1 - Factors affecting cable choice:
2 - 6 Resistivity: it is the resistance offered by the material to the flow of current per unit length, and expressed in ohm / cm².
3 - CONDUCTORS:
-any material supporting current flow is called conductor.
-material of a conductor should have many free electrons, and since metals contain the freest electrons, so metals are the best conductors.
-the common materials used as conductors are: COPPER and ALUMINIUM.
3 - 1 COPPER:
-it is used in cables as a conductor because of its low resistance.
-the common properties of copper as a conductor are:
*resistance of a wire of standard annealed copper, one meter long and of uniform mass section of 1mm² is 0.017241 ohm.
*constant mass temperature coefficient of resistance is 0.00393/cº
*the density is 8.89gm / cm³.
-the international electro-technical commission (IEC) established an international annealed copper standard (IACS) for the resistivity of annealed copper for which the conductivity is equal to 100%.
3 - 2 ALUMINIUM:
-it is commonly used as a conductor since 1945 due to its low cost, good electrical conductivity, good tensile strength, low density and excellent resistance to corrosion.
-it contains a minimum of 99.50% of pure aluminium with a controlled amount of impurities.
-it is usually treated by adding boron to remove titanium, vanadium and zirconium which are harmful to electrical conductivity.
