The reinforced steel cable of an aluminum conductor (ACSR) is a high capacity, high capacity conductor commonly used in power lines above. The outer strand is a high purity aluminum, chosen for its excellent conductivity, low weight and low cost. The cord is steel for extra strength to help support the weight of the conductor. Steel is a higher strength of aluminum which allows increased mechanical stress to be applied to conductors. Steel also has a lower elastic and inelastic deformation (permanent elongation) due to mechanical loading (eg wind and ice) as well as lower thermal expansion coefficients under current loading. This property allows the ACSR to slump significantly less than all aluminum conductors. Per Commission of the United Nations (IEC) and the naming convention of the CSA Group (formerly the Canadian Standards Association or CSA), ACSR designated A1 / S1A.