The aluminium inner layer is constructed with trapezoid wires that contain the high strength Al-clad steel core, creating a gap filled with high temperature resistant grease. Outer Al layers could be round shaped or trapezoid in case of alternative compact designs.
The low sag conductor operation is based on the lower coefficient of thermal expansion of the steel core as regards the aluminium layers. Conductor sagging is made tensioning the steel core only, keeping the aluminium layers without mechanical stress.
The construction of ZTACIR conductor is similar to standard ACSR, but the main difference is the material used for the core that is Invar alloy. Invar alloy contents 36% of Nickel and provides to the material a very low coefficient of thermal expansion.