Re: Does wire wear by losing conductivity or gaining resistance with age?

Greetings:

Reference: Reference Data for Radio Engineers, Howard Sams and Company

Conductivity and Resistivity are the same property of conductors
specified as reciprocals of each other. This means that:

Resistivity = one divided by Conductivity (measured in ohm - centimeters)

Conductivity = one divided by Resistivity (measured in mho-
centimeters to the minus one power.)


The resistivity of a conductor is a measure of the resistance of a one
centimeter cube of the material. From this number you can then
calculate the resistance of any shape of conductor, such as wires,
bars, strips etc. by measuring its volume.

Answer: Why does normal wire wear with time?

Most, but not all, conductors are metals. Metals have resitivity and a
Temperature Coefficient of expansion which is a measure of how much a
conductor expands or contracts when the temperature changes. Depending
on the environment that the wire is in, these temperature changes can
be very large or very small and they can cycle from hot to cold every
day or at some other function of time such as take offs and landings.

When a metal expands and contracts it becomes work hardened and
becomes more brittle with each cycle. You can demonstrate this by
taking a solid piece of wire such as a coat hanger and bend it back
and forth. As the wire bends it becomes hot and more brittle and
eventually breaks. The same thing happens to wires that are
temperature cycled through many expansions and contractions. Engineers
must leave enough slack in hanging wires to minimize stress in wires
as they change length during temperature cycles.

Another factor in wire aging is corrosion. Depending on the
environment, corrosion can be a small factor or a large factor . Salt
water and the sea air are very corrosive and as the wire surface
corrodes into oxides, the wire’s resistance grows and the wire’s
strength decreases with age. In extreme cases the wire can break from
the effects of corrosion. .Some metals, such as aluminum, form a thin
oxide layer when they oxidize which actually protects the wire from
further corrosion effects. However, aluminum has a resistivity that is
12 times greater than copper and requires thicker wires for carrying
the same amount of electrical current as copper wires. However,
aluminum wires weigh less than copper and they are used in aircraft
electrical systems for high current applications. A modern airliner
has hundreds of miles of electrical wire in it. Silver and gold have a
slightly lower resistivity than copper, and also develop protective
oxide coatings; however, silver and gold are very expensive to use as
wire except for very small circuits such as on integrated circuit
chips.

Best regards for the New Year, Your Mad Scientist
Adrian Popa