ASTM B857 defines requirements for shaped wire compact concentric-lay-stranded aluminum conductors, coated-steel supported (ACSS/TW). These specialized overhead electrical conductors utilize trapezoidal aluminum wires compacted around a steel core to optimize cross-sectional efficiency.
Construction:
Central core: Round steel wire(s)
Outer layers: Two or more layers of trapezoidal-shaped aluminum 1350-0 wires
Electrical:
Minimum electrical resistivity requirements
Material resistivity and density use SI units as standard
Designation:
Conductor sizes compatible with standard ACSR/ACSS dimensions (Table 1/2/3 referenced but not shown)
Units:
Inch-pound units are primary standard
Parenthetical SI conversions are informational only
Welding:
Electric-butt welds, cold-pressure welds, or cold-upset welds permitted in finished aluminum wires during stranding.
Validation:
Rated strength determined through mechanical tests
Mass, density, and resistivity must meet specifications
Geometry Optimization:
Conductors sized to match diameters/cross-sections of standard ACSR/ACSS (per Scope 1.3)
Space Efficiency:
Increases aluminum area within a given diameter or
Reduces conductor diameter for a given aluminum area
Compatibility:
Facilitates direct substitution for standard ACSR/ACSS in existing infrastructure
Performance Validation:
Post-stranding resistivity and strength verification ensures reliability
Exclusively for overhead electrical conductors in power transmission systems.
Typical applications include:
High-voltage lines requiring compact designs
Retrofitting projects needing space-optimized replacements
Corridors with clearance constraints
