4 concentric layers of aluminium. The outer strands are high-purity aluminium, chosen types of acsr conductors pdf its excellent conductivity, low weight and low cost.
The center strand is steel for additional strength to help support the weight of the conductor. Steel is higher strength than aluminium which allows for increased mechanical tension to be applied on the conductor. These properties allow ACSR to sag significantly less than all-aluminium conductors.
The aluminium alloy and temper used for the outer strands in the United States and Canada is normally 1350-H19 and elsewhere is 1370-H19, each with 99. The temper of the aluminium is defined by the aluminium version’s suffix, which in the case of H19 is extra hard.
To extend the service life of the steel strands used for the conductor core they are normally galvanized, or coated with another material to prevent corrosion. The diameters of the strands used for both the aluminum and steel strands vary for different ACSR conductors. Higher strength steel may also be used. Class C zinc coatings are thicker than class A and provide increased corrosion protection at the expense of reduced tensile strength.
A regular strength galvanized steel core with Class C coating thickness would be designated GC2. An ultra-high-strength galvanized steel core with class A coating thickness would be designated GA5. The use of higher strength steel cores increases the tensile strength of the conductor allowing for higher tensions which results in lower sag. These coatings provide increased corrosion protection and heat resistance compared to zinc alone.