Standard Specification for Concentric-Lay-Stranded Aluminum-Alloy 6201-T81 Conductors (AAAC) — a homogeneous all-aluminum-alloy bare overhead phase conductor engineered to deliver a superior strength-to-weight ratio, higher corrosion resistance than ACSR, and excellent conductivity for primary and secondary distribution lines, sub-transmission circuits, and coastal transmission environments.
ASTM B399 covers concentric-lay-stranded conductors made entirely from round 6201-T81 aluminum-alloy wires (per ASTM B398), for use as bare phase conductors in overhead electrical power systems. Unlike AAC (which uses pure 1350-H19 aluminium) or ACSR (which combines aluminium with a galvanised steel core), AAAC is a fully homogeneous alloy conductor — every strand is identical 6201-T81, eliminating bimetallic corrosion entirely.
The 6201-T81 alloy, a magnesium-silicide (Al-Mg-Si) heat-treatable alloy, delivers a tensile strength roughly twice that of AAC while retaining high conductivity (52.5% IACS minimum). This gives AAAC a strength-to-weight ratio comparable to ACSR but with substantially lower total weight and far better corrosion resistance, making it the preferred phase conductor for medium-voltage distribution (Class AA), coastal and marine transmission lines, river and sea crossings, and covered-line conductor cores (Class A).
AAAC per ASTM B399 is a homogeneous concentric-lay-stranded conductor. Every wire in the cross-section is an identical 6201-T81 aluminum-alloy wire — solution heat-treated, cold-drawn, and artificially aged to achieve the hard-temper mechanical and electrical properties. There is no steel core, no cladding, and no differing aluminium grade; the conductor behaves as a single metallurgical system with uniform thermal expansion and elastic modulus throughout.
Round hard-drawn wire of Al-Mg-Si 6201 alloy in T81 temper (solution heat-treated, cold worked, then artificially aged). Each wire meets ASTM B398 for minimum tensile strength, elongation, conductivity (≥52.5% IACS), and surface finish. No mixing of different alloys or tempers is permitted.
Wires are concentrically stranded with each successive layer having 6 more wires than the previous. Standard configurations: 7-wire (1+6), 19-wire (1+6+12), 37-wire (1+6+12+18), and 61-wire (1+6+12+18+24). Adjacent layers are laid in opposite directions (reversing lay) for geometric stability.
Class AA — standard bare conductors for overhead transmission and distribution, with the smoother round-wire surface profile. Class A — slightly tighter stranding and tolerances, intended for conductors that will subsequently be covered with weather-resistant insulating materials (as the core of covered-line wire).
Cold-pressure butt welds and fusion welds in individual wires are permitted only before final drawing to the specified diameter, and a minimum distance between joints within a completed stranded length is enforced to guarantee full tensile continuity and to prevent weld clustering in any single layer.
Representative sizes for AAAC per ASTM B399, using the traditional US tree-name code designations. Rated breaking strength (RBS) reflects the aggregate tensile load of all 6201-T81 aluminum-alloy wires. DC resistance corrected to 20 °C, 52.5% IACS.
| Code Name | Size (kcmil / mm²) | No. of Wires | Wire Dia. (mm) | OD (mm) | Mass (kg/km) | RBS (kN) | DC Resist. (Ω/km @ 20 °C) |
|---|---|---|---|---|---|---|---|
| Akron | 30.6 mm² (#2 AWG) | 7 | 2.36 | 7.08 | 84 | 9.7 | 1.093 |
| Alliance | 48.7 mm² (1/0 AWG) | 7 | 2.98 | 8.94 | 134 | 15.5 | 0.686 |
| Butte | 77.5 mm² (3/0 AWG) | 7 | 3.76 | 11.28 | 213 | 24.7 | 0.431 |
| Canton | 243 kcmil / 123 mm² | 7 | 4.74 | 14.22 | 338 | 38.3 | 0.271 |
| Darien | 307 kcmil / 155 mm² | 19 | 3.23 | 16.15 | 426 | 48.3 | 0.215 |
| Elgin | 394 kcmil / 200 mm² | 19 | 3.66 | 18.29 | 549 | 62.3 | 0.167 |
| Flint | 740.8 kcmil / 375 mm² | 37 | 3.59 | 25.16 | 1,031 | 117.1 | 0.0889 |
| Greeley | 927.2 kcmil / 470 mm² | 37 | 4.02 | 28.14 | 1,290 | 146.5 | 0.0710 |
ASTM B399 requires the following tests on individual 6201-T81 wires (per ASTM B398) and on the completed stranded conductor:
AAAC per ASTM B399 is the specification of choice wherever a utility or EPC project needs higher tensile strength than AAC (1350-H19) can offer, but without the long-term corrosion liabilities of the ACSR steel core. Typical deployments include medium-voltage overhead distribution (11 kV, 22 kV, 33 kV), sub-transmission at 66 kV and 132 kV, river and sea crossings requiring long spans and excellent fatigue resistance, and coastal and island networks exposed to salt fog — where ACSR galvanised steel cores historically suffer accelerated corrosion. Because every strand is the same 6201-T81 alloy, there is no galvanic mismatch, and because the alloy itself forms a continuous passive aluminium-oxide film across the full conductor surface, AAAC typically delivers a service life exceeding that of equivalent ACSR in aggressive atmospheres while reducing transmission tower loading thanks to its lower unit weight. In the USA, Canada, Latin America, Africa, and much of Southeast Asia, ASTM B399 is the dominant specification for new AAAC procurement.
Official Standards & References
Direct from the factory floor in Henan, China — we manufacture ACSR conductors to ASTM, IEC, BS, and other standards for utility and EPC projects.
Henan Zhong Dong Cable Co., Ltd.
3,000,000+ km annual output · Serving 50+ countries
Share your project specs and quantity — our senior engineer will reply with a verified quote within 24 hours.
🔒 Your inquiry stays confidential. We never share contact info with third parties.
