Standard Specification for Concentric-Lay-Stranded Aluminum Conductors, Coated-Steel Supported (ACSS) for use as bare overhead electrical conductors in transmission and distribution lines.
ASTM B856 covers round wire concentric-lay-stranded aluminum conductors with a coated steel core (ACSS), intended exclusively for use as bare overhead electrical conductors in transmission and distribution line applications.
Unlike conventional ACSR, the aluminum wires in ACSS are in the fully annealed (O temper) soft condition, meaning the steel core bears virtually all mechanical tensile load. This design eliminates long-term creep-related sag and enables operation at high temperatures without permanent loss of rated tensile strength. Mechanical and electrical properties of the aluminum wires are verified after stranding, ensuring final conductor performance.
ACSS is a composite concentric-lay-stranded conductor. A coated steel core carries the mechanical tensile load, while one or more layers of round, fully annealed aluminum 1350-O wires are stranded concentrically around it to provide the current-carrying cross-section.
High-strength round steel wires with Galfan® (Zn–5% Al alloy), Class A zinc coating, or aluminum cladding. Single or stranded per ASTM B500/B500M, B498, or B502. Carries virtually all mechanical tensile load.
One or more concentric layers of round aluminum 1350-O wires, fully annealed. Standard stranding configurations include 26/7, 30/7, 54/7, 54/19, and 45/7 (Al/Steel wire counts).
Fully annealed ("O" temper) 1350 aluminum alloy per ASTM B609. Minimum 63% IACS electrical conductivity. Soft temper eliminates creep-induced sag and supports high-temperature operation.
Electric-butt welds, cold-pressure welds, and electric-butt cold-upset welds are permitted in individual aluminum wires during stranding. No joints allowed in the finished conductor.
Representative codeword sizes from ASTM B856. All use 26/7 Al/Steel stranding unless otherwise noted. Actual dimensions may vary slightly between manufacturers.
| Codeword | Size (kcmil) | Stranding (Al/St) | Nom. OD (mm) | Nom. Mass (kg/km) |
|---|---|---|---|---|
| PARTRIDGE | 266.8 | 26/7 | 18.06 | 743 |
| HAWK | 477 | 26/7 | 21.79 | 1,010 |
| DRAKE | 795 | 26/7 | 28.14 | 1,629 |
| CARDINAL | 954 | 54/7 | 30.35 | 1,867 |
| GROSBEAK | 636 | 26/7 | 25.25 | 1,452 |
| LAPWING | 1,590 | 45/7 | 38.35 | 2,900 |
| CHUKAR | 1,780 | 84/19 | 40.13 | 3,022 |
ASTM B856 mandates testing after stranding to verify the final conductor's performance:
ACSS is engineered to share the same outer diameter and stranding geometry as standard ACSR conductors, allowing direct reconductoring of existing lines without replacing towers, crossarms, insulators, or suspension hardware. By operating at temperatures up to 250 °C, it can more than double the thermal ampacity of the line while retaining the same sag clearances. This makes ACSS per ASTM B856 the most practical and cost-effective solution for uprating transmission and distribution infrastructure without major civil works.
Official Standards & References
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