not based on guessing,
but is the result of years of actual observations.
When I buy cables for my HDTV to DVD player connection,
I want a good connection that will remain that way for years
to come without corrosion or tarnish being an issue. If
this is not important to you, then by all means buy some
cheap cables,
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