On 2017/01/06 7:17 AM,
pf...@aol.com wrote:
> On Friday, January 6, 2017 at 9:52:54 AM UTC-5,
avag...@gmail.com wrote:
>
>>> SNIPPAGE<<
>
> a) Wire conductivity, irrespective of material, is a function of surface area and gauge amongst other factors. So, if 14-gauge wire is then divided into strands, the final product with the most strands will have the most surface area, and so by some factor greater conductivity.
At 60 Hz in copper, the skin depth is about 8.5 mm, slightly thicker
than gauge 0.
You are talking about skin effect which is only starts to show above a
few kilohertz, otherwise the raw diameter of the wire is what carries
the current. Multi-strand wire (such as power cords, or speaker wire) is
convenient as it flexes, but it carries no more current than an
equivalent solid core wire at frequencies under around 10kHz. For
transmission towers where the outer diameter of the wire is much larger
that 8.5mm dia, then uses multi-stranded wire to get around it.
>
> b) Using material conductivity hierarchy, the most conductive material wants to be on the surface. Aluminum is a much poorer conductor than copper. All other things being equal, aluminum coated copper will be a poorer conductor than copper-coated aluminum (or steel: c.f. CopperWeld).
If you are comparing wire coated with aluminum vs a copper wire of the
same diameter as the coated, then yes, the plain copper would conduct
more current.
>
> c) Corrosion is a factor, but not much of one. Alumina (AKA Aluminum Oxide) is an excellent insulator, as well as being quite inert. As aluminum wire acquires an oxide coating very nearly immediately upon exposure to air, that will reduce conductivity on the immediate surface of the wire. But as that coating is only a very few nanometers thick, the effect is near-zero overall. Copper oxides and sulfates as well as various other 'salts' are variously conductive, but also can be rectifiers, so there will be some effect on overall conductivity in the presence of these materials. BUT, copper is not a very active metal, so oxidation under normal atmospheric and environmental conditions is low and slow. Similar to Aluminum, but for different reasons.
Of course corrosion will show up as a problem at connection points, but
rarely does it matter for regular wire. Battery leakage though was a big
problem with electronics designed in the 70s to 90s - but that mostly
affect circuit boards and the connectors to them. Battery and salt are
factors for wire corrosion in vehicles.
> d) Electrolysis is always a factor when dissimilar metals are forced into a conductive connection in the presence of oxygen or other oxidizers. For an interesting experiment, take an ordinary 16D nail, wrap a bit of copper wire around it, and place it in a glass of ordinary tap water. In an adjacent glass place a similar nail, no copper. Then a bit of copper, no nail. Do the same with an aluminum wire bonded to a copper wire (mere wrapping may not insure sufficient connectivity for electrolysis to take place. Copper clad materials generally do not suffer as there is very limited surface area exposed.
Interesting. Thanks. The results probably depend on the hardness of your
water...
>
> Enjoy!
>
> Peter Wieck
> Melrose Park, PA
>
Indeed, have a good day!
John :-#)#
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