Standard Specification for Concentric-Lay-Stranded Aluminum Conductors, Coated-Steel Reinforced (ACSR) — the global workhorse bare overhead transmission and distribution conductor, combining hard-drawn 1350-H19 aluminum wires for current conduction with a coated-steel core for tensile strength. The specification defines nine coated-core variants spanning standard, high-strength, extra-high-strength, and ultra-high-strength grades with zinc, Zn-5%Al-MM, or aluminized coatings.
ASTM B232 covers concentric-lay-stranded ACSR conductors made from round 1350-H19 hard-drawn aluminum wires (per ASTM B230) and a round, coated steel core (per ASTM B498, B606, B802, B803, B957, B958, or B341 depending on the variant). ACSR is the most widely deployed overhead phase conductor in the world — the dominant choice for bulk transmission from sub-transmission (66 kV, 110 kV) through HV (220 kV, 230 kV), EHV (345 kV, 400 kV, 500 kV), and UHV (735 kV, 765 kV, 1000 kV+).
The composite construction is the key: the aluminum layers carry the current with excellent conductivity (min. 61.2% IACS), while the steel core provides the mechanical tensile strength required for long-span overhead lines, heavy ice and wind loading, and reduced sag under maximum operating temperature. Nine variants allow the designer to match the exact strength grade and coating type to the span, loading, and environmental conditions — from standard galvanizing on routine inland distribution lines up to Zn-5%Al-MM coated ultra-high-strength cores for record-span river crossings.
ACSR per ASTM B232 is a composite bimetallic concentric-lay-stranded conductor. The central core is one, seven, nineteen, or thirty-seven coated steel wires stranded together to form the mechanical backbone. Around this core, one or more layers of 1350-H19 hard-drawn aluminum wires are concentrically applied, with each successive aluminum layer laid in the opposite direction to the one below for geometric stability and torsional balance.
Round 1350-H19 (99.5%+ purity, extra-hard temper) aluminum wires per ASTM B230, providing min. 61.2% IACS conductivity. These wires carry substantially all of the operating current, with the skin effect concentrating AC current in the outer layer for additional effective conductivity.
High-carbon steel wires with one of three coating systems: hot-dip galvanizing (Zn, ASTM B498), Zn-5%Al-Mischmetal "Galfan" (ASTM B802), or aluminized (ASTM B341). Available in four tensile grades: Standard, High-Strength (HS), Extra-High-Strength (EHS), and Ultra-High-Strength (UHS).
Common configurations include 6/1, 18/1 (high-conductivity), 24/7, 26/7, 30/7, 30/19, 45/7, 54/7, 54/19, and 72/7. The aluminum-to-steel cross-section ratio determines the trade-off between ampacity (more aluminum) and strength (more steel) for the specific span and loading conditions.
Class A — regular galvanizing (standard inland). Class B — approximately 2× zinc mass (coastal and light-industrial). Class C — approximately 3× zinc mass (heavy industrial, marine, and aggressive atmospheres). Zn-5%Al-MM "Galfan" coatings typically deliver 2–3× the atmospheric corrosion life of equivalent-mass zinc.
Representative ACSR sizes per ASTM B232 using the traditional US bird-name code designations. Rated breaking strength (RBS) reflects the combined tensile load capacity of the aluminum layers and steel core. DC resistance corrected to 20 °C, Class A galvanized core, standard strength grade unless noted.
| Code Name | Size (AWG / kcmil) | Stranding (Al / St) | Al Dia. (mm) | OD (mm) | Mass (kg/km) | RBS (kN) | DC Resist. (Ω/km @ 20 °C) |
|---|---|---|---|---|---|---|---|
| Raven | 1/0 AWG | 6 / 1 | 2.67 | 8.01 | 216 | 19.5 | 0.8547 |
| Penguin | 4/0 AWG | 6 / 1 | 3.78 | 11.34 | 432 | 38.0 | 0.4263 |
| Partridge | 266.8 kcmil | 26 / 7 | 2.57 | 16.28 | 547 | 51.5 | 0.2128 |
| Ibis | 397.5 kcmil | 26 / 7 | 3.14 | 19.88 | 814 | 75.6 | 0.1432 |
| Pelican | 477 kcmil | 18 / 1 | 3.99 | 19.95 | 739 | 53.6 | 0.1196 |
| Hawk | 477 kcmil | 26 / 7 | 3.44 | 21.79 | 977 | 86.6 | 0.1197 |
| Drake | 795 kcmil | 26 / 7 | 4.44 | 28.14 | 1,628 | 140.1 | 0.0719 |
| Cardinal | 954 kcmil | 54 / 7 | 3.38 | 30.38 | 1,832 | 155.7 | 0.0600 |
ASTM B232 requires verification on individual aluminum wires (per ASTM B230), individual coated steel core wires (per the applicable B498/B606/B802/B803/B957/B958/B341 standard), and on the completed stranded conductor:
ACSR per ASTM B232 is, by a significant margin, the most widely manufactured and deployed bare overhead conductor in the world. From medium-voltage rural distribution in Southeast Asia and Africa, through 230 kV transmission backbones across North and South America, to 500 kV and 765 kV bulk power corridors spanning North American and Chinese utility networks, ACSR remains the default specification because no other conductor family offers the same combination of very high tensile strength, competitive conductivity, a century of proven service performance, and mature hardware ecosystems (splices, dead-ends, armor rods, dampers, clamps) built specifically around its geometry. The nine variant designations within B232 give the designer fine control: Class A galvanizing for ordinary inland lines, Class C galvanizing or Zn-5%Al-MM coatings for coastal and industrial corrosion zones, and HS through UHS strength grades to optimize long river crossings and heavy-ice loading regions. Bird-name code designations (Raven, Partridge, Ibis, Pelican, Hawk, Drake, Cardinal, etc.) remain the universal procurement language across utilities, EPC contractors, and distributors globally.
Official Standards & References
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