CABLE/CONDUCTOR MATERIAL CONSIDERATIONS

CABLE/CONDUCTOR MATERIAL CONSIDERATIONS

What are the factors considered in making electrical conductors?

There are several high conductivity metals that may be used as conductor. A conductor is a metallic material which allows electric current to flow through it with less resistance. The best conductor material is silver but due to its high cost per unit weight and being one of the precious metals, it is not economical to use in the transmission and distribution of electricity. Comparatively, gold with its excellent corrosion resistance and lower resistivitythan aluminum is also a good conductor but, same as silver, is very costly.

Resistance and Conductivity

Resistance is the opposition of an object to the passage of electric current. For direct current, resistance isdependent on the material length, cross-sectional are and resistivity. The electrical resistance of a conductor is inverselt proportional t the cross-sectional area or diameter of a conductor.

Weight

Although aluminum has only about sixty-one percent (61%) of the conductivity of copper, its lightness makes long spans possible. Aluminun's low density is one of its important advantages. Also, its relatively large diameter for a given conductiviy reduces corona which contributes to the losses of the wire.

Ampacity

In general, current ratings of aluminum cables are about 78%-80% of those copper cables of the same conductor size. An aluminum cable needs to be thicker than a copper cable in order o have the same current carrying capacity.

Voltage Regulation

Reactance is negligible in allDC circuits and, in AC circuits with small conductors of sizes equal to or less than 60mm2. Voltage drops for a copper conductor and an aluminum conductor with 1.6 times the cross sectional area would be the same. However,in AC circuits with large conductors, the resistance value is influenced by skin and proximity effect, and the reatance becomes important.

Short Circuit

Copper conductors have higher capabilites in short circuit operations than aluminum conductors. However, for covered and insulated conductors the thermal limitations of the materials which form part of conductor should be considered before making such comparison.

Other Factors.

Aluminum oxidizes rapidly when exposed to air, a thin corrosion resistance film having a high dielectric strength forms quickly. Thus, additional care must betaken when making connections. Material of terminal connections should be taken into consideration since this could corrode the aluminum conductor.