Posted by TokaMundo on 08/27/05 22:49

On Sat, 27 Aug 2005 19:33:29 GMT, "Mark Jones"
<noemail@mindspring.com> Gave us:

>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.

Silver IS used in its pure form, for electrical contacts ALL THE
TIME. Its surface oxides do NOT pose an electrical issue.


> Copper suffers from the same
>problem, only it is much slower to develop tarnish on its
>surface.

Copper oxidizes faster than silver, and its oxides are poorer
conductors than the base strata.

> Gold can be exposed to the air for thousands of
>years and still shine like the day it was first mined.

Bullshit. Platinum can handle air exposure for about a hundred
years before noticeable converted atoms can be found on its surface.
Gold oxidizes faster than platinum, so it would fall inside that
window.

>
>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.

You managed another correct observation.

> 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.

If you are doing outside, weathered connections, you should be
applying an anti-oxidant paste or grease to all of your pins and
sockets during the installation. Done correctly, silver and copper
(though copper is not used in the industry) would last just fine.

The only place one finds bare copper in low power signalling is the
center conductor of CATV coax. It is a copper plated steel wire.

It too requires an anti-oxidant application during connection. All
one has to do is follow the proper techniques discovered over the
decades for low power, low voltage signal connections.

> Gold contacts reduce the
>rate at which problems occur. This is not based on guessing,
>but is the result of years of actual observations.

Knowing the whys and wherefors does one better than watching and
guessing ever will.

>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.

The TV and the player needs them as well. In fact, they are what
usually ages.

> If
>this is not important to you, then by all means buy some
>cheap cables,
>
"cheap" cables work fine if applied correctly.

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