Standard Specification for Concentric-Lay-Stranded Aluminum-Alloy Conductors, Steel-Reinforced (AACSR) (6201) for use as bare overhead electrical conductors in transmission and distribution lines requiring high mechanical strength and long spans.
ASTM B711 covers concentric-lay-stranded aluminum-alloy 6201-T81 conductors with a coated steel reinforcing core (AACSR), intended for use as bare overhead electrical conductors in transmission and distribution applications, particularly where high mechanical strength and long spans are required.
Unlike standard ACSR (pure aluminum 1350) and ACSS (annealed aluminum), the aluminum wires in AACSR use 6201-T81 aluminum-magnesium-silicon alloy in a hardened temper, giving both the aluminum layers and the steel core a role in carrying mechanical tensile load. This makes AACSR the preferred choice for extra-long spans, river crossings, and mountainous terrain where conventional conductors would require intermediate towers.
AACSR is a dual-load-path composite conductor. The coated steel core and the high-strength 6201-T81 aluminum alloy outer layers share the mechanical tensile load, providing a significantly higher rated breaking strength than ACSR of the same cross-section and weight.
High-strength galvanized steel wires (Class A, B, or C zinc coating) or aluminum-clad steel (AW). Single wire for smaller sizes; multi-wire stranded core (7 or 19 wires) for larger sizes per ASTM B498 or B502.
One or more concentric layers of round 6201-T81 aluminum-magnesium-silicon alloy wires, solution heat-treated, cold-worked, and artificially aged. Common stranding: 26/7, 30/7, 54/7, 54/19, 84/19 (Al alloy/Steel wire counts).
Aluminum 6201 alloy (Al–0.6%Mg–0.7%Si) in T81 temper. Minimum tensile strength 295 MPa, minimum 52.5% IACS electrical conductivity. Both aluminum layers and steel core contribute to rated breaking strength.
For marine, coastal, or highly polluted environments, additional corrosion protection is available through grease application to the steel core, or full infusion of the complete conductor with corrosion-inhibiting compound.
Representative sizes per ASTM B711 Table. Sizes expressed in total conductor area (mm²). DC resistance corrected to 20 °C. Actual values may vary slightly between manufacturers.
| Total Area (mm²) | Stranding (Al/St) | Nom. OD (mm) | Nom. Mass (kg/km) | RBS (daN) | DC Resist. (Ω/km @ 20 °C) |
|---|---|---|---|---|---|
| 163 | 26/7 | 16.6 | 560 | 7,500 | 0.240 |
| 232 | 26/7 | 19.8 | 800 | 10,600 | 0.168 |
| 291 | 26/7 | 22.2 | 1,010 | 12,900 | 0.135 |
| 413 | 26/7 | 26.4 | 1,433 | 18,300 | 0.0950 |
| 563 | 54/19 | 30.9 | 1,873 | 22,900 | 0.0673 |
| 800 | 54/19 | 36.8 | 2,665 | 32,200 | 0.0474 |
| 1,081 | 84/19 | 42.8 | 3,395 | 39,100 | 0.0337 |
ASTM B711 mandates the following tests to verify conductor performance:
AACSR per ASTM B711 is widely specified for transmission lines requiring fewer and more widely spaced towers — river crossings, gorges, mountain passes, and coastal approach spans. The combination of high-strength 6201-T81 aluminum alloy and a steel reinforcing core delivers a rated breaking strength considerably higher than ACSR of the same overall diameter, allowing greater sag clearance at long spans without increasing conductor weight. Its low mass-to-strength ratio also reduces tower loading in heavy ice and wind conditions.
Official Standards & References
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